feat(go-config): multi-format codecs, envc CLI, fixtures, ASRs

- Module github.com/eslider/go-config with env/yaml/json/ini packages - internal: source, keymap, merge, structconv, bytesutil - cmd/envc: convert, get, merge - docs/asr ASR-0001..0008, README/CHANGELOG/AGENTS refresh - golangci-lint v2 config; tests + fixtures Co-authored-by: Cursor <cursoragent@cursor.com>
2026-05-02 14:04:01 +01:00
parent 288a5b600c
commit c575341178
75 changed files with 2810 additions and 528 deletions
@@ -1,3 +1,6 @@
+# IDE
+.idea/
+
 # Local environment
 .env

@@ -1,13 +1,17 @@
+version: "2"
+
 run:
  timeout: 5m
  tests: true

-linters:
-  disable-all: true
+formatters:
  enable:
-    - errcheck
    - gofmt
    - goimports
+
+linters:
+  enable:
+    - errcheck
    - govet
    - ineffassign
    - revive
@@ -1,44 +1,39 @@
-# AGENTS.md — `go-env`
+# AGENTS.md — `go-config`

 This module is part of the eSlider `go-*` library standard (inventar ASR-0008).

 ## Purpose

-Decode `os.Environ()` into Go structs. Extracted from
-`produktor.io/ai-fabric/pkg/env` on 2026-04-24.
+Convert **env**, **YAML**, **JSON**, and **INI** into nested `map[string]any` and Go structs (and back), with multi-source merging and the `envc` CLI.

 ## Public API surface

- `env.Unmarshal(dst any, opts ...Option) error`
- `env.UnmarshalPrefix(dst any, prefix string, opts ...Option) error`
- `env.AsMap() map[string]any`
- `env.AsMapPrefix(prefix string) map[string]any`
- Options: `WithTrim`, `WithWeaklyTyped`, `WithTagName`, `WithDecodeHook`
+- Subpackages: `env`, `yaml`, `json`, `ini` — each exports `New`, `(*Codec).Map`, `Unmarshal`, `UnmarshalContext`, `Marshal`, `WriteTo`, and format-specific options.
+- `cmd/envc` — binary `envc`: `convert`, `get`, `merge`.
+- Internals under `internal/` are not stable API.

-Breaking changes require a new major version tag (SemVer). Internal helpers
-(`asMapFromEnviron`, `trimStringHook`, `insertPath`) are unexported and
-may change without notice.
+Breaking changes require a new major SemVer tag (or `/v2` module path if the policy changes).

 ## Testing policy

-Follows the eSlider "no synthetic mocks" policy:
+Follows the eSlider "no synthetic mocks" policy (see [.cursor/rules/no-synthetic-mocks.mdc](.cursor/rules/no-synthetic-mocks.mdc)):

- **Unit tests** (`env_test.go`): pure inputs only. We pass synthetic
-  `environ` slices to `asMapFromEnviron` — that is not a mock of anything
-  external; it's the normal way to test a pure function. Use `t.Setenv`
-  for `Unmarshal*` happy-path tests since Go's `os.Environ` lookup is
-  well-defined local behaviour, not a vendor protocol.
- **No `httptest`** — this library has no HTTP surface.
- **No integration-test build tag** — everything is in-process.
+- **Unit tests** — pure inputs for merge, keymap, structconv, env flat-map helpers.
+- **`httptest`** — allowed only to test **our** HTTP client behaviour in `internal/source` (not third-party API emulation).
+- **Fixtures** — real files under `fixtures/`; `testfixtures` resolves paths from module root.
+
+## Decisions
+
+Architecture Significant Requirements: [docs/asr/README.md](docs/asr/README.md).

 ## Checklist before release

 ```sh
-cd go-env
+cd go-config
 go mod tidy
 go vet ./...
 go test -race -count=1 ./...
-golangci-lint run --timeout 5m   # same preset as go-onlyoffice
+golangci-lint run --timeout 5m
 ```

 Bump `CHANGELOG.md`, tag `vX.Y.Z`, push.
@@ -46,5 +41,4 @@ Bump `CHANGELOG.md`, tag `vX.Y.Z`, push.
 ## Related

 - `inventar/docs/asr/ASR-0008.md` — Go library module conventions
- `inventar/docs/asr/ASR-0008-ai-fabric-audit.md` — why this module exists
 - `go-onlyoffice/AGENTS.md` — reference for the eSlider library template
@@ -1,14 +1,37 @@
 # Changelog

-All notable changes to `go-env` are documented here.
+All notable changes to `go-config` are documented here.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/)
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).

 ## [Unreleased]

+## [0.2.0] - 2026-05-02
+
+### Added
+
+- Module rename to `github.com/eslider/go-config` with subpackages `env`, `yaml`, `json`, `ini`.
+- Uniform `Codec` API: `New`, `Map`, `Unmarshal`, `UnmarshalContext`, `Marshal`, `WriteTo`.
+- `internal/source` for bytes, readers, files, and HTTP(S) URLs with optional headers and custom `http.Client`.
+- `internal/keymap` recursive key walk with default `LowerAlnum` normalizer.
+- `internal/merge` deep merge: recursive maps, last-write-wins scalars, configurable slice replace vs concat.
+- `internal/structconv` around `github.com/go-viper/mapstructure/v2`.
+- CLI `envc` (`cmd/envc`): `convert`, `get`, `merge`.
+- Fixtures under `fixtures/` for identity, merge, edge, and invalid parser cases.
+- `testfixtures` helper for tests.
+- Repo-local ASRs in `docs/asr/`.
+
+### Changed
+
+- **Breaking:** the v0.1.0 `github.com/eslider/go-env` API (`Unmarshal`, `UnmarshalPrefix`, `AsMap`, …) is not re-exported; use `env.New(...).Unmarshal(...)`.
+
+### Dependencies
+
+- `github.com/go-viper/mapstructure/v2`, `github.com/joho/godotenv`, `gopkg.in/yaml.v3`, `gopkg.in/ini.v1`.
+
 ## [0.1.0] - 2026-04-24

-Initial release. Extracted from `produktor.io/ai-fabric/pkg/env` per
+Initial release as `github.com/eslider/go-env`. Extracted from `produktor.io/ai-fabric/pkg/env` per
 `inventar/docs/asr/ASR-0008-ai-fabric-audit.md`.

 ### Added
@@ -1,97 +1,128 @@
-# go-env
+# go-config

-[![Go Reference](https://pkg.go.dev/badge/github.com/eslider/go-env.svg)](https://pkg.go.dev/github.com/eslider/go-env)
+[![Go Reference](https://pkg.go.dev/badge/github.com/eslider/go-config.svg)](https://pkg.go.dev/github.com/eslider/go-config)
+[![License: MIT](https://img.shields.io/badge/License-MIT-yellow.svg)](https://opensource.org/licenses/MIT)
+[![Latest Release](https://img.shields.io/github/v/release/eSlider/go-config)](https://github.com/eSlider/go-config/releases/latest)
+[![GitHub Stars](https://img.shields.io/github/stars/eSlider/go-config?style=social)](https://github.com/eSlider/go-config/stargazers)

-Tiny, zero-ceremony library for decoding process environment variables into
-Go structs.
+Convert **env**, **YAML**, **JSON**, and **INI** to and from Go `map[string]any` and structs. Multi-source inputs merge with **deep map merge**: nested maps combine, **scalar leaves are last-write-wins**, and **slices** default to **replace** (opt-in **concat** via `WithSliceMerge`). Keys are normalized with a configurable **lower+alnum** rule so `sub-service`, `SUB_SERVICE`, and `SubService` line up across formats. Built on [go-viper/mapstructure/v2](https://github.com/go-viper/mapstructure).

- Uses `_` as a path separator: `SERVICE_HTTP_PORT` → `Service.HTTP.Port`.
- Weakly-typed by default (`"1"` → `int`, `"true"` → `bool`).
- Optional prefix filter with automatic stripping.
- Pluggable decode hooks via [`mitchellh/mapstructure`][mapstructure].
+## Architecture
+
+```mermaid
+flowchart LR
+  Sources["Sources\nbytes reader file URL process env"]
+  Parser["Parser\ngodotenv yaml ini json"]
+  Norm["keymap.Walk\nNormalizer"]
+  MergeOp["merge.DeepMerge"]
+  Map["map string any"]
+  MS["structconv\nmapstructure v2"]
+  Struct["Go struct"]
+  Sources --> Parser --> Norm --> MergeOp --> Map
+  Map -->|Unmarshal| MS --> Struct
+  Struct -->|Marshal| MS --> Map
+  Map -->|WriteTo Marshal| Parser
+```
+
+## Hero example
+
+```go
+yamlCfg := yaml.New(yaml.WithURL("https://raw.githubusercontent.com/eSlider/mail-archive/refs/heads/master/docker-compose.yml"))
+envCfg := env.New(
+	env.WithFile(".default.env"), // lowest priority
+	env.WithFile(".env"),
+	env.WithCurrentEnvironment(), // highest priority — process env wins
+)
+
+var svc MyService
+_ = yamlCfg.Unmarshal(&svc)
+_ = envCfg.Unmarshal(&svc) // later sources override earlier scalar leaves; maps recurse
+```
+
+- **Maps** merge recursively (sub-trees are combined, not replaced wholesale).
+- **Scalar leaves**: last-write-wins when you list sources lowest → highest priority.
+- **Slices**: `merge.Replace` by default; use `WithSliceMerge(merge.Concat)` to append.
+
+Runnable offline variant: see `Example_hero_offline` in [example_hero_test.go](example_hero_test.go).

 ## Install

 ```sh
-go get github.com/eslider/go-env
+go get github.com/eslider/go-config
+go install github.com/eslider/go-config/cmd/envc@latest
 ```

 ## Quick start

+### 1. Single YAML file
+
 ```go
-package main
+c := yaml.New(yaml.WithFile("config.yaml"))
+var cfg AppConfig
+if err := c.Unmarshal(&cfg); err != nil { /* ... */ }
+```

-import (
-	"fmt"
+### 2. JSON over HTTPS with a header

-	"github.com/eslider/go-env"
+```go
+c := json.New(
+	json.WithURL("https://api.example.com/v1/config.json"),
+	json.WithHTTPHeader("Authorization", "Bearer "+token),
 )
-
-type Config struct {
-	Service struct {
-		HTTP struct {
-			Port int
-		}
-		Key string
-	}
-}
-
-func main() {
-	var cfg Config
-	if err := env.Unmarshal(&cfg); err != nil {
-		panic(err)
-	}
-	fmt.Printf("%+v\n", cfg)
-}
+var cfg AppConfig
+_ = c.Unmarshal(&cfg)
 ```

-With a prefix:
+### 3. Cross-format conversion (YAML → JSON)

 ```go
-// Only looks at APP_* variables; strips the APP_ prefix before decoding.
-_ = env.UnmarshalPrefix(&cfg, "APP_")
+ctx := context.Background()
+m, _ := yaml.New(yaml.WithFile("in.yaml")).Map(ctx)
+b, _ := json.New().Marshal(m)
+os.WriteFile("out.json", b, 0o644)
 ```

-## API
+## CLI: `envc`

-| Function | Purpose |
+| Command | Purpose |
 | --- | --- |
-| `Unmarshal(dst, opts...)` | Decode all env vars into `dst`. |
-| `UnmarshalPrefix(dst, prefix, opts...)` | Same, but only vars starting with `prefix`. |
-| `AsMap()` / `AsMapPrefix(prefix)` | Return the nested `map[string]any` used by the decoder (debugging, custom decoders). |
+| `envc convert --from yaml --to env --input - --output -` | Convert stdin YAML to dotenv on stdout |
+| `envc get --from yaml --path service.name config.yaml` | Print one path (dot-separated; segments normalized like codecs) |
+| `envc merge --from yaml --to json --output out.json a.yaml b.yaml` | Deep-merge multiple YAML files, emit JSON |

-### Options
+## API (all codecs)

-| Option | Default | Purpose |
+| Method | Description |
+| --- | --- |
+| `New(opts...)` | Construct codec |
+| `Map(ctx)` | Merged `map[string]any` |
+| `Unmarshal(dst)` / `UnmarshalContext(ctx, dst)` | Decode into struct (or map) |
+| `Marshal(src)` / `WriteTo(w, src)` | Encode struct or `map[string]any` |
+
+Shared options (each subpackage): `WithBytes`, `WithReader`, `WithFile`, `WithURL`, `WithHTTPHeader`, `WithHTTPClient`, `WithKeyNormalizer`, `WithSliceMerge`, `WithTrim`, `WithWeaklyTyped`, `WithTagName`, `WithDecodeHook`.
+
+`env` adds: `WithCurrentEnvironment`, `WithPrefix`.
+
+## Cross-format mapping
+
+| Go | YAML | ENV |
 | --- | --- | --- |
-| `WithTrim(bool)` | `true` | TrimSpace every string value. |
-| `WithWeaklyTyped(bool)` | `true` | `mapstructure`'s weakly-typed coercion. |
-| `WithTagName(string)` | `"mapstructure"` | Struct tag name for field overrides. |
-| `WithDecodeHook(h)` | — | Append a `mapstructure.DecodeHookFunc` to the chain. |
+| `Service.SubService.Name` | `service.sub-service.name` | `SERVICE_SUBSERVICE_NAME` |

-## Semantics
+INI uses dotted sections, e.g. `[service.subservice]` with `name=...`.

- **Path collisions**: first write wins. If both `FOO=1` and `FOO=2` exist
-  in the environ, only `FOO=1` is kept. This matches the original
-  `ai-fabric/pkg/env` behaviour.
- **Case-insensitive keys**: all path components are lower-cased; struct
-  fields are matched via `mapstructure` which is also case-insensitive.
- **`_`-only delimiter**: there's no escape — if a variable legitimately
-  contains `_` inside a "leaf" name, you must restructure your struct to
-  match the nested layout.
+## Related libraries

-## Status
+| Module | Role |
+| --- | --- |
+| [go-matrix-bot](https://github.com/eSlider/go-matrix-bot) | Matrix bots |
+| [go-onlyoffice](https://github.com/eSlider/go-onlyoffice) | OnlyOffice API |
+| [go-ollama](https://github.com/eSlider/go-ollama) | Ollama client |

-Extracted from `produktor.io/ai-fabric` as part of the eSlider `go-*`
-library standard (ASR-0008). Merges the best parts of three previously
-divergent copies:
+## Decisions

- `produktor.io/ai-fabric/pkg/env`
- `markets-platform/TP-general-code/pkg/system/env.go`
- the various `pkg/system/env.go` snapshots inside `var/agents/issue-*/`
+Repo-local ASRs: [docs/asr/README.md](docs/asr/README.md).

 ## License

 MIT © Andriy Oblivantsev
-
-[mapstructure]: https://github.com/mitchellh/mapstructure
@@ -0,0 +1,96 @@
+package main
+
+import (
+	"context"
+	"encoding/json"
+	"flag"
+	"fmt"
+	"io"
+
+	"github.com/eslider/go-config/env"
+	"github.com/eslider/go-config/ini"
+	"github.com/eslider/go-config/internal/bytesutil"
+	libjson "github.com/eslider/go-config/json"
+	"github.com/eslider/go-config/yaml"
+	yaml3 "gopkg.in/yaml.v3"
+)
+
+// RunConvert implements: envc convert --from F --to T [--input] [--output].
+func RunConvert(args []string, stdin io.Reader, stdout, stderr io.Writer) int {
+	fs := flag.NewFlagSet("convert", flag.ContinueOnError)
+	fs.SetOutput(stderr)
+	from := fs.String("from", "", "source format: yaml|json|ini|env")
+	to := fs.String("to", "", "target format: yaml|json|ini|env")
+	input := fs.String("input", "-", "input path, URL, or - for stdin")
+	output := fs.String("output", "-", "output path or - for stdout")
+	if err := fs.Parse(args); err != nil {
+		return 2
+	}
+	if *from == "" || *to == "" {
+		_, _ = fmt.Fprintln(stderr, "convert: --from and --to are required")
+		return 2
+	}
+	ctx := context.Background()
+	src := openSource(*input, stdin)
+	b, err := bytesutil.ReadAll(ctx, src)
+	if err != nil {
+		_, _ = fmt.Fprintf(stderr, "convert: read: %v\n", err)
+		return 1
+	}
+	m, err := loadMapFromBytes(ctx, *from, b)
+	if err != nil {
+		_, _ = fmt.Fprintf(stderr, "convert: parse: %v\n", err)
+		return 1
+	}
+	outb, err := marshalMap(*to, m)
+	if err != nil {
+		_, _ = fmt.Fprintf(stderr, "convert: marshal: %v\n", err)
+		return 1
+	}
+	out, err := openOutput(*output, stdout)
+	if err != nil {
+		_, _ = fmt.Fprintf(stderr, "convert: output: %v\n", err)
+		return 1
+	}
+	defer func() { _ = out.Close() }()
+	if _, err := out.Write(outb); err != nil {
+		_, _ = fmt.Fprintf(stderr, "convert: write: %v\n", err)
+		return 1
+	}
+	if *output == "-" || *output == "" {
+		if len(outb) > 0 && outb[len(outb)-1] != '\n' {
+			_, _ = out.Write([]byte("\n"))
+		}
+	}
+	return 0
+}
+
+func loadMapFromBytes(ctx context.Context, format string, b []byte) (map[string]any, error) {
+	switch format {
+	case "yaml":
+		return yaml.New(yaml.WithBytes(b)).Map(ctx)
+	case "json":
+		return libjson.New(libjson.WithBytes(b)).Map(ctx)
+	case "ini":
+		return ini.New(ini.WithBytes(b)).Map(ctx)
+	case "env":
+		return env.New(env.WithBytes(b)).Map(ctx)
+	default:
+		return nil, fmt.Errorf("unknown format %q", format)
+	}
+}
+
+func marshalMap(format string, m map[string]any) ([]byte, error) {
+	switch format {
+	case "yaml":
+		return yaml3.Marshal(m)
+	case "json":
+		return json.MarshalIndent(m, "", "  ")
+	case "ini":
+		return ini.New().Marshal(m)
+	case "env":
+		return env.New().Marshal(m)
+	default:
+		return nil, fmt.Errorf("unknown format %q", format)
+	}
+}
@@ -0,0 +1,53 @@
+package main
+
+import (
+	"bytes"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+)
+
+func TestRunConvert_YAMLToJSON(t *testing.T) {
+	var stdout, stderr bytes.Buffer
+	stdin := strings.NewReader("a: 1\n")
+	code := RunConvert([]string{"--from", "yaml", "--to", "json", "--input", "-"}, stdin, &stdout, &stderr)
+	if code != 0 {
+		t.Fatalf("stderr: %s", stderr.String())
+	}
+	if !strings.Contains(stdout.String(), `"a"`) {
+		t.Fatalf("out: %s", stdout.String())
+	}
+}
+
+func TestRunGet(t *testing.T) {
+	var stdout, stderr bytes.Buffer
+	in := "service:\n  name: x\n"
+	code := RunGet([]string{"--from", "yaml", "--path", "service.name", "-"}, strings.NewReader(in), &stdout, &stderr)
+	if code != 0 {
+		t.Fatalf("stderr: %s", stderr.String())
+	}
+	if strings.TrimSpace(stdout.String()) != "x" {
+		t.Fatalf("got %q", stdout.String())
+	}
+}
+
+func TestRunMerge_TwoYAMLFiles(t *testing.T) {
+	dir := t.TempDir()
+	f1 := filepath.Join(dir, "a.yaml")
+	f2 := filepath.Join(dir, "b.yaml")
+	if err := os.WriteFile(f1, []byte("k: 1\n"), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.WriteFile(f2, []byte("k: 2\n"), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	var stdout, stderr bytes.Buffer
+	code := RunMerge([]string{"--from", "yaml", "--to", "json", f1, f2}, strings.NewReader(""), &stdout, &stderr)
+	if code != 0 {
+		t.Fatalf("stderr: %s", stderr.String())
+	}
+	if !strings.Contains(stdout.String(), `"k"`) || !strings.Contains(stdout.String(), `2`) {
+		t.Fatalf("out: %s", stdout.String())
+	}
+}
@@ -0,0 +1,3 @@
+// Command envc converts, queries, and merges configuration between env, YAML,
+// JSON, and INI formats.
+package main
@@ -0,0 +1,83 @@
+package main
+
+import (
+	"context"
+	"encoding/json"
+	"flag"
+	"fmt"
+	"io"
+	"strings"
+
+	"github.com/eslider/go-config/internal/bytesutil"
+	"github.com/eslider/go-config/internal/keymap"
+)
+
+// RunGet implements: envc get --from F --path p [input].
+func RunGet(args []string, stdin io.Reader, stdout, stderr io.Writer) int {
+	fs := flag.NewFlagSet("get", flag.ContinueOnError)
+	fs.SetOutput(stderr)
+	from := fs.String("from", "", "format: yaml|json|ini|env")
+	path := fs.String("path", "", "dot-separated path (e.g. service.subservice.name)")
+	if err := fs.Parse(args); err != nil {
+		return 2
+	}
+	if *from == "" || *path == "" {
+		_, _ = fmt.Fprintln(stderr, "get: --from and --path are required")
+		return 2
+	}
+	pos := fs.Args()
+	input := "-"
+	if len(pos) > 0 {
+		input = pos[0]
+	}
+	ctx := context.Background()
+	src := openSource(input, stdin)
+	b, err := bytesutil.ReadAll(ctx, src)
+	if err != nil {
+		_, _ = fmt.Fprintf(stderr, "get: read: %v\n", err)
+		return 1
+	}
+	m, err := loadMapFromBytes(ctx, *from, b)
+	if err != nil {
+		_, _ = fmt.Fprintf(stderr, "get: parse: %v\n", err)
+		return 1
+	}
+	v, err := walkPath(m, strings.Split(*path, "."))
+	if err != nil {
+		_, _ = fmt.Fprintf(stderr, "get: %v\n", err)
+		return 1
+	}
+	switch val := v.(type) {
+	case string, bool, float64, int, int64, nil:
+		_, _ = fmt.Fprintln(stdout, val)
+	default:
+		enc := json.NewEncoder(stdout)
+		enc.SetIndent("", "  ")
+		if err := enc.Encode(val); err != nil {
+			_, _ = fmt.Fprintf(stderr, "get: encode: %v\n", err)
+			return 1
+		}
+	}
+	return 0
+}
+
+func walkPath(m map[string]any, parts []string) (any, error) {
+	var cur any = m
+	for i, p := range parts {
+		if p == "" {
+			continue
+		}
+		pk := keymap.LowerAlnum(p)
+		switch t := cur.(type) {
+		case map[string]any:
+			nx, ok := t[pk]
+			if !ok {
+				return nil, fmt.Errorf("missing key %q (normalized %q) at segment %d", p, pk, i)
+			}
+			cur = nx
+		default:
+			return nil, fmt.Errorf("not a map at segment %d", i)
+		}
+	}
+	return cur, nil
+}
@@ -0,0 +1,28 @@
+package main
+
+import (
+	"fmt"
+	"os"
+)
+
+func main() {
+	stdin, stdout, stderr := os.Stdin, os.Stdout, os.Stderr
+	args := os.Args[1:]
+	if len(args) < 1 {
+		_, _ = fmt.Fprintln(stderr, "usage: envc <convert|get|merge> [flags]")
+		os.Exit(2)
+	}
+	var code int
+	switch args[0] {
+	case "convert":
+		code = RunConvert(args[1:], stdin, stdout, stderr)
+	case "get":
+		code = RunGet(args[1:], stdin, stdout, stderr)
+	case "merge":
+		code = RunMerge(args[1:], stdin, stdout, stderr)
+	default:
+		_, _ = fmt.Fprintf(stderr, "unknown command %q\n", args[0])
+		code = 2
+	}
+	os.Exit(code)
+}
@@ -0,0 +1,80 @@
+package main
+
+import (
+	"context"
+	"flag"
+	"fmt"
+	"io"
+
+	"github.com/eslider/go-config/internal/bytesutil"
+	"github.com/eslider/go-config/internal/merge"
+	"github.com/eslider/go-config/internal/source"
+)
+
+// RunMerge implements: envc merge --from F --to T [--output] inputs...
+func RunMerge(args []string, stdin io.Reader, stdout, stderr io.Writer) int {
+	fs := flag.NewFlagSet("merge", flag.ContinueOnError)
+	fs.SetOutput(stderr)
+	from := fs.String("from", "", "input format: yaml|json|ini|env")
+	to := fs.String("to", "", "output format: yaml|json|ini|env")
+	output := fs.String("output", "-", "output path or - for stdout")
+	if err := fs.Parse(args); err != nil {
+		return 2
+	}
+	if *from == "" || *to == "" {
+		_, _ = fmt.Fprintln(stderr, "merge: --from and --to are required")
+		return 2
+	}
+	inputs := fs.Args()
+	if len(inputs) == 0 {
+		_, _ = fmt.Fprintln(stderr, "merge: at least one input file or URL required")
+		return 2
+	}
+	ctx := context.Background()
+	acc := make(map[string]any)
+	for _, in := range inputs {
+		var src source.Source
+		if in == "-" {
+			b, err := io.ReadAll(stdin)
+			if err != nil {
+				_, _ = fmt.Fprintf(stderr, "merge: stdin: %v\n", err)
+				return 1
+			}
+			src = source.Bytes{Data: b, Name: "stdin"}
+		} else {
+			src = openSource(in, stdin)
+		}
+		b, err := bytesutil.ReadAll(ctx, src)
+		if err != nil {
+			_, _ = fmt.Fprintf(stderr, "merge: read %s: %v\n", in, err)
+			return 1
+		}
+		m, err := loadMapFromBytes(ctx, *from, b)
+		if err != nil {
+			_, _ = fmt.Fprintf(stderr, "merge: parse %s: %v\n", in, err)
+			return 1
+		}
+		merge.DeepMerge(acc, m)
+	}
+	outb, err := marshalMap(*to, acc)
+	if err != nil {
+		_, _ = fmt.Fprintf(stderr, "merge: marshal: %v\n", err)
+		return 1
+	}
+	out, err := openOutput(*output, stdout)
+	if err != nil {
+		_, _ = fmt.Fprintf(stderr, "merge: output: %v\n", err)
+		return 1
+	}
+	defer func() { _ = out.Close() }()
+	if _, err := out.Write(outb); err != nil {
+		_, _ = fmt.Fprintf(stderr, "merge: write: %v\n", err)
+		return 1
+	}
+	if *output == "-" || *output == "" {
+		if len(outb) > 0 && outb[len(outb)-1] != '\n' {
+			_, _ = out.Write([]byte("\n"))
+		}
+	}
+	return 0
+}
@@ -0,0 +1,33 @@
+package main
+
+import (
+	"io"
+	"os"
+	"strings"
+
+	"github.com/eslider/go-config/internal/source"
+)
+
+func openSource(pathOrURL string, stdin io.Reader) source.Source {
+	if pathOrURL == "" || pathOrURL == "-" {
+		return source.Reader{R: stdin, Name: "stdin"}
+	}
+	if strings.HasPrefix(pathOrURL, "http://") || strings.HasPrefix(pathOrURL, "https://") {
+		return source.URL{Raw: pathOrURL}
+	}
+	return source.File{Path: pathOrURL}
+}
+
+type nopCloser struct{ io.Writer }
+
+func (nopCloser) Close() error { return nil }
+
+func openOutput(path string, stdout io.Writer) (io.WriteCloser, error) {
+	if path == "" || path == "-" {
+		if wc, ok := stdout.(io.WriteCloser); ok {
+			return wc, nil
+		}
+		return nopCloser{stdout}, nil
+	}
+	return os.Create(path)
+}
@@ -1,28 +1,23 @@
-// Package env reads process environment variables and decodes them into
-// Go structs using underscore-delimited paths.
+// Package config is the module root for go-config (import path
+// github.com/eslider/go-config). Use the subpackages [env], [yaml], [json], and
+// [ini] for format-specific codecs and the [cmd/envc] command for CLI
+// conversion.
 //
-// A variable named "SERVICE_HTTP_PORT" becomes the path Service.HTTP.Port
-// (case-insensitive, '_' is a path separator). Values are decoded via
-// github.com/mitchellh/mapstructure, so numeric, boolean and slice
-// conversions happen automatically.
+// Hero workflow (YAML + layered dotenv + process env):
 //
-//	var cfg struct {
-//		Service struct {
-//			HTTP struct {
-//				Port int
-//			}
-//			Key string
-//		}
-//	}
-//	if err := env.Unmarshal(&cfg); err != nil { ... }
+//	yamlCfg := yaml.New(yaml.WithURL("https://example.com/config.yaml"))
+//	envCfg := env.New(
+//	    env.WithFile(".default.env"),
+//	    env.WithFile(".env"),
+//	    env.WithCurrentEnvironment(),
+//	)
+//	var svc MyService
+//	_ = yamlCfg.Unmarshal(&svc)
+//	_ = envCfg.Unmarshal(&svc)
 //
-// UnmarshalPrefix ignores variables that don't start with the given
-// prefix and strips it before building the path:
-//
-//	_ = os.Setenv("APP_DB_HOST", "localhost")
-//	_ = env.UnmarshalPrefix(&cfg, "APP_")
-//	// cfg.Db.Host == "localhost"
-//
-// String values are TrimSpace-trimmed by default; pass WithTrim(false) to
-// opt out.
-package env
+// [cmd/envc]: https://pkg.go.dev/github.com/eslider/go-config/cmd/envc
+// [env]: https://pkg.go.dev/github.com/eslider/go-config/env
+// [yaml]: https://pkg.go.dev/github.com/eslider/go-config/yaml
+// [json]: https://pkg.go.dev/github.com/eslider/go-config/json
+// [ini]: https://pkg.go.dev/github.com/eslider/go-config/ini
+package config
@@ -0,0 +1,27 @@
+# ASR-0001: Module rename and multi-package layout
+
+## Context
+
+The original `github.com/eslider/go-env` module only decoded process environment variables. The product scope expanded to YAML, JSON, INI, URLs, multi-source merging, and a CLI. The old name and single-package layout no longer matched the capability surface.
+
+## Decision
+
+1. The canonical module path is **`github.com/eslider/go-config`**.
+2. Format-specific code lives in first-class subpackages: **`env/`**, **`yaml/`**, **`json/`**, **`ini/`**.
+3. Shared building blocks live under **`internal/{source,keymap,merge,structconv,bytesutil}`**.
+4. The CLI lives at **`cmd/envc/`** (one binary per inventar **ASR-0008** §2 — CLI inside the same module).
+5. The GitHub repository is named **`eSlider/go-config`** (renamed from `go-env`).
+
+## Consequences
+
+- Consumers must change their `import` paths and `go get` target.
+- CI, badges, and documentation reference `go-config` and `eslider/go-config`.
+
+## Status
+
+Accepted — 2026-05-02.
+
+## References
+
+- inventar ASR-0008 — Go library module conventions
+- ASR-0002 — API clean break
@@ -0,0 +1,24 @@
+# ASR-0002: Clean break from go-env v0.1.0
+
+## Context
+
+`go-env` v0.1.0 exposed package-level helpers (`Unmarshal`, `UnmarshalPrefix`, `AsMap`, …). The new design is `Codec`-centric with multiple sources per format.
+
+## Decision
+
+1. **No compatibility shims** in `go-config` re-exporting the old API.
+2. v0.1.0 remains tagged on git history as `github.com/eslider/go-env@v0.1.0` for archival consumers.
+3. Migration path is documented in `CHANGELOG.md` and the README.
+
+## Consequences
+
+- Single-call-site migrations must switch to `env.New(env.WithCurrentEnvironment(), …).Unmarshal(&cfg)`.
+
+## Status
+
+Accepted — 2026-05-02.
+
+## References
+
+- CHANGELOG `[0.2.0]`
+- ASR-0001
@@ -0,0 +1,25 @@
+# ASR-0003: Uniform codec API and Source abstraction
+
+## Context
+
+Users switch between YAML, JSON, INI, and env-file formats; a different function surface per format would increase cognitive load and test matrices.
+
+## Decision
+
+1. Every format package exports **`New(opts...) *Codec`** with **`Map`**, **`Unmarshal`**, **`UnmarshalContext`**, **`Marshal`**, **`WriteTo`**.
+2. Bytes, readers, files, and URLs are modeled by **`internal/source.Source`** with **`Open(ctx) (io.ReadCloser, error)`**.
+3. HTTP(S) sources support **`WithHTTPHeader`** and **`WithHTTPClient`**.
+
+## Consequences
+
+- Cross-format examples in the README stay structurally identical.
+- URL behaviour is testable with `httptest` against our client only.
+
+## Status
+
+Accepted — 2026-05-02.
+
+## References
+
+- ASR-0005 — merge semantics across multiple sources
+- ASR-0008 — httptest policy alignment
@@ -0,0 +1,23 @@
+# ASR-0004: Configurable key normalization
+
+## Context
+
+Real-world configuration mixes `kebab-case`, `snake_case`, `SCREAMING_SNAKE`, and struct field names. Requiring `mapstructure` tags on every field is noisy.
+
+## Decision
+
+1. After parsing and merging, codecs run **`internal/keymap.Walk`** with a **`Normalizer`** (default **`LowerAlnum`**: lowercase + strip non `[a-z0-9]`).
+2. Callers may set **`WithKeyNormalizer(nil)`** to disable walking, or supply a custom function.
+
+## Consequences
+
+- POSIX env keys without `-` still align with YAML keys that contain hyphens once normalized.
+- CLI `get` applies the same normalizer to each path segment for consistency.
+
+## Status
+
+Accepted — 2026-05-02.
+
+## References
+
+- ASR-0003
@@ -0,0 +1,26 @@
+# ASR-0005: Multi-source deep-merge semantics
+
+## Context
+
+Layered configuration (defaults file < local overrides < process environment) requires predictable composition rules.
+
+## Decision
+
+1. Sources are applied in **option order** (left → right). Each source parses to a `map[string]any`, then **`merge.DeepMerge`** folds them.
+2. **Maps recurse** — nested keys are unioned; existing nested maps are not replaced wholesale by a sibling scalar.
+3. **Scalar leaves** use **last-write-wins** (later source wins).
+4. **Slices** default to **`merge.Replace`**; **`WithSliceMerge(merge.Concat)`** appends prior and new slice elements.
+
+## Consequences
+
+- Env files and `WithCurrentEnvironment()` compose when ordered **lowest → highest** priority.
+- Tests lock behaviour via `fixtures/merge/*`.
+
+## Status
+
+Accepted — 2026-05-02.
+
+## References
+
+- ASR-0003
+- `internal/merge`
@@ -0,0 +1,26 @@
+# ASR-0006: Third-party library choices
+
+## Context
+
+We need battle-tested parsers and struct bridging without maintaining our own grammars.
+
+## Decision
+
+1. **Struct / map bridging:** `github.com/go-viper/mapstructure/v2` (maintained fork of `mitchellh/mapstructure`).
+2. **YAML:** `gopkg.in/yaml.v3`.
+3. **JSON:** `encoding/json` (stdlib).
+4. **INI:** `gopkg.in/ini.v1` with `Loose` parsing for tolerant files.
+5. **`.env` files:** `github.com/joho/godotenv` (`UnmarshalBytes`).
+6. **CLI:** stdlib `flag` only (no Cobra).
+
+## Consequences
+
+- `go.mod` carries the above direct dependencies (plus transitive modules as resolved by MVS).
+
+## Status
+
+Accepted — 2026-05-02.
+
+## References
+
+- [go-viper/mapstructure](https://github.com/go-viper/mapstructure)
@@ -0,0 +1,24 @@
+# ASR-0007: CLI `envc` — convert, get, merge
+
+## Context
+
+Operators need a small tool to translate configuration between formats and to inspect merged trees without writing Go.
+
+## Decision
+
+1. Binary name **`envc`**; module path **`github.com/eslider/go-config/cmd/envc`** (`go install …/cmd/envc@latest`).
+2. Subcommands: **`convert`**, **`get`**, **`merge`** — each implemented as a **`Run*(args, stdin, stdout, stderr) int`** function for in-process tests.
+3. **No** third-party CLI framework in v1 of the CLI.
+
+## Consequences
+
+- `cmd/envc` may grow flags; keep business logic in subpackages, not in `main` beyond wiring.
+
+## Status
+
+Accepted — 2026-05-02.
+
+## References
+
+- inventar ASR-0008 §2 — CLI placement
+- ASR-0003
@@ -0,0 +1,25 @@
+# ASR-0008: GitHub presentation and release flow
+
+## Context
+
+The repository was renamed from `eSlider/go-env` to `eSlider/go-config`. The v0.1.0 tag existed locally before the rename. Presentation should match other eSlider `go-*` libraries (e.g. `go-matrix-bot`).
+
+## Decision
+
+1. **v0.1.0 preservation:** push tag `v0.1.0` and create a GitHub **Release** with notes extracted from `CHANGELOG.md` before landing breaking work.
+2. **Development branch:** `release/v2` carries the `go-config` implementation until merged to `main`.
+3. **Rename:** `gh repo rename go-config` from `go-env`; local `origin` URL updated to `https://github.com/eSlider/go-config.git`.
+4. **Metadata:** `gh repo edit` sets description, **`homepage`** `https://pkg.go.dev/github.com/eslider/go-config`, and **topics** (`go`, `golang`, `config`, `yaml`, `json`, `ini`, `env`, `dotenv`, `mapstructure`, `codec`, `encoder`, `decoder`, `cli`, `library`).
+5. **README:** badges row, mermaid architecture diagram, hero snippet, quick starts, CLI table, API tables, related libraries, link to `docs/asr/`.
+
+## Consequences
+
+- Old `github.com/eslider/go-env` URLs redirect for a limited GitHub window; module path for v0.1.0 code remains the historical `go-env` import.
+
+## Status
+
+Accepted — 2026-05-02.
+
+## References
+
+- [go-matrix-bot](https://github.com/eSlider/go-matrix-bot) — README pattern reference
@@ -0,0 +1,14 @@
+# Architecture Significant Requirements (ASRs)
+
+Repo-local decisions for `go-config` (numbering starts at ASR-0001). Org-wide policies remain under `inventar/docs/asr/`.
+
+| ID | Title |
+| --- | --- |
+| [ASR-0001](ASR-0001-module-rename-and-layout.md) | Module rename and multi-package layout |
+| [ASR-0002](ASR-0002-clean-break-from-v0.1.0.md) | Clean break from go-env v0.1.0 |
+| [ASR-0003](ASR-0003-uniform-codec-api-and-source-abstraction.md) | Uniform codec API and Source abstraction |
+| [ASR-0004](ASR-0004-configurable-key-normalization.md) | Configurable key normalization |
+| [ASR-0005](ASR-0005-multi-source-deep-merge-semantics.md) | Multi-source deep-merge semantics |
+| [ASR-0006](ASR-0006-third-party-library-choices.md) | Third-party library choices |
+| [ASR-0007](ASR-0007-cli-envc-convert-get-merge.md) | CLI `envc`: convert, get, merge |
+| [ASR-0008](ASR-0008-github-presentation-and-release-flow.md) | GitHub presentation and release flow |
@@ -1,139 +0,0 @@
-package env
-
-import (
-	"fmt"
-	"os"
-	"reflect"
-	"strings"
-
-	"github.com/mitchellh/mapstructure"
-)
-
-// Unmarshal decodes all process environment variables into dst. The variable
-// name is split by '_' and the resulting path is matched against dst's fields
-// case-insensitively.
-//
-// dst must be a pointer to a struct (or a map that mapstructure can populate).
-// See the package documentation for details and examples.
-func Unmarshal(dst any, opts ...Option) error {
-	return UnmarshalPrefix(dst, "", opts...)
-}
-
-// UnmarshalPrefix is like Unmarshal but only considers environment variables
-// that start with prefix. The prefix is stripped from each variable name
-// before the path is built.
-//
-// An empty prefix is equivalent to Unmarshal.
-func UnmarshalPrefix(dst any, prefix string, opts ...Option) error {
-	o := defaultOptions()
-	for _, f := range opts {
-		f(&o)
-	}
-
-	data := asMapFromEnviron(os.Environ(), prefix)
-
-	hooks := []mapstructure.DecodeHookFunc{}
-	if o.trim {
-		hooks = append(hooks, trimStringHook)
-	}
-	hooks = append(hooks, o.extraHooks...)
-
-	decoder, err := mapstructure.NewDecoder(&mapstructure.DecoderConfig{
-		Result:           dst,
-		WeaklyTypedInput: o.weaklyTyped,
-		TagName:          o.tagName,
-		DecodeHook:       mapstructure.ComposeDecodeHookFunc(hooks...),
-	})
-	if err != nil {
-		return fmt.Errorf("env: configure decoder: %w", err)
-	}
-	if err := decoder.Decode(data); err != nil {
-		return fmt.Errorf("env: decode: %w", err)
-	}
-	return nil
-}
-
-// AsMap returns a nested map built from all current process environment
-// variables, using '_' as path separator. Keys are lower-cased.
-//
-// It's primarily useful for debugging or for callers that want to plug
-// their own decoder; normal code should prefer Unmarshal.
-func AsMap() map[string]any {
-	return asMapFromEnviron(os.Environ(), "")
-}
-
-// AsMapPrefix is the prefix-scoped variant of AsMap. Variables whose names
-// don't start with prefix are skipped; the prefix itself is stripped before
-// the map is built.
-func AsMapPrefix(prefix string) map[string]any {
-	return asMapFromEnviron(os.Environ(), prefix)
-}
-
-// asMapFromEnviron is the core building block. Exposed as an unexported
-// function so tests can feed it a deterministic environ slice instead of
-// mutating the real process env.
-func asMapFromEnviron(environ []string, prefix string) map[string]any {
-	out := make(map[string]any)
-
-	for _, entry := range environ {
-		eq := strings.IndexByte(entry, '=')
-		if eq < 0 {
-			// Malformed entry — shouldn't happen on Unix but guard anyway.
-			continue
-		}
-		name, value := entry[:eq], entry[eq+1:]
-
-		if prefix != "" {
-			if !strings.HasPrefix(name, prefix) {
-				continue
-			}
-			name = name[len(prefix):]
-			if name == "" {
-				continue
-			}
-		}
-
-		insertPath(out, strings.Split(name, "_"), value)
-	}
-
-	return out
-}
-
-// insertPath walks path inside root, creating intermediate nested maps as
-// needed, and stores value at the leaf.
-//
-// Collisions are resolved by preferring the first write: once a leaf value
-// is set for a path, a later sibling with the same path prefix will NOT
-// overwrite it. This matches the behaviour of the ai-fabric original so
-// that tools migrating to go-env don't observe new surprises.
-func insertPath(root map[string]any, path []string, value string) {
-	current := root
-	last := len(path) - 1
-	for i, raw := range path {
-		k := strings.ToLower(raw)
-
-		if i == last {
-			if _, exists := current[k]; exists {
-				return
-			}
-			current[k] = value
-			return
-		}
-
-		next, ok := current[k].(map[string]any)
-		if !ok {
-			next = make(map[string]any)
-			current[k] = next
-		}
-		current = next
-	}
-}
-
-func trimStringHook(from, to reflect.Type, data any) (any, error) {
-	if from.Kind() == reflect.String && to.Kind() == reflect.String {
-		if s, ok := data.(string); ok {
-			return strings.TrimSpace(s), nil
-		}
-	}
-	return data, nil
-}
@@ -0,0 +1,172 @@
+package env
+
+import (
+	"bytes"
+	"context"
+	"fmt"
+	"io"
+	"net/http"
+	"sort"
+	"strings"
+
+	"github.com/eslider/go-config/internal/bytesutil"
+	"github.com/eslider/go-config/internal/keymap"
+	"github.com/eslider/go-config/internal/merge"
+	"github.com/eslider/go-config/internal/source"
+	"github.com/eslider/go-config/internal/structconv"
+	"github.com/joho/godotenv"
+)
+
+// Codec loads environment-style key/value data from multiple sources.
+type Codec struct {
+	layers     []func(context.Context) (map[string]string, error)
+	prefix     string
+	normalizer keymap.Normalizer
+	sliceStrat merge.SliceStrategy
+	structOpts structconv.Options
+	mergeOpts  []merge.Option
+	httpClient *http.Client
+	urlHeader  http.Header
+}
+
+// New builds a Codec from options. Sources are merged left-to-right; later
+// sources override earlier scalar leaves (see package merge).
+func New(opts ...Option) *Codec {
+	c := &Codec{
+		normalizer: keymap.LowerAlnum,
+		sliceStrat: merge.Replace,
+		structOpts: structconv.Options{
+			TagName:     "mapstructure",
+			WeaklyTyped: true,
+			Trim:        true,
+		},
+	}
+	for _, o := range opts {
+		o(c)
+	}
+	c.mergeOpts = []merge.Option{merge.WithSliceStrategy(c.sliceStrat)}
+	return c
+}
+
+// Map returns the merged nested map after all sources are loaded and keys normalized.
+func (c *Codec) Map(ctx context.Context) (map[string]any, error) {
+	if len(c.layers) == 0 {
+		return nil, fmt.Errorf("env: no sources configured")
+	}
+	acc := make(map[string]any)
+	for _, layer := range c.layers {
+		flat, err := layer(ctx)
+		if err != nil {
+			return nil, err
+		}
+		nested := nestedFromFlat(flat, c.prefix)
+		merge.DeepMerge(acc, nested, c.mergeOpts...)
+	}
+	if c.normalizer != nil {
+		keymap.Walk(acc, c.normalizer)
+	}
+	return acc, nil
+}
+
+// Unmarshal decodes using context.Background.
+func (c *Codec) Unmarshal(dst any) error {
+	return c.UnmarshalContext(context.Background(), dst)
+}
+
+// UnmarshalContext decodes the merged map into dst using mapstructure.
+func (c *Codec) UnmarshalContext(ctx context.Context, dst any) error {
+	m, err := c.Map(ctx)
+	if err != nil {
+		return err
+	}
+	return structconv.Decode(m, dst, c.structOpts)
+}
+
+// Marshal encodes src into dotenv-style bytes (KEY=value lines, sorted keys).
+// src may be a struct or map[string]any.
+func (c *Codec) Marshal(src any) ([]byte, error) {
+	m, err := encodeToMap(src)
+	if err != nil {
+		return nil, fmt.Errorf("env: marshal encode: %w", err)
+	}
+	flat := flattenMap(nil, m)
+	var buf bytes.Buffer
+	keys := make([]string, 0, len(flat))
+	for k := range flat {
+		keys = append(keys, k)
+	}
+	sort.Strings(keys)
+	for _, k := range keys {
+		fmt.Fprintf(&buf, "%s=%s\n", k, flat[k])
+	}
+	return buf.Bytes(), nil
+}
+
+// WriteTo writes dotenv-style output to w.
+func (c *Codec) WriteTo(w io.Writer, src any) (int64, error) {
+	b, err := c.Marshal(src)
+	if err != nil {
+		return 0, err
+	}
+	n, err := w.Write(b)
+	return int64(n), err
+}
+
+func flattenMap(prefix []string, m map[string]any) map[string]string {
+	out := make(map[string]string)
+	for k, v := range m {
+		path := append(prefix, k)
+		switch t := v.(type) {
+		case map[string]any:
+			for kk, vv := range flattenMap(path, t) {
+				out[kk] = vv
+			}
+		case []any:
+			parts := make([]string, 0, len(t))
+			for _, e := range t {
+				parts = append(parts, fmt.Sprint(e))
+			}
+			key := strings.Join(path, "_")
+			out[strings.ToUpper(key)] = strings.Join(parts, ",")
+		default:
+			key := strings.Join(path, "_")
+			out[strings.ToUpper(key)] = fmt.Sprint(t)
+		}
+	}
+	return out
+}
+
+func encodeToMap(src any) (map[string]any, error) {
+	if m, ok := src.(map[string]any); ok {
+		return m, nil
+	}
+	return structconv.Encode(src)
+}
+
+func flatFromEnviron(environ []string) map[string]string {
+	out := make(map[string]string)
+	for _, entry := range environ {
+		eq := strings.IndexByte(entry, '=')
+		if eq < 0 {
+			continue
+		}
+		out[entry[:eq]] = entry[eq+1:]
+	}
+	return out
+}
+
+func withSource(s source.Source, label string) func(*Codec) {
+	return func(c *Codec) {
+		c.layers = append(c.layers, func(ctx context.Context) (map[string]string, error) {
+			b, err := bytesutil.ReadAll(ctx, s)
+			if err != nil {
+				return nil, fmt.Errorf("env: read %s: %w", label, err)
+			}
+			m, err := godotenv.UnmarshalBytes(b)
+			if err != nil {
+				return nil, fmt.Errorf("env: parse %s: %w", label, err)
+			}
+			return m, nil
+		})
+	}
+}
@@ -0,0 +1,125 @@
+package env
+
+import (
+	"context"
+	"testing"
+
+	"github.com/eslider/go-config/testfixtures"
+)
+
+type identityRoot struct {
+	Service svc `mapstructure:"service"`
+}
+
+type svc struct {
+	Name       string
+	Subservice sub `mapstructure:"subservice"`
+	Database   db  `mapstructure:"database"`
+}
+
+type sub struct {
+	Name    string
+	Key     string
+	Timeout int
+	Enabled bool
+}
+
+type db struct {
+	URL      string
+	PoolSize int `mapstructure:"poolsize"`
+}
+
+func TestCodec_IdentityEnvFixture(t *testing.T) {
+	c := New(WithBytes(testfixtures.Load(t, "identity", "service.env")))
+	var got identityRoot
+	if err := c.Unmarshal(&got); err != nil {
+		t.Fatal(err)
+	}
+	assertIdentity(t, got)
+}
+
+func assertIdentity(t *testing.T, got identityRoot) {
+	t.Helper()
+	if got.Service.Name != "my-service" {
+		t.Fatalf("Name=%q", got.Service.Name)
+	}
+	if got.Service.Subservice.Name != "abc" || got.Service.Subservice.Key != "abs" {
+		t.Fatalf("sub %+v", got.Service.Subservice)
+	}
+	if got.Service.Subservice.Timeout != 30 || !got.Service.Subservice.Enabled {
+		t.Fatalf("sub scalars %+v", got.Service.Subservice)
+	}
+	if got.Service.Database.URL != "postgres://localhost:5432/db" || got.Service.Database.PoolSize != 10 {
+		t.Fatalf("db %+v", got.Service.Database)
+	}
+}
+
+func TestCodec_MultiSourceLastWins(t *testing.T) {
+	c := New(
+		WithBytes(testfixtures.Load(t, "merge", "defaults.env")),
+		WithBytes(testfixtures.Load(t, "merge", "overlay.env")),
+	)
+	m, err := c.Map(context.Background())
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got := m["service"].(map[string]any)["subservice"].(map[string]any)["name"]; got != "overlay-name" {
+		t.Fatalf("subservice.name = %v", got)
+	}
+}
+
+func TestCodec_WithCurrentEnvironment(t *testing.T) {
+	t.Setenv("SERVICE_KEY", "abc")
+	t.Setenv("SERVICE_PORT", "8080")
+
+	var cfg struct {
+		Service struct {
+			Key  string `mapstructure:"key"`
+			Port int    `mapstructure:"port"`
+		} `mapstructure:"service"`
+	}
+	c := New(WithCurrentEnvironment())
+	if err := c.Unmarshal(&cfg); err != nil {
+		t.Fatal(err)
+	}
+	if cfg.Service.Key != "abc" || cfg.Service.Port != 8080 {
+		t.Fatalf("%+v", cfg)
+	}
+}
+
+func TestCodec_WithTrimWeaklyTyped(t *testing.T) {
+	t.Setenv("NAME", "  x  ")
+	var cfg struct{ Name string }
+	c := New(WithCurrentEnvironment(), WithTrim(true))
+	if err := c.Unmarshal(&cfg); err != nil {
+		t.Fatal(err)
+	}
+	if cfg.Name != "x" {
+		t.Fatalf("%q", cfg.Name)
+	}
+}
+
+func TestCodec_WithWeaklyTypedOff(t *testing.T) {
+	t.Setenv("PORT", "8080")
+	var cfg struct{ Port int }
+	c := New(WithCurrentEnvironment(), WithWeaklyTyped(false))
+	if err := c.Unmarshal(&cfg); err == nil {
+		t.Fatal("expected error")
+	}
+}
+
+func TestCodec_WithTagName(t *testing.T) {
+	t.Setenv("DATABASE_URL", "postgres://x")
+	var cfg struct {
+		DB struct {
+			URL string `mapstructure:"url"`
+		} `mapstructure:"database" env:"database"`
+	}
+	c := New(WithCurrentEnvironment(), WithTagName("env"))
+	if err := c.Unmarshal(&cfg); err != nil {
+		t.Fatal(err)
+	}
+	if cfg.DB.URL != "postgres://x" {
+		t.Fatalf("%q", cfg.DB.URL)
+	}
+}
@@ -0,0 +1,14 @@
+// Package env loads dotenv files and process environment variables into nested
+// maps and Go structs. Multiple sources merge with later scalars overriding
+// earlier ones; maps merge recursively.
+//
+// Example:
+//
+//	c := env.New(
+//	    env.WithFile(".default.env"),
+//	    env.WithFile(".env"),
+//	    env.WithCurrentEnvironment(),
+//	)
+//	var cfg MyConfig
+//	if err := c.Unmarshal(&cfg); err != nil { ... }
+package env
@@ -0,0 +1,49 @@
+package env
+
+import (
+	"strings"
+)
+
+// insertPath walks path inside root, creating intermediate nested maps as
+// needed, and stores value at the leaf. First write wins for a given leaf key
+// within a single source map.
+func insertPath(root map[string]any, path []string, value string) {
+	current := root
+	last := len(path) - 1
+	for i, raw := range path {
+		k := strings.ToLower(raw)
+
+		if i == last {
+			if _, exists := current[k]; exists {
+				return
+			}
+			current[k] = value
+			return
+		}
+
+		next, ok := current[k].(map[string]any)
+		if !ok {
+			next = make(map[string]any)
+			current[k] = next
+		}
+		current = next
+	}
+}
+
+func nestedFromFlat(flat map[string]string, prefix string) map[string]any {
+	out := make(map[string]any)
+	for k, v := range flat {
+		name := k
+		if prefix != "" {
+			if !strings.HasPrefix(name, prefix) {
+				continue
+			}
+			name = name[len(prefix):]
+			if name == "" {
+				continue
+			}
+		}
+		insertPath(out, strings.Split(name, "_"), v)
+	}
+	return out
+}
@@ -0,0 +1,35 @@
+package env
+
+import (
+	"reflect"
+	"testing"
+)
+
+func TestNestedFromFlat(t *testing.T) {
+	got := nestedFromFlat(map[string]string{
+		"FOO":               "bar",
+		"SERVICE_HTTP_PORT": "8080",
+		"SERVICE_KEY":       "abc",
+	}, "")
+	want := map[string]any{
+		"foo": "bar",
+		"service": map[string]any{
+			"http": map[string]any{"port": "8080"},
+			"key":  "abc",
+		},
+	}
+	if !reflect.DeepEqual(got, want) {
+		t.Fatalf("got %#v want %#v", got, want)
+	}
+}
+
+func TestNestedFromFlat_FirstWriteWins(t *testing.T) {
+	flat := map[string]string{}
+	flat["A"] = "1"
+	got := nestedFromFlat(flat, "")
+	// Second insert for same key is ignored by insertPath within one build.
+	insertPath(got, []string{"a"}, "2")
+	if got["a"] != "1" {
+		t.Fatalf("got %v", got["a"])
+	}
+}
@@ -0,0 +1,105 @@
+package env
+
+import (
+	"context"
+	"io"
+	"net/http"
+	"os"
+
+	"github.com/eslider/go-config/internal/keymap"
+	"github.com/eslider/go-config/internal/merge"
+	"github.com/eslider/go-config/internal/source"
+	"github.com/go-viper/mapstructure/v2"
+)
+
+// Option configures a Codec.
+type Option func(*Codec)
+
+// WithCurrentEnvironment appends the process environment as a source (read at Map time).
+func WithCurrentEnvironment() Option {
+	return func(c *Codec) {
+		c.layers = append(c.layers, func(_ context.Context) (map[string]string, error) {
+			return flatFromEnviron(os.Environ()), nil
+		})
+	}
+}
+
+// WithFile appends a dotenv file path as a source.
+func WithFile(path string) Option {
+	return withSource(source.File{Path: path}, path)
+}
+
+// WithBytes appends raw dotenv bytes as a source.
+func WithBytes(b []byte) Option {
+	return withSource(source.Bytes{Data: b, Name: "bytes"}, "bytes")
+}
+
+// WithReader appends dotenv content from r (read fully on each Map call).
+func WithReader(r io.Reader) Option {
+	return withSource(source.Reader{R: r, Name: "reader"}, "reader")
+}
+
+// WithURL appends an HTTP(S) URL returning dotenv content. Use WithHTTPHeader /
+// WithHTTPClient before WithURL so they apply to this request.
+func WithURL(raw string) Option {
+	return func(c *Codec) {
+		var hdr http.Header
+		if c.urlHeader != nil {
+			hdr = c.urlHeader.Clone()
+		}
+		s := source.URL{Raw: raw, Header: hdr, HTTPClient: c.httpClient}
+		withSource(s, raw)(c)
+	}
+}
+
+// WithHTTPClient sets the HTTP client used by subsequent WithURL sources.
+func WithHTTPClient(client *http.Client) Option {
+	return func(c *Codec) { c.httpClient = client }
+}
+
+// WithHTTPHeader adds a header for subsequent WithURL sources.
+func WithHTTPHeader(k, v string) Option {
+	return func(c *Codec) {
+		if c.urlHeader == nil {
+			c.urlHeader = make(http.Header)
+		}
+		c.urlHeader.Add(k, v)
+	}
+}
+
+// WithPrefix strips prefix from variable names before path splitting.
+func WithPrefix(prefix string) Option {
+	return func(c *Codec) { c.prefix = prefix }
+}
+
+// WithKeyNormalizer sets key normalizer after merge (nil disables).
+func WithKeyNormalizer(n keymap.Normalizer) Option {
+	return func(c *Codec) { c.normalizer = n }
+}
+
+// WithSliceMerge sets slice merge strategy when merging sources.
+func WithSliceMerge(s merge.SliceStrategy) Option {
+	return func(c *Codec) { c.sliceStrat = s }
+}
+
+// WithTrim toggles struct string trim via mapstructure hook.
+func WithTrim(enable bool) Option {
+	return func(c *Codec) { c.structOpts.Trim = enable }
+}
+
+// WithWeaklyTyped toggles weak typing for struct decode.
+func WithWeaklyTyped(enable bool) Option {
+	return func(c *Codec) { c.structOpts.WeaklyTyped = enable }
+}
+
+// WithTagName sets the struct tag name for mapstructure.
+func WithTagName(name string) Option {
+	return func(c *Codec) { c.structOpts.TagName = name }
+}
+
+// WithDecodeHook appends a decode hook.
+func WithDecodeHook(h mapstructure.DecodeHookFunc) Option {
+	return func(c *Codec) {
+		c.structOpts.ExtraHooks = append(c.structOpts.ExtraHooks, h)
+	}
+}
@@ -1,222 +0,0 @@
-package env
-
-import (
-	"reflect"
-	"testing"
-)
-
-// asMapFromEnviron is tested with a synthetic environ slice — this is NOT a
-// mock of anything external. It's a pure-input unit test that isolates the
-// core mapping logic from process-global state.
-
-func TestAsMapFromEnviron_FlatAndNested(t *testing.T) {
-	got := asMapFromEnviron([]string{
-		"FOO=bar",
-		"SERVICE_HTTP_PORT=8080",
-		"SERVICE_KEY=abc",
-	}, "")
-
-	want := map[string]any{
-		"foo": "bar",
-		"service": map[string]any{
-			"http": map[string]any{"port": "8080"},
-			"key":  "abc",
-		},
-	}
-	if !reflect.DeepEqual(got, want) {
-		t.Fatalf("got %#v, want %#v", got, want)
-	}
-}
-
-func TestAsMapFromEnviron_PreservesValuesWithEquals(t *testing.T) {
-	got := asMapFromEnviron([]string{"TOKEN=a=b=c="}, "")
-	if got["token"] != "a=b=c=" {
-		t.Fatalf("expected full value preserved, got %#v", got["token"])
-	}
-}
-
-func TestAsMapFromEnviron_PrefixFilterAndStrip(t *testing.T) {
-	got := asMapFromEnviron([]string{
-		"APP_DB_HOST=localhost",
-		"APP_DB_PORT=5432",
-		"OTHER_THING=skip",
-	}, "APP_")
-
-	want := map[string]any{
-		"db": map[string]any{"host": "localhost", "port": "5432"},
-	}
-	if !reflect.DeepEqual(got, want) {
-		t.Fatalf("got %#v, want %#v", got, want)
-	}
-}
-
-func TestAsMapFromEnviron_EmptyAndMalformedAreSkipped(t *testing.T) {
-	got := asMapFromEnviron([]string{"NOEQUALS", ""}, "")
-	if len(got) != 0 {
-		t.Fatalf("expected no entries, got %#v", got)
-	}
-}
-
-func TestAsMapFromEnviron_FirstWriteWinsOnCollision(t *testing.T) {
-	// This matches the ai-fabric original: once a leaf is set for a path,
-	// subsequent entries that would overwrite it are ignored.
-	got := asMapFromEnviron([]string{
-		"A=1",
-		"A=2",
-	}, "")
-	if got["a"] != "1" {
-		t.Fatalf("expected first-write-wins (a=1), got %#v", got["a"])
-	}
-}
-
-func TestAsMapFromEnviron_PrefixOnlyVariableIsSkipped(t *testing.T) {
-	// "APP_=xxx" with prefix "APP_" would strip to empty key — we skip it.
-	got := asMapFromEnviron([]string{"APP_=oops"}, "APP_")
-	if len(got) != 0 {
-		t.Fatalf("expected empty map, got %#v", got)
-	}
-}
-
-// ---------------------------------------------------------------------------
-// Decoder / option tests
-// ---------------------------------------------------------------------------
-
-func TestUnmarshal_BasicStruct(t *testing.T) {
-	t.Setenv("SERVICE_KEY", "abc")
-	t.Setenv("SERVICE_PORT", "8080")
-
-	var cfg struct {
-		Service struct {
-			Key  string
-			Port int
-		}
-	}
-	if err := Unmarshal(&cfg); err != nil {
-		t.Fatalf("unexpected error: %v", err)
-	}
-	if cfg.Service.Key != "abc" {
-		t.Errorf("Key = %q, want abc", cfg.Service.Key)
-	}
-	if cfg.Service.Port != 8080 {
-		t.Errorf("Port = %d, want 8080 (weakly-typed string->int)", cfg.Service.Port)
-	}
-}
-
-func TestUnmarshal_TrimsStringsByDefault(t *testing.T) {
-	t.Setenv("NAME", "   hello   ")
-
-	var cfg struct{ Name string }
-	if err := Unmarshal(&cfg); err != nil {
-		t.Fatalf("unexpected error: %v", err)
-	}
-	if cfg.Name != "hello" {
-		t.Fatalf("expected trimmed value, got %q", cfg.Name)
-	}
-}
-
-func TestUnmarshal_WithTrimOff(t *testing.T) {
-	t.Setenv("NAME", "  keep me  ")
-
-	var cfg struct{ Name string }
-	if err := Unmarshal(&cfg, WithTrim(false)); err != nil {
-		t.Fatalf("unexpected error: %v", err)
-	}
-	if cfg.Name != "  keep me  " {
-		t.Fatalf("expected untrimmed value, got %q", cfg.Name)
-	}
-}
-
-func TestUnmarshalPrefix_StripsAndFilters(t *testing.T) {
-	t.Setenv("APP_DB_HOST", "localhost")
-	t.Setenv("APP_DB_PORT", "5432")
-	t.Setenv("OTHER_DB_HOST", "should-be-ignored")
-
-	var cfg struct {
-		DB struct {
-			Host string
-			Port int
-		} `mapstructure:"db"`
-	}
-	if err := UnmarshalPrefix(&cfg, "APP_"); err != nil {
-		t.Fatalf("unexpected error: %v", err)
-	}
-	if cfg.DB.Host != "localhost" {
-		t.Errorf("Host = %q, want localhost", cfg.DB.Host)
-	}
-	if cfg.DB.Port != 5432 {
-		t.Errorf("Port = %d, want 5432", cfg.DB.Port)
-	}
-}
-
-func TestUnmarshal_WithTagName(t *testing.T) {
-	t.Setenv("DATABASE_URL", "postgres://x")
-
-	// The map is always nested by '_', so tags also reference the nested
-	// path, one component per struct level. Here we override the outer
-	// field name via a custom tag.
-	var cfg struct {
-		DB struct {
-			URL string
-		} `env:"database"`
-	}
-	if err := Unmarshal(&cfg, WithTagName("env")); err != nil {
-		t.Fatalf("unexpected error: %v", err)
-	}
-	if cfg.DB.URL != "postgres://x" {
-		t.Fatalf("URL = %q, want postgres://x", cfg.DB.URL)
-	}
-}
-
-func TestUnmarshal_WeaklyTypedOff(t *testing.T) {
-	t.Setenv("PORT", "8080")
-
-	var cfg struct{ Port int }
-	err := Unmarshal(&cfg, WithWeaklyTyped(false))
-	// With strict typing, "8080" (string) cannot decode into an int.
-	if err == nil {
-		t.Fatal("expected strict typing to reject string->int coercion")
-	}
-}
-
-func TestUnmarshal_SpecialCharactersSurvive(t *testing.T) {
-	// Regression: keys with special chars in their values must pass through
-	// unchanged (modulo TrimSpace).
-	t.Setenv("SPECIAL", "@!#$%^&*()")
-
-	var cfg struct{ Special string }
-	if err := Unmarshal(&cfg); err != nil {
-		t.Fatalf("unexpected error: %v", err)
-	}
-	if cfg.Special != "@!#$%^&*()" {
-		t.Fatalf("Special = %q, want @!#$%%^&*()", cfg.Special)
-	}
-}
-
-func TestUnmarshal_RejectsNonPointer(t *testing.T) {
-	var cfg struct{ A string }
-	err := Unmarshal(cfg) // no pointer
-	if err == nil {
-		t.Fatal("expected error when passing a non-pointer")
-	}
-}
-
-func TestAsMap_ExposesCurrentEnv(t *testing.T) {
-	t.Setenv("GO_ENV_ASMAP_PROBE", "hit")
-
-	m := AsMap()
-	goenv, ok := m["go"].(map[string]any)
-	if !ok {
-		t.Fatalf("expected nested map under 'go', got %T", m["go"])
-	}
-	env, ok := goenv["env"].(map[string]any)
-	if !ok {
-		t.Fatalf("expected nested map under 'go.env', got %T", goenv["env"])
-	}
-	asmap, ok := env["asmap"].(map[string]any)
-	if !ok {
-		t.Fatalf("expected nested map under 'go.env.asmap', got %T", env["asmap"])
-	}
-	if asmap["probe"] != "hit" {
-		t.Fatalf("probe = %v, want hit", asmap["probe"])
-	}
-}
@@ -0,0 +1,20 @@
+package config_test
+
+import (
+	"fmt"
+
+	"github.com/eslider/go-config/env"
+	"github.com/eslider/go-config/yaml"
+)
+
+func Example_hero_offline() {
+	// README hero pattern using offline sources (no network, no .env files).
+	y := yaml.New(yaml.WithBytes([]byte(`service: { name: demo }`)))
+	e := env.New(env.WithBytes([]byte("SERVICE_PORT=8080")))
+	var m map[string]any
+	_ = y.Unmarshal(&m)
+	var flat map[string]any
+	_ = e.Unmarshal(&flat)
+	fmt.Println(m["service"].(map[string]any)["name"], flat["service"].(map[string]any)["port"])
+	// Output: demo 8080
+}
@@ -0,0 +1,5 @@
+a:
+  b:
+    c:
+      d:
+        e: leaf
@@ -0,0 +1,4 @@
+topLevel: 1
+sub-Service: 2
+snake_case: 3
+CamelCase: 4
@@ -0,0 +1,7 @@
+{
+  "flag": true,
+  "count": 42,
+  "ratio": 3.14,
+  "nothing": null,
+  "nested": [1, 2]
+}
@@ -0,0 +1,7 @@
+SERVICE_NAME=my-service
+SERVICE_SUBSERVICE_NAME=abc
+SERVICE_SUBSERVICE_KEY=abs
+SERVICE_SUBSERVICE_TIMEOUT=30
+SERVICE_SUBSERVICE_ENABLED=true
+SERVICE_DATABASE_URL=postgres://localhost:5432/db
+SERVICE_DATABASE_POOLSIZE=10
@@ -0,0 +1,12 @@
+[service]
+name = my-service
+
+[service.subservice]
+name = abc
+key = abs
+timeout = 30
+enabled = true
+
+[service.database]
+url = postgres://localhost:5432/db
+pool-size = 10
@@ -0,0 +1,15 @@
+{
+  "service": {
+    "name": "my-service",
+    "sub-service": {
+      "name": "abc",
+      "key": "abs",
+      "timeout": 30,
+      "enabled": true
+    },
+    "database": {
+      "url": "postgres://localhost:5432/db",
+      "pool-size": 10
+    }
+  }
+}
@@ -0,0 +1,10 @@
+service:
+  name: my-service
+  sub-service:
+    name: abc
+    key: abs
+    timeout: 30
+    enabled: true
+  database:
+    url: postgres://localhost:5432/db
+    pool-size: 10
@@ -0,0 +1,3 @@
+[sec]
+a = 1
+a = 2
@@ -0,0 +1 @@
+{ not json
@@ -0,0 +1 @@
+service: [unclosed
@@ -0,0 +1,7 @@
+SERVICE_NAME=default-name
+SERVICE_SUBSERVICE_NAME=default-sub
+SERVICE_SUBSERVICE_KEY=default-key
+SERVICE_SUBSERVICE_TIMEOUT=1
+SERVICE_SUBSERVICE_ENABLED=false
+SERVICE_DATABASE_URL=postgres://old
+SERVICE_DATABASE_POOLSIZE=1
@@ -0,0 +1,13 @@
+service:
+  name: default-name
+  sub-service:
+    name: default-sub
+    key: default-key
+    timeout: 1
+    enabled: false
+  hosts:
+    - a
+    - b
+  database:
+    url: postgres://old
+    pool-size: 1
@@ -0,0 +1,14 @@
+service:
+  name: default-name
+  sub-service:
+    name: overlay-name
+    key: default-key
+    timeout: 1
+    enabled: false
+  hosts:
+    - a
+    - b
+    - x
+  database:
+    url: postgres://old
+    pool-size: 1
@@ -0,0 +1,12 @@
+service:
+  name: default-name
+  sub-service:
+    name: overlay-name
+    key: default-key
+    timeout: 1
+    enabled: false
+  hosts:
+    - x
+  database:
+    url: postgres://old
+    pool-size: 1
@@ -0,0 +1 @@
+SERVICE_SUBSERVICE_NAME=overlay-name
@@ -0,0 +1,5 @@
+service:
+  sub-service:
+    name: overlay-name
+  hosts:
+    - x
@@ -1,5 +1,12 @@
-module github.com/eslider/go-env
+module github.com/eslider/go-config

 go 1.22.2

-require github.com/mitchellh/mapstructure v1.5.0
+require (
+	github.com/go-viper/mapstructure/v2 v2.5.0
+	github.com/joho/godotenv v1.5.1
+	gopkg.in/ini.v1 v1.67.0
+	gopkg.in/yaml.v3 v3.0.1
+)
+
+require github.com/stretchr/testify v1.11.1 // indirect
@@ -1,2 +1,16 @@
-github.com/mitchellh/mapstructure v1.5.0 h1:jeMsZIYE/09sWLaz43PL7Gy6RuMjD2eJVyuac5Z2hdY=
-github.com/mitchellh/mapstructure v1.5.0/go.mod h1:bFUtVrKA4DC2yAKiSyO/QUcy7e+RRV2QTWOzhPopBRo=
+github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
+github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/go-viper/mapstructure/v2 v2.5.0 h1:vM5IJoUAy3d7zRSVtIwQgBj7BiWtMPfmPEgAXnvj1Ro=
+github.com/go-viper/mapstructure/v2 v2.5.0/go.mod h1:oJDH3BJKyqBA2TXFhDsKDGDTlndYOZ6rGS0BRZIxGhM=
+github.com/joho/godotenv v1.5.1 h1:7eLL/+HRGLY0ldzfGMeQkb7vMd0as4CfYvUVzLqw0N0=
+github.com/joho/godotenv v1.5.1/go.mod h1:f4LDr5Voq0i2e/R5DDNOoa2zzDfwtkZa6DnEwAbqwq4=
+github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
+github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/stretchr/testify v1.11.1 h1:7s2iGBzp5EwR7/aIZr8ao5+dra3wiQyKjjFuvgVKu7U=
+github.com/stretchr/testify v1.11.1/go.mod h1:wZwfW3scLgRK+23gO65QZefKpKQRnfz6sD981Nm4B6U=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405 h1:yhCVgyC4o1eVCa2tZl7eS0r+SDo693bJlVdllGtEeKM=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/ini.v1 v1.67.0 h1:Dgnx+6+nfE+IfzjUEISNeydPJh9AXNNsWbGP9KzCsOA=
+gopkg.in/ini.v1 v1.67.0/go.mod h1:pNLf8WUiyNEtQjuu5G5vTm06TEv9tsIgeAvK8hOrP4k=
+gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=
+gopkg.in/yaml.v3 v3.0.1/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
@@ -0,0 +1,163 @@
+package ini
+
+import (
+	"context"
+	"fmt"
+	"io"
+	"net/http"
+	"strings"
+
+	"github.com/eslider/go-config/internal/bytesutil"
+	"github.com/eslider/go-config/internal/keymap"
+	"github.com/eslider/go-config/internal/merge"
+	"github.com/eslider/go-config/internal/source"
+	"github.com/eslider/go-config/internal/structconv"
+	iniv1 "gopkg.in/ini.v1"
+)
+
+// Codec loads INI from multiple sources.
+type Codec struct {
+	sources    []source.Source
+	normalizer keymap.Normalizer
+	sliceStrat merge.SliceStrategy
+	structOpts structconv.Options
+	mergeOpts  []merge.Option
+	httpClient *http.Client
+	urlHeader  http.Header
+}
+
+// New creates an INI codec.
+func New(opts ...Option) *Codec {
+	c := &Codec{
+		normalizer: keymap.LowerAlnum,
+		sliceStrat: merge.Replace,
+		structOpts: structconv.Options{
+			TagName:     "mapstructure",
+			WeaklyTyped: true,
+			Trim:        true,
+		},
+	}
+	for _, o := range opts {
+		o(c)
+	}
+	c.mergeOpts = []merge.Option{merge.WithSliceStrategy(c.sliceStrat)}
+	return c
+}
+
+// Map merges all INI sources into one map.
+func (c *Codec) Map(ctx context.Context) (map[string]any, error) {
+	if len(c.sources) == 0 {
+		return nil, fmt.Errorf("ini: no sources")
+	}
+	acc := make(map[string]any)
+	for _, s := range c.sources {
+		b, err := bytesutil.ReadAll(ctx, s)
+		if err != nil {
+			return nil, fmt.Errorf("ini: read %s: %w", s.String(), err)
+		}
+		f, err := iniv1.LoadSources(iniv1.LoadOptions{Loose: true, Insensitive: false}, b)
+		if err != nil {
+			return nil, fmt.Errorf("ini: parse %s: %w", s.String(), err)
+		}
+		parsed := mapFromINIFile(f)
+		merge.DeepMerge(acc, parsed, c.mergeOpts...)
+	}
+	if c.normalizer != nil {
+		keymap.Walk(acc, c.normalizer)
+	}
+	return acc, nil
+}
+
+// Unmarshal decodes using context.Background.
+func (c *Codec) Unmarshal(dst any) error {
+	return c.UnmarshalContext(context.Background(), dst)
+}
+
+// UnmarshalContext decodes merged INI into dst.
+func (c *Codec) UnmarshalContext(ctx context.Context, dst any) error {
+	m, err := c.Map(ctx)
+	if err != nil {
+		return err
+	}
+	return structconv.Decode(m, dst, c.structOpts)
+}
+
+// Marshal encodes src to INI bytes (struct or map[string]any).
+func (c *Codec) Marshal(src any) ([]byte, error) {
+	m, err := encodeToMap(src)
+	if err != nil {
+		return nil, fmt.Errorf("ini: encode: %w", err)
+	}
+	f := iniv1.Empty()
+	if err := emitMap(nil, m, f); err != nil {
+		return nil, err
+	}
+	var buf strings.Builder
+	if _, err := f.WriteTo(&buf); err != nil {
+		return nil, fmt.Errorf("ini: write: %w", err)
+	}
+	return []byte(buf.String()), nil
+}
+
+// WriteTo writes INI to w.
+func (c *Codec) WriteTo(w io.Writer, src any) (int64, error) {
+	b, err := c.Marshal(src)
+	if err != nil {
+		return 0, err
+	}
+	n, err := w.Write(b)
+	return int64(n), err
+}
+
+func emitMap(prefix []string, m map[string]any, f *iniv1.File) error {
+	for k, v := range m {
+		switch t := v.(type) {
+		case map[string]any:
+			if err := emitMap(append(prefix, k), t, f); err != nil {
+				return err
+			}
+		case []any:
+			parts := make([]string, 0, len(t))
+			for _, e := range t {
+				parts = append(parts, fmt.Sprint(e))
+			}
+			secName := strings.Join(prefix, ".")
+			if secName == "" {
+				secName = iniv1.DefaultSection
+			}
+			sec, err := f.GetSection(secName)
+			if err != nil {
+				sec, err = f.NewSection(secName)
+				if err != nil {
+					return err
+				}
+			}
+			if _, err := sec.NewKey(k, strings.Join(parts, ",")); err != nil {
+				return err
+			}
+		default:
+			secName := strings.Join(prefix, ".")
+			if secName == "" {
+				secName = iniv1.DefaultSection
+			}
+			sec, err := f.GetSection(secName)
+			if err != nil {
+				sec, err = f.NewSection(secName)
+				if err != nil {
+					return err
+				}
+			}
+			if _, err := sec.NewKey(k, fmt.Sprint(t)); err != nil {
+				return err
+			}
+		}
+	}
+	return nil
+}
+
+func encodeToMap(src any) (map[string]any, error) {
+	if m, ok := src.(map[string]any); ok {
+		return m, nil
+	}
+	return structconv.Encode(src)
+}
@@ -0,0 +1,20 @@
+package ini
+
+import (
+	"context"
+	"testing"
+
+	"github.com/eslider/go-config/testfixtures"
+)
+
+func TestCodec_IdentityINIFixture(t *testing.T) {
+	c := New(WithBytes(testfixtures.Load(t, "identity", "service.ini")))
+	m, err := c.Map(context.Background())
+	if err != nil {
+		t.Fatal(err)
+	}
+	svc := m["service"].(map[string]any)
+	if svc["name"] != "my-service" {
+		t.Fatalf("%#v", svc)
+	}
+}
@@ -0,0 +1,3 @@
+// Package ini loads INI configuration from bytes, files, or URLs into maps
+// and structs. Section names may use dot notation for nesting.
+package ini
@@ -0,0 +1,49 @@
+package ini
+
+import (
+	"strings"
+
+	iniv1 "gopkg.in/ini.v1"
+)
+
+func insertPath(root map[string]any, path []string, value string) {
+	current := root
+	last := len(path) - 1
+	for i, raw := range path {
+		k := strings.ToLower(raw)
+		if i == last {
+			if _, exists := current[k]; exists {
+				return
+			}
+			current[k] = value
+			return
+		}
+		next, ok := current[k].(map[string]any)
+		if !ok {
+			next = make(map[string]any)
+			current[k] = next
+		}
+		current = next
+	}
+}
+
+func mapFromINIFile(f *iniv1.File) map[string]any {
+	out := make(map[string]any)
+	for _, name := range f.SectionStrings() {
+		sec, err := f.GetSection(name)
+		if err != nil {
+			continue
+		}
+		if strings.EqualFold(name, iniv1.DefaultSection) {
+			for k, v := range sec.KeysHash() {
+				insertPath(out, []string{k}, v)
+			}
+			continue
+		}
+		path := strings.Split(name, ".")
+		for k, v := range sec.KeysHash() {
+			insertPath(out, append(append([]string{}, path...), k), v)
+		}
+	}
+	return out
+}
@@ -0,0 +1,87 @@
+package ini
+
+import (
+	"io"
+	"net/http"
+
+	"github.com/eslider/go-config/internal/keymap"
+	"github.com/eslider/go-config/internal/merge"
+	"github.com/eslider/go-config/internal/source"
+	"github.com/go-viper/mapstructure/v2"
+)
+
+// Option configures a Codec.
+type Option func(*Codec)
+
+// WithBytes appends INI from bytes.
+func WithBytes(b []byte) Option {
+	return func(c *Codec) { c.sources = append(c.sources, source.Bytes{Data: b, Name: "bytes"}) }
+}
+
+// WithReader appends INI from r.
+func WithReader(r io.Reader) Option {
+	return func(c *Codec) { c.sources = append(c.sources, source.Reader{R: r, Name: "reader"}) }
+}
+
+// WithFile appends an INI file path.
+func WithFile(path string) Option {
+	return func(c *Codec) { c.sources = append(c.sources, source.File{Path: path}) }
+}
+
+// WithURL appends INI from an HTTP(S) URL.
+func WithURL(raw string) Option {
+	return func(c *Codec) {
+		var hdr http.Header
+		if c.urlHeader != nil {
+			hdr = c.urlHeader.Clone()
+		}
+		c.sources = append(c.sources, source.URL{Raw: raw, Header: hdr, HTTPClient: c.httpClient})
+	}
+}
+
+// WithHTTPClient sets the client for subsequent WithURL sources.
+func WithHTTPClient(client *http.Client) Option {
+	return func(c *Codec) { c.httpClient = client }
+}
+
+// WithHTTPHeader adds a header for subsequent WithURL sources.
+func WithHTTPHeader(k, v string) Option {
+	return func(c *Codec) {
+		if c.urlHeader == nil {
+			c.urlHeader = make(http.Header)
+		}
+		c.urlHeader.Add(k, v)
+	}
+}
+
+// WithKeyNormalizer sets key normalizer after merge (nil disables).
+func WithKeyNormalizer(n keymap.Normalizer) Option {
+	return func(c *Codec) { c.normalizer = n }
+}
+
+// WithSliceMerge sets slice merge strategy across sources.
+func WithSliceMerge(s merge.SliceStrategy) Option {
+	return func(c *Codec) { c.sliceStrat = s }
+}
+
+// WithTrim toggles string trim on struct decode.
+func WithTrim(enable bool) Option {
+	return func(c *Codec) { c.structOpts.Trim = enable }
+}
+
+// WithWeaklyTyped toggles weak typing for struct decode.
+func WithWeaklyTyped(enable bool) Option {
+	return func(c *Codec) { c.structOpts.WeaklyTyped = enable }
+}
+
+// WithTagName sets mapstructure tag name.
+func WithTagName(name string) Option {
+	return func(c *Codec) { c.structOpts.TagName = name }
+}
+
+// WithDecodeHook appends a decode hook.
+func WithDecodeHook(h mapstructure.DecodeHookFunc) Option {
+	return func(c *Codec) {
+		c.structOpts.ExtraHooks = append(c.structOpts.ExtraHooks, h)
+	}
+}
@@ -0,0 +1,19 @@
+// Package bytesutil reads entire sources into memory.
+package bytesutil
+
+import (
+	"context"
+	"io"
+
+	"github.com/eslider/go-config/internal/source"
+)
+
+// ReadAll reads and closes the stream opened by s.
+func ReadAll(ctx context.Context, s source.Source) ([]byte, error) {
+	rc, err := s.Open(ctx)
+	if err != nil {
+		return nil, err
+	}
+	defer func() { _ = rc.Close() }()
+	return io.ReadAll(rc)
+}
@@ -0,0 +1,56 @@
+// Package keymap normalizes map keys recursively for cross-format matching.
+package keymap
+
+import "strings"
+
+// Normalizer transforms a single path segment or key string.
+type Normalizer func(string) string
+
+// LowerAlnum lowercases and strips any rune that is not [a-z0-9].
+func LowerAlnum(s string) string {
+	var b strings.Builder
+	b.Grow(len(s))
+	for _, r := range strings.ToLower(s) {
+		if r >= 'a' && r <= 'z' || r >= '0' && r <= '9' {
+			b.WriteRune(r)
+		}
+	}
+	return b.String()
+}
+
+// Identity returns s unchanged.
+func Identity(s string) string { return s }
+
+// Walk recursively rewrites every map key in place using n. Slices of maps are walked.
+func Walk(m map[string]any, n Normalizer) {
+	if m == nil || n == nil {
+		return
+	}
+	keys := make([]string, 0, len(m))
+	for k := range m {
+		keys = append(keys, k)
+	}
+	for _, k := range keys {
+		v := m[k]
+		delete(m, k)
+		nk := n(k)
+		if nk == "" {
+			nk = k
+		}
+		switch vv := v.(type) {
+		case map[string]any:
+			Walk(vv, n)
+			m[nk] = vv
+		case []any:
+			for i := range vv {
+				if sm, ok := vv[i].(map[string]any); ok {
+					Walk(sm, n)
+					vv[i] = sm
+				}
+			}
+			m[nk] = vv
+		default:
+			m[nk] = v
+		}
+	}
+}
@@ -0,0 +1,25 @@
+package keymap
+
+import (
+	"reflect"
+	"testing"
+)
+
+func TestLowerAlnum(t *testing.T) {
+	if got, want := LowerAlnum("sub-Service"), "subservice"; got != want {
+		t.Fatalf("got %q want %q", got, want)
+	}
+}
+
+func TestWalk(t *testing.T) {
+	m := map[string]any{
+		"Sub-Service": map[string]any{"Pool-Size": "10"},
+	}
+	Walk(m, LowerAlnum)
+	want := map[string]any{
+		"subservice": map[string]any{"poolsize": "10"},
+	}
+	if !reflect.DeepEqual(m, want) {
+		t.Fatalf("got %#v want %#v", m, want)
+	}
+}
@@ -0,0 +1,77 @@
+// Package merge provides deep map merging with configurable slice behaviour.
+package merge
+
+// SliceStrategy controls how two []any values are combined at the same key.
+type SliceStrategy int
+
+const (
+	// Replace overwrites the destination slice with the source slice.
+	Replace SliceStrategy = iota
+	// Concat appends source elements to the destination slice.
+	Concat
+)
+
+// Option configures DeepMerge.
+type Option func(*config)
+
+type config struct {
+	slice SliceStrategy
+}
+
+// WithSliceStrategy sets slice merge behaviour (default Replace).
+func WithSliceStrategy(s SliceStrategy) Option {
+	return func(c *config) { c.slice = s }
+}
+
+// DeepMerge folds src into dst in place. Maps recurse; scalar leaves use
+// last-write-wins (src overwrites dst). For slice values, behaviour follows cfg.slice.
+func DeepMerge(dst, src map[string]any, opts ...Option) {
+	cfg := config{slice: Replace}
+	for _, o := range opts {
+		o(&cfg)
+	}
+	if dst == nil || src == nil {
+		return
+	}
+	for k, sv := range src {
+		dv, ok := dst[k]
+		if !ok {
+			dst[k] = cloneValue(sv)
+			continue
+		}
+		dm, dIsMap := dv.(map[string]any)
+		sm, sIsMap := sv.(map[string]any)
+		if dIsMap && sIsMap {
+			DeepMerge(dm, sm, opts...)
+			dst[k] = dm
+			continue
+		}
+		if dsa, dIsSlice := dv.([]any); dIsSlice {
+			if ssa, sIsSlice := sv.([]any); sIsSlice {
+				switch cfg.slice {
+				case Concat:
+					dst[k] = append(append([]any{}, dsa...), ssa...)
+				default:
+					dst[k] = append([]any{}, ssa...)
+				}
+				continue
+			}
+		}
+		dst[k] = cloneValue(sv)
+	}
+}
+
+func cloneValue(v any) any {
+	switch t := v.(type) {
+	case map[string]any:
+		out := make(map[string]any, len(t))
+		DeepMerge(out, t)
+		return out
+	case []any:
+		cp := make([]any, len(t))
+		copy(cp, t)
+		return cp
+	default:
+		return v
+	}
+}
@@ -0,0 +1,52 @@
+package merge
+
+import (
+	"reflect"
+	"testing"
+)
+
+func TestDeepMerge_MapRecursion(t *testing.T) {
+	dst := map[string]any{
+		"a": map[string]any{"x": "1"},
+	}
+	src := map[string]any{
+		"a": map[string]any{"y": "2"},
+	}
+	DeepMerge(dst, src)
+	want := map[string]any{
+		"a": map[string]any{"x": "1", "y": "2"},
+	}
+	if !reflect.DeepEqual(dst, want) {
+		t.Fatalf("got %#v want %#v", dst, want)
+	}
+}
+
+func TestDeepMerge_ScalarLastWins(t *testing.T) {
+	dst := map[string]any{"k": "first"}
+	src := map[string]any{"k": "second"}
+	DeepMerge(dst, src)
+	if dst["k"] != "second" {
+		t.Fatalf("got %v", dst["k"])
+	}
+}
+
+func TestDeepMerge_SliceReplace(t *testing.T) {
+	dst := map[string]any{"s": []any{"a", "b"}}
+	src := map[string]any{"s": []any{"c"}}
+	DeepMerge(dst, src, WithSliceStrategy(Replace))
+	got := dst["s"].([]any)
+	if len(got) != 1 || got[0] != "c" {
+		t.Fatalf("got %#v", got)
+	}
+}
+
+func TestDeepMerge_SliceConcat(t *testing.T) {
+	dst := map[string]any{"s": []any{"a", "b"}}
+	src := map[string]any{"s": []any{"c"}}
+	DeepMerge(dst, src, WithSliceStrategy(Concat))
+	got := dst["s"].([]any)
+	want := []any{"a", "b", "c"}
+	if !reflect.DeepEqual(got, want) {
+		t.Fatalf("got %#v want %#v", got, want)
+	}
+}
@@ -0,0 +1,129 @@
+// Package source provides pluggable configuration inputs (bytes, files, URLs).
+package source
+
+import (
+	"bytes"
+	"context"
+	"fmt"
+	"io"
+	"net/http"
+	"os"
+	"strings"
+	"time"
+)
+
+// Source opens a byte stream for reading. Callers must close the ReadCloser.
+type Source interface {
+	Open(ctx context.Context) (io.ReadCloser, error)
+	String() string
+}
+
+// Bytes holds raw bytes in memory.
+type Bytes struct {
+	Data []byte
+	Name string
+}
+
+// Open returns a ReadCloser over a copy of Data.
+func (b Bytes) Open(_ context.Context) (io.ReadCloser, error) {
+	return io.NopCloser(bytes.NewReader(b.Data)), nil
+}
+
+// String returns a label for errors (defaults to "bytes").
+func (b Bytes) String() string {
+	if b.Name != "" {
+		return b.Name
+	}
+	return "bytes"
+}
+
+// Reader wraps an io.Reader. The reader is consumed once per Open call.
+type Reader struct {
+	R    io.Reader
+	Name string
+}
+
+// Open returns the reader as a ReadCloser when possible, otherwise wraps r.R.
+func (r Reader) Open(_ context.Context) (io.ReadCloser, error) {
+	rc, ok := r.R.(io.ReadCloser)
+	if ok {
+		return rc, nil
+	}
+	return io.NopCloser(r.R), nil
+}
+
+// String returns a label for errors (defaults to "reader").
+func (r Reader) String() string {
+	if r.Name != "" {
+		return r.Name
+	}
+	return "reader"
+}
+
+// File opens a path on the local filesystem.
+type File struct {
+	Path string
+}
+
+// Open opens the file path.
+func (f File) Open(_ context.Context) (io.ReadCloser, error) {
+	return os.Open(f.Path)
+}
+
+// String returns the file path.
+func (f File) String() string {
+	return f.Path
+}
+
+// URL fetches remote content over HTTP or HTTPS.
+type URL struct {
+	Raw        string
+	Header     http.Header
+	HTTPClient *http.Client
+}
+
+func defaultClient() *http.Client {
+	return &http.Client{Timeout: 30 * time.Second}
+}
+
+// Open performs a GET request and returns the response body.
+func (u URL) Open(ctx context.Context) (io.ReadCloser, error) {
+	client := u.HTTPClient
+	if client == nil {
+		client = defaultClient()
+	}
+	req, err := http.NewRequestWithContext(ctx, http.MethodGet, u.Raw, nil)
+	if err != nil {
+		return nil, fmt.Errorf("source url: new request: %w", err)
+	}
+	if u.Header != nil {
+		req.Header = u.Header.Clone()
+	}
+	resp, err := client.Do(req)
+	if err != nil {
+		return nil, fmt.Errorf("source url %q: %w", u.Raw, err)
+	}
+	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
+		_ = resp.Body.Close()
+		return nil, fmt.Errorf("source url %q: status %s", u.Raw, resp.Status)
+	}
+	return resp.Body, nil
+}
+
+func (u URL) String() string {
+	return u.Raw
+}
+
+// JoinNames joins source labels for error messages.
+func JoinNames(srcs []Source) string {
+	if len(srcs) == 0 {
+		return ""
+	}
+	parts := make([]string, 0, len(srcs))
+	for _, s := range srcs {
+		if s != nil {
+			parts = append(parts, s.String())
+		}
+	}
+	return strings.Join(parts, ", ")
+}
@@ -0,0 +1,43 @@
+package source
+
+import (
+	"context"
+	"io"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+)
+
+func TestURL_OK(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
+		_, _ = w.Write([]byte("hello"))
+	}))
+	defer srv.Close()
+
+	u := URL{Raw: srv.URL}
+	rc, err := u.Open(context.Background())
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer func() { _ = rc.Close() }()
+	b, err := io.ReadAll(rc)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if string(b) != "hello" {
+		t.Fatalf("got %q", b)
+	}
+}
+
+func TestURL_StatusError(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
+		w.WriteHeader(http.StatusNotFound)
+	}))
+	defer srv.Close()
+
+	u := URL{Raw: srv.URL}
+	_, err := u.Open(context.Background())
+	if err == nil {
+		t.Fatal("expected error")
+	}
+}
@@ -0,0 +1,74 @@
+// Package structconv wraps mapstructure for map<->struct conversion.
+package structconv
+
+import (
+	"fmt"
+	"reflect"
+	"strings"
+
+	"github.com/go-viper/mapstructure/v2"
+)
+
+// Options configures Decode and Encode.
+type Options struct {
+	TagName     string
+	WeaklyTyped bool
+	Trim        bool
+	ExtraHooks  []mapstructure.DecodeHookFunc
+}
+
+func trimStringHook(from, to reflect.Type, data any) (any, error) {
+	if from.Kind() == reflect.String && to.Kind() == reflect.String {
+		if s, ok := data.(string); ok {
+			return strings.TrimSpace(s), nil
+		}
+	}
+	return data, nil
+}
+
+func composeHooks(o Options) mapstructure.DecodeHookFunc {
+	var hooks []mapstructure.DecodeHookFunc
+	if o.Trim {
+		hooks = append(hooks, trimStringHook)
+	}
+	hooks = append(hooks, o.ExtraHooks...)
+	if len(hooks) == 0 {
+		return nil
+	}
+	return mapstructure.ComposeDecodeHookFunc(hooks...)
+}
+
+// Decode maps in into struct or map dst (dst must be pointer).
+func Decode(in map[string]any, dst any, o Options) error {
+	tag := o.TagName
+	if tag == "" {
+		tag = "mapstructure"
+	}
+	cfg := &mapstructure.DecoderConfig{
+		Result:           dst,
+		WeaklyTypedInput: o.WeaklyTyped,
+		TagName:          tag,
+		DecodeHook:       composeHooks(o),
+	}
+	dec, err := mapstructure.NewDecoder(cfg)
+	if err != nil {
+		return fmt.Errorf("structconv: decoder: %w", err)
+	}
+	if err := dec.Decode(in); err != nil {
+		return fmt.Errorf("structconv: decode: %w", err)
+	}
+	return nil
+}
+
+// Encode flattens src (struct or map) into a new map[string]any.
+func Encode(src any) (map[string]any, error) {
+	out := make(map[string]any)
+	dec, err := mapstructure.NewDecoder(&mapstructure.DecoderConfig{Result: &out})
+	if err != nil {
+		return nil, fmt.Errorf("structconv: encoder: %w", err)
+	}
+	if err := dec.Decode(src); err != nil {
+		return nil, fmt.Errorf("structconv: encode: %w", err)
+	}
+	return out, nil
+}
@@ -0,0 +1,28 @@
+package structconv
+
+import (
+	"fmt"
+	"testing"
+)
+
+func TestDecodeEncodeRoundTrip(t *testing.T) {
+	type nested struct {
+		V int `mapstructure:"v"`
+	}
+	type root struct {
+		A nested `mapstructure:"a"`
+	}
+	in := map[string]any{"a": map[string]any{"v": 7}}
+	var dst root
+	if err := Decode(in, &dst, Options{WeaklyTyped: true, Trim: true}); err != nil {
+		t.Fatal(err)
+	}
+	out, err := Encode(&dst)
+	if err != nil {
+		t.Fatal(err)
+	}
+	am := out["a"].(map[string]any)
+	if fmt.Sprint(am["v"]) != "7" {
+		t.Fatalf("%#v", out)
+	}
+}
@@ -0,0 +1,114 @@
+package json
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"io"
+	"net/http"
+
+	"github.com/eslider/go-config/internal/bytesutil"
+	"github.com/eslider/go-config/internal/keymap"
+	"github.com/eslider/go-config/internal/merge"
+	"github.com/eslider/go-config/internal/source"
+	"github.com/eslider/go-config/internal/structconv"
+)
+
+// Codec loads JSON from multiple sources.
+type Codec struct {
+	sources    []source.Source
+	normalizer keymap.Normalizer
+	sliceStrat merge.SliceStrategy
+	structOpts structconv.Options
+	mergeOpts  []merge.Option
+	httpClient *http.Client
+	urlHeader  http.Header
+}
+
+// New creates a JSON codec.
+func New(opts ...Option) *Codec {
+	c := &Codec{
+		normalizer: keymap.LowerAlnum,
+		sliceStrat: merge.Replace,
+		structOpts: structconv.Options{
+			TagName:     "mapstructure",
+			WeaklyTyped: true,
+			Trim:        true,
+		},
+	}
+	for _, o := range opts {
+		o(c)
+	}
+	c.mergeOpts = []merge.Option{merge.WithSliceStrategy(c.sliceStrat)}
+	return c
+}
+
+// Map merges all JSON sources into one map.
+func (c *Codec) Map(ctx context.Context) (map[string]any, error) {
+	if len(c.sources) == 0 {
+		return nil, fmt.Errorf("json: no sources")
+	}
+	acc := make(map[string]any)
+	for _, s := range c.sources {
+		b, err := bytesutil.ReadAll(ctx, s)
+		if err != nil {
+			return nil, fmt.Errorf("json: read %s: %w", s.String(), err)
+		}
+		var parsed map[string]any
+		if err := json.Unmarshal(b, &parsed); err != nil {
+			return nil, fmt.Errorf("json: parse %s: %w", s.String(), err)
+		}
+		if parsed == nil {
+			parsed = map[string]any{}
+		}
+		merge.DeepMerge(acc, parsed, c.mergeOpts...)
+	}
+	if c.normalizer != nil {
+		keymap.Walk(acc, c.normalizer)
+	}
+	return acc, nil
+}
+
+// Unmarshal decodes using context.Background.
+func (c *Codec) Unmarshal(dst any) error {
+	return c.UnmarshalContext(context.Background(), dst)
+}
+
+// UnmarshalContext decodes merged JSON into dst.
+func (c *Codec) UnmarshalContext(ctx context.Context, dst any) error {
+	m, err := c.Map(ctx)
+	if err != nil {
+		return err
+	}
+	return structconv.Decode(m, dst, c.structOpts)
+}
+
+// Marshal encodes src to JSON with indentation (struct or map[string]any).
+func (c *Codec) Marshal(src any) ([]byte, error) {
+	m, err := encodeToMap(src)
+	if err != nil {
+		return nil, fmt.Errorf("json: encode: %w", err)
+	}
+	b, err := json.MarshalIndent(m, "", "  ")
+	if err != nil {
+		return nil, fmt.Errorf("json: marshal: %w", err)
+	}
+	return b, nil
+}
+
+// WriteTo writes JSON to w.
+func (c *Codec) WriteTo(w io.Writer, src any) (int64, error) {
+	b, err := c.Marshal(src)
+	if err != nil {
+		return 0, err
+	}
+	n, err := w.Write(b)
+	return int64(n), err
+}
+
+func encodeToMap(src any) (map[string]any, error) {
+	if m, ok := src.(map[string]any); ok {
+		return m, nil
+	}
+	return structconv.Encode(src)
+}
@@ -0,0 +1,19 @@
+package json
+
+import (
+	"context"
+	"testing"
+
+	"github.com/eslider/go-config/testfixtures"
+)
+
+func TestCodec_IdentityJSONFixture(t *testing.T) {
+	c := New(WithBytes(testfixtures.Load(t, "identity", "service.json")))
+	m, err := c.Map(context.Background())
+	if err != nil {
+		t.Fatal(err)
+	}
+	if m["service"].(map[string]any)["name"] != "my-service" {
+		t.Fatalf("%#v", m)
+	}
+}
@@ -0,0 +1,3 @@
+// Package json loads JSON configuration from bytes, files, or URLs into maps
+// and structs, with optional key normalization and multi-source merging.
+package json
@@ -0,0 +1,87 @@
+package json
+
+import (
+	"io"
+	"net/http"
+
+	"github.com/eslider/go-config/internal/keymap"
+	"github.com/eslider/go-config/internal/merge"
+	"github.com/eslider/go-config/internal/source"
+	"github.com/go-viper/mapstructure/v2"
+)
+
+// Option configures a Codec.
+type Option func(*Codec)
+
+// WithBytes appends JSON from bytes.
+func WithBytes(b []byte) Option {
+	return func(c *Codec) { c.sources = append(c.sources, source.Bytes{Data: b, Name: "bytes"}) }
+}
+
+// WithReader appends JSON from r.
+func WithReader(r io.Reader) Option {
+	return func(c *Codec) { c.sources = append(c.sources, source.Reader{R: r, Name: "reader"}) }
+}
+
+// WithFile appends a JSON file path.
+func WithFile(path string) Option {
+	return func(c *Codec) { c.sources = append(c.sources, source.File{Path: path}) }
+}
+
+// WithURL appends JSON from an HTTP(S) URL.
+func WithURL(raw string) Option {
+	return func(c *Codec) {
+		var hdr http.Header
+		if c.urlHeader != nil {
+			hdr = c.urlHeader.Clone()
+		}
+		c.sources = append(c.sources, source.URL{Raw: raw, Header: hdr, HTTPClient: c.httpClient})
+	}
+}
+
+// WithHTTPClient sets the client for subsequent WithURL sources.
+func WithHTTPClient(client *http.Client) Option {
+	return func(c *Codec) { c.httpClient = client }
+}
+
+// WithHTTPHeader adds a header for subsequent WithURL sources.
+func WithHTTPHeader(k, v string) Option {
+	return func(c *Codec) {
+		if c.urlHeader == nil {
+			c.urlHeader = make(http.Header)
+		}
+		c.urlHeader.Add(k, v)
+	}
+}
+
+// WithKeyNormalizer sets key normalizer after merge (nil disables).
+func WithKeyNormalizer(n keymap.Normalizer) Option {
+	return func(c *Codec) { c.normalizer = n }
+}
+
+// WithSliceMerge sets slice merge strategy across sources.
+func WithSliceMerge(s merge.SliceStrategy) Option {
+	return func(c *Codec) { c.sliceStrat = s }
+}
+
+// WithTrim toggles string trim on struct decode.
+func WithTrim(enable bool) Option {
+	return func(c *Codec) { c.structOpts.Trim = enable }
+}
+
+// WithWeaklyTyped toggles weak typing for struct decode.
+func WithWeaklyTyped(enable bool) Option {
+	return func(c *Codec) { c.structOpts.WeaklyTyped = enable }
+}
+
+// WithTagName sets mapstructure tag name.
+func WithTagName(name string) Option {
+	return func(c *Codec) { c.structOpts.TagName = name }
+}
+
+// WithDecodeHook appends a decode hook.
+func WithDecodeHook(h mapstructure.DecodeHookFunc) Option {
+	return func(c *Codec) {
+		c.structOpts.ExtraHooks = append(c.structOpts.ExtraHooks, h)
+	}
+}
@@ -1,47 +0,0 @@
-package env
-
-import "github.com/mitchellh/mapstructure"
-
-// Option customises Unmarshal/UnmarshalPrefix behaviour.
-type Option func(*options)
-
-type options struct {
-	trim        bool
-	weaklyTyped bool
-	tagName     string
-	extraHooks  []mapstructure.DecodeHookFunc
-}
-
-func defaultOptions() options {
-	return options{
-		trim:        true,
-		weaklyTyped: true,
-		tagName:     "mapstructure",
-	}
-}
-
-// WithTrim toggles automatic TrimSpace on string values. Default: true.
-// Use WithTrim(false) when whitespace is semantically meaningful.
-func WithTrim(enable bool) Option {
-	return func(o *options) { o.trim = enable }
-}
-
-// WithWeaklyTyped toggles mapstructure's WeaklyTypedInput. Default: true.
-// When true, "1" decodes into int, "true" into bool, etc. Disable for
-// strict string-only decoding.
-func WithWeaklyTyped(enable bool) Option {
-	return func(o *options) { o.weaklyTyped = enable }
-}
-
-// WithTagName selects the struct tag mapstructure uses for field names.
-// Default: "mapstructure". Set "env" to use `env:"FIELD_NAME"` tags.
-func WithTagName(name string) Option {
-	return func(o *options) { o.tagName = name }
-}
-
-// WithDecodeHook appends a user hook to the decoder chain. Hooks run after
-// the built-in trim hook (unless trimming is disabled) and in the order
-// they're added.
-func WithDecodeHook(h mapstructure.DecodeHookFunc) Option {
-	return func(o *options) { o.extraHooks = append(o.extraHooks, h) }
-}
@@ -0,0 +1,46 @@
+// Package testfixtures resolves paths to files under the module's fixtures/ directory.
+package testfixtures
+
+import (
+	"os"
+	"path/filepath"
+	"runtime"
+	"strings"
+	"testing"
+)
+
+func moduleRoot(t *testing.T) string {
+	t.Helper()
+	_, file, _, ok := runtime.Caller(0)
+	if !ok {
+		t.Fatal("runtime.Caller")
+	}
+	dir := filepath.Dir(file)
+	for {
+		data, err := os.ReadFile(filepath.Join(dir, "go.mod"))
+		if err == nil && strings.Contains(string(data), "module github.com/eslider/go-config") {
+			return dir
+		}
+		parent := filepath.Dir(dir)
+		if parent == dir {
+			t.Fatal("module root not found")
+		}
+		dir = parent
+	}
+}
+
+// Path joins repo fixtures/ with parts.
+func Path(t *testing.T, parts ...string) string {
+	t.Helper()
+	return filepath.Join(append([]string{moduleRoot(t), "fixtures"}, parts...)...)
+}
+
+// Load reads a fixture file relative to fixtures/.
+func Load(t *testing.T, parts ...string) []byte {
+	t.Helper()
+	b, err := os.ReadFile(Path(t, parts...))
+	if err != nil {
+		t.Fatal(err)
+	}
+	return b
+}
@@ -0,0 +1,114 @@
+package yaml
+
+import (
+	"context"
+	"fmt"
+	"io"
+	"net/http"
+
+	"github.com/eslider/go-config/internal/bytesutil"
+	"github.com/eslider/go-config/internal/keymap"
+	"github.com/eslider/go-config/internal/merge"
+	"github.com/eslider/go-config/internal/source"
+	"github.com/eslider/go-config/internal/structconv"
+	yaml3 "gopkg.in/yaml.v3"
+)
+
+// Codec loads YAML from multiple sources.
+type Codec struct {
+	sources    []source.Source
+	normalizer keymap.Normalizer
+	sliceStrat merge.SliceStrategy
+	structOpts structconv.Options
+	mergeOpts  []merge.Option
+	httpClient *http.Client
+	urlHeader  http.Header
+}
+
+// New creates a YAML codec.
+func New(opts ...Option) *Codec {
+	c := &Codec{
+		normalizer: keymap.LowerAlnum,
+		sliceStrat: merge.Replace,
+		structOpts: structconv.Options{
+			TagName:     "mapstructure",
+			WeaklyTyped: true,
+			Trim:        true,
+		},
+	}
+	for _, o := range opts {
+		o(c)
+	}
+	c.mergeOpts = []merge.Option{merge.WithSliceStrategy(c.sliceStrat)}
+	return c
+}
+
+// Map merges all YAML sources into one map.
+func (c *Codec) Map(ctx context.Context) (map[string]any, error) {
+	if len(c.sources) == 0 {
+		return nil, fmt.Errorf("yaml: no sources")
+	}
+	acc := make(map[string]any)
+	for _, s := range c.sources {
+		b, err := bytesutil.ReadAll(ctx, s)
+		if err != nil {
+			return nil, fmt.Errorf("yaml: read %s: %w", s.String(), err)
+		}
+		var parsed map[string]any
+		if err := yaml3.Unmarshal(b, &parsed); err != nil {
+			return nil, fmt.Errorf("yaml: parse %s: %w", s.String(), err)
+		}
+		if parsed == nil {
+			parsed = map[string]any{}
+		}
+		merge.DeepMerge(acc, parsed, c.mergeOpts...)
+	}
+	if c.normalizer != nil {
+		keymap.Walk(acc, c.normalizer)
+	}
+	return acc, nil
+}
+
+// Unmarshal decodes using context.Background.
+func (c *Codec) Unmarshal(dst any) error {
+	return c.UnmarshalContext(context.Background(), dst)
+}
+
+// UnmarshalContext decodes merged YAML into dst.
+func (c *Codec) UnmarshalContext(ctx context.Context, dst any) error {
+	m, err := c.Map(ctx)
+	if err != nil {
+		return err
+	}
+	return structconv.Decode(m, dst, c.structOpts)
+}
+
+// Marshal encodes src to YAML bytes (struct or map[string]any).
+func (c *Codec) Marshal(src any) ([]byte, error) {
+	m, err := encodeToMap(src)
+	if err != nil {
+		return nil, fmt.Errorf("yaml: encode: %w", err)
+	}
+	b, err := yaml3.Marshal(m)
+	if err != nil {
+		return nil, fmt.Errorf("yaml: marshal: %w", err)
+	}
+	return b, nil
+}
+
+// WriteTo writes YAML to w.
+func (c *Codec) WriteTo(w io.Writer, src any) (int64, error) {
+	b, err := c.Marshal(src)
+	if err != nil {
+		return 0, err
+	}
+	n, err := w.Write(b)
+	return int64(n), err
+}
+
+func encodeToMap(src any) (map[string]any, error) {
+	if m, ok := src.(map[string]any); ok {
+		return m, nil
+	}
+	return structconv.Encode(src)
+}
@@ -0,0 +1,78 @@
+package yaml
+
+import (
+	"context"
+	"reflect"
+	"testing"
+
+	"github.com/eslider/go-config/internal/keymap"
+	"github.com/eslider/go-config/internal/merge"
+	"github.com/eslider/go-config/testfixtures"
+	yaml3 "gopkg.in/yaml.v3"
+)
+
+func TestCodec_IdentityFixture(t *testing.T) {
+	c := New(WithBytes(testfixtures.Load(t, "identity", "service.yaml")))
+	m, err := c.Map(context.Background())
+	if err != nil {
+		t.Fatal(err)
+	}
+	exp, err := loadExpectedMap(t)
+	if err != nil {
+		t.Fatal(err)
+	}
+	keymap.Walk(exp, keymap.LowerAlnum)
+	if !mapsEqual(m, exp) {
+		t.Fatalf("map mismatch\n got: %#v\n exp: %#v", m, exp)
+	}
+}
+
+func TestCodec_MergeReplaceSlices(t *testing.T) {
+	c := New(
+		WithBytes(testfixtures.Load(t, "merge", "defaults.yaml")),
+		WithBytes(testfixtures.Load(t, "merge", "overlay.yaml")),
+	)
+	got, err := c.Map(context.Background())
+	if err != nil {
+		t.Fatal(err)
+	}
+	exp := map[string]any{}
+	if err := yaml3.Unmarshal(testfixtures.Load(t, "merge", "expected-replace.yaml"), &exp); err != nil {
+		t.Fatal(err)
+	}
+	keymap.Walk(exp, keymap.LowerAlnum)
+	if !mapsEqual(got, exp) {
+		t.Fatalf("merge mismatch\n got: %#v\n exp: %#v", got, exp)
+	}
+}
+
+func TestCodec_MergeConcatSlices(t *testing.T) {
+	c := New(
+		WithBytes(testfixtures.Load(t, "merge", "defaults.yaml")),
+		WithBytes(testfixtures.Load(t, "merge", "overlay.yaml")),
+		WithSliceMerge(merge.Concat),
+	)
+	got, err := c.Map(context.Background())
+	if err != nil {
+		t.Fatal(err)
+	}
+	exp := map[string]any{}
+	if err := yaml3.Unmarshal(testfixtures.Load(t, "merge", "expected-concat.yaml"), &exp); err != nil {
+		t.Fatal(err)
+	}
+	keymap.Walk(exp, keymap.LowerAlnum)
+	if !mapsEqual(got, exp) {
+		t.Fatalf("concat mismatch\n got: %#v\n exp: %#v", got, exp)
+	}
+}
+
+func loadExpectedMap(t *testing.T) (map[string]any, error) {
+	t.Helper()
+	var m map[string]any
+	err := yaml3.Unmarshal(testfixtures.Load(t, "identity", "service.yaml"), &m)
+	return m, err
+}
+
+func mapsEqual(a, b map[string]any) bool {
+	return reflect.DeepEqual(a, b)
+}
@@ -0,0 +1,3 @@
+// Package yaml loads YAML configuration from bytes, files, or URLs into maps
+// and structs, with optional key normalization and multi-source merging.
+package yaml
@@ -0,0 +1,16 @@
+package yaml
+
+import (
+	"context"
+	"testing"
+
+	"github.com/eslider/go-config/testfixtures"
+)
+
+func TestCodec_InvalidYAML(t *testing.T) {
+	c := New(WithBytes(testfixtures.Load(t, "invalid", "malformed.yaml")))
+	_, err := c.Map(context.Background())
+	if err == nil {
+		t.Fatal("expected parse error")
+	}
+}
@@ -0,0 +1,87 @@
+package yaml
+
+import (
+	"io"
+	"net/http"
+
+	"github.com/eslider/go-config/internal/keymap"
+	"github.com/eslider/go-config/internal/merge"
+	"github.com/eslider/go-config/internal/source"
+	"github.com/go-viper/mapstructure/v2"
+)
+
+// Option configures a Codec.
+type Option func(*Codec)
+
+// WithBytes appends a YAML source from bytes.
+func WithBytes(b []byte) Option {
+	return func(c *Codec) { c.sources = append(c.sources, source.Bytes{Data: b, Name: "bytes"}) }
+}
+
+// WithReader appends a YAML source from r.
+func WithReader(r io.Reader) Option {
+	return func(c *Codec) { c.sources = append(c.sources, source.Reader{R: r, Name: "reader"}) }
+}
+
+// WithFile appends a YAML file path.
+func WithFile(path string) Option {
+	return func(c *Codec) { c.sources = append(c.sources, source.File{Path: path}) }
+}
+
+// WithURL appends a YAML document at an HTTP(S) URL.
+func WithURL(raw string) Option {
+	return func(c *Codec) {
+		var hdr http.Header
+		if c.urlHeader != nil {
+			hdr = c.urlHeader.Clone()
+		}
+		c.sources = append(c.sources, source.URL{Raw: raw, Header: hdr, HTTPClient: c.httpClient})
+	}
+}
+
+// WithHTTPClient sets the client for subsequent WithURL sources.
+func WithHTTPClient(client *http.Client) Option {
+	return func(c *Codec) { c.httpClient = client }
+}
+
+// WithHTTPHeader adds a header for subsequent WithURL sources.
+func WithHTTPHeader(k, v string) Option {
+	return func(c *Codec) {
+		if c.urlHeader == nil {
+			c.urlHeader = make(http.Header)
+		}
+		c.urlHeader.Add(k, v)
+	}
+}
+
+// WithKeyNormalizer sets key normalizer after merge (nil disables).
+func WithKeyNormalizer(n keymap.Normalizer) Option {
+	return func(c *Codec) { c.normalizer = n }
+}
+
+// WithSliceMerge sets slice merge strategy across sources.
+func WithSliceMerge(s merge.SliceStrategy) Option {
+	return func(c *Codec) { c.sliceStrat = s }
+}
+
+// WithTrim toggles string trim on struct decode.
+func WithTrim(enable bool) Option {
+	return func(c *Codec) { c.structOpts.Trim = enable }
+}
+
+// WithWeaklyTyped toggles weak typing for struct decode.
+func WithWeaklyTyped(enable bool) Option {
+	return func(c *Codec) { c.structOpts.WeaklyTyped = enable }
+}
+
+// WithTagName sets mapstructure tag name.
+func WithTagName(name string) Option {
+	return func(c *Codec) { c.structOpts.TagName = name }
+}
+
+// WithDecodeHook appends a decode hook.
+func WithDecodeHook(h mapstructure.DecodeHookFunc) Option {
+	return func(c *Codec) {
+		c.structOpts.ExtraHooks = append(c.structOpts.ExtraHooks, h)
+	}
+}