#!/usr/bin/env python3
"""Validate markdown links, glossary anchors, and readability rules."""

from __future__ import annotations

import argparse
import re
import sys
from pathlib import Path

try:
    import yaml
except ImportError:  # pragma: no cover - stdlib fallback for minimal envs
    yaml = None  # type: ignore[assignment]

ROOT = Path(__file__).resolve().parents[1]
RULES_PATH = Path(__file__).with_name("docs_rules.yaml")

LINK_RE = re.compile(r"!?\[[^\]]*\]\(([^)]+)\)")
BARE_SEE_RE = re.compile(r"(?<![\[(/])see\s+(\d{2})(?![\w-])", re.IGNORECASE)
SKIP_SCHEMES = ("http://", "https://", "mailto:", "tel:", "#")


def load_rules(path: Path = RULES_PATH) -> dict:
    text = path.read_text(encoding="utf-8")
    if yaml is not None:
        return yaml.safe_load(text)
    raise RuntimeError("PyYAML is required to load docs_rules.yaml")


def slug_heading(text: str) -> str:
    """Anchor slug used in this repository's glossary links."""
    text = text.strip()
    text = re.sub(r"\s&\s", " — ", text)
    if " — " in text:
        left, right = text.split(" — ", 1)
        return f"{_slug_part(left)}--{_slug_part(right)}"
    return _slug_part(text)


def _slug_part(text: str) -> str:
    slug = text.strip().lower()
    slug = re.sub(r"[^\w\s-]", "", slug)
    slug = re.sub(r"\s+", "-", slug)
    return slug


def collect_anchors(md_path: Path) -> set[str]:
    anchors: set[str] = set()
    for line in md_path.read_text(encoding="utf-8").splitlines():
        if line.startswith("##"):
            anchors.add(slug_heading(line.lstrip("#").strip()))
    return anchors


def expand_markdown_paths(patterns: list[str]) -> list[Path]:
    files: set[Path] = set()
    for pattern in patterns:
        for path in ROOT.glob(pattern):
            if path.is_file() and path.suffix == ".md":
                files.add(path)
    return sorted(files)


def split_link_target(raw: str) -> tuple[str, str | None]:
    target = raw.strip()
    if target.startswith("<") and target.endswith(">"):
        target = target[1:-1]
    if "#" in target:
        path_part, fragment = target.split("#", 1)
        return path_part, fragment or None
    return target, None


def resolve_path(source: Path, link_path: str) -> Path | None:
    if not link_path or link_path.startswith(SKIP_SCHEMES):
        return None
    candidate = (source.parent / link_path).resolve()
    try:
        candidate.relative_to(ROOT.resolve())
    except ValueError:
        return None
    return candidate


def is_glossary_link(link_path: str, rules: dict) -> bool:
    glossary = rules["glossary"]["file"].replace("\\", "/")
    normalized = link_path.replace("\\", "/")
    return (
        normalized == glossary
        or normalized.endswith("/" + glossary)
        or normalized.endswith(glossary.split("/")[-1])
    )


def check_file(
    md_path: Path,
    rules: dict,
    anchor_cache: dict[Path, set[str]],
) -> tuple[list[str], list[str]]:
    errors: list[str] = []
    warnings: list[str] = []
    rel = md_path.relative_to(ROOT)
    text = md_path.read_text(encoding="utf-8")

    if rules.get("readability", {}).get("forbid_bare_see_refs"):
        prose = re.sub(r"`[^`]*`", "", text)
        for match in BARE_SEE_RE.finditer(prose):
            errors.append(
                f"{rel}:{_line_no(text, match.start())}: bare cross-ref "
                f"'see {match.group(1)}' — use a markdown link"
            )

    for match in LINK_RE.finditer(text):
        raw = match.group(1)
        if any(raw.startswith(s) for s in SKIP_SCHEMES):
            continue

        link_path, fragment = split_link_target(raw)
        if not link_path.endswith(".md"):
            continue

        for banned in rules.get("banned_link_targets", []):
            if banned in link_path.replace("\\", "/"):
                errors.append(
                    f"{rel}:{_line_no(text, match.start())}: banned link target "
                    f"'{link_path}'"
                )

        target = resolve_path(md_path, link_path)
        if target is None:
            errors.append(
                f"{rel}:{_line_no(text, match.start())}: link escapes repo or "
                f"is invalid: {raw}"
            )
            continue
        if not target.is_file():
            errors.append(
                f"{rel}:{_line_no(text, match.start())}: broken link "
                f"{link_path} -> {target.relative_to(ROOT)}"
            )
            continue

        if fragment:
            if target not in anchor_cache:
                anchor_cache[target] = collect_anchors(target)
            if fragment not in anchor_cache[target]:
                errors.append(
                    f"{rel}:{_line_no(text, match.start())}: unknown anchor "
                    f"#{fragment} in {target.relative_to(ROOT)}"
                )

        if fragment and is_glossary_link(link_path, rules):
            section_anchors = set(rules.get("glossary_section_anchors", []))
            if fragment in section_anchors:
                warnings.append(
                    f"{rel}:{_line_no(text, match.start())}: glossary section "
                    f"link #{fragment} — prefer a ### term anchor where one exists"
                )

    return errors, warnings


def _line_no(text: str, index: int) -> int:
    return text.count("\n", 0, index) + 1


def run_checks(warnings_as_errors: bool = False) -> int:
    rules = load_rules(ROOT / "scripts/docs_rules.yaml")
    anchor_cache: dict[Path, set[str]] = {}
    all_errors: list[str] = []
    all_warnings: list[str] = []

    glossary_path = ROOT / rules["glossary"]["file"]
    anchor_cache[glossary_path] = collect_anchors(glossary_path)

    for md_path in expand_markdown_paths(rules["markdown_paths"]):
        errors, warnings = check_file(md_path, rules, anchor_cache)
        all_errors.extend(errors)
        all_warnings.extend(warnings)

    if all_warnings:
        print("Documentation warnings:")
        for msg in sorted(all_warnings):
            print(f"  warning: {msg}")
        print()

    if all_errors:
        print("Documentation errors:")
        for msg in sorted(all_errors):
            print(f"  error: {msg}")
        print(f"\n{len(all_errors)} error(s), {len(all_warnings)} warning(s)")
        return 1

    if warnings_as_errors and all_warnings:
        print(f"\n{len(all_warnings)} warning(s) treated as errors")
        return 1

    print(
        f"Documentation checks passed "
        f"({len(expand_markdown_paths(rules['markdown_paths']))} files, "
        f"{len(all_warnings)} warning(s))"
    )
    return 0


def main() -> None:
    parser = argparse.ArgumentParser(description=__doc__)
    parser.add_argument(
        "--warnings-as-errors",
        action="store_true",
        help="Exit non-zero when section-link warnings are present",
    )
    args = parser.parse_args()
    sys.exit(run_checks(warnings_as_errors=args.warnings_as_errors))


if __name__ == "__main__":
    main()