feat: Go SearXNG client; throttled is not absence (#16)

internal/websearch/cache.go

@@ -0,0 +1,97 @@
+package websearch
+
+import (
+	"database/sql"
+	"encoding/json"
+	"os"
+	"path/filepath"
+
+	_ "modernc.org/sqlite"
+)
+
+const cacheSchema = `
+CREATE TABLE IF NOT EXISTS responses (
+  key     TEXT PRIMARY KEY,
+  fetched REAL NOT NULL,
+  payload TEXT NOT NULL
+);
+CREATE TABLE IF NOT EXISTS meta (
+  key   TEXT PRIMARY KEY,
+  value REAL NOT NULL
+);
+`
+
+type Cache struct {
+	db *sql.DB
+}
+
+func OpenCache(path string) (*Cache, error) {
+	if err := os.MkdirAll(filepath.Dir(path), 0o700); err != nil {
+		return nil, err
+	}
+	db, err := sql.Open("sqlite", path)
+	if err != nil {
+		return nil, err
+	}
+	if _, err := db.Exec(cacheSchema); err != nil {
+		db.Close()
+		return nil, err
+	}
+	return &Cache{db: db}, nil
+}
+
+func (c *Cache) Close() error {
+	if c == nil || c.db == nil {
+		return nil
+	}
+	return c.db.Close()
+}
+
+func (c *Cache) Get(key string, ttl, now float64) (*Payload, error) {
+	var fetched float64
+	var raw string
+	err := c.db.QueryRow("SELECT fetched, payload FROM responses WHERE key = ?", key).Scan(&fetched, &raw)
+	if err == sql.ErrNoRows {
+		return nil, nil
+	}
+	if err != nil {
+		return nil, err
+	}
+	if now-fetched > ttl {
+		return nil, nil
+	}
+	var p Payload
+	if err := json.Unmarshal([]byte(raw), &p); err != nil {
+		return nil, err
+	}
+	return &p, nil
+}
+
+func (c *Cache) Put(key string, p Payload, now float64) error {
+	raw, err := json.Marshal(p)
+	if err != nil {
+		return err
+	}
+	_, err = c.db.Exec(
+		"INSERT OR REPLACE INTO responses (key, fetched, payload) VALUES (?, ?, ?)",
+		key, now, string(raw),
+	)
+	return err
+}
+
+func (c *Cache) LastCall() (*float64, error) {
+	var v float64
+	err := c.db.QueryRow("SELECT value FROM meta WHERE key = 'last_call'").Scan(&v)
+	if err == sql.ErrNoRows {
+		return nil, nil
+	}
+	if err != nil {
+		return nil, err
+	}
+	return &v, nil
+}
+
+func (c *Cache) MarkCall(now float64) error {
+	_, err := c.db.Exec("INSERT OR REPLACE INTO meta (key, value) VALUES ('last_call', ?)", now)
+	return err
+}