package media

import (
	"context"
	"database/sql"
	"fmt"
	"os"
	"path/filepath"
	"sync"
)

// CoverExtractor pulls cover art out of a media file and writes it under
// cacheDir, returning the path to the written image.
//
// Modules register one per media kind. It runs lazily on first request and the
// result is recorded in the assets table, so the cost is paid once.
type CoverExtractor func(ctx context.Context, db *sql.DB, item Item, absPath, cacheDir string) (string, error)

var (
	coverMu         sync.RWMutex
	coverExtractors = map[string]CoverExtractor{}
)

// RegisterCoverExtractor installs the extractor for a media kind. A later
// registration replaces an earlier one.
func RegisterCoverExtractor(kind string, fn CoverExtractor) {
	coverMu.Lock()
	defer coverMu.Unlock()
	coverExtractors[kind] = fn
}

// CoverPath returns the cached cover path for an item, extracting it if
// necessary. The bool is false when no cover could be produced — which is a
// normal outcome, not an error, so callers return a placeholder rather than a
// 500.
func CoverPath(ctx context.Context, db *sql.DB, item Item, cacheDir string) (string, bool, error) {
	// Already extracted and recorded?
	var path string
	err := db.QueryRowContext(ctx, `
		SELECT path FROM assets WHERE item_id = ? AND role = 'cover' LIMIT 1`, item.ID).Scan(&path)
	if err == nil {
		if _, statErr := os.Stat(path); statErr == nil {
			return path, true, nil
		}
		// Recorded but gone: fall through and re-extract.
	} else if err != sql.ErrNoRows {
		return "", false, fmt.Errorf("media: lookup cover: %w", err)
	}

	coverMu.RLock()
	extract, ok := coverExtractors[item.Kind]
	coverMu.RUnlock()
	if !ok {
		return "", false, nil
	}

	outPath, err := extract(ctx, db, item, item.AbsPath(), cacheDir)
	if err != nil {
		return "", false, fmt.Errorf("media: extract cover: %w", err)
	}
	if outPath == "" {
		return "", false, nil
	}

	if _, err := db.ExecContext(ctx, `
		INSERT INTO assets (item_id, role, path) VALUES (?, 'cover', ?)
		ON CONFLICT (item_id, role, path) DO NOTHING`, item.ID, outPath); err != nil {
		return "", false, fmt.Errorf("media: record cover: %w", err)
	}
	return outPath, true, nil
}

// ── helpers for extractors ─────────────────────────────────────────────

// CoverCacheDir returns (and creates) the per-kind cover cache directory.
func CoverCacheDir(cacheDir, kind string) (string, error) {
	dir := filepath.Join(cacheDir, "covers", kind)
	if err := os.MkdirAll(dir, 0o750); err != nil {
		return "", err
	}
	return dir, nil
}