package library

import (
	"errors"
	"fmt"
	"os"
	"path/filepath"
	"time"

	"yellowjacket/backend/coverart"
)

var errNoLibrariesConfigured = errors.New(
	"no libraries configured for rescan",
)

// FullRescan clears the queue and player, wipes all library data
// (database records and cover art files), and performs a fresh
// scan of every library in the database.  The returned ScanMetrics
// reflects the last library scanned; clear-phase durations are
// folded into its totals.
func (l *Library) FullRescan() (*ScanMetrics, error) {
	l.logger.Info("beginning full library rescan")

	// Resolve all libraries from the database.
	libs, err := l.db.Queries.GetAllLibraries(l.ctx)
	if err != nil {
		return nil, fmt.Errorf(
			"could not get libraries for rescan: %w", err,
		)
	}

	if len(libs) == 0 {
		return nil, errNoLibrariesConfigured
	}

	// Run the pre-clear hook (e.g. clear queue / stop playback)
	// before wiping data so the player is not referencing
	// now-deleted tracks.
	clearQueueStart := time.Now()

	if l.rescanHooks.PreClear != nil {
		l.rescanHooks.PreClear()
	}

	clearQueueDur := time.Since(clearQueueStart)

	// Clear all library data (DB + cover art files).
	clearDBStart := time.Now()

	if err := l.clearLibraryTables(); err != nil {
		return nil, fmt.Errorf(
			"could not clear library tables: %w", err,
		)
	}

	clearDBDur := time.Since(clearDBStart)

	clearFilesStart := time.Now()

	if err := l.clearCoverArtFiles(); err != nil {
		return nil, fmt.Errorf(
			"could not clear cover art files: %w", err,
		)
	}

	clearFilesDur := time.Since(clearFilesStart)

	l.logger.Info("library data cleared successfully")

	// Scan the first library directly (bypassing the queue) so
	// we get ScanMetrics back.  Queue remaining libraries so
	// they run sequentially via the scan coordinator.
	metrics := l.scanInternal(libs[0].ID, libs[0].Name, libs[0].Path)

	for _, lib := range libs[1:] {
		if scanErr := l.ScanLibrary(lib.ID); scanErr != nil {
			l.logger.Error("could not queue library for rescan",
				"libraryID", lib.ID, "err", scanErr)
		}
	}

	// Drain the queue in a goroutine so any queued libraries
	// scan sequentially.  scanInternal was called directly (not
	// via startScan), so drainQueue hasn't been invoked yet.
	go l.drainQueue()

	if metrics != nil {
		metrics.ClearQueue = clearQueueDur
		metrics.ClearDatabase = clearDBDur
		metrics.ClearCoverFiles = clearFilesDur

		// Include clear-phase durations in the total so the
		// displayed value reflects true wall-clock time.
		metrics.Total += clearQueueDur +
			clearDBDur + clearFilesDur
	}

	// Run the post-scan hook (e.g. restore playlists from M3U8
	// files) now that audio_files are populated again.
	if l.rescanHooks.PostScan != nil {
		l.rescanHooks.PostScan()
	}

	return metrics, nil
}

// clearLibraryTables deletes all library-related rows in FK-safe
// order within a single transaction.
func (l *Library) clearLibraryTables() error {
	tx, err := l.db.BeginTx()
	if err != nil {
		return fmt.Errorf("could not begin transaction: %w", err)
	}

	defer func() {
		_ = tx.Rollback()
	}()

	txq := l.db.Queries.WithTx(tx)

	// Phase 1: leaf tables (nothing references these).
	if err := txq.ClearQueueTracks(l.ctx); err != nil {
		return fmt.Errorf("could not clear queue tracks: %w", err)
	}

	// A full rescan is the "start over" button, and it is the only way
	// back for a path removed from the library by mistake: the file is
	// still on disk, but nothing else will ever import it again while
	// its exclusion stands.  Until there is a UI for managing the list,
	// clearing it here is the escape hatch.
	if err := txq.ClearExcludedPaths(l.ctx); err != nil {
		return fmt.Errorf("could not clear excluded paths: %w", err)
	}

	// Preserve playlist tracks across rescan: populate phantom
	// metadata for all linked tracks before audio_files are deleted.
	// ON DELETE SET NULL will null out audio_file_id, converting them
	// to phantoms that ResolvePhantomTracksAfterScan can re-link.
	if _, err := tx.ExecContext(l.ctx, `
		UPDATE playlist_tracks
		SET
			phantom_title = COALESCE(phantom_title, (
				SELECT tm.title FROM track_metadata tm
				WHERE tm.id = playlist_tracks.audio_file_id
			)),
			phantom_artist = COALESCE(phantom_artist, (
				SELECT tm.artist_name FROM track_metadata tm
				WHERE tm.id = playlist_tracks.audio_file_id
			)),
			phantom_album = COALESCE(phantom_album, (
				SELECT tm.album FROM track_metadata tm
				WHERE tm.id = playlist_tracks.audio_file_id
			)),
			phantom_duration_ms = COALESCE(phantom_duration_ms, (
				SELECT af.length_milliseconds FROM audio_files af
				WHERE af.id = playlist_tracks.audio_file_id
			)),
			phantom_file_path = COALESCE(phantom_file_path, (
				SELECT af.file_path FROM audio_files af
				WHERE af.id = playlist_tracks.audio_file_id
			))
		WHERE audio_file_id IS NOT NULL
	`); err != nil {
		return fmt.Errorf(
			"could not preserve playlist track metadata: %w", err,
		)
	}

	// Phase 2: the files.  file_genres cascades with them.
	if err := txq.DeleteAllAudioFiles(l.ctx); err != nil {
		return fmt.Errorf(
			"could not clear audio files: %w", err,
		)
	}

	if err := txq.DeleteAllAlbums(l.ctx); err != nil {
		return fmt.Errorf(
			"could not clear albums: %w", err,
		)
	}

	// Phase 3: root tables.
	if err := txq.DeleteAllCoverArt(l.ctx); err != nil {
		return fmt.Errorf(
			"could not clear cover art: %w", err,
		)
	}

	if err := txq.DeleteAllArtists(l.ctx); err != nil {
		return fmt.Errorf(
			"could not clear artists: %w", err,
		)
	}

	if err := txq.DeleteAllGenres(l.ctx); err != nil {
		return fmt.Errorf(
			"could not clear genres: %w", err,
		)
	}

	if err := tx.Commit(); err != nil {
		return fmt.Errorf(
			"could not commit library clear transaction: %w", err,
		)
	}

	// Clear FTS5 search index AFTER the transaction.
	// ClearSearchIndex drops and recreates the contentless FTS5
	// virtual table, which cannot run inside a transaction.
	if err := l.db.ClearSearchIndex(); err != nil {
		return fmt.Errorf(
			"could not clear search index: %w", err,
		)
	}

	l.logger.Info("all library tables cleared")

	return nil
}

// clearCoverArtFiles removes all files from the covers directory.
func (l *Library) clearCoverArtFiles() error {
	coverDir, err := coverart.CoversDir()
	if err != nil {
		return fmt.Errorf(
			"could not resolve covers directory: %w", err,
		)
	}

	entries, err := os.ReadDir(coverDir)
	if err != nil {
		if os.IsNotExist(err) {
			return nil
		}

		return fmt.Errorf(
			"could not read covers directory: %w", err,
		)
	}

	var removed int

	for _, entry := range entries {
		if entry.IsDir() {
			continue
		}

		path := filepath.Join(coverDir, entry.Name())
		if err := os.Remove(path); err != nil {
			l.logger.Warn(
				"could not remove cover art file",
				"path", path, "err", err,
			)

			continue
		}

		removed++
	}

	l.logger.Info("cover art files removed", "count", removed)

	return nil
}