package monitor

import (
	"context"
	"fmt"
	"log/slog"
	"sync"
	"time"

	"ym-dl/internal/config"
	"ym-dl/internal/downloader"
	"ym-dl/internal/storage"
	"ym-dl/internal/yandex"
)

// Monitor periodically checks for new releases from configured artists
type Monitor struct {
	cfg          *config.Config
	yandexClient *yandex.YandexClient
	storage      *storage.Storage
	downloader   *downloader.Downloader
	logger       *slog.Logger

	mu           sync.Mutex
	stopCh       chan struct{}
	wg           sync.WaitGroup
	running      bool
}

// NewMonitor creates a new monitor
func NewMonitor(cfg *config.Config, yandexClient *yandex.YandexClient, storage *storage.Storage, downloader *downloader.Downloader, logger *slog.Logger) *Monitor {
	return &Monitor{
		cfg:          cfg,
		yandexClient: yandexClient,
		storage:      storage,
		downloader:   downloader,
		logger:       logger,
		stopCh:       make(chan struct{}),
	}
}

// Start starts the monitor loop
func (m *Monitor) Start(ctx context.Context) error {
	m.mu.Lock()
	if m.running {
		m.mu.Unlock()
		return fmt.Errorf("monitor already running")
	}
	m.running = true
	m.mu.Unlock()

	m.wg.Add(1)
	go m.runLoop(ctx)

	return nil
}

// Stop stops the monitor
func (m *Monitor) Stop() {
	m.mu.Lock()
	if !m.running {
		m.mu.Unlock()
		return
	}
	m.running = false
	close(m.stopCh)
	m.mu.Unlock()

	m.wg.Wait()
}

// runLoop is the main monitoring loop
func (m *Monitor) runLoop(ctx context.Context) {
	defer m.wg.Done()

	interval, err := m.cfg.GetMonitorInterval()
	if err != nil {
		m.logger.Error("invalid monitor interval", "error", err)
		return
	}

	ticker := time.NewTicker(interval)
	defer ticker.Stop()

	// Run initial check
	m.checkAllArtists(ctx)

	for {
		select {
		case <-ctx.Done():
			return
		case <-m.stopCh:
			return
		case <-ticker.C:
			m.checkAllArtists(ctx)
		}
	}
}

// checkAllArtists checks all configured artists for new releases
func (m *Monitor) checkAllArtists(ctx context.Context) {
	m.logger.Info("starting artist check", "artist_count", len(m.cfg.Artists))

	for _, artist := range m.cfg.Artists {
		select {
		case <-ctx.Done():
			return
		case <-m.stopCh:
			return
		default:
		}

		m.checkArtist(ctx, artist.ID)
	}
}

// checkArtist checks a single artist for new tracks and albums
func (m *Monitor) checkArtist(ctx context.Context, artistID int) {
	m.logger.Info("checking artist", "artist_id", artistID)

	// Get artist info
	artist, err := m.yandexClient.GetArtistInfo(ctx, artistID)
	if err != nil {
		m.logger.Error("failed to get artist info", "artist_id", artistID, "error", err)
		return
	}

	m.logger.Info("artist info", "artist_id", artistID, "name", artist.Name)

	// Check for new tracks
	m.checkArtistTracks(ctx, artistID, artist.Name)

	// Check for new albums
	m.checkArtistAlbums(ctx, artistID, artist.Name)
}

// checkArtistTracks checks for new tracks from an artist
func (m *Monitor) checkArtistTracks(ctx context.Context, artistID int, artistName string) {
	page := 0
	pageSize := 500

	for {
		tracks, err := m.yandexClient.GetArtistTracks(ctx, artistID, page, pageSize)
		if err != nil {
			m.logger.Error("failed to get artist tracks", "artist_id", artistID, "page", page, "error", err)
			return
		}

		if len(tracks) == 0 {
			break
		}

		newTracks := 0
		for _, track := range tracks {
			if !m.storage.IsTrackDownloaded(track.ID) {
				m.logger.Info("new track found", "track_id", track.ID, "artist", artistName)
				result := m.downloader.DownloadTrack(ctx, track.ID)
				if result.Success {
					newTracks++
				} else {
					m.logger.Error("failed to download track", "track_id", track.ID, "error", result.Error)
				}
			}
		}

		m.logger.Info("track check complete", "artist_id", artistID, "new_tracks", newTracks, "page", page)

		if len(tracks) < pageSize {
			break
		}
		page++
	}
}

// checkArtistAlbums checks for new albums from an artist
func (m *Monitor) checkArtistAlbums(ctx context.Context, artistID int, artistName string) {
	page := 0
	pageSize := 500

	for {
		albums, err := m.yandexClient.GetArtistAlbums(ctx, artistID, page, pageSize)
		if err != nil {
			m.logger.Error("failed to get artist albums", "artist_id", artistID, "page", page, "error", err)
			return
		}

		if len(albums) == 0 {
			break
		}

		newAlbums := 0
		for _, album := range albums {
			albumIDStr := album.ID
			if !m.isAlbumDownloaded(albumIDStr, album.TrackCount) {
				m.logger.Info("new album found", "album_id", albumIDStr, "title", album.Title, "artist", artistName)
				results := m.downloader.DownloadAlbum(ctx, album.ID)
				success := false
				for _, r := range results {
					if r.Success {
						success = true
						break
					}
				}
				if success {
					newAlbums++
				} else {
					m.logger.Error("failed to download album", "album_id", albumIDStr, "title", album.Title)
				}
			}
		}

		m.logger.Info("album check complete", "artist_id", artistID, "new_albums", newAlbums, "page", page)

		if len(albums) < pageSize {
			break
		}
		page++
	}
}

// isAlbumDownloaded checks if an album has been fully downloaded.
// An album is considered downloaded only if all its expected tracks (by TrackCount)
// are present in the storage index. If TrackCount is 0 (unknown), the album is
// never considered pre-downloaded to avoid skipping compilation albums
// where only some tracks were fetched individually.
func (m *Monitor) isAlbumDownloaded(albumID string, expectedTrackCount int) bool {
	if expectedTrackCount <= 0 {
		return false // Unknown track count — download anyway to be safe
	}

	downloadedCount := 0
	for _, trackID := range m.storage.GetDownloadedTracks() {
		meta, ok := m.storage.GetTrackMeta(trackID)
		if ok && meta.AlbumID == albumID {
			downloadedCount++
		}
	}

	return downloadedCount >= expectedTrackCount
}