// Package service — playback history / favourites / playlists.
//
// These three concerns are intentionally co-located: they all sit between
// "the user" and "a media item" and share the same join-table flavour. A
// dedicated PlaybackService keeps the wiring simple and lets handlers
// dispatch by feature instead of by repository.
package service

import (
	"context"
	"errors"
	"time"

	"go.uber.org/zap"

	"github.com/ShukeBta/MediaStationGo/internal/model"
	"github.com/ShukeBta/MediaStationGo/internal/repository"
)

// PlaybackService bundles history / favourite / playlist business logic.
type PlaybackService struct {
	log  *zap.Logger
	repo *repository.Container
}

// NewPlaybackService is the constructor.
func NewPlaybackService(log *zap.Logger, repo *repository.Container) *PlaybackService {
	return &PlaybackService{log: log, repo: repo}
}

// ─── History ────────────────────────────────────────────────────────────────

// RecordProgress upserts the resume position for a (user, media) pair. A
// position within 30 seconds of the duration auto-flags the item as
// completed so the home page can hide it from "Continue Watching".
func (p *PlaybackService) RecordProgress(ctx context.Context, userID, mediaID string, position, duration int64) error {
	if userID == "" || mediaID == "" {
		return errors.New("missing user or media")
	}
	completed := duration > 0 && position >= duration-30_000
	h := &model.PlaybackHistory{
		UserID:     userID,
		MediaID:    mediaID,
		PositionMs: position,
		DurationMs: duration,
		WatchedAt:  time.Now(),
		Completed:  completed,
	}
	return p.repo.History.Upsert(ctx, h)
}

// HistoryItem joins the playback row with its media so the API consumer
// gets a fully-populated card without a second round-trip.
type HistoryItem struct {
	model.PlaybackHistory
	Media *model.Media `json:"media,omitempty"`
}

// RecentHistory returns the most recently-watched items for a user. We
// fetch the history rows first then attach each Media row in a single
// follow-up query.
func (p *PlaybackService) RecentHistory(ctx context.Context, userID string, limit int) ([]HistoryItem, error) {
	rows, err := p.repo.History.ListByUser(ctx, userID, limit)
	if err != nil {
		return nil, err
	}
	items := make([]HistoryItem, 0, len(rows))
	for i := range rows {
		var m model.Media
		if err := p.repo.DB.Where("id = ?", rows[i].MediaID).First(&m).Error; err == nil {
			items = append(items, HistoryItem{PlaybackHistory: rows[i], Media: &m})
		} else {
			items = append(items, HistoryItem{PlaybackHistory: rows[i]})
		}
	}
	return items, nil
}

// ─── Favourites ─────────────────────────────────────────────────────────────

// ToggleFavourite flips the favourite flag and reports the new state.
func (p *PlaybackService) ToggleFavourite(ctx context.Context, userID, mediaID string) (bool, error) {
	return p.repo.Favorite.Toggle(ctx, userID, mediaID)
}

// ListFavourites returns every favourited media for a user.
func (p *PlaybackService) ListFavourites(ctx context.Context, userID string) ([]model.Media, error) {
	favs, err := p.repo.Favorite.ListByUser(ctx, userID)
	if err != nil {
		return nil, err
	}
	if len(favs) == 0 {
		return nil, nil
	}
	ids := make([]string, len(favs))
	for i, f := range favs {
		ids[i] = f.MediaID
	}
	var out []model.Media
	err = p.repo.DB.Where("id IN ?", ids).
		Order("created_at desc").Find(&out).Error
	return out, err
}

// ─── Playlists ──────────────────────────────────────────────────────────────

// CreatePlaylist persists a new playlist owned by userID.
func (p *PlaybackService) CreatePlaylist(ctx context.Context, userID, name string, isPublic bool) (*model.Playlist, error) {
	if name == "" {
		return nil, errors.New("name required")
	}
	pl := &model.Playlist{UserID: userID, Name: name, IsPublic: isPublic}
	if err := p.repo.Playlist.Create(ctx, pl); err != nil {
		return nil, err
	}
	return pl, nil
}

// ListPlaylists returns every playlist owned by userID.
func (p *PlaybackService) ListPlaylists(ctx context.Context, userID string) ([]model.Playlist, error) {
	return p.repo.Playlist.ListByUser(ctx, userID)
}

// PlaylistDetail returns the playlist together with its ordered media items.
type PlaylistDetail struct {
	Playlist model.Playlist `json:"playlist"`
	Items    []model.Media  `json:"items"`
}

// GetPlaylist returns the playlist + its ordered media. Visibility is
// enforced at the handler level; the service trusts callers.
func (p *PlaybackService) GetPlaylist(ctx context.Context, playlistID string) (*PlaylistDetail, error) {
	var pl model.Playlist
	if err := p.repo.DB.Where("id = ?", playlistID).First(&pl).Error; err != nil {
		return nil, err
	}
	var rows []model.PlaylistItem
	if err := p.repo.DB.
		Where("playlist_id = ?", playlistID).
		Order("position asc").
		Find(&rows).Error; err != nil {
		return nil, err
	}
	if len(rows) == 0 {
		return &PlaylistDetail{Playlist: pl}, nil
	}
	ids := make([]string, len(rows))
	for i, r := range rows {
		ids[i] = r.MediaID
	}
	var media []model.Media
	if err := p.repo.DB.Where("id IN ?", ids).Find(&media).Error; err != nil {
		return nil, err
	}
	// Preserve playlist order.
	byID := make(map[string]model.Media, len(media))
	for _, m := range media {
		byID[m.ID] = m
	}
	ordered := make([]model.Media, 0, len(rows))
	for _, r := range rows {
		if m, ok := byID[r.MediaID]; ok {
			ordered = append(ordered, m)
		}
	}
	return &PlaylistDetail{Playlist: pl, Items: ordered}, nil
}

// AddToPlaylist appends a media item to the end of a playlist.
func (p *PlaybackService) AddToPlaylist(ctx context.Context, playlistID, mediaID string) error {
	var count int64
	if err := p.repo.DB.Model(&model.PlaylistItem{}).
		Where("playlist_id = ?", playlistID).Count(&count).Error; err != nil {
		return err
	}
	item := &model.PlaylistItem{
		PlaylistID: playlistID,
		MediaID:    mediaID,
		Position:   int(count) + 1,
	}
	return p.repo.DB.Create(item).Error
}

// RemoveFromPlaylist removes a media item from a playlist (idempotent).
func (p *PlaybackService) RemoveFromPlaylist(ctx context.Context, playlistID, mediaID string) error {
	return p.repo.DB.
		Where("playlist_id = ? AND media_id = ?", playlistID, mediaID).
		Delete(&model.PlaylistItem{}).Error
}

// DeletePlaylist removes a playlist and all of its items.
func (p *PlaybackService) DeletePlaylist(ctx context.Context, playlistID string) error {
	if err := p.repo.DB.Where("playlist_id = ?", playlistID).
		Delete(&model.PlaylistItem{}).Error; err != nil {
		return err
	}
	return p.repo.DB.Where("id = ?", playlistID).Delete(&model.Playlist{}).Error
}