package discover

import (
	"context"
	"encoding/base64"
	"fmt"
	"strconv"
	"strings"
	"time"

	"github.com/google/uuid"
	"go.uber.org/zap"
	"gorm.io/gorm"

	"veza-backend-api/internal/models"
)

const (
	MaxTagsPerTrack   = 10
	MaxTagLength      = 30
	MaxGenresPerTrack = 3
)

// Service v0.10.1 F351-F355: Tags, genres, discover, follow
type Service struct {
	db     *gorm.DB
	logger *zap.Logger
}

// NewService creates a discover service
func NewService(db *gorm.DB, logger *zap.Logger) *Service {
	return &Service{db: db, logger: logger}
}

// SyncTrackTags syncs track_tags from tag names. Validates max 10, 30 chars each.
func (s *Service) SyncTrackTags(ctx context.Context, trackID uuid.UUID, tagNames []string) error {
	if len(tagNames) > MaxTagsPerTrack {
		return fmt.Errorf("max %d tags per track", MaxTagsPerTrack)
	}
	normalized := make([]string, 0, len(tagNames))
	seen := make(map[string]bool)
	for _, t := range tagNames {
		name := strings.TrimSpace(strings.ToLower(t))
		if name == "" || seen[name] {
			continue
		}
		if len(name) > MaxTagLength {
			return fmt.Errorf("tag max %d chars: %q", MaxTagLength, t)
		}
		normalized = append(normalized, name)
		seen[name] = true
	}
	if len(normalized) > MaxTagsPerTrack {
		return fmt.Errorf("max %d tags per track", MaxTagsPerTrack)
	}

	// Delete existing track_tags and decrement use_count
	var existing []models.TrackTag
	if err := s.db.WithContext(ctx).Where("track_id = ?", trackID).Find(&existing).Error; err != nil {
		return fmt.Errorf("find existing tags: %w", err)
	}
	for _, tt := range existing {
		s.db.Model(&models.Tag{}).Where("id = ?", tt.TagID).UpdateColumn("use_count", gorm.Expr("use_count - 1"))
	}
	if err := s.db.WithContext(ctx).Where("track_id = ?", trackID).Delete(&models.TrackTag{}).Error; err != nil {
		return fmt.Errorf("delete track tags: %w", err)
	}

	// Denormalized array for tracks.tags (backward compat)
	tagsArray := make([]string, 0, len(normalized))

	for _, name := range normalized {
		var tag models.Tag
		err := s.db.WithContext(ctx).Where("name = ?", name).First(&tag).Error
		if err == gorm.ErrRecordNotFound {
			tag = models.Tag{Name: name}
			if err := s.db.WithContext(ctx).Create(&tag).Error; err != nil {
				return fmt.Errorf("create tag %q: %w", name, err)
			}
		} else if err != nil {
			return fmt.Errorf("find tag %q: %w", name, err)
		}
		if err := s.db.WithContext(ctx).Create(&models.TrackTag{TrackID: trackID, TagID: tag.ID}).Error; err != nil {
			return fmt.Errorf("link tag: %w", err)
		}
		s.db.Model(&models.Tag{}).Where("id = ?", tag.ID).UpdateColumn("use_count", gorm.Expr("use_count + 1"))
		tagsArray = append(tagsArray, tag.Name)
	}

	// Update denormalized tracks.tags
	return s.db.WithContext(ctx).Model(&models.Track{}).Where("id = ?", trackID).
		Update("tags", tagsArray).Error
}

// SyncTrackGenres syncs track_genres from genre slugs. Validates max 3, must exist in taxonomy.
func (s *Service) SyncTrackGenres(ctx context.Context, trackID uuid.UUID, genreSlugs []string) error {
	if len(genreSlugs) > MaxGenresPerTrack {
		return fmt.Errorf("max %d genres per track", MaxGenresPerTrack)
	}
	normalized := make([]string, 0, len(genreSlugs))
	seen := make(map[string]bool)
	for _, g := range genreSlugs {
		slug := strings.TrimSpace(strings.ToLower(g))
		if slug == "" || seen[slug] {
			continue
		}
		var genre models.Genre
		if err := s.db.WithContext(ctx).Where("slug = ?", slug).First(&genre).Error; err != nil {
			if err == gorm.ErrRecordNotFound {
				return fmt.Errorf("unknown genre: %q", slug)
			}
			return fmt.Errorf("find genre: %w", err)
		}
		normalized = append(normalized, genre.Slug)
		seen[slug] = true
	}
	if len(normalized) > MaxGenresPerTrack {
		return fmt.Errorf("max %d genres per track", MaxGenresPerTrack)
	}

	if err := s.db.WithContext(ctx).Where("track_id = ?", trackID).Delete(&models.TrackGenre{}).Error; err != nil {
		return fmt.Errorf("delete track genres: %w", err)
	}
	for i, slug := range normalized {
		if err := s.db.WithContext(ctx).Create(&models.TrackGenre{
			TrackID:   trackID,
			GenreSlug: slug,
			Position:  i,
		}).Error; err != nil {
			return fmt.Errorf("link genre: %w", err)
		}
	}

	// Update legacy tracks.genre (first genre)
	primary := ""
	if len(normalized) > 0 {
		primary = normalized[0]
	}
	return s.db.WithContext(ctx).Model(&models.Track{}).Where("id = ?", trackID).
		Update("genre", primary).Error
}

// ListGenres returns all genres from taxonomy
func (s *Service) ListGenres(ctx context.Context) ([]*models.Genre, error) {
	var list []*models.Genre
	if err := s.db.WithContext(ctx).Order("name").Find(&list).Error; err != nil {
		return nil, err
	}
	return list, nil
}

// GetTracksByGenre F353: browse by genre, chronological, cursor pagination
func (s *Service) GetTracksByGenre(ctx context.Context, genreSlug string, limit int, cursor string) ([]*models.Track, string, error) {
	if limit <= 0 {
		limit = 20
	}
	if limit > 50 {
		limit = 50
	}
	slug := strings.TrimSpace(strings.ToLower(genreSlug))
	var g models.Genre
	if err := s.db.WithContext(ctx).Where("slug = ?", slug).First(&g).Error; err != nil {
		if err == gorm.ErrRecordNotFound {
			return nil, "", fmt.Errorf("genre not found: %s", slug)
		}
		return nil, "", err
	}

	query := s.db.WithContext(ctx).Model(&models.Track{}).
		Joins("INNER JOIN track_genres ON track_genres.track_id = tracks.id AND track_genres.genre_slug = ?", g.Slug).
		Where("tracks.status = ?", models.TrackStatusCompleted).
		Where("tracks.is_public = ?", true)

	var cursorCreatedAt int64
	var cursorID uuid.UUID
	if cursor != "" {
		decoded, err := base64.RawURLEncoding.DecodeString(cursor)
		if err == nil {
			parts := strings.SplitN(string(decoded), "|", 2)
			if len(parts) == 2 {
				if ts, err := strconv.ParseInt(parts[0], 10, 64); err == nil {
					cursorCreatedAt = ts
				}
				if uid, err := uuid.Parse(parts[1]); err == nil {
					cursorID = uid
				}
			}
		}
	}
	if cursor != "" && (cursorCreatedAt != 0 || cursorID != uuid.Nil) {
		query = query.Where("(tracks.created_at, tracks.id) < (?, ?)", time.Unix(0, cursorCreatedAt), cursorID)
	}
	query = query.Order("tracks.created_at DESC, tracks.id DESC").Limit(limit + 1)

	var tracks []*models.Track
	if err := query.Preload("User").Find(&tracks).Error; err != nil {
		return nil, "", fmt.Errorf("get tracks by genre: %w", err)
	}

	var nextCursor string
	if len(tracks) > limit {
		last := tracks[limit-1]
		nextCursor = base64.RawURLEncoding.EncodeToString([]byte(
			fmt.Sprintf("%d|%s", last.CreatedAt.UnixNano(), last.ID.String())))
		tracks = tracks[:limit]
	}
	return tracks, nextCursor, nil
}

// GetTracksByTag F353: browse by tag, chronological, cursor pagination
func (s *Service) GetTracksByTag(ctx context.Context, tagName string, limit int, cursor string) ([]*models.Track, string, error) {
	if limit <= 0 {
		limit = 20
	}
	if limit > 50 {
		limit = 50
	}
	name := strings.TrimSpace(strings.ToLower(tagName))
	var tag models.Tag
	if err := s.db.WithContext(ctx).Where("name = ?", name).First(&tag).Error; err != nil {
		if err == gorm.ErrRecordNotFound {
			return nil, "", fmt.Errorf("tag not found: %s", tagName)
		}
		return nil, "", err
	}

	query := s.db.WithContext(ctx).Model(&models.Track{}).
		Joins("INNER JOIN track_tags ON track_tags.track_id = tracks.id AND track_tags.tag_id = ?", tag.ID).
		Where("tracks.status = ?", models.TrackStatusCompleted).
		Where("tracks.is_public = ?", true)

	var cursorCreatedAt int64
	var cursorID uuid.UUID
	if cursor != "" {
		decoded, err := base64.RawURLEncoding.DecodeString(cursor)
		if err == nil {
			parts := strings.SplitN(string(decoded), "|", 2)
			if len(parts) == 2 {
				if ts, err := strconv.ParseInt(parts[0], 10, 64); err == nil {
					cursorCreatedAt = ts
				}
				if uid, err := uuid.Parse(parts[1]); err == nil {
					cursorID = uid
				}
			}
		}
	}
	if cursor != "" && (cursorCreatedAt != 0 || cursorID != uuid.Nil) {
		query = query.Where("(tracks.created_at, tracks.id) < (?, ?)", time.Unix(0, cursorCreatedAt), cursorID)
	}
	query = query.Order("tracks.created_at DESC, tracks.id DESC").Limit(limit + 1)

	var tracks []*models.Track
	if err := query.Preload("User").Find(&tracks).Error; err != nil {
		return nil, "", fmt.Errorf("get tracks by tag: %w", err)
	}

	var nextCursor string
	if len(tracks) > limit {
		last := tracks[limit-1]
		nextCursor = base64.RawURLEncoding.EncodeToString([]byte(
			fmt.Sprintf("%d|%s", last.CreatedAt.UnixNano(), last.ID.String())))
		tracks = tracks[:limit]
	}
	return tracks, nextCursor, nil
}

// FollowGenre F354
func (s *Service) FollowGenre(ctx context.Context, userID uuid.UUID, genreSlug string) error {
	slug := strings.TrimSpace(strings.ToLower(genreSlug))
	var g models.Genre
	if err := s.db.WithContext(ctx).Where("slug = ?", slug).First(&g).Error; err != nil {
		if err == gorm.ErrRecordNotFound {
			return fmt.Errorf("genre not found: %s", slug)
		}
		return err
	}
	return s.db.WithContext(ctx).FirstOrCreate(&models.UserGenreFollow{
		UserID:    userID,
		GenreSlug: g.Slug,
	}).Error
}

// UnfollowGenre F354
func (s *Service) UnfollowGenre(ctx context.Context, userID uuid.UUID, genreSlug string) error {
	slug := strings.TrimSpace(strings.ToLower(genreSlug))
	res := s.db.WithContext(ctx).Where("user_id = ? AND genre_slug = ?", userID, slug).
		Delete(&models.UserGenreFollow{})
	if res.Error != nil {
		return res.Error
	}
	return nil
}

// FollowTag F354
func (s *Service) FollowTag(ctx context.Context, userID uuid.UUID, tagName string) error {
	name := strings.TrimSpace(strings.ToLower(tagName))
	var tag models.Tag
	if err := s.db.WithContext(ctx).Where("name = ?", name).First(&tag).Error; err != nil {
		if err == gorm.ErrRecordNotFound {
			return fmt.Errorf("tag not found: %s", tagName)
		}
		return err
	}
	return s.db.WithContext(ctx).FirstOrCreate(&models.UserTagFollow{
		UserID: userID,
		TagID:  tag.ID,
	}).Error
}

// UnfollowTag F354
func (s *Service) UnfollowTag(ctx context.Context, userID uuid.UUID, tagName string) error {
	name := strings.TrimSpace(strings.ToLower(tagName))
	var tag models.Tag
	if err := s.db.WithContext(ctx).Where("name = ?", name).First(&tag).Error; err != nil {
		if err == gorm.ErrRecordNotFound {
			return nil // idempotent
		}
		return err
	}
	res := s.db.WithContext(ctx).Where("user_id = ? AND tag_id = ?", userID, tag.ID).
		Delete(&models.UserTagFollow{})
	return res.Error
}

// IsFollowingGenre returns true if user follows the genre
func (s *Service) IsFollowingGenre(ctx context.Context, userID uuid.UUID, genreSlug string) (bool, error) {
	slug := strings.TrimSpace(strings.ToLower(genreSlug))
	var count int64
	err := s.db.WithContext(ctx).Model(&models.UserGenreFollow{}).
		Where("user_id = ? AND genre_slug = ?", userID, slug).Count(&count).Error
	return count > 0, err
}

// IsFollowingTag returns true if user follows the tag
func (s *Service) IsFollowingTag(ctx context.Context, userID uuid.UUID, tagName string) (bool, error) {
	name := strings.TrimSpace(strings.ToLower(tagName))
	var tag models.Tag
	if err := s.db.WithContext(ctx).Where("name = ?", name).First(&tag).Error; err != nil {
		return false, nil
	}
	var count int64
	err := s.db.WithContext(ctx).Model(&models.UserTagFollow{}).
		Where("user_id = ? AND tag_id = ?", userID, tag.ID).Count(&count).Error
	return count > 0, err
}

// GetEditorialPlaylists F141 v0.10.4: playlists curatoriales visibles dans Discover
func (s *Service) GetEditorialPlaylists(ctx context.Context, limit int, cursor string) ([]*models.Playlist, string, error) {
	if limit <= 0 {
		limit = 20
	}
	if limit > 50 {
		limit = 50
	}

	query := s.db.WithContext(ctx).Model(&models.Playlist{}).
		Where("is_editorial = ?", true).
		Where("is_public = ?", true).
		Where("deleted_at IS NULL")

	var cursorCreatedAt int64
	var cursorID uuid.UUID
	if cursor != "" {
		decoded, err := base64.RawURLEncoding.DecodeString(cursor)
		if err == nil {
			parts := strings.SplitN(string(decoded), "|", 2)
			if len(parts) == 2 {
				if ts, err := strconv.ParseInt(parts[0], 10, 64); err == nil {
					cursorCreatedAt = ts
				}
				if uid, err := uuid.Parse(parts[1]); err == nil {
					cursorID = uid
				}
			}
		}
	}
	if cursor != "" && (cursorCreatedAt != 0 || cursorID != uuid.Nil) {
		query = query.Where("(playlists.created_at, playlists.id) < (?, ?)", time.Unix(0, cursorCreatedAt), cursorID)
	}
	query = query.Order("playlists.created_at DESC, playlists.id DESC").Limit(limit + 1)

	var playlists []*models.Playlist
	if err := query.Preload("User").Find(&playlists).Error; err != nil {
		return nil, "", fmt.Errorf("get editorial playlists: %w", err)
	}

	var nextCursor string
	if len(playlists) > limit {
		last := playlists[limit-1]
		nextCursor = base64.RawURLEncoding.EncodeToString([]byte(
			fmt.Sprintf("%d|%s", last.CreatedAt.UnixNano(), last.ID.String())))
		playlists = playlists[:limit]
	}
	return playlists, nextCursor, nil
}

// GetTracksFromFollowedGenres F355: nouveautés dans les genres suivis
func (s *Service) GetTracksFromFollowedGenres(ctx context.Context, userID uuid.UUID, limit int, cursor string) ([]*models.Track, string, error) {
	if limit <= 0 {
		limit = 20
	}
	if limit > 50 {
		limit = 50
	}

	sub := s.db.WithContext(ctx).Model(&models.Track{}).
		Select("DISTINCT tracks.id").
		Joins("INNER JOIN track_genres ON track_genres.track_id = tracks.id").
		Joins("INNER JOIN user_genre_follows ON user_genre_follows.genre_slug = track_genres.genre_slug AND user_genre_follows.user_id = ?", userID).
		Where("tracks.status = ?", models.TrackStatusCompleted).
		Where("tracks.is_public = ?", true)

	var cursorCreatedAt int64
	var cursorID uuid.UUID
	if cursor != "" {
		decoded, err := base64.RawURLEncoding.DecodeString(cursor)
		if err == nil {
			parts := strings.SplitN(string(decoded), "|", 2)
			if len(parts) == 2 {
				if ts, err := strconv.ParseInt(parts[0], 10, 64); err == nil {
					cursorCreatedAt = ts
				}
				if uid, err := uuid.Parse(parts[1]); err == nil {
					cursorID = uid
				}
			}
		}
	}
	if cursor != "" && (cursorCreatedAt != 0 || cursorID != uuid.Nil) {
		sub = sub.Where("(tracks.created_at, tracks.id) < (?, ?)", time.Unix(0, cursorCreatedAt), cursorID)
	}

	var trackIDs []uuid.UUID
	if err := sub.Order("tracks.created_at DESC, tracks.id DESC").Limit(limit + 1).Pluck("tracks.id", &trackIDs).Error; err != nil {
		return nil, "", fmt.Errorf("get track ids: %w", err)
	}
	if len(trackIDs) == 0 {
		return []*models.Track{}, "", nil
	}

	var tracks []*models.Track
	if err := s.db.WithContext(ctx).Preload("User").Where("id IN ?", trackIDs).
		Order("created_at DESC, id DESC").Find(&tracks).Error; err != nil {
		return nil, "", fmt.Errorf("get tracks: %w", err)
	}

	var nextCursor string
	if len(tracks) > limit {
		last := tracks[limit-1]
		nextCursor = base64.RawURLEncoding.EncodeToString([]byte(
			fmt.Sprintf("%d|%s", last.CreatedAt.UnixNano(), last.ID.String())))
		tracks = tracks[:limit]
	}
	return tracks, nextCursor, nil
}