package social

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

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

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

// SocialService gère les interactions sociales
type SocialService interface {
	CreatePost(ctx context.Context, userID uuid.UUID, content string, attachments map[string]uuid.UUID) (*Post, error)
	GetGlobalFeed(ctx context.Context, limit, offset int, feedType string, userID *uuid.UUID) ([]FeedItem, error)
	GetGlobalFeedWithCursor(ctx context.Context, limit int, cursor, feedType string, userID *uuid.UUID) ([]FeedItem, string, error) // v0.931: keyset cursor
	GetUserFeed(ctx context.Context, userID uuid.UUID, limit, offset int) ([]FeedItem, error)

	GetPostsByUser(ctx context.Context, userID uuid.UUID, limit, offset int) ([]Post, error)

	// Interactions
	ToggleLike(ctx context.Context, userID uuid.UUID, targetID uuid.UUID, targetType string) (bool, error)
	AddComment(ctx context.Context, userID uuid.UUID, targetID uuid.UUID, targetType string, content string) (*Comment, error)

	// Internal
	CreateActivityPost(ctx context.Context, userID uuid.UUID, content string, meta map[string]interface{}) error

	// Trending (v0.203 Lot L)
	GetTrendingHashtags(ctx context.Context, limit int) ([]TrendingTag, error)
}

// Service implémente SocialService
type Service struct {
	db           *gorm.DB
	logger       *zap.Logger
	cacheService *services.CacheService // optional, for trending cache
}

// SetCacheService définit le service de cache (optionnel, pour trending)
func (s *Service) SetCacheService(cache *services.CacheService) {
	s.cacheService = cache
}

// NewService crée une nouvelle instance du service social
func NewService(db *gorm.DB, logger *zap.Logger) *Service {
	return &Service{
		db:     db,
		logger: logger,
	}
}

// CreatePost crée une nouvelle publication
func (s *Service) CreatePost(ctx context.Context, userID uuid.UUID, content string, attachments map[string]uuid.UUID) (*Post, error) {
	post := &Post{
		UserID:  userID,
		Content: content,
		Type:    PostTypeStatus,
	}

	// Handle attachments
	if trackID, ok := attachments["track_id"]; ok {
		post.TrackID = &trackID
		post.Type = PostTypeShare
	}
	if playlistID, ok := attachments["playlist_id"]; ok {
		post.PlaylistID = &playlistID
		post.Type = PostTypeShare
	}

	if err := s.db.Create(post).Error; err != nil {
		s.logger.Error("Failed to create post", zap.Error(err), zap.String("user_id", userID.String()))
		return nil, err
	}

	return post, nil
}

// GetGlobalFeed récupère un flux d'activité global (S1.2, S1.6: enrichi, type filter)
func (s *Service) GetGlobalFeed(ctx context.Context, limit, offset int, feedType string, userID *uuid.UUID) ([]FeedItem, error) {
	query := s.db.WithContext(ctx).Model(&Post{})
	if feedType == "following" && userID != nil {
		// Posts from users that current user follows
		query = query.Joins("INNER JOIN follows ON follows.followed_id = posts.user_id AND follows.follower_id = ?", *userID)
	} else if feedType == "groups" && userID != nil {
		// S2.4: Posts from members of groups the current user belongs to
		// Subquery: user_ids that share at least one group with current user
		subQuery := s.db.WithContext(ctx).Model(&GroupMember{}).
			Select("DISTINCT gm2.user_id").
			Joins("INNER JOIN group_members gm2 ON group_members.group_id = gm2.group_id AND gm2.user_id != ?", *userID).
			Where("group_members.user_id = ?", *userID)
		query = query.Where("posts.user_id IN (?)", subQuery)
	}
	var posts []Post
	if err := query.Order("posts.created_at desc").Limit(limit).Offset(offset).Find(&posts).Error; err != nil {
		return nil, err
	}
	return s.enrichFeedFromPosts(ctx, posts)
}

// GetGlobalFeedWithCursor uses keyset pagination on (created_at, id) for consistent performance (v0.931).
// Cursor format: base64(created_at_unix_nano|uuid). Returns feed items and next cursor.
func (s *Service) GetGlobalFeedWithCursor(ctx context.Context, limit int, cursor, feedType string, userID *uuid.UUID) ([]FeedItem, string, error) {
	query := s.db.WithContext(ctx).Model(&Post{})
	if feedType == "following" && userID != nil {
		query = query.Joins("INNER JOIN follows ON follows.followed_id = posts.user_id AND follows.follower_id = ?", *userID)
	} else if feedType == "groups" && userID != nil {
		subQuery := s.db.WithContext(ctx).Model(&GroupMember{}).
			Select("DISTINCT gm2.user_id").
			Joins("INNER JOIN group_members gm2 ON group_members.group_id = gm2.group_id AND gm2.user_id != ?", *userID).
			Where("group_members.user_id = ?", *userID)
		query = query.Where("posts.user_id IN (?)", subQuery)
	}

	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("(posts.created_at, posts.id) < (?, ?)", time.Unix(0, cursorCreatedAt), cursorID)
	}

	if limit <= 0 {
		limit = 20
	}
	if limit > 50 {
		limit = 50
	}
	query = query.Order("posts.created_at desc, posts.id desc").Limit(limit + 1)

	var posts []Post
	if err := query.Find(&posts).Error; err != nil {
		return nil, "", err
	}

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

	feed, err := s.enrichFeedFromPosts(ctx, posts)
	if err != nil {
		return nil, "", err
	}
	return feed, nextCursor, nil
}

func (s *Service) enrichFeedFromPosts(ctx context.Context, posts []Post) ([]FeedItem, error) {
	var feed []FeedItem
	actorIDs := make(map[uuid.UUID]bool)
	var trackIDs []uuid.UUID
	for _, p := range posts {
		actorIDs[p.UserID] = true
		if p.TrackID != nil {
			trackIDs = append(trackIDs, *p.TrackID)
		}
	}

	actors := make(map[uuid.UUID]struct{ Name, Avatar string })
	if len(actorIDs) > 0 {
		ids := make([]uuid.UUID, 0, len(actorIDs))
		for id := range actorIDs {
			ids = append(ids, id)
		}
		var users []models.User
		if err := s.db.WithContext(ctx).Where("id IN ?", ids).Find(&users).Error; err == nil {
			for _, u := range users {
				name := u.Username
				if u.FirstName != "" || u.LastName != "" {
					name = (u.FirstName + " " + u.LastName)
					if name = strings.TrimSpace(name); name == "" {
						name = u.Username
					}
				}
				actors[u.ID] = struct{ Name, Avatar string }{Name: name, Avatar: u.Avatar}
			}
		}
	}

	tracks := make(map[uuid.UUID]*models.Track)
	if len(trackIDs) > 0 {
		var tr []models.Track
		if err := s.db.WithContext(ctx).Where("id IN ?", trackIDs).Find(&tr).Error; err == nil {
			for i := range tr {
				tracks[tr[i].ID] = &tr[i]
			}
		}
	}

	for _, p := range posts {
		targetType := "none"
		targetID := uuid.Nil

		if p.TrackID != nil {
			targetType = "track"
			targetID = *p.TrackID
		} else if p.PlaylistID != nil {
			targetType = "playlist"
			targetID = *p.PlaylistID
		}

		item := FeedItem{
			ID:         fmt.Sprintf("post:%s", p.ID.String()),
			Type:       ActivityPost,
			ActorID:    p.UserID,
			TargetID:   targetID,
			TargetType: targetType,
			Content:    p.Content,
			CreatedAt:  p.CreatedAt,
		}

		if a, ok := actors[p.UserID]; ok {
			item.ActorName = a.Name
			item.ActorAvatar = a.Avatar
		}

		if targetType == "track" {
			if t, ok := tracks[targetID]; ok {
				item.Track = &FeedItemTrack{
					ID:       t.ID.String(),
					Title:    t.Title,
					Artist:   t.Artist,
					CoverURL: t.CoverArtPath,
					Duration: formatDuration(t.Duration),
					Genre:    t.Genre,
				}
			}
		}

		if p.Type == PostTypeActivity {
			item.Type = ActivityPurchase
		}

		feed = append(feed, item)
	}
	return feed, nil
}

func formatDuration(seconds int) string {
	m := seconds / 60
	s := seconds % 60
	return fmt.Sprintf("%d:%02d", m, s)
}

// GetUserFeed récupère le flux d'un utilisateur (posts from people they follow + their own)
// NOTE: For now it just returns their own posts as FeedItems, keeping meaningful naming.
func (s *Service) GetUserFeed(ctx context.Context, userID uuid.UUID, limit, offset int) ([]FeedItem, error) {
	var posts []Post
	if err := s.db.Where("user_id = ?", userID).Order("created_at desc").Limit(limit).Offset(offset).Find(&posts).Error; err != nil {
		return nil, err
	}

	var feed []FeedItem
	for _, p := range posts {
		item := FeedItem{
			ID:         fmt.Sprintf("post:%s", p.ID.String()),
			Type:       ActivityPost,
			ActorID:    p.UserID,
			Content:    p.Content,
			CreatedAt:  p.CreatedAt,
			TargetType: "user_wall",
		}
		feed = append(feed, item)
	}

	return feed, nil
}

// GetPostsByUser récupère les posts d'un utilisateur spécifique
func (s *Service) GetPostsByUser(ctx context.Context, userID uuid.UUID, limit, offset int) ([]Post, error) {
	var posts []Post
	if err := s.db.Where("user_id = ?", userID).Order("created_at desc").Limit(limit).Offset(offset).Find(&posts).Error; err != nil {
		return nil, err
	}
	return posts, nil
}

// ToggleLike ajoute ou supprime un like
// Transactionnelle : SELECT like + DELETE/CREATE + UPDATE compteur dans une seule transaction
func (s *Service) ToggleLike(ctx context.Context, userID uuid.UUID, targetID uuid.UUID, targetType string) (bool, error) {
	var liked bool

	err := s.db.WithContext(ctx).Transaction(func(tx *gorm.DB) error {
		// 1. VÉRIFICATION : Like existe déjà ? (SELECT dans la transaction)
		var like Like
		err := tx.Where("user_id = ? AND target_id = ? AND target_type = ?", userID, targetID, targetType).First(&like).Error

		if err == nil {
			// 2a. Mode UNLIKE : Like existe, on le supprime
			if err := tx.Delete(&like).Error; err != nil {
				return fmt.Errorf("ToggleLike: failed to delete like: %w", err)
			}

			// 3a. Décrémenter le compteur si c'est un post (dans la transaction)
			if targetType == "post" {
				if err := tx.Model(&Post{}).Where("id = ?", targetID).Update("like_count", gorm.Expr("like_count - 1")).Error; err != nil {
					return fmt.Errorf("ToggleLike: failed to decrement like_count: %w", err)
				}
			}

			liked = false
			return nil
		} else if err == gorm.ErrRecordNotFound {
			// 2b. Mode LIKE : Like n'existe pas, on le crée
			// Vérifier d'abord que la ressource existe (pour les posts)
			if targetType == "post" {
				var post Post
				if err := tx.Where("id = ?", targetID).First(&post).Error; err != nil {
					if err == gorm.ErrRecordNotFound {
						return fmt.Errorf("ToggleLike: post not found: %w", err)
					}
					return fmt.Errorf("ToggleLike: failed to check post existence: %w", err)
				}
			}

			like = Like{
				UserID:     userID,
				TargetID:   targetID,
				TargetType: targetType,
			}
			if err := tx.Create(&like).Error; err != nil {
				return fmt.Errorf("ToggleLike: failed to create like: %w", err)
			}

			// 3b. Incrémenter le compteur si c'est un post (dans la transaction)
			if targetType == "post" {
				if err := tx.Model(&Post{}).Where("id = ?", targetID).Update("like_count", gorm.Expr("like_count + 1")).Error; err != nil {
					return fmt.Errorf("ToggleLike: failed to increment like_count: %w", err)
				}
			}

			liked = true
			return nil
		} else {
			return fmt.Errorf("ToggleLike: failed to check like existence: %w", err)
		}
	})

	if err != nil {
		return false, err // Rollback automatique si erreur
	}

	return liked, nil
}

// AddComment ajoute un commentaire
// Transactionnelle : CREATE comment + UPDATE compteur dans une seule transaction
func (s *Service) AddComment(ctx context.Context, userID uuid.UUID, targetID uuid.UUID, targetType string, content string) (*Comment, error) {
	var comment *Comment

	err := s.db.WithContext(ctx).Transaction(func(tx *gorm.DB) error {
		// 1. VALIDATION : Post existe ? (SELECT dans la transaction si targetType == "post")
		if targetType == "post" {
			var post Post
			if err := tx.First(&post, "id = ?", targetID).Error; err != nil {
				if err == gorm.ErrRecordNotFound {
					return fmt.Errorf("post not found")
				}
				return fmt.Errorf("AddComment: failed to validate post: %w", err)
			}
		}

		// 2. CRÉATION : Commentaire (INSERT dans la transaction)
		comment = &Comment{
			UserID:     userID,
			TargetID:   targetID,
			TargetType: targetType,
			Content:    content,
		}
		if err := tx.Create(comment).Error; err != nil {
			return fmt.Errorf("AddComment: failed to create comment: %w", err)
		}

		// 3. MISE À JOUR : Compteur (UPDATE dans la transaction)
		if targetType == "post" {
			if err := tx.Model(&Post{}).Where("id = ?", targetID).Update("comment_count", gorm.Expr("comment_count + 1")).Error; err != nil {
				return fmt.Errorf("AddComment: failed to increment comment_count: %w", err)
			}
		}

		// 4. RETOUR nil = commit automatique
		return nil
	})

	if err != nil {
		return nil, err // Rollback automatique si erreur
	}

	return comment, nil
}

// CreateActivityPost crée un post automatique pour une activité (ex: Achat)
func (s *Service) CreateActivityPost(ctx context.Context, userID uuid.UUID, content string, meta map[string]interface{}) error {
	post := &Post{
		UserID:  userID,
		Content: content,
		Type:    PostTypeActivity,
	}

	if trackIDStr, ok := meta["track_id"].(string); ok {
		if trackID, err := uuid.Parse(trackIDStr); err == nil {
			post.TrackID = &trackID
		}
	}

	return s.db.Create(post).Error
}