veza/veza-backend-api/internal/core/analytics/handler.go

package analytics

import (
	"context"
	"encoding/json"
	"net/http"
	"strconv"
	"strings"
	"time"

	"veza-backend-api/internal/common"
	apperrors "veza-backend-api/internal/errors"
	"veza-backend-api/internal/handlers"

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

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

// AnalyticsServiceInterface defines the interface for AnalyticsService
type AnalyticsServiceInterface interface {
	GetTrackStats(ctx context.Context, trackID uuid.UUID) (*types.TrackStats, error)
	GetPlaysOverTime(ctx context.Context, trackID uuid.UUID, startDate, endDate time.Time, interval string) ([]services.PlayTimePoint, error)
}

// AnalyticsJobWorkerInterface defines the interface for JobWorker (analytics related)
type AnalyticsJobWorkerInterface interface {
	EnqueueAnalyticsJob(eventName string, userID *uuid.UUID, payload map[string]interface{})
}

// AnalyticsServiceWithDB extends AnalyticsServiceInterface with DB access for GetAnalytics
type AnalyticsServiceWithDB interface {
	AnalyticsServiceInterface
	GetDB() *gorm.DB
}

// Handler handles analytics HTTP requests (core domain, ADR-001)
type Handler struct {
	analyticsService AnalyticsServiceInterface
	jobWorker        AnalyticsJobWorkerInterface
	logger           *zap.Logger
}

// NewHandler creates a new analytics handler
func NewHandler(analyticsService *services.AnalyticsService, logger *zap.Logger) *Handler {
	if logger == nil {
		logger = zap.NewNop()
	}
	return &Handler{
		analyticsService: analyticsService,
		logger:           logger,
	}
}

// NewHandlerWithInterface creates a handler with interfaces (for testing)
func NewHandlerWithInterface(analyticsService AnalyticsServiceInterface, logger *zap.Logger) *Handler {
	if logger == nil {
		logger = zap.NewNop()
	}
	return &Handler{
		analyticsService: analyticsService,
		logger:           logger,
	}
}

// SetJobWorker sets the JobWorker for recording analytics events
func (h *Handler) SetJobWorker(jobWorker AnalyticsJobWorkerInterface) {
	h.jobWorker = jobWorker
}

// RecordEventRequest represents the request for recording a custom analytics event
type RecordEventRequest struct {
	EventName string                 `json:"event_name" binding:"required,min=1,max=100" validate:"required,min=1,max=100"`
	Payload   map[string]interface{} `json:"payload,omitempty" validate:"omitempty"`
}

// RecordEvent handles POST /api/v1/analytics/events
func (h *Handler) RecordEvent(c *gin.Context) {
	var req RecordEventRequest
	if !common.BindAndValidateJSON(c, &req) {
		return
	}

	var userID *uuid.UUID
	if uid, ok := c.Get("user_id"); ok {
		if uidUUID, ok := uid.(uuid.UUID); ok {
			userID = &uidUUID
		}
	}

	if h.jobWorker == nil {
		handlers.RespondWithAppError(c, apperrors.New(apperrors.ErrCodeInternal, "analytics service not available"))
		return
	}

	h.jobWorker.EnqueueAnalyticsJob(req.EventName, userID, req.Payload)

	handlers.RespondSuccess(c, http.StatusOK, gin.H{
		"message":    "event recorded",
		"event_name": req.EventName,
	})
}

// GetTrafficSources handles GET /api/v1/analytics/traffic-sources
// Returns empty until traffic source tracking is implemented (track_plays has no source column)
func (h *Handler) GetTrafficSources(c *gin.Context) {
	handlers.RespondSuccess(c, http.StatusOK, gin.H{"sources": []gin.H{}})
}

// GetDeviceBreakdown handles GET /api/v1/analytics/device-breakdown
// Returns mobile/desktop counts from track_plays for the user's tracks
func (h *Handler) GetDeviceBreakdown(c *gin.Context) {
	userIDInterface, exists := c.Get("user_id")
	if !exists {
		handlers.RespondWithAppError(c, apperrors.New(apperrors.ErrCodeUnauthorized, "authentication required"))
		return
	}
	userID, ok := userIDInterface.(uuid.UUID)
	if !ok {
		handlers.RespondWithAppError(c, apperrors.New(apperrors.ErrCodeInternal, "invalid user id"))
		return
	}

	analyticsSvc, ok := h.analyticsService.(AnalyticsServiceWithDB)
	if !ok {
		handlers.RespondSuccess(c, http.StatusOK, gin.H{"mobile": 0, "desktop": 0})
		return
	}

	var deviceCounts []struct {
		Device string `gorm:"column:device"`
		Count  int64  `gorm:"column:cnt"`
	}
	if err := analyticsSvc.GetDB().WithContext(c.Request.Context()).
		Table("track_plays tp").
		Select("tp.device, COUNT(*) as cnt").
		Joins("JOIN tracks t ON t.id = tp.track_id").
		Where("t.creator_id = ?", userID).
		Group("tp.device").
		Find(&deviceCounts).Error; err != nil {
		h.logger.Warn("Failed to fetch device breakdown", zap.Error(err))
		handlers.RespondSuccess(c, http.StatusOK, gin.H{"mobile": 0, "desktop": 0})
		return
	}

	var mobile, desktop int64
	for _, d := range deviceCounts {
		dev := strings.ToLower(strings.TrimSpace(d.Device))
		if dev == "" || dev == "desktop" || dev == "web" {
			desktop += d.Count
		} else if dev == "mobile" || dev == "tablet" || strings.Contains(dev, "mobile") || strings.Contains(dev, "tablet") {
			mobile += d.Count
		} else {
			desktop += d.Count
		}
	}

	handlers.RespondSuccess(c, http.StatusOK, gin.H{
		"mobile":  mobile,
		"desktop": desktop,
	})
}

// GetCreatorStats handles GET /api/v1/analytics/creator/stats
// Aggregates playback_analytics for the authenticated creator's tracks
func (h *Handler) GetCreatorStats(c *gin.Context) {
	userIDInterface, exists := c.Get("user_id")
	if !exists {
		handlers.RespondWithAppError(c, apperrors.New(apperrors.ErrCodeUnauthorized, "authentication required"))
		return
	}
	userID, ok := userIDInterface.(uuid.UUID)
	if !ok {
		handlers.RespondWithAppError(c, apperrors.New(apperrors.ErrCodeInternal, "invalid user id"))
		return
	}

	analyticsSvc, ok := h.analyticsService.(AnalyticsServiceWithDB)
	if !ok {
		handlers.RespondSuccess(c, http.StatusOK, gin.H{
			"total_plays":             int64(0),
			"unique_listeners":        int64(0),
			"average_completion_rate": float64(0),
			"plays_by_day":            []int64{},
			"period":                  gin.H{"start_date": "", "end_date": "", "days": 0},
		})
		return
	}

	daysStr := c.DefaultQuery("days", "30")
	days, err := strconv.Atoi(daysStr)
	if err != nil || days < 1 {
		days = 30
	}

	var startDate, endDate *time.Time
	if startDateStr := c.Query("start_date"); startDateStr != "" {
		if parsed, err := time.Parse(time.RFC3339, startDateStr); err == nil {
			startDate = &parsed
		}
	}
	if endDateStr := c.Query("end_date"); endDateStr != "" {
		if parsed, err := time.Parse(time.RFC3339, endDateStr); err == nil {
			endDate = &parsed
		}
	}
	if startDate == nil || endDate == nil {
		now := time.Now()
		if endDate == nil {
			endDate = &now
		}
		if startDate == nil {
			calculatedStart := endDate.AddDate(0, 0, -days)
			startDate = &calculatedStart
		}
	}

	ctx := c.Request.Context()
	db := analyticsSvc.GetDB()

	var totalPlays int64
	db.WithContext(ctx).Table("playback_analytics pa").
		Joins("JOIN tracks t ON t.id = pa.track_id").
		Where("t.creator_id = ? AND pa.started_at >= ? AND pa.started_at <= ?", userID, startDate, endDate).
		Count(&totalPlays)

	var uniqueListeners int64
	db.WithContext(ctx).Table("playback_analytics pa").
		Joins("JOIN tracks t ON t.id = pa.track_id").
		Where("t.creator_id = ? AND pa.started_at >= ? AND pa.started_at <= ?", userID, startDate, endDate).
		Select("COUNT(DISTINCT pa.user_id)").
		Scan(&uniqueListeners)

	var avgCompletion float64
	db.WithContext(ctx).Table("playback_analytics pa").
		Joins("JOIN tracks t ON t.id = pa.track_id").
		Where("t.creator_id = ? AND pa.started_at >= ? AND pa.started_at <= ?", userID, startDate, endDate).
		Select("COALESCE(AVG(pa.completion_rate), 0)").
		Scan(&avgCompletion)

	var dayCounts []struct {
		Day   string `gorm:"column:day"`
		Count int64  `gorm:"column:cnt"`
	}
	db.WithContext(ctx).Table("playback_analytics pa").
		Joins("JOIN tracks t ON t.id = pa.track_id").
		Select("DATE(pa.started_at) as day, COUNT(*) as cnt").
		Where("t.creator_id = ? AND pa.started_at >= ? AND pa.started_at <= ?", userID, startDate, endDate).
		Group("DATE(pa.started_at)").
		Order("day ASC").
		Find(&dayCounts)

	playsByDay := make([]int64, len(dayCounts))
	for i, d := range dayCounts {
		playsByDay[i] = d.Count
	}
	if len(playsByDay) == 0 {
		playsByDay = []int64{0}
	}

	handlers.RespondSuccess(c, http.StatusOK, gin.H{
		"total_plays":             totalPlays,
		"unique_listeners":        uniqueListeners,
		"average_completion_rate": avgCompletion,
		"plays_by_day":            playsByDay,
		"period": gin.H{
			"start_date": startDate.Format(time.RFC3339),
			"end_date":   endDate.Format(time.RFC3339),
			"days":       days,
		},
	})
}

// GetCreatorExport handles GET /api/v1/analytics/creator/export?format=csv|json
func (h *Handler) GetCreatorExport(c *gin.Context) {
	userIDInterface, exists := c.Get("user_id")
	if !exists {
		handlers.RespondWithAppError(c, apperrors.New(apperrors.ErrCodeUnauthorized, "authentication required"))
		return
	}
	userID, ok := userIDInterface.(uuid.UUID)
	if !ok {
		handlers.RespondWithAppError(c, apperrors.New(apperrors.ErrCodeInternal, "invalid user id"))
		return
	}

	analyticsSvc, ok := h.analyticsService.(AnalyticsServiceWithDB)
	if !ok {
		handlers.RespondWithAppError(c, apperrors.New(apperrors.ErrCodeInternal, "analytics service unavailable"))
		return
	}

	format := strings.ToLower(c.DefaultQuery("format", "json"))
	if format != "csv" && format != "json" {
		handlers.RespondWithAppError(c, apperrors.NewValidationError("format must be csv or json"))
		return
	}

	days := 30
	if d := c.Query("days"); d != "" {
		if n, err := strconv.Atoi(d); err == nil && n > 0 && n <= 365 {
			days = n
		}
	}
	endDate := time.Now()
	startDate := endDate.AddDate(0, 0, -days)
	ctx := c.Request.Context()
	db := analyticsSvc.GetDB()

	var rows []struct {
		TrackID uuid.UUID `gorm:"column:track_id"`
		Title   string    `gorm:"column:title"`
		Date    string    `gorm:"column:day"`
		Plays   int64     `gorm:"column:cnt"`
	}

	db.WithContext(ctx).Table("track_plays tp").
		Joins("JOIN tracks t ON t.id = tp.track_id").
		Select("tp.track_id, t.title, DATE(tp.played_at) as day, COUNT(*) as cnt").
		Where("t.creator_id = ? AND tp.played_at >= ? AND tp.played_at <= ?", userID, startDate, endDate).
		Group("tp.track_id, t.title, DATE(tp.played_at)").
		Order("day ASC, cnt DESC").
		Find(&rows)

	if format == "json" {
		exportRows := make([]gin.H, len(rows))
		for i, r := range rows {
			exportRows[i] = gin.H{"track_id": r.TrackID.String(), "title": r.Title, "date": r.Date, "plays": r.Plays}
		}
		exportData := gin.H{
			"period": gin.H{"start_date": startDate.Format(time.RFC3339), "end_date": endDate.Format(time.RFC3339), "days": days},
			"rows":   exportRows,
		}
		c.Header("Content-Disposition", "attachment; filename=veza-creator-export.json")
		c.Data(http.StatusOK, "application/json", []byte(mustJSON(exportData)))
		return
	}

	var b strings.Builder
	b.WriteString("track_id,title,date,plays\n")
	for _, r := range rows {
		b.WriteString(r.TrackID.String())
		b.WriteString(",")
		b.WriteString(escapeCSV(r.Title))
		b.WriteString(",")
		b.WriteString(r.Date)
		b.WriteString(",")
		b.WriteString(strconv.FormatInt(r.Plays, 10))
		b.WriteString("\n")
	}
	c.Header("Content-Disposition", "attachment; filename=veza-creator-export.csv")
	c.Data(http.StatusOK, "text/csv", []byte(b.String()))
}

func escapeCSV(s string) string {
	if strings.ContainsAny(s, ",\"\n") {
		return `"` + strings.ReplaceAll(s, `"`, `""`) + `"`
	}
	return s
}

func mustJSON(v interface{}) []byte {
	// Use simple JSON marshalling - gin has json package
	data, _ := json.Marshal(v)
	return data
}

// GetCreatorCharts handles GET /api/v1/analytics/creator/charts
func (h *Handler) GetCreatorCharts(c *gin.Context) {
	userIDInterface, exists := c.Get("user_id")
	if !exists {
		handlers.RespondWithAppError(c, apperrors.New(apperrors.ErrCodeUnauthorized, "authentication required"))
		return
	}
	userID, ok := userIDInterface.(uuid.UUID)
	if !ok {
		handlers.RespondWithAppError(c, apperrors.New(apperrors.ErrCodeInternal, "invalid user id"))
		return
	}

	analyticsSvc, ok := h.analyticsService.(AnalyticsServiceWithDB)
	if !ok {
		handlers.RespondSuccess(c, http.StatusOK, gin.H{
			"plays_per_day": []gin.H{},
			"top_tracks":    []gin.H{},
			"period":        gin.H{"start_date": "", "end_date": "", "days": 0},
		})
		return
	}

	daysStr := c.DefaultQuery("days", "30")
	days, _ := strconv.Atoi(daysStr)
	if days < 1 {
		days = 30
	}
	endDate := time.Now()
	startDate := endDate.AddDate(0, 0, -days)

	ctx := c.Request.Context()
	db := analyticsSvc.GetDB()

	var dayRows []struct {
		Day   string `gorm:"column:day"`
		Count int64  `gorm:"column:cnt"`
	}
	db.WithContext(ctx).Table("track_plays tp").
		Joins("JOIN tracks t ON t.id = tp.track_id").
		Select("DATE(tp.played_at) as day, COUNT(*) as cnt").
		Where("t.creator_id = ? AND tp.played_at >= ? AND tp.played_at <= ?", userID, startDate, endDate).
		Group("DATE(tp.played_at)").
		Order("day ASC").
		Find(&dayRows)

	playsPerDay := make([]gin.H, len(dayRows))
	for i, r := range dayRows {
		playsPerDay[i] = gin.H{"date": r.Day, "count": r.Count}
	}

	var topRows []struct {
		TrackID   uuid.UUID `gorm:"column:track_id"`
		Title     string    `gorm:"column:title"`
		PlayCount int64     `gorm:"column:play_count"`
	}
	db.WithContext(ctx).Table("track_plays tp").
		Joins("JOIN tracks t ON t.id = tp.track_id").
		Select("tp.track_id, t.title, COUNT(*) as play_count").
		Where("t.creator_id = ? AND tp.played_at >= ? AND tp.played_at <= ?", userID, startDate, endDate).
		Group("tp.track_id, t.title").
		Order("play_count DESC").
		Limit(10).
		Find(&topRows)

	topTracks := make([]gin.H, len(topRows))
	for i, r := range topRows {
		topTracks[i] = gin.H{"track_id": r.TrackID.String(), "title": r.Title, "plays": r.PlayCount}
	}

	handlers.RespondSuccess(c, http.StatusOK, gin.H{
		"plays_per_day": playsPerDay,
		"top_tracks":    topTracks,
		"period": gin.H{
			"start_date": startDate.Format(time.RFC3339),
			"end_date":   endDate.Format(time.RFC3339),
			"days":       days,
		},
	})
}

// GetAnalytics handles GET /api/v1/analytics
func (h *Handler) GetAnalytics(c *gin.Context) {
	userIDInterface, exists := c.Get("user_id")
	if !exists {
		handlers.RespondWithAppError(c, apperrors.New(apperrors.ErrCodeUnauthorized, "authentication required"))
		return
	}

	userID, ok := userIDInterface.(uuid.UUID)
	if !ok {
		handlers.RespondWithAppError(c, apperrors.New(apperrors.ErrCodeInternal, "invalid user id"))
		return
	}

	daysStr := c.DefaultQuery("days", "30")
	days, err := strconv.Atoi(daysStr)
	if err != nil || days < 1 {
		days = 30
	}

	var startDate, endDate *time.Time
	if startDateStr := c.Query("start_date"); startDateStr != "" {
		if parsed, err := time.Parse(time.RFC3339, startDateStr); err == nil {
			startDate = &parsed
		}
	}
	if endDateStr := c.Query("end_date"); endDateStr != "" {
		if parsed, err := time.Parse(time.RFC3339, endDateStr); err == nil {
			endDate = &parsed
		}
	}

	if startDate == nil || endDate == nil {
		now := time.Now()
		if endDate == nil {
			endDate = &now
		}
		if startDate == nil {
			calculatedStart := endDate.AddDate(0, 0, -days)
			startDate = &calculatedStart
		}
	}

	ctx := c.Request.Context()

	analyticsSvc, ok := h.analyticsService.(AnalyticsServiceWithDB)
	if !ok {
		handlers.RespondWithAppError(c, apperrors.New(apperrors.ErrCodeInternal, "analytics service type error"))
		return
	}

	var tracks []struct {
		ID            uuid.UUID `gorm:"column:id"`
		Title         string    `gorm:"column:title"`
		PlayCount     int64     `gorm:"column:play_count"`
		LikeCount     int64     `gorm:"column:like_count"`
		DownloadCount int64     `gorm:"column:download_count"`
	}

	if err := analyticsSvc.GetDB().WithContext(ctx).
		Table("tracks").
		Select("id, title, play_count, like_count, COALESCE(download_count, 0) as download_count").
		Where("creator_id = ?", userID).
		Find(&tracks).Error; err != nil {
		h.logger.Error("Failed to fetch user tracks", zap.Error(err))
		handlers.RespondWithAppError(c, apperrors.New(apperrors.ErrCodeInternal, "failed to fetch tracks"))
		return
	}

	totalTracks := len(tracks)
	var totalPlays, totalLikes, totalDownloads int64
	for _, track := range tracks {
		totalPlays += track.PlayCount
		totalLikes += track.LikeCount
		totalDownloads += track.DownloadCount
	}

	avgPlayCount := float64(0)
	if totalTracks > 0 {
		avgPlayCount = float64(totalPlays) / float64(totalTracks)
	}

	topTracks := make([]gin.H, 0, 5)
	sortedTracks := make([]struct {
		ID        uuid.UUID
		Title     string
		PlayCount int64
		LikeCount int64
	}, len(tracks))
	for i, t := range tracks {
		sortedTracks[i] = struct {
			ID        uuid.UUID
			Title     string
			PlayCount int64
			LikeCount int64
		}{t.ID, t.Title, t.PlayCount, t.LikeCount}
	}

	for i := 0; i < len(sortedTracks)-1; i++ {
		for j := i + 1; j < len(sortedTracks); j++ {
			if sortedTracks[i].PlayCount < sortedTracks[j].PlayCount {
				sortedTracks[i], sortedTracks[j] = sortedTracks[j], sortedTracks[i]
			}
		}
	}

	for i := 0; i < 5 && i < len(sortedTracks); i++ {
		topTracks = append(topTracks, gin.H{
			"id":         sortedTracks[i].ID.String(),
			"title":      sortedTracks[i].Title,
			"play_count": sortedTracks[i].PlayCount,
			"like_count": sortedTracks[i].LikeCount,
			"plays":      sortedTracks[i].PlayCount,
			"change":     0,
			"revenue":    0.0,
		})
	}

	var playlists []struct {
		ID         uuid.UUID `gorm:"column:id"`
		Name       string    `gorm:"column:name"`
		PlayCount  int64     `gorm:"column:play_count"`
		LikeCount  int64     `gorm:"column:like_count"`
		ShareCount int64     `gorm:"column:share_count"`
	}

	playlistsError := analyticsSvc.GetDB().WithContext(ctx).
		Table("playlists").
		Select("id, name, COALESCE(play_count, 0) as play_count, COALESCE(like_count, 0) as like_count, COALESCE(share_count, 0) as share_count").
		Where("user_id = ?", userID).
		Find(&playlists).Error

	if playlistsError != nil {
		h.logger.Warn("Failed to fetch user playlists, continuing with empty playlists data", zap.Error(playlistsError))
		playlists = nil
	}

	totalPlaylists := len(playlists)
	var playlistPlays, playlistLikes, playlistShares int64
	for _, playlist := range playlists {
		playlistPlays += playlist.PlayCount
		playlistLikes += playlist.LikeCount
		playlistShares += playlist.ShareCount
	}

	avgPlaylistPlayCount := float64(0)
	if totalPlaylists > 0 {
		avgPlaylistPlayCount = float64(playlistPlays) / float64(totalPlaylists)
	}

	topPlaylists := make([]gin.H, 0, 5)
	sortedPlaylists := make([]struct {
		ID        uuid.UUID
		Name      string
		PlayCount int64
		LikeCount int64
	}, len(playlists))
	for i, p := range playlists {
		sortedPlaylists[i] = struct {
			ID        uuid.UUID
			Name      string
			PlayCount int64
			LikeCount int64
		}{p.ID, p.Name, p.PlayCount, p.LikeCount}
	}

	for i := 0; i < len(sortedPlaylists)-1; i++ {
		for j := i + 1; j < len(sortedPlaylists); j++ {
			if sortedPlaylists[i].PlayCount < sortedPlaylists[j].PlayCount {
				sortedPlaylists[i], sortedPlaylists[j] = sortedPlaylists[j], sortedPlaylists[i]
			}
		}
	}

	for i := 0; i < 5 && i < len(sortedPlaylists); i++ {
		topPlaylists = append(topPlaylists, gin.H{
			"id":         sortedPlaylists[i].ID.String(),
			"name":       sortedPlaylists[i].Name,
			"play_count": sortedPlaylists[i].PlayCount,
			"like_count": sortedPlaylists[i].LikeCount,
		})
	}

	// P3.2: Additional fields for frontend GlobalStats contract
	var followersCount int64
	if err := analyticsSvc.GetDB().WithContext(ctx).
		Table("follows").
		Where("followed_id = ?", userID).
		Count(&followersCount).Error; err != nil {
		h.logger.Warn("Failed to fetch followers count", zap.Error(err))
	}

	var totalRevenue float64
	if err := analyticsSvc.GetDB().WithContext(ctx).
		Table("order_items").
		Select("COALESCE(SUM(oi.price), 0)").
		Joins("JOIN orders o ON o.id = order_items.order_id").
		Joins("JOIN products p ON p.id = order_items.product_id").
		Where("p.seller_id = ? AND o.status IN ('completed', 'paid')", userID).
		Scan(&totalRevenue).Error; err != nil {
		h.logger.Warn("Failed to fetch seller revenue", zap.Error(err))
	}

	// Sparklines: plays per day for user's tracks (last N days)
	var sparklinePlays []int64
	var dayCounts []struct {
		Day   string `gorm:"column:day"`
		Count int64  `gorm:"column:cnt"`
	}
	if err := analyticsSvc.GetDB().WithContext(ctx).
		Table("track_plays tp").
		Select("DATE(tp.played_at) as day, COUNT(*) as cnt").
		Joins("JOIN tracks t ON t.id = tp.track_id").
		Where("t.creator_id = ? AND tp.played_at >= ? AND tp.played_at <= ?", userID, startDate, endDate).
		Group("DATE(tp.played_at)").
		Order("day ASC").
		Find(&dayCounts).Error; err == nil && len(dayCounts) > 0 {
		sparklinePlays = make([]int64, len(dayCounts))
		for i, d := range dayCounts {
			sparklinePlays[i] = d.Count
		}
	}
	if len(sparklinePlays) == 0 {
		sparklinePlays = []int64{0}
	}

	// Trends: % change vs previous period (simplified: use 0 if no prior data)
	trends := gin.H{
		"plays":     float64(0),
		"revenue":   float64(0),
		"followers": float64(0),
		"views":     float64(0),
	}

	analyticsData := gin.H{
		"tracks": gin.H{
			"total_tracks":       totalTracks,
			"total_plays":        totalPlays,
			"total_likes":        totalLikes,
			"total_downloads":    totalDownloads,
			"average_play_count": avgPlayCount,
			"top_tracks":         topTracks,
		},
		"playlists": gin.H{
			"total_playlists":    totalPlaylists,
			"total_plays":        playlistPlays,
			"total_likes":        playlistLikes,
			"total_shares":       playlistShares,
			"average_play_count": avgPlaylistPlayCount,
			"top_playlists":      topPlaylists,
		},
		"period": gin.H{
			"start_date": startDate.Format(time.RFC3339),
			"end_date":   endDate.Format(time.RFC3339),
			"days":       days,
		},
		// P3.2: Frontend GlobalStats contract
		"total_tracks":  totalTracks,
		"total_plays":   totalPlays,
		"total_revenue": totalRevenue,
		"followers":     followersCount,
		"profile_views": 0,
		"trends":        trends,
		"sparklines": gin.H{
			"plays":     sparklinePlays,
			"revenue":   []float64{0},
			"followers": []int64{0},
			"views":     []int64{0},
		},
	}

	handlers.RespondSuccess(c, http.StatusOK, analyticsData)
}

// GetTrackAnalyticsDashboard handles GET /api/v1/analytics/tracks/:id
// SECURITY(REM-004): Verifies track ownership before returning analytics (prevents IDOR).
func (h *Handler) GetTrackAnalyticsDashboard(c *gin.Context) {
	trackIDStr := c.Param("id")
	if trackIDStr == "" {
		handlers.RespondWithAppError(c, apperrors.NewValidationError("track id is required"))
		return
	}

	trackID, err := uuid.Parse(trackIDStr)
	if err != nil {
		handlers.RespondWithAppError(c, apperrors.NewValidationError("invalid track id"))
		return
	}

	// Verify ownership: only the track creator can view analytics
	userID, exists := common.GetUserIDFromContext(c)
	if !exists {
		handlers.RespondWithAppError(c, apperrors.New(apperrors.ErrCodeUnauthorized, "unauthorized"))
		return
	}
	analyticsSvc, ok := h.analyticsService.(AnalyticsServiceWithDB)
	if !ok {
		handlers.RespondWithAppError(c, apperrors.New(apperrors.ErrCodeInternal, "analytics service unavailable"))
		return
	}
	var creatorIDStr string
	if err := analyticsSvc.GetDB().WithContext(c.Request.Context()).
		Table("tracks").Select("creator_id").
		Where("id = ?", trackID).Scan(&creatorIDStr).Error; err != nil || creatorIDStr == "" {
		handlers.RespondWithAppError(c, apperrors.NewNotFoundError("track"))
		return
	}
	creatorID, _ := uuid.Parse(creatorIDStr)
	if creatorID != userID {
		handlers.RespondWithAppError(c, apperrors.New(apperrors.ErrCodeForbidden, "you do not own this track"))
		return
	}

	stats, err := h.analyticsService.GetTrackStats(c.Request.Context(), trackID)
	if err != nil {
		if err.Error() == "track not found" {
			handlers.RespondWithAppError(c, apperrors.NewNotFoundError("track"))
			return
		}
		handlers.RespondWithAppError(c, apperrors.Wrap(apperrors.ErrCodeInternal, "Failed to get track stats", err))
		return
	}

	startDate := time.Now().AddDate(0, 0, -30)
	endDate := time.Now()
	playsOverTime, err := h.analyticsService.GetPlaysOverTime(c.Request.Context(), trackID, startDate, endDate, "day")
	if err != nil {
		playsOverTime = []services.PlayTimePoint{}
	}

	dashboard := gin.H{
		"track_id": trackID.String(),
		"stats": gin.H{
			"total_plays":      stats.TotalPlays,
			"unique_listeners": stats.UniqueListeners,
			"average_duration": stats.AverageDuration,
			"completion_rate":  stats.CompletionRate,
		},
		"plays_over_time": playsOverTime,
		"period": gin.H{
			"start_date": startDate.Format(time.RFC3339),
			"end_date":   endDate.Format(time.RFC3339),
			"days":       30,
		},
	}

	handlers.RespondSuccess(c, http.StatusOK, gin.H{
		"dashboard": dashboard,
	})
}