package services

import (
	"context"
	"encoding/json"
	"fmt"
	"time"

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

// AnalyticsAggregationService provides aggregation and processing for analytics events
// BE-SVC-008: Implement analytics aggregation service
type AnalyticsAggregationService struct {
	db     *gorm.DB
	logger *zap.Logger
}

// NewAnalyticsAggregationService creates a new analytics aggregation service
func NewAnalyticsAggregationService(db *gorm.DB, logger *zap.Logger) *AnalyticsAggregationService {
	if logger == nil {
		logger = zap.NewNop()
	}
	return &AnalyticsAggregationService{
		db:     db,
		logger: logger,
	}
}

// AnalyticsEvent represents an analytics event from the database
type AnalyticsEvent struct {
	ID        uuid.UUID  `gorm:"type:uuid;primaryKey"`
	EventName string     `gorm:"not null;index:idx_analytics_events_name"`
	UserID    *uuid.UUID `gorm:"type:uuid;index:idx_analytics_events_user_id"`
	Payload   string     `gorm:"type:jsonb"`
	CreatedAt time.Time  `gorm:"autoCreateTime;index:idx_analytics_events_created_at"`
}

// TableName defines the table name for GORM
func (AnalyticsEvent) TableName() string {
	return "analytics_events"
}

// AnalyticsAggregationPeriod represents the period type for analytics aggregation
type AnalyticsAggregationPeriod string

const (
	AnalyticsPeriodHour  AnalyticsAggregationPeriod = "hour"
	AnalyticsPeriodDay   AnalyticsAggregationPeriod = "day"
	AnalyticsPeriodWeek  AnalyticsAggregationPeriod = "week"
	AnalyticsPeriodMonth AnalyticsAggregationPeriod = "month"
)

// EventAggregationParams represents parameters for event aggregation
type EventAggregationParams struct {
	EventNames []string                   // Filter by event names (empty = all events)
	UserID     *uuid.UUID                 // Filter by user ID (nil = all users)
	StartDate  time.Time                  // Start date for aggregation
	EndDate    time.Time                  // End date for aggregation
	Period     AnalyticsAggregationPeriod // Aggregation period (hour, day, week, month)
}

// EventAggregationResult represents aggregated analytics data
type EventAggregationResult struct {
	Period         string                 `json:"period"` // Format: YYYY-MM-DD, YYYY-WW, YYYY-MM, etc.
	EventName      string                 `json:"event_name"`
	EventCount     int64                  `json:"event_count"`
	UniqueUsers    int64                  `json:"unique_users"`
	FirstEventAt   *time.Time             `json:"first_event_at,omitempty"`
	LastEventAt    *time.Time             `json:"last_event_at,omitempty"`
	AveragePerUser float64                `json:"average_per_user"`          // Average events per user
	PayloadSummary map[string]interface{} `json:"payload_summary,omitempty"` // Aggregated payload data
}

// AggregationSummary represents the complete aggregation result
type AggregationSummary struct {
	Results           []EventAggregationResult   `json:"results"`
	TotalEvents       int64                      `json:"total_events"`
	TotalUniqueUsers  int64                      `json:"total_unique_users"`
	Period            AnalyticsAggregationPeriod `json:"period"`
	StartDate         time.Time                  `json:"start_date"`
	EndDate           time.Time                  `json:"end_date"`
	EventTypeCounts   map[string]int64           `json:"event_type_counts"`             // Count by event name
	UserActivityCount map[string]int64           `json:"user_activity_count,omitempty"` // Count by user (if UserID not specified)
}

// AggregateEvents aggregates analytics events according to the specified parameters
func (s *AnalyticsAggregationService) AggregateEvents(
	ctx context.Context,
	params EventAggregationParams,
) (*AggregationSummary, error) {
	// Validate period
	if params.Period != AnalyticsPeriodHour && params.Period != AnalyticsPeriodDay &&
		params.Period != AnalyticsPeriodWeek && params.Period != AnalyticsPeriodMonth {
		return nil, fmt.Errorf("invalid period: %s (must be hour, day, week, or month)", params.Period)
	}

	// Validate date range
	if params.StartDate.After(params.EndDate) {
		return nil, fmt.Errorf("start date must be before end date")
	}

	// Build base query
	query := s.db.WithContext(ctx).Model(&AnalyticsEvent{}).
		Where("created_at >= ? AND created_at <= ?", params.StartDate, params.EndDate)

	// Filter by event names
	if len(params.EventNames) > 0 {
		query = query.Where("event_name IN ?", params.EventNames)
	}

	// Filter by user ID
	if params.UserID != nil {
		query = query.Where("user_id = ?", *params.UserID)
	}

	// Determine date format based on period
	var dateFormat string
	switch params.Period {
	case AnalyticsPeriodHour:
		dateFormat = "YYYY-MM-DD HH24:00:00"
	case AnalyticsPeriodDay:
		dateFormat = "YYYY-MM-DD"
	case AnalyticsPeriodWeek:
		dateFormat = "IYYY-IW" // ISO year and week
	case AnalyticsPeriodMonth:
		dateFormat = "YYYY-MM"
	default:
		dateFormat = "YYYY-MM-DD"
	}

	// Aggregate by period and event name
	var aggregationResults []struct {
		Period      string    `gorm:"column:period"`
		EventName   string    `gorm:"column:event_name"`
		EventCount  int64     `gorm:"column:event_count"`
		UniqueUsers int64     `gorm:"column:unique_users"`
		FirstEvent  time.Time `gorm:"column:first_event"`
		LastEvent   time.Time `gorm:"column:last_event"`
	}

	// Use PostgreSQL date_trunc or to_char for period grouping
	periodExpr := fmt.Sprintf("to_char(created_at, '%s')", dateFormat)
	if params.Period == AnalyticsPeriodHour {
		periodExpr = "date_trunc('hour', created_at)"
	}

	if err := query.
		Select(fmt.Sprintf(`
			%s as period,
			event_name,
			COUNT(*) as event_count,
			COUNT(DISTINCT user_id) as unique_users,
			MIN(created_at) as first_event,
			MAX(created_at) as last_event
		`, periodExpr)).
		Group("period, event_name").
		Order("period ASC, event_name ASC").
		Scan(&aggregationResults).Error; err != nil {
		return nil, fmt.Errorf("failed to aggregate events: %w", err)
	}

	// Convert to EventAggregationResult
	results := make([]EventAggregationResult, 0, len(aggregationResults))
	eventTypeCounts := make(map[string]int64)
	totalEvents := int64(0)

	for _, agg := range aggregationResults {
		// Calculate average per user
		avgPerUser := 0.0
		if agg.UniqueUsers > 0 {
			avgPerUser = float64(agg.EventCount) / float64(agg.UniqueUsers)
		}

		// Get payload summary for this event type and period
		payloadSummary := s.getPayloadSummary(ctx, agg.EventName, agg.Period, params)

		result := EventAggregationResult{
			Period:         agg.Period,
			EventName:      agg.EventName,
			EventCount:     agg.EventCount,
			UniqueUsers:    agg.UniqueUsers,
			FirstEventAt:   &agg.FirstEvent,
			LastEventAt:    &agg.LastEvent,
			AveragePerUser: avgPerUser,
			PayloadSummary: payloadSummary,
		}

		results = append(results, result)

		// Accumulate totals
		eventTypeCounts[agg.EventName] += agg.EventCount
		totalEvents += agg.EventCount

		// Note: We can't easily get unique users across all periods without another query
		// For now, we'll use a separate query for total unique users
	}

	// Get total unique users
	var totalUniqueUsers int64
	uniqueUserQuery := s.db.WithContext(ctx).Model(&AnalyticsEvent{}).
		Where("created_at >= ? AND created_at <= ?", params.StartDate, params.EndDate)
	if len(params.EventNames) > 0 {
		uniqueUserQuery = uniqueUserQuery.Where("event_name IN ?", params.EventNames)
	}
	if params.UserID != nil {
		uniqueUserQuery = uniqueUserQuery.Where("user_id = ?", *params.UserID)
	}
	if err := uniqueUserQuery.
		Distinct("user_id").
		Where("user_id IS NOT NULL").
		Count(&totalUniqueUsers).Error; err != nil {
		s.logger.Warn("Failed to count unique users", zap.Error(err))
	}

	// Get user activity count if UserID is not specified
	userActivityCount := make(map[string]int64)
	if params.UserID == nil {
		var userCounts []struct {
			UserID     uuid.UUID `gorm:"column:user_id"`
			EventCount int64     `gorm:"column:event_count"`
		}
		userQuery := s.db.WithContext(ctx).Model(&AnalyticsEvent{}).
			Where("created_at >= ? AND created_at <= ? AND user_id IS NOT NULL", params.StartDate, params.EndDate)
		if len(params.EventNames) > 0 {
			userQuery = userQuery.Where("event_name IN ?", params.EventNames)
		}
		if err := userQuery.
			Select("user_id, COUNT(*) as event_count").
			Group("user_id").
			Order("event_count DESC").
			Limit(100). // Limit to top 100 users
			Scan(&userCounts).Error; err == nil {
			for _, uc := range userCounts {
				userActivityCount[uc.UserID.String()] = uc.EventCount
			}
		}
	}

	return &AggregationSummary{
		Results:           results,
		TotalEvents:       totalEvents,
		TotalUniqueUsers:  totalUniqueUsers,
		Period:            params.Period,
		StartDate:         params.StartDate,
		EndDate:           params.EndDate,
		EventTypeCounts:   eventTypeCounts,
		UserActivityCount: userActivityCount,
	}, nil
}

// getPayloadSummary extracts and aggregates common payload fields
func (s *AnalyticsAggregationService) getPayloadSummary(
	ctx context.Context,
	eventName string,
	period string,
	params EventAggregationParams,
) map[string]interface{} {
	// Get sample events for this period to analyze payload structure
	var events []AnalyticsEvent
	query := s.db.WithContext(ctx).Model(&AnalyticsEvent{}).
		Where("event_name = ? AND created_at >= ? AND created_at <= ?", eventName, params.StartDate, params.EndDate).
		Limit(100) // Sample size

	if err := query.Find(&events).Error; err != nil || len(events) == 0 {
		return nil
	}

	// Analyze payload structure
	payloadSummary := make(map[string]interface{})
	fieldCounts := make(map[string]int)
	fieldValues := make(map[string][]interface{})

	for _, event := range events {
		var payload map[string]interface{}
		if err := json.Unmarshal([]byte(event.Payload), &payload); err != nil {
			continue
		}

		// Count field occurrences and collect sample values
		for key, value := range payload {
			fieldCounts[key]++
			if len(fieldValues[key]) < 10 { // Keep up to 10 sample values
				fieldValues[key] = append(fieldValues[key], value)
			}
		}
	}

	// Build summary with most common fields
	for field, count := range fieldCounts {
		if count >= len(events)/2 { // Field present in at least 50% of events
			payloadSummary[field] = map[string]interface{}{
				"occurrence_count": count,
				"sample_values":    fieldValues[field][:min(5, len(fieldValues[field]))],
			}
		}
	}

	return payloadSummary
}

// GetEventCounts returns simple event counts by event name
func (s *AnalyticsAggregationService) GetEventCounts(
	ctx context.Context,
	startDate, endDate time.Time,
	eventNames []string,
) (map[string]int64, error) {
	query := s.db.WithContext(ctx).Model(&AnalyticsEvent{}).
		Where("created_at >= ? AND created_at <= ?", startDate, endDate)

	if len(eventNames) > 0 {
		query = query.Where("event_name IN ?", eventNames)
	}

	var results []struct {
		EventName  string `gorm:"column:event_name"`
		EventCount int64  `gorm:"column:event_count"`
	}

	if err := query.
		Select("event_name, COUNT(*) as event_count").
		Group("event_name").
		Order("event_count DESC").
		Scan(&results).Error; err != nil {
		return nil, fmt.Errorf("failed to get event counts: %w", err)
	}

	counts := make(map[string]int64)
	for _, r := range results {
		counts[r.EventName] = r.EventCount
	}

	return counts, nil
}

// GetTopEvents returns the top N events by count
func (s *AnalyticsAggregationService) GetTopEvents(
	ctx context.Context,
	startDate, endDate time.Time,
	limit int,
) ([]EventAggregationResult, error) {
	if limit <= 0 {
		limit = 10
	}
	if limit > 100 {
		limit = 100
	}

	var results []struct {
		EventName   string    `gorm:"column:event_name"`
		EventCount  int64     `gorm:"column:event_count"`
		UniqueUsers int64     `gorm:"column:unique_users"`
		LastEvent   time.Time `gorm:"column:last_event"`
	}

	if err := s.db.WithContext(ctx).Model(&AnalyticsEvent{}).
		Where("created_at >= ? AND created_at <= ?", startDate, endDate).
		Select(`
			event_name,
			COUNT(*) as event_count,
			COUNT(DISTINCT user_id) as unique_users,
			MAX(created_at) as last_event
		`).
		Group("event_name").
		Order("event_count DESC").
		Limit(limit).
		Scan(&results).Error; err != nil {
		return nil, fmt.Errorf("failed to get top events: %w", err)
	}

	aggregationResults := make([]EventAggregationResult, len(results))
	for i, r := range results {
		avgPerUser := 0.0
		if r.UniqueUsers > 0 {
			avgPerUser = float64(r.EventCount) / float64(r.UniqueUsers)
		}
		aggregationResults[i] = EventAggregationResult{
			EventName:      r.EventName,
			EventCount:     r.EventCount,
			UniqueUsers:    r.UniqueUsers,
			LastEventAt:    &r.LastEvent,
			AveragePerUser: avgPerUser,
		}
	}

	return aggregationResults, nil
}

// min returns the minimum of two integers
func min(a, b int) int {
	if a < b {
		return a
	}
	return b
}