package services

import (
	"context"
	"fmt"
	"time"

	"github.com/breakpilot/billing-service/internal/database"
	"github.com/breakpilot/billing-service/internal/models"
	"github.com/google/uuid"
)

// UsageService handles usage tracking operations
type UsageService struct {
	db                 *database.DB
	entitlementService *EntitlementService
}

// NewUsageService creates a new UsageService
func NewUsageService(db *database.DB, entitlementService *EntitlementService) *UsageService {
	return &UsageService{
		db:                 db,
		entitlementService: entitlementService,
	}
}

// TrackUsage tracks usage for a user
func (s *UsageService) TrackUsage(ctx context.Context, userIDStr, usageType string, quantity int) error {
	userID, err := uuid.Parse(userIDStr)
	if err != nil {
		return fmt.Errorf("invalid user ID: %w", err)
	}

	// Get current period start (beginning of current month)
	now := time.Now()
	periodStart := time.Date(now.Year(), now.Month(), 1, 0, 0, 0, 0, time.UTC)

	// Upsert usage summary
	query := `
		INSERT INTO usage_summary (user_id, usage_type, period_start, total_count)
		VALUES ($1, $2, $3, $4)
		ON CONFLICT (user_id, usage_type, period_start) DO UPDATE SET
			total_count = usage_summary.total_count + EXCLUDED.total_count,
			updated_at = NOW()
	`

	_, err = s.db.Pool.Exec(ctx, query, userID, usageType, periodStart, quantity)
	if err != nil {
		return fmt.Errorf("failed to track usage: %w", err)
	}

	// Also update entitlements cache
	return s.entitlementService.IncrementUsage(ctx, userID, usageType, quantity)
}

// GetUsageSummary returns usage summary for a user
func (s *UsageService) GetUsageSummary(ctx context.Context, userID uuid.UUID) (*models.UsageInfo, error) {
	// Get entitlements (which include current usage)
	ent, err := s.entitlementService.getUserEntitlements(ctx, userID)
	if err != nil || ent == nil {
		return nil, err
	}

	// Calculate percentages
	aiPercent := 0.0
	if ent.AIRequestsLimit > 0 {
		aiPercent = float64(ent.AIRequestsUsed) / float64(ent.AIRequestsLimit) * 100
	}

	docPercent := 0.0
	if ent.DocumentsLimit > 0 {
		docPercent = float64(ent.DocumentsUsed) / float64(ent.DocumentsLimit) * 100
	}

	// Get period dates
	now := time.Now()
	periodStart := time.Date(now.Year(), now.Month(), 1, 0, 0, 0, 0, time.UTC)
	periodEnd := periodStart.AddDate(0, 1, 0).Add(-time.Second)

	return &models.UsageInfo{
		AIRequestsUsed:    ent.AIRequestsUsed,
		AIRequestsLimit:   ent.AIRequestsLimit,
		AIRequestsPercent: aiPercent,
		DocumentsUsed:     ent.DocumentsUsed,
		DocumentsLimit:    ent.DocumentsLimit,
		DocumentsPercent:  docPercent,
		PeriodStart:       periodStart.Format("2006-01-02"),
		PeriodEnd:         periodEnd.Format("2006-01-02"),
	}, nil
}

// CheckUsageAllowed checks if a user is allowed to perform a usage action
func (s *UsageService) CheckUsageAllowed(ctx context.Context, userIDStr, usageType string) (*models.CheckUsageResponse, error) {
	userID, err := uuid.Parse(userIDStr)
	if err != nil {
		return &models.CheckUsageResponse{
			Allowed: false,
			Message: "Invalid user ID",
		}, nil
	}

	// Get entitlements
	ent, err := s.entitlementService.getUserEntitlements(ctx, userID)
	if err != nil {
		return &models.CheckUsageResponse{
			Allowed: false,
			Message: "Failed to get entitlements",
		}, nil
	}

	if ent == nil {
		return &models.CheckUsageResponse{
			Allowed: false,
			Message: "No subscription found",
		}, nil
	}

	var currentUsage, limit int
	switch usageType {
	case "ai_request":
		currentUsage = ent.AIRequestsUsed
		limit = ent.AIRequestsLimit
	case "document_created":
		currentUsage = ent.DocumentsUsed
		limit = ent.DocumentsLimit
	default:
		return &models.CheckUsageResponse{
			Allowed: true,
			Message: "Unknown usage type - allowing",
		}, nil
	}

	remaining := limit - currentUsage
	allowed := remaining > 0

	response := &models.CheckUsageResponse{
		Allowed:      allowed,
		CurrentUsage: currentUsage,
		Limit:        limit,
		Remaining:    remaining,
	}

	if !allowed {
		response.Message = fmt.Sprintf("Usage limit reached for %s (%d/%d)", usageType, currentUsage, limit)
	}

	return response, nil
}

// GetUsageHistory returns usage history for a user
func (s *UsageService) GetUsageHistory(ctx context.Context, userID uuid.UUID, months int) ([]models.UsageSummary, error) {
	query := `
		SELECT id, user_id, usage_type, period_start, total_count, created_at, updated_at
		FROM usage_summary
		WHERE user_id = $1
		  AND period_start >= $2
		ORDER BY period_start DESC, usage_type
	`

	// Calculate start date
	startDate := time.Now().AddDate(0, -months, 0)
	startDate = time.Date(startDate.Year(), startDate.Month(), 1, 0, 0, 0, 0, time.UTC)

	rows, err := s.db.Pool.Query(ctx, query, userID, startDate)
	if err != nil {
		return nil, err
	}
	defer rows.Close()

	var summaries []models.UsageSummary
	for rows.Next() {
		var summary models.UsageSummary
		err := rows.Scan(
			&summary.ID, &summary.UserID, &summary.UsageType,
			&summary.PeriodStart, &summary.TotalCount,
			&summary.CreatedAt, &summary.UpdatedAt,
		)
		if err != nil {
			return nil, err
		}
		summaries = append(summaries, summary)
	}

	return summaries, nil
}

// ResetPeriodUsage resets usage for a new billing period
func (s *UsageService) ResetPeriodUsage(ctx context.Context, userID uuid.UUID) error {
	now := time.Now()
	newPeriodStart := time.Date(now.Year(), now.Month(), 1, 0, 0, 0, 0, time.UTC)
	newPeriodEnd := newPeriodStart.AddDate(0, 1, 0).Add(-time.Second)

	return s.entitlementService.ResetUsageCounters(ctx, userID, &newPeriodStart, &newPeriodEnd)
}