package services

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

	"github.com/rs/zerolog/log"
	"github.com/stripe/stripe-go/v81"
	portalsession "github.com/stripe/stripe-go/v81/billingportal/session"
	checkoutsession "github.com/stripe/stripe-go/v81/checkout/session"
	"github.com/stripe/stripe-go/v81/customer"
	"github.com/stripe/stripe-go/v81/webhook"

	"github.com/treytartt/casera-api/internal/apperrors"
	"github.com/treytartt/casera-api/internal/models"
	"github.com/treytartt/casera-api/internal/repositories"
)

// StripeService handles Stripe checkout, portal, and webhook processing
// for web-based subscription purchases.
type StripeService struct {
	subscriptionRepo *repositories.SubscriptionRepository
	userRepo         *repositories.UserRepository
	webhookSecret    string
}

// NewStripeService creates a new Stripe service. It initializes the global
// Stripe API key from the STRIPE_SECRET_KEY environment variable. If the key
// is not set, a warning is logged but the service is still returned (matching
// the pattern used by the Apple/Google IAP clients).
func NewStripeService(
	subscriptionRepo *repositories.SubscriptionRepository,
	userRepo *repositories.UserRepository,
) *StripeService {
	key := os.Getenv("STRIPE_SECRET_KEY")
	if key == "" {
		log.Warn().Msg("STRIPE_SECRET_KEY not set, Stripe integration will not work")
	} else {
		stripe.Key = key
		log.Info().Msg("Stripe API key configured")
	}

	webhookSecret := os.Getenv("STRIPE_WEBHOOK_SECRET")
	if webhookSecret == "" {
		log.Warn().Msg("STRIPE_WEBHOOK_SECRET not set, webhook verification will fail")
	}

	return &StripeService{
		subscriptionRepo: subscriptionRepo,
		userRepo:         userRepo,
		webhookSecret:    webhookSecret,
	}
}

// CreateCheckoutSession creates a Stripe Checkout Session for a web subscription purchase.
// It ensures the user has a Stripe customer record and configures the session with a trial
// period if the user has not used their trial yet.
func (s *StripeService) CreateCheckoutSession(userID uint, priceID string, successURL string, cancelURL string) (string, error) {
	// Get or create the user's subscription record
	sub, err := s.subscriptionRepo.GetOrCreate(userID)
	if err != nil {
		return "", apperrors.Internal(err)
	}

	// Get the user's email for the Stripe customer
	user, err := s.userRepo.FindByID(userID)
	if err != nil {
		return "", apperrors.Internal(err)
	}

	// Get or create a Stripe customer
	stripeCustomerID, err := s.getOrCreateStripeCustomer(sub, user)
	if err != nil {
		return "", apperrors.Internal(err)
	}

	// Build the checkout session parameters
	params := &stripe.CheckoutSessionParams{
		Customer:  stripe.String(stripeCustomerID),
		Mode:      stripe.String(string(stripe.CheckoutSessionModeSubscription)),
		SuccessURL: stripe.String(successURL),
		CancelURL:  stripe.String(cancelURL),
		ClientReferenceID: stripe.String(fmt.Sprintf("%d", userID)),
		LineItems: []*stripe.CheckoutSessionLineItemParams{
			{
				Price:    stripe.String(priceID),
				Quantity: stripe.Int64(1),
			},
		},
	}

	// Offer a trial period if the user has not used their trial yet
	if !sub.TrialUsed {
		trialDays, err := s.getTrialDays()
		if err != nil {
			log.Warn().Err(err).Msg("Failed to get trial duration from settings, skipping trial")
		} else if trialDays > 0 {
			params.SubscriptionData = &stripe.CheckoutSessionSubscriptionDataParams{
				TrialPeriodDays: stripe.Int64(int64(trialDays)),
			}
		}
	}

	session, err := checkoutsession.New(params)
	if err != nil {
		log.Error().Err(err).Uint("user_id", userID).Msg("Failed to create Stripe checkout session")
		return "", apperrors.Internal(err)
	}

	log.Info().
		Uint("user_id", userID).
		Str("session_id", session.ID).
		Str("price_id", priceID).
		Msg("Stripe checkout session created")

	return session.URL, nil
}

// CreatePortalSession creates a Stripe Customer Portal session so the user
// can manage their subscription (cancel, change plan, update payment method).
func (s *StripeService) CreatePortalSession(userID uint, returnURL string) (string, error) {
	sub, err := s.subscriptionRepo.FindByUserID(userID)
	if err != nil {
		return "", apperrors.NotFound("error.subscription_not_found")
	}

	if sub.StripeCustomerID == nil || *sub.StripeCustomerID == "" {
		return "", apperrors.BadRequest("error.no_stripe_customer")
	}

	params := &stripe.BillingPortalSessionParams{
		Customer:  sub.StripeCustomerID,
		ReturnURL: stripe.String(returnURL),
	}

	session, err := portalsession.New(params)
	if err != nil {
		log.Error().Err(err).Uint("user_id", userID).Msg("Failed to create Stripe portal session")
		return "", apperrors.Internal(err)
	}

	return session.URL, nil
}

// HandleWebhookEvent verifies and processes a Stripe webhook event.
// It handles checkout completion, subscription lifecycle changes, and invoice events.
func (s *StripeService) HandleWebhookEvent(payload []byte, signature string) error {
	event, err := webhook.ConstructEvent(payload, signature, s.webhookSecret)
	if err != nil {
		log.Warn().Err(err).Msg("Stripe webhook signature verification failed")
		return apperrors.BadRequest("error.invalid_webhook_signature")
	}

	log.Info().
		Str("event_type", string(event.Type)).
		Str("event_id", event.ID).
		Msg("Processing Stripe webhook event")

	switch event.Type {
	case "checkout.session.completed":
		return s.handleCheckoutCompleted(event)
	case "customer.subscription.updated":
		return s.handleSubscriptionUpdated(event)
	case "customer.subscription.deleted":
		return s.handleSubscriptionDeleted(event)
	case "invoice.paid":
		return s.handleInvoicePaid(event)
	case "invoice.payment_failed":
		return s.handleInvoicePaymentFailed(event)
	default:
		log.Debug().Str("event_type", string(event.Type)).Msg("Unhandled Stripe webhook event type")
		return nil
	}
}

// handleCheckoutCompleted processes a successful checkout session. It links the Stripe
// customer and subscription to the user's record and upgrades them to Pro.
func (s *StripeService) handleCheckoutCompleted(event stripe.Event) error {
	var session stripe.CheckoutSession
	if err := json.Unmarshal(event.Data.Raw, &session); err != nil {
		log.Error().Err(err).Msg("Failed to unmarshal checkout session from webhook")
		return apperrors.Internal(err)
	}

	// Extract the user ID from client_reference_id
	var userID uint
	if _, err := fmt.Sscanf(session.ClientReferenceID, "%d", &userID); err != nil {
		log.Error().Str("client_reference_id", session.ClientReferenceID).Msg("Invalid client_reference_id in checkout session")
		return apperrors.BadRequest("error.invalid_client_reference_id")
	}

	// Get or create the subscription record
	sub, err := s.subscriptionRepo.GetOrCreate(userID)
	if err != nil {
		return apperrors.Internal(err)
	}

	// Save Stripe customer and subscription IDs
	if session.Customer != nil {
		sub.StripeCustomerID = &session.Customer.ID
	}
	if session.Subscription != nil {
		sub.StripeSubscriptionID = &session.Subscription.ID
	}

	if err := s.subscriptionRepo.Update(sub); err != nil {
		return apperrors.Internal(err)
	}

	// Upgrade to Pro. Use a far-future expiry for now; the invoice.paid event
	// will set the real period_end once the first invoice is finalized.
	expiresAt := time.Now().UTC().AddDate(1, 0, 0)
	if err := s.subscriptionRepo.UpgradeToPro(userID, expiresAt, models.PlatformStripe); err != nil {
		return apperrors.Internal(err)
	}

	customerID := ""
	if session.Customer != nil {
		customerID = session.Customer.ID
	}
	subscriptionID := ""
	if session.Subscription != nil {
		subscriptionID = session.Subscription.ID
	}
	log.Info().
		Uint("user_id", userID).
		Str("stripe_customer_id", customerID).
		Str("stripe_subscription_id", subscriptionID).
		Msg("Checkout completed, user upgraded to Pro")

	// TODO: Send push notification to user's devices when subscription activates

	return nil
}

// handleSubscriptionUpdated processes subscription status changes. It upgrades or
// downgrades the user depending on the subscription's current status.
func (s *StripeService) handleSubscriptionUpdated(event stripe.Event) error {
	var subscription stripe.Subscription
	if err := json.Unmarshal(event.Data.Raw, &subscription); err != nil {
		log.Error().Err(err).Msg("Failed to unmarshal subscription from webhook")
		return apperrors.Internal(err)
	}

	sub, err := s.findSubscriptionByStripeID(subscription.ID)
	if err != nil {
		return err
	}

	switch subscription.Status {
	case stripe.SubscriptionStatusActive, stripe.SubscriptionStatusTrialing:
		// Subscription is healthy, ensure user is Pro
		expiresAt := time.Unix(subscription.CurrentPeriodEnd, 0).UTC()
		if err := s.subscriptionRepo.UpgradeToPro(sub.UserID, expiresAt, models.PlatformStripe); err != nil {
			return apperrors.Internal(err)
		}
		log.Info().Uint("user_id", sub.UserID).Str("status", string(subscription.Status)).Msg("Stripe subscription active")

	case stripe.SubscriptionStatusPastDue:
		log.Warn().Uint("user_id", sub.UserID).Msg("Stripe subscription past due, waiting for retry")
		// Don't downgrade yet; Stripe will retry the payment automatically.

	case stripe.SubscriptionStatusCanceled, stripe.SubscriptionStatusUnpaid:
		// Check if the user has active subscriptions from other sources before downgrading
		if s.isActiveFromOtherSources(sub) {
			log.Info().
				Uint("user_id", sub.UserID).
				Str("status", string(subscription.Status)).
				Msg("Stripe subscription ended but user has other active sources, keeping Pro")
			return nil
		}
		if err := s.subscriptionRepo.DowngradeToFree(sub.UserID); err != nil {
			return apperrors.Internal(err)
		}
		log.Info().Uint("user_id", sub.UserID).Str("status", string(subscription.Status)).Msg("User downgraded to Free after Stripe subscription ended")
	}

	return nil
}

// handleSubscriptionDeleted processes a subscription that has been fully cancelled
// and is no longer active. It downgrades the user unless they have active subscriptions
// from other sources (Apple, Google).
func (s *StripeService) handleSubscriptionDeleted(event stripe.Event) error {
	var subscription stripe.Subscription
	if err := json.Unmarshal(event.Data.Raw, &subscription); err != nil {
		log.Error().Err(err).Msg("Failed to unmarshal subscription from webhook")
		return apperrors.Internal(err)
	}

	sub, err := s.findSubscriptionByStripeID(subscription.ID)
	if err != nil {
		return err
	}

	// Check multi-source before downgrading
	if s.isActiveFromOtherSources(sub) {
		log.Info().
			Uint("user_id", sub.UserID).
			Msg("Stripe subscription deleted but user has other active sources, keeping Pro")
		return nil
	}

	if err := s.subscriptionRepo.DowngradeToFree(sub.UserID); err != nil {
		return apperrors.Internal(err)
	}

	log.Info().Uint("user_id", sub.UserID).Msg("User downgraded to Free after Stripe subscription deleted")

	// TODO: Send push notification to user's devices about subscription ending

	return nil
}

// handleInvoicePaid processes a successful invoice payment. It updates the subscription
// expiry to the current billing period's end date and ensures the user is on Pro.
func (s *StripeService) handleInvoicePaid(event stripe.Event) error {
	var invoice stripe.Invoice
	if err := json.Unmarshal(event.Data.Raw, &invoice); err != nil {
		log.Error().Err(err).Msg("Failed to unmarshal invoice from webhook")
		return apperrors.Internal(err)
	}

	// Only process subscription invoices
	if invoice.Subscription == nil {
		return nil
	}

	sub, err := s.findSubscriptionByStripeID(invoice.Subscription.ID)
	if err != nil {
		return err
	}

	// Update expiry from the invoice's period end
	expiresAt := time.Unix(invoice.PeriodEnd, 0).UTC()
	if err := s.subscriptionRepo.UpgradeToPro(sub.UserID, expiresAt, models.PlatformStripe); err != nil {
		return apperrors.Internal(err)
	}

	log.Info().
		Uint("user_id", sub.UserID).
		Time("expires_at", expiresAt).
		Msg("Invoice paid, subscription renewed")

	return nil
}

// handleInvoicePaymentFailed logs a warning when a payment fails. We do not downgrade
// the user here because Stripe will automatically retry the payment according to its
// Smart Retries schedule.
func (s *StripeService) handleInvoicePaymentFailed(event stripe.Event) error {
	var invoice stripe.Invoice
	if err := json.Unmarshal(event.Data.Raw, &invoice); err != nil {
		log.Error().Err(err).Msg("Failed to unmarshal invoice from webhook")
		return apperrors.Internal(err)
	}

	if invoice.Subscription == nil {
		return nil
	}

	sub, err := s.findSubscriptionByStripeID(invoice.Subscription.ID)
	if err != nil {
		// If we can't find the subscription, just log and return
		log.Warn().Str("stripe_subscription_id", invoice.Subscription.ID).Msg("Invoice payment failed for unknown subscription")
		return nil
	}

	log.Warn().
		Uint("user_id", sub.UserID).
		Str("invoice_id", invoice.ID).
		Msg("Stripe invoice payment failed, Stripe will retry automatically")

	return nil
}

// isActiveFromOtherSources checks if the user has active subscriptions from Apple or Google
// that should prevent a downgrade when the Stripe subscription ends.
func (s *StripeService) isActiveFromOtherSources(sub *models.UserSubscription) bool {
	now := time.Now().UTC()

	// Check Apple subscription
	if sub.HasAppleSubscription() && sub.Tier == models.TierPro && sub.ExpiresAt != nil && now.Before(*sub.ExpiresAt) && sub.Platform != models.PlatformStripe {
		return true
	}

	// Check Google subscription
	if sub.HasGoogleSubscription() && sub.Tier == models.TierPro && sub.ExpiresAt != nil && now.Before(*sub.ExpiresAt) && sub.Platform != models.PlatformStripe {
		return true
	}

	// Check active trial
	if sub.IsTrialActive() {
		return true
	}

	return false
}

// getOrCreateStripeCustomer returns the existing Stripe customer ID from the subscription
// record, or creates a new Stripe customer and persists the ID.
func (s *StripeService) getOrCreateStripeCustomer(sub *models.UserSubscription, user *models.User) (string, error) {
	// If we already have a Stripe customer, return it
	if sub.StripeCustomerID != nil && *sub.StripeCustomerID != "" {
		return *sub.StripeCustomerID, nil
	}

	// Create a new Stripe customer
	params := &stripe.CustomerParams{
		Email: stripe.String(user.Email),
		Name:  stripe.String(user.GetFullName()),
	}
	params.AddMetadata("casera_user_id", fmt.Sprintf("%d", user.ID))

	c, err := customer.New(params)
	if err != nil {
		return "", fmt.Errorf("failed to create Stripe customer: %w", err)
	}

	// Save the customer ID to the subscription record
	sub.StripeCustomerID = &c.ID
	if err := s.subscriptionRepo.Update(sub); err != nil {
		return "", fmt.Errorf("failed to save Stripe customer ID: %w", err)
	}

	log.Info().
		Uint("user_id", user.ID).
		Str("stripe_customer_id", c.ID).
		Msg("Created new Stripe customer")

	return c.ID, nil
}

// findSubscriptionByStripeID looks up a UserSubscription by its Stripe subscription ID.
func (s *StripeService) findSubscriptionByStripeID(stripeSubID string) (*models.UserSubscription, error) {
	sub, err := s.subscriptionRepo.FindByStripeSubscriptionID(stripeSubID)
	if err != nil {
		log.Warn().Str("stripe_subscription_id", stripeSubID).Err(err).Msg("Subscription not found for Stripe ID")
		return nil, apperrors.NotFound("error.subscription_not_found")
	}
	return sub, nil
}

// getTrialDays reads the trial duration from SubscriptionSettings.
func (s *StripeService) getTrialDays() (int, error) {
	settings, err := s.subscriptionRepo.GetSettings()
	if err != nil {
		return 0, err
	}
	if !settings.TrialEnabled {
		return 0, nil
	}
	return settings.TrialDurationDays, nil
}