package processor

import (
	"context"
	"fmt"
	"time"

	"apskel-pos-be/internal/client"
	"apskel-pos-be/internal/entities"
	"apskel-pos-be/internal/mappers"
	"apskel-pos-be/internal/models"

	"github.com/google/uuid"
)

// NotificationRepository is the interface the processor depends on.
type NotificationRepository interface {
	Create(ctx context.Context, notification *entities.Notification) error
	GetByID(ctx context.Context, id uuid.UUID) (*entities.Notification, error)
	Update(ctx context.Context, notification *entities.Notification) error
	Delete(ctx context.Context, id uuid.UUID) error
	List(ctx context.Context, filters map[string]interface{}, limit, offset int) ([]*entities.Notification, int64, error)
}

// NotificationReceiverRepository is the interface the processor depends on.
type NotificationReceiverRepository interface {
	Create(ctx context.Context, receiver *entities.NotificationReceiver) error
	BulkCreate(ctx context.Context, receivers []*entities.NotificationReceiver) error
	GetByID(ctx context.Context, id uuid.UUID) (*entities.NotificationReceiver, error)
	GetByNotificationAndUser(ctx context.Context, notificationID, userID uuid.UUID) (*entities.NotificationReceiver, error)
	Update(ctx context.Context, receiver *entities.NotificationReceiver) error
	ListByUserID(ctx context.Context, userID uuid.UUID, isRead *bool, limit, offset int) ([]*entities.NotificationReceiver, int64, error)
	CountUnreadByUserID(ctx context.Context, userID uuid.UUID) (int64, error)
	SoftDeleteByID(ctx context.Context, id uuid.UUID) error
}

// NotificationDeliveryRepository is the interface the processor depends on.
type NotificationDeliveryRepository interface {
	Create(ctx context.Context, delivery *entities.NotificationDelivery) error
	BulkCreate(ctx context.Context, deliveries []*entities.NotificationDelivery) error
	GetByID(ctx context.Context, id uuid.UUID) (*entities.NotificationDelivery, error)
	Update(ctx context.Context, delivery *entities.NotificationDelivery) error
	ListByReceiverID(ctx context.Context, receiverID uuid.UUID) ([]*entities.NotificationDelivery, error)
}

// NotificationUserRepository is a minimal interface to fetch user devices.
type NotificationUserDeviceRepository interface {
	GetByUserID(ctx context.Context, userID uuid.UUID) ([]*entities.UserDevice, error)
}

// NotificationUserRepository is a minimal interface to fetch users by org.
type NotificationUserRepository interface {
	GetActiveUsers(ctx context.Context, organizationID uuid.UUID) ([]*entities.User, error)
}

// NotificationProcessor defines the business logic interface.
type NotificationProcessor interface {
	Send(ctx context.Context, req *models.SendNotificationRequest) (*models.NotificationResponse, error)
	Broadcast(ctx context.Context, req *models.BroadcastNotificationRequest) (*models.NotificationResponse, error)
	MarkAsRead(ctx context.Context, receiverID, userID uuid.UUID) (*models.NotificationReceiverResponse, error)
	MarkAllAsRead(ctx context.Context, userID uuid.UUID) error
	DeleteForUser(ctx context.Context, receiverID, userID uuid.UUID) error
	ListForUser(ctx context.Context, req *models.ListNotificationsRequest) ([]*models.NotificationReceiverResponse, int64, int64, error)
	GetByID(ctx context.Context, id uuid.UUID) (*models.NotificationResponse, error)
}

type NotificationProcessorImpl struct {
	notificationRepo NotificationRepository
	receiverRepo     NotificationReceiverRepository
	deliveryRepo     NotificationDeliveryRepository
	userDeviceRepo   NotificationUserDeviceRepository
	userRepo         NotificationUserRepository
	fcmClient        client.FCMClient
}

func NewNotificationProcessor(
	notificationRepo NotificationRepository,
	receiverRepo NotificationReceiverRepository,
	deliveryRepo NotificationDeliveryRepository,
	userDeviceRepo NotificationUserDeviceRepository,
	userRepo NotificationUserRepository,
	fcmClient client.FCMClient,
) *NotificationProcessorImpl {
	return &NotificationProcessorImpl{
		notificationRepo: notificationRepo,
		receiverRepo:     receiverRepo,
		deliveryRepo:     deliveryRepo,
		userDeviceRepo:   userDeviceRepo,
		userRepo:         userRepo,
		fcmClient:        fcmClient,
	}
}

// Send creates a notification and dispatches it to the given receiver user IDs via FCM.
func (p *NotificationProcessorImpl) Send(ctx context.Context, req *models.SendNotificationRequest) (*models.NotificationResponse, error) {
	if len(req.ReceiverIDs) == 0 {
		return nil, fmt.Errorf("at least one receiver_id is required")
	}

	notification := &entities.Notification{
		Title:          req.Title,
		Body:           req.Body,
		Type:           req.Type,
		Category:       req.Category,
		Priority:       req.Priority,
		ImageURL:       req.ImageURL,
		ActionURL:      req.ActionURL,
		NotifiableType: req.NotifiableType,
		NotifiableID:   req.NotifiableID,
		Data:           req.Data,
		ScheduledAt:    req.ScheduledAt,
		ExpiredAt:      req.ExpiredAt,
		CreatedBy:      req.CreatedBy,
	}

	if err := p.notificationRepo.Create(ctx, notification); err != nil {
		return nil, fmt.Errorf("failed to create notification: %w", err)
	}

	// Create receiver records and dispatch FCM per user.
	for _, userID := range req.ReceiverIDs {
		receiver := &entities.NotificationReceiver{
			NotificationID: notification.ID,
			UserID:         userID,
		}
		if err := p.receiverRepo.Create(ctx, receiver); err != nil {
			// Log but continue for other receivers.
			continue
		}

		p.dispatchFCMToUser(ctx, receiver, notification)
	}

	// Mark notification as sent.
	now := time.Now()
	notification.SentAt = &now
	_ = p.notificationRepo.Update(ctx, notification)

	return mappers.NotificationEntityToResponse(notification), nil
}

// Broadcast sends a notification to all active users in an organization.
func (p *NotificationProcessorImpl) Broadcast(ctx context.Context, req *models.BroadcastNotificationRequest) (*models.NotificationResponse, error) {
	users, err := p.userRepo.GetActiveUsers(ctx, req.OrganizationID)
	if err != nil {
		return nil, fmt.Errorf("failed to fetch organization users: %w", err)
	}

	notification := &entities.Notification{
		Title:          req.Title,
		Body:           req.Body,
		Type:           req.Type,
		Category:       req.Category,
		Priority:       req.Priority,
		ImageURL:       req.ImageURL,
		ActionURL:      req.ActionURL,
		NotifiableType: req.NotifiableType,
		NotifiableID:   req.NotifiableID,
		Data:           req.Data,
		ScheduledAt:    req.ScheduledAt,
		ExpiredAt:      req.ExpiredAt,
		CreatedBy:      req.CreatedBy,
	}

	if err := p.notificationRepo.Create(ctx, notification); err != nil {
		return nil, fmt.Errorf("failed to create notification: %w", err)
	}

	// Build receiver records in bulk.
	receivers := make([]*entities.NotificationReceiver, 0, len(users))
	for _, u := range users {
		receivers = append(receivers, &entities.NotificationReceiver{
			NotificationID: notification.ID,
			UserID:         u.ID,
		})
	}

	if err := p.receiverRepo.BulkCreate(ctx, receivers); err != nil {
		return nil, fmt.Errorf("failed to create notification receivers: %w", err)
	}

	// Dispatch FCM for each receiver.
	for _, receiver := range receivers {
		p.dispatchFCMToUser(ctx, receiver, notification)
	}

	now := time.Now()
	notification.SentAt = &now
	_ = p.notificationRepo.Update(ctx, notification)

	return mappers.NotificationEntityToResponse(notification), nil
}

// MarkAsRead marks a single notification receiver record as read.
func (p *NotificationProcessorImpl) MarkAsRead(ctx context.Context, receiverID, userID uuid.UUID) (*models.NotificationReceiverResponse, error) {
	receiver, err := p.receiverRepo.GetByID(ctx, receiverID)
	if err != nil {
		return nil, fmt.Errorf("notification not found: %w", err)
	}

	if receiver.UserID != userID {
		return nil, fmt.Errorf("unauthorized: notification does not belong to user")
	}

	if !receiver.IsRead {
		now := time.Now()
		receiver.IsRead = true
		receiver.ReadAt = &now
		if err := p.receiverRepo.Update(ctx, receiver); err != nil {
			return nil, fmt.Errorf("failed to mark notification as read: %w", err)
		}
	}

	return mappers.NotificationReceiverEntityToResponse(receiver), nil
}

// MarkAllAsRead marks all unread notifications for a user as read.
func (p *NotificationProcessorImpl) MarkAllAsRead(ctx context.Context, userID uuid.UUID) error {
	isRead := false
	receivers, _, err := p.receiverRepo.ListByUserID(ctx, userID, &isRead, 1000, 0)
	if err != nil {
		return fmt.Errorf("failed to fetch unread notifications: %w", err)
	}

	now := time.Now()
	for _, r := range receivers {
		r.IsRead = true
		r.ReadAt = &now
		_ = p.receiverRepo.Update(ctx, r)
	}

	return nil
}

// DeleteForUser soft-deletes a notification receiver record for a user.
func (p *NotificationProcessorImpl) DeleteForUser(ctx context.Context, receiverID, userID uuid.UUID) error {
	receiver, err := p.receiverRepo.GetByID(ctx, receiverID)
	if err != nil {
		return fmt.Errorf("notification not found: %w", err)
	}

	if receiver.UserID != userID {
		return fmt.Errorf("unauthorized: notification does not belong to user")
	}

	return p.receiverRepo.SoftDeleteByID(ctx, receiverID)
}

// ListForUser returns paginated notifications for a user.
// Returns: receivers, total, unreadCount, error
func (p *NotificationProcessorImpl) ListForUser(ctx context.Context, req *models.ListNotificationsRequest) ([]*models.NotificationReceiverResponse, int64, int64, error) {
	offset := (req.Page - 1) * req.Limit

	receivers, total, err := p.receiverRepo.ListByUserID(ctx, req.UserID, req.IsRead, req.Limit, offset)
	if err != nil {
		return nil, 0, 0, fmt.Errorf("failed to list notifications: %w", err)
	}

	unreadCount, err := p.receiverRepo.CountUnreadByUserID(ctx, req.UserID)
	if err != nil {
		unreadCount = 0
	}

	responses := mappers.NotificationReceiverEntitiesToResponses(receivers)
	return responses, total, unreadCount, nil
}

// GetByID returns a single notification by its ID.
func (p *NotificationProcessorImpl) GetByID(ctx context.Context, id uuid.UUID) (*models.NotificationResponse, error) {
	notification, err := p.notificationRepo.GetByID(ctx, id)
	if err != nil {
		return nil, fmt.Errorf("notification not found: %w", err)
	}
	return mappers.NotificationEntityToResponse(notification), nil
}

// dispatchFCMToUser fetches all FCM tokens for a user and sends the push notification.
func (p *NotificationProcessorImpl) dispatchFCMToUser(ctx context.Context, receiver *entities.NotificationReceiver, notification *entities.Notification) {
	if p.fcmClient == nil {
		return
	}

	devices, err := p.userDeviceRepo.GetByUserID(ctx, receiver.UserID)
	if err != nil || len(devices) == 0 {
		return
	}

	// Build FCM data payload.
	data := map[string]string{
		"notification_id":          notification.ID.String(),
		"notification_receiver_id": receiver.ID.String(),
		"type":                     notification.Type,
		"category":                 notification.Category,
		"action_url":               notification.ActionURL,
	}

	// Collect valid FCM tokens and create delivery records.
	tokens := make([]string, 0, len(devices))
	deliveries := make([]*entities.NotificationDelivery, 0, len(devices))

	for _, device := range devices {
		if device.FCMToken == "" {
			continue
		}
		tokens = append(tokens, device.FCMToken)
		deliveries = append(deliveries, &entities.NotificationDelivery{
			NotificationReceiverID: receiver.ID,
			UserDeviceID:           device.ID,
			Channel:                entities.NotificationChannelPush,
			DeliveryStatus:         entities.NotificationDeliveryStatusPending,
			Provider:               entities.NotificationProviderFirebase,
		})
	}

	if len(tokens) == 0 {
		return
	}

	// Persist delivery records before sending.
	_ = p.deliveryRepo.BulkCreate(ctx, deliveries)

	// Send via FCM multicast.
	now := time.Now()
	sendErr := p.fcmClient.SendMulticastNotification(ctx, tokens, notification.Title, notification.Body, data)

	// Update delivery status.
	for _, delivery := range deliveries {
		if sendErr != nil {
			delivery.DeliveryStatus = entities.NotificationDeliveryStatusFailed
			delivery.FailedAt = &now
			delivery.FailureReason = sendErr.Error()
		} else {
			delivery.DeliveryStatus = entities.NotificationDeliveryStatusSent
			delivery.SentAt = &now
		}
		_ = p.deliveryRepo.Update(ctx, delivery)
	}
}