package service

import (
	"context"
	"crypto/rand"
	"encoding/json"
	"errors"
	"fmt"
	"net/url"

	"github.com/gochat/gochat/internal/model"
	"github.com/gochat/gochat/internal/repository"
	"gorm.io/gorm"
)

// WebhookSubscriptionService provides business logic for managing webhook subscriptions.
// Reference: Chatwoot webhook integration + P2B M8 spec
type WebhookSubscriptionService struct {
	webhookSubRepo *repository.WebhookSubscriptionRepo
}

var allowedWebhookSubscriptions = map[string]struct{}{
	"conversation_status_changed": {},
	"conversation_updated":        {},
	"conversation_created":        {},
	"contact_created":             {},
	"contact_updated":             {},
	"message_created":             {},
	"message_updated":             {},
	"webwidget_triggered":         {},
	"inbox_created":               {},
	"inbox_updated":               {},
	"conversation_typing_on":      {},
	"conversation_typing_off":     {},
}

// WebhookSubscriptionMutation is the Chatwoot account webhook create/update payload.
type WebhookSubscriptionMutation struct {
	InboxID       *uint    `json:"inbox_id"`
	Name          string   `json:"name"`
	URL           string   `json:"url"`
	Subscriptions []string `json:"subscriptions"`
}

// NewWebhookSubscriptionService creates a new WebhookSubscription service with required dependencies.
func NewWebhookSubscriptionService(webhookSubRepo *repository.WebhookSubscriptionRepo) *WebhookSubscriptionService {
	return &WebhookSubscriptionService{
		webhookSubRepo: webhookSubRepo,
	}
}

// ListSubscriptions retrieves all webhook subscriptions for an account.
func (s *WebhookSubscriptionService) ListSubscriptions(ctx context.Context, accountID uint) ([]model.WebhookSubscription, error) {
	return s.webhookSubRepo.ListByAccount(ctx, accountID)
}

// CreateSubscription creates a new webhook subscription with a generated signing secret.
func (s *WebhookSubscriptionService) CreateSubscription(ctx context.Context, accountID uint, webhookURL string, events []string) (*model.WebhookSubscription, error) {
	req := WebhookSubscriptionMutation{URL: webhookURL, Subscriptions: events}
	return s.CreateWebhook(ctx, accountID, req)
}

// CreateWebhook creates a Chatwoot-compatible account webhook.
func (s *WebhookSubscriptionService) CreateWebhook(ctx context.Context, accountID uint, req WebhookSubscriptionMutation) (*model.WebhookSubscription, error) {
	if err := validateWebhookMutation(req, true); err != nil {
		return nil, err
	}
	if existing, err := s.webhookSubRepo.FindByAccountAndURL(ctx, accountID, req.URL); err == nil && existing.ID != 0 {
		return nil, fmt.Errorf("url has already been taken")
	} else if err != nil && !errors.Is(err, gorm.ErrRecordNotFound) {
		return nil, err
	}

	eventsJSON, err := json.Marshal(req.Subscriptions)
	if err != nil {
		return nil, fmt.Errorf("marshal events: %w", err)
	}

	// Generate a random signing secret for HMAC-SHA256 webhook payload signing
	secret, err := generateWebhookSecret()
	if err != nil {
		return nil, fmt.Errorf("generate secret: %w", err)
	}

	sub := &model.WebhookSubscription{
		AccountID: accountID,
		InboxID:   req.InboxID,
		Name:      req.Name,
		URL:       req.URL,
		Events:    eventsJSON,
		Secret:    secret,
		Active:    true,
	}
	if err := s.webhookSubRepo.Create(ctx, sub); err != nil {
		return nil, err
	}
	return sub, nil
}

// UpdateSubscription updates a webhook subscription's URL, events, or active status.
func (s *WebhookSubscriptionService) UpdateSubscription(ctx context.Context, id uint, url string, events []string, active bool) (*model.WebhookSubscription, error) {
	sub, err := s.webhookSubRepo.FindByID(ctx, id)
	if err != nil {
		return nil, fmt.Errorf("find subscription: %w", err)
	}

	if url != "" {
		sub.URL = url
	}
	if len(events) > 0 {
		eventsJSON, err := json.Marshal(events)
		if err != nil {
			return nil, fmt.Errorf("marshal events: %w", err)
		}
		sub.Events = eventsJSON
	}
	sub.Active = active

	if err := s.webhookSubRepo.Update(ctx, sub); err != nil {
		return nil, err
	}
	return sub, nil
}

// UpdateWebhook updates a Chatwoot-compatible account webhook scoped to the account.
func (s *WebhookSubscriptionService) UpdateWebhook(ctx context.Context, accountID, id uint, req WebhookSubscriptionMutation) (*model.WebhookSubscription, error) {
	if err := validateWebhookMutation(req, false); err != nil {
		return nil, err
	}
	sub, err := s.webhookSubRepo.FindByAccountAndID(ctx, accountID, id)
	if err != nil {
		return nil, fmt.Errorf("find subscription: %w", err)
	}
	if req.URL != "" && req.URL != sub.URL {
		if existing, err := s.webhookSubRepo.FindByAccountAndURL(ctx, accountID, req.URL); err == nil && existing.ID != sub.ID {
			return nil, fmt.Errorf("url has already been taken")
		} else if err != nil && !errors.Is(err, gorm.ErrRecordNotFound) {
			return nil, err
		}
		sub.URL = req.URL
	}
	sub.Name = req.Name
	sub.InboxID = req.InboxID
	eventsJSON, err := json.Marshal(req.Subscriptions)
	if err != nil {
		return nil, fmt.Errorf("marshal events: %w", err)
	}
	sub.Events = eventsJSON
	sub.Active = true

	if err := s.webhookSubRepo.Update(ctx, sub); err != nil {
		return nil, err
	}
	return s.webhookSubRepo.FindByAccountAndID(ctx, accountID, id)
}

// DeleteWebhook deletes a Chatwoot-compatible account webhook scoped to the account.
func (s *WebhookSubscriptionService) DeleteWebhook(ctx context.Context, accountID, id uint) error {
	if _, err := s.webhookSubRepo.FindByAccountAndID(ctx, accountID, id); err != nil {
		return fmt.Errorf("find subscription: %w", err)
	}
	return s.webhookSubRepo.Delete(ctx, id)
}

// GetWebhook retrieves a Chatwoot-compatible account webhook scoped to the account.
func (s *WebhookSubscriptionService) GetWebhook(ctx context.Context, accountID, id uint) (*model.WebhookSubscription, error) {
	return s.webhookSubRepo.FindByAccountAndID(ctx, accountID, id)
}

// DeleteSubscription soft-deletes a webhook subscription.
func (s *WebhookSubscriptionService) DeleteSubscription(ctx context.Context, id uint) error {
	return s.webhookSubRepo.Delete(ctx, id)
}

// GetSubscription retrieves a single webhook subscription by ID.
func (s *WebhookSubscriptionService) GetSubscription(ctx context.Context, id uint) (*model.WebhookSubscription, error) {
	return s.webhookSubRepo.FindByID(ctx, id)
}

// ListDeliveries retrieves recent delivery records for a subscription.
func (s *WebhookSubscriptionService) ListDeliveries(ctx context.Context, subscriptionID uint, limit int) ([]model.WebhookDelivery, error) {
	return s.webhookSubRepo.ListDeliveriesBySubscription(ctx, subscriptionID, limit)
}

// generateWebhookSecret creates a random 32-byte hex-encoded secret for HMAC signing.
func generateWebhookSecret() (string, error) {
	b := make([]byte, 32)
	if _, err := rand.Read(b); err != nil {
		return "", err
	}
	return fmt.Sprintf("%x", b), nil
}

func validateWebhookMutation(req WebhookSubscriptionMutation, requireURL bool) error {
	if requireURL || req.URL != "" {
		u, err := url.ParseRequestURI(req.URL)
		if err != nil || u == nil || (u.Scheme != "http" && u.Scheme != "https") || u.Host == "" {
			return fmt.Errorf("url is invalid")
		}
	}
	if len(req.Subscriptions) == 0 {
		return fmt.Errorf("subscriptions is invalid")
	}
	seen := map[string]struct{}{}
	for _, subscription := range req.Subscriptions {
		if _, ok := allowedWebhookSubscriptions[subscription]; !ok {
			return fmt.Errorf("subscriptions is invalid")
		}
		if _, ok := seen[subscription]; ok {
			return fmt.Errorf("subscriptions is invalid")
		}
		seen[subscription] = struct{}{}
	}
	return nil
}