package facebook

// FacebookService provides high-level operations for Facebook Messenger and Instagram DM channels.
// Reference: Chatwoot app/services/facebook_service.rb
//
// This service coordinates between:
// - ChannelFacebook / ChannelInstagram model (CRUD)
// - FacebookProvider / InstagramProvider (Graph API calls)
// - Repository (GORM persistence)
// - IncomingProcessor / OutgoingProcessor (pipeline integration)
//
// Design: Service pattern follows Chatwoot's service layer where each channel
// has a service module that wraps channel-specific business logic.
// Facebook and Instagram share this service since Instagram DMs use the FB Graph API.

import (
	"context"
	"fmt"
	"os"
	"time"

	"github.com/go-resty/resty/v2"

	channelmodel "github.com/gochat/gochat/internal/model/channel"
	"github.com/gochat/gochat/internal/model"
	applogger "github.com/gochat/gochat/pkg/logger"
)

// Service handles Facebook/Instagram channel business logic.
type Service struct {
	client *resty.Client
	repo   *Repository
	graphAPIBase string
	appID        string
	appSecret    string
}

// NewService creates a new Facebook/Instagram service.
func NewService(repo *Repository) *Service {
	client := resty.New()
	client.SetTimeout(30 * time.Second)
	client.SetRetryCount(3)
	client.SetRetryWaitTime(1 * time.Second)
	client.SetRetryMaxWaitTime(5 * time.Second)

	graphAPIBase := getEnvOrDefault("FB_GRAPH_API_BASE", "https://graph.facebook.com/v18.0")
	appID := getEnvOrDefault("FB_APP_ID", "")
	appSecret := getEnvOrDefault("FB_APP_SECRET", "")

	return &Service{
		client:       client,
		repo:         repo,
		graphAPIBase: graphAPIBase,
		appID:        appID,
		appSecret:    appSecret,
	}
}

// === Facebook Channel CRUD ===

// CreateFacebookChannel creates a new Facebook Messenger channel.
// Reference: Chatwoot FacebookPagesController#create
// Flow: validate page_access_token → create ChannelFacebook → setup webhook → create Inbox
func (s *Service) CreateFacebookChannel(ctx context.Context, accountID uint, pageID string, pageAccessToken string, webhookVerifyToken string) (*channelmodel.ChannelFacebook, error) {
	// Step 1: Validate page access token via Graph API (Chatwoot: ensure_valid_page_token)
	pageInfo, err := s.validatePageAccessToken(ctx, pageID, pageAccessToken)
	if err != nil {
		return nil, fmt.Errorf("facebook page access token validation failed: %w", err)
	}

	ch := &channelmodel.ChannelFacebook{
		AccountID:          accountID,
		PageID:             pageID,
		PageAccessToken:    pageAccessToken,
		PageName:           pageInfo.Name,
		AppID:              s.appID,
		WebhookVerifyToken: webhookVerifyToken,
	}

	// Check if the page has a linked Instagram business account
	if pageInfo.InstagramBusinessAccount != nil && pageInfo.InstagramBusinessAccount.ID != "" {
		ch.InstagramBusinessAccountID = pageInfo.InstagramBusinessAccount.ID
	}

	// Step 2: Persist channel (via repository)
	if err := s.repo.CreateFacebook(ctx, ch); err != nil {
		return nil, fmt.Errorf("failed to create ChannelFacebook: %w", err)
	}

	// Step 3: Setup webhook subscription
	fbProvider := NewFacebookProvider()
	if err := fbProvider.setupWebhookSubscription(ctx, s.appID, pageID, pageAccessToken, webhookVerifyToken); err != nil {
		applogger.L().Warn("Facebook webhook subscription setup failed (can retry later)",
			"error", err, "page_id", pageID)
	}

	applogger.L().Info("Facebook channel created",
		"account_id", accountID, "page_id", pageID, "page_name", pageInfo.Name)
	return ch, nil
}

// UpdateFacebookChannel updates an existing Facebook channel.
// Reference: Chatwoot FacebookPagesController#update
func (s *Service) UpdateFacebookChannel(ctx context.Context, channelID uint, params map[string]interface{}) (*channelmodel.ChannelFacebook, error) {
	ch, err := s.repo.GetFacebookByID(ctx, channelID)
	if err != nil {
		return nil, fmt.Errorf("failed to fetch ChannelFacebook: %w", err)
	}

	if token, ok := params["page_access_token"].(string); ok && token != "" {
		// Re-validate new token
		_, validateErr := s.validatePageAccessToken(ctx, ch.PageID, token)
		if validateErr != nil {
			return nil, fmt.Errorf("new page_access_token validation failed: %w", validateErr)
		}
		ch.PageAccessToken = token
	}

	if name, ok := params["page_name"].(string); ok {
		ch.PageName = name
	}

	if err := s.repo.UpdateFacebook(ctx, ch); err != nil {
		return nil, fmt.Errorf("failed to update ChannelFacebook: %w", err)
	}

	applogger.L().Info("Facebook channel updated", "id", channelID)
	return ch, nil
}

// DeleteFacebookChannel removes a Facebook channel and its webhook subscription.
// Reference: Chatwoot FacebookPagesController#destroy + after_destroy :delete_facebook_page
func (s *Service) DeleteFacebookChannel(ctx context.Context, channelID uint) error {
	ch, err := s.repo.GetFacebookByID(ctx, channelID)
	if err != nil {
		return fmt.Errorf("failed to fetch ChannelFacebook for deletion: %w", err)
	}

	// Unsubscribe webhook
	fbProvider := NewFacebookProvider()
	fbProvider.unsubscribeWebhook(ctx, s.appID, ch.PageID, ch.PageAccessToken)

	if err := s.repo.DeleteFacebook(ctx, channelID); err != nil {
		return fmt.Errorf("failed to delete ChannelFacebook: %w", err)
	}

	applogger.L().Info("Facebook channel deleted", "id", channelID)
	return nil
}

// === Instagram Channel CRUD ===

// CreateInstagramChannel creates a new Instagram DM channel.
// Reference: Chatwoot InstagramController#create
// Flow: validate ig account → create ChannelInstagram → setup webhook (via FB Page) → create Inbox
func (s *Service) CreateInstagramChannel(ctx context.Context, accountID uint, igAccountID string, pageAccessToken string, connectedFBPageID string, webhookVerifyToken string) (*channelmodel.ChannelInstagram, error) {
	// Step 1: Validate Instagram account via Graph API
	igProfile, err := s.validateInstagramAccount(ctx, igAccountID, pageAccessToken)
	if err != nil {
		return nil, fmt.Errorf("instagram account validation failed: %w", err)
	}

	// Step 2: Resolve Instagram Business Account ID from FB Page
	igBusinessAccountID := igAccountID
	pageInfo, pageErr := s.fetchFBPageInfo(ctx, connectedFBPageID, pageAccessToken)
	if pageErr == nil && pageInfo.InstagramBusinessAccount != nil {
		igBusinessAccountID = pageInfo.InstagramBusinessAccount.ID
	}

	ch := &channelmodel.ChannelInstagram{
		AccountID:                  accountID,
		InstagramAccountID:         igAccountID,
		InstagramBusinessAccountID: igBusinessAccountID,
		PageAccessToken:            pageAccessToken,
		ConnectedFBPageID:          connectedFBPageID,
		InstagramAccountName:       igProfile.Username,
	}

	// Step 3: Persist channel
	if err := s.repo.CreateInstagram(ctx, ch); err != nil {
		return nil, fmt.Errorf("failed to create ChannelInstagram: %w", err)
	}

	// Step 4: Setup webhook subscription via FB Page
	fbProvider := NewFacebookProvider()
	if err := fbProvider.setupWebhookSubscription(ctx, s.appID, connectedFBPageID, pageAccessToken, webhookVerifyToken); err != nil {
		applogger.L().Warn("Instagram webhook subscription setup failed (can retry later)",
			"error", err, "ig_account_id", igAccountID)
	}

	applogger.L().Info("Instagram channel created",
		"account_id", accountID, "ig_account_id", igAccountID, "ig_username", igProfile.Username)
	return ch, nil
}

// UpdateInstagramChannel updates an existing Instagram channel.
func (s *Service) UpdateInstagramChannel(ctx context.Context, channelID uint, params map[string]interface{}) (*channelmodel.ChannelInstagram, error) {
	ch, err := s.repo.GetInstagramByID(ctx, channelID)
	if err != nil {
		return nil, fmt.Errorf("failed to fetch ChannelInstagram: %w", err)
	}

	if token, ok := params["page_access_token"].(string); ok && token != "" {
		_, validateErr := s.validateInstagramAccount(ctx, ch.InstagramAccountID, token)
		if validateErr != nil {
			return nil, fmt.Errorf("new page_access_token validation failed: %w", validateErr)
		}
		ch.PageAccessToken = token
	}

	if name, ok := params["instagram_account_name"].(string); ok {
		ch.InstagramAccountName = name
	}

	if err := s.repo.UpdateInstagram(ctx, ch); err != nil {
		return nil, fmt.Errorf("failed to update ChannelInstagram: %w", err)
	}

	applogger.L().Info("Instagram channel updated", "id", channelID)
	return ch, nil
}

// DeleteInstagramChannel removes an Instagram channel.
func (s *Service) DeleteInstagramChannel(ctx context.Context, channelID uint) error {
	ch, err := s.repo.GetInstagramByID(ctx, channelID)
	if err != nil {
		return fmt.Errorf("failed to fetch ChannelInstagram for deletion: %w", err)
	}

	// Unsubscribe webhook via FB Page
	fbProvider := NewFacebookProvider()
	fbProvider.unsubscribeWebhook(ctx, s.appID, ch.ConnectedFBPageID, ch.PageAccessToken)

	if err := s.repo.DeleteInstagram(ctx, channelID); err != nil {
		return fmt.Errorf("failed to delete ChannelInstagram: %w", err)
	}

	applogger.L().Info("Instagram channel deleted", "id", channelID)
	return nil
}

// === Token Management ===

// RefreshPageAccessToken refreshes a long-lived Facebook Page access token.
// Reference: Chatwoot RefreshOauthTokenService for Facebook
// Facebook long-lived tokens expire after ~60 days; refresh before expiry.
func (s *Service) RefreshPageAccessToken(ctx context.Context, channelID uint, channelType string) error {
	switch channelType {
	case "facebook":
		ch, err := s.repo.GetFacebookByID(ctx, channelID)
		if err != nil {
			return fmt.Errorf("failed to fetch ChannelFacebook for token refresh: %w", err)
		}
		newToken, refreshErr := s.exchangeLongLivedToken(ctx, ch.PageAccessToken)
		if refreshErr != nil {
			// Mark as requiring reauthorization
			ch.ReauthorizationRequired = true
			s.repo.UpdateFacebook(ctx, ch)
			return fmt.Errorf("token refresh failed, marked for reauthorization: %w", refreshErr)
		}
		ch.PageAccessToken = newToken.AccessToken
		ch.ReauthorizationRequired = false
		return s.repo.UpdateFacebook(ctx, ch)

	case "instagram":
		ch, err := s.repo.GetInstagramByID(ctx, channelID)
		if err != nil {
			return fmt.Errorf("failed to fetch ChannelInstagram for token refresh: %w", err)
		}
		newToken, refreshErr := s.exchangeLongLivedToken(ctx, ch.PageAccessToken)
		if refreshErr != nil {
			ch.ReauthorizationRequired = true
			s.repo.UpdateInstagram(ctx, ch)
			return fmt.Errorf("token refresh failed, marked for reauthorization: %w", refreshErr)
		}
		ch.PageAccessToken = newToken.AccessToken
		ch.ReauthorizationRequired = false
		return s.repo.UpdateInstagram(ctx, ch)

	default:
		return fmt.Errorf("unsupported channel type for token refresh: %s", channelType)
	}
}

// === Graph API Helpers ===

// validatePageAccessToken validates a Facebook Page access token via the Graph API.
func (s *Service) validatePageAccessToken(ctx context.Context, pageID string, pageAccessToken string) (*FBPageInfo, error) {
	ctx, cancel := context.WithTimeout(ctx, 10*time.Second)
	defer cancel()

	resp, err := s.client.R().
		SetContext(ctx).
		SetQueryParams(map[string]string{
			"fields":       "id,name,access_token,instagram_business_account{id}",
			"access_token": pageAccessToken,
		}).
		SetResult(&FBPageInfo{}).
		Get(fmt.Sprintf("%s/%s", s.graphAPIBase, pageID))

	if err != nil {
		return nil, fmt.Errorf("page validation API call failed: %w", err)
	}

	if resp.StatusCode() != 200 {
		return nil, fmt.Errorf("page not found or token invalid (HTTP %d)", resp.StatusCode())
	}

	return resp.Result().(*FBPageInfo), nil
}

// validateInstagramAccount validates an Instagram Business account via Graph API.
func (s *Service) validateInstagramAccount(ctx context.Context, igAccountID string, pageAccessToken string) (*IGUserProfile, error) {
	ctx, cancel := context.WithTimeout(ctx, 10*time.Second)
	defer cancel()

	resp, err := s.client.R().
		SetContext(ctx).
		SetQueryParams(map[string]string{
			"fields":       "id,username,name,profile_picture_url,biography",
			"access_token": pageAccessToken,
		}).
		SetResult(&IGUserProfile{}).
		Get(fmt.Sprintf("%s/%s", s.graphAPIBase, igAccountID))

	if err != nil {
		return nil, fmt.Errorf("instagram account validation API call failed: %w", err)
	}

	if resp.StatusCode() != 200 {
		return nil, fmt.Errorf("instagram account not found (HTTP %d)", resp.StatusCode())
	}

	return resp.Result().(*IGUserProfile), nil
}

// fetchFBPageInfo fetches Facebook Page info including linked Instagram account.
func (s *Service) fetchFBPageInfo(ctx context.Context, pageID string, pageAccessToken string) (*FBPageInfo, error) {
	ctx, cancel := context.WithTimeout(ctx, 10*time.Second)
	defer cancel()

	resp, err := s.client.R().
		SetContext(ctx).
		SetQueryParams(map[string]string{
			"fields":       "id,name,instagram_business_account{id,username}",
			"access_token": pageAccessToken,
		}).
		SetResult(&FBPageInfo{}).
		Get(fmt.Sprintf("%s/%s", s.graphAPIBase, pageID))

	if err != nil {
		return nil, fmt.Errorf("page info fetch failed: %w", err)
	}

	if resp.StatusCode() != 200 {
		return nil, fmt.Errorf("page info fetch returned HTTP %d", resp.StatusCode())
	}

	return resp.Result().(*FBPageInfo), nil
}

// exchangeLongLivedToken exchanges a short-lived or expiring long-lived token for a fresh long-lived token.
// Reference: https://developers.facebook.com/docs/facebook-login/guides/access-tokens/get-long-lived
func (s *Service) exchangeLongLivedToken(ctx context.Context, currentToken string) (*FBLongLivedTokenResponse, error) {
	resp, err := s.client.R().
		SetContext(ctx).
		SetQueryParams(map[string]string{
			"grant_type":        "fb_exchange_token",
			"client_id":         s.appID,
			"client_secret":     s.appSecret,
			"fb_exchange_token": currentToken,
		}).
		SetResult(&FBLongLivedTokenResponse{}).
		Get(fmt.Sprintf("%s/oauth/access_token", s.graphAPIBase))

	if err != nil {
		return nil, fmt.Errorf("token exchange API call failed: %w", err)
	}

	if resp.StatusCode() != 200 {
		return nil, fmt.Errorf("token exchange returned HTTP %d", resp.StatusCode())
	}

	return resp.Result().(*FBLongLivedTokenResponse), nil
}

// === Contact Resolution ===

// FetchFacebookUserProfile fetches a Facebook user profile via the Graph API.
// Used for contact creation/update when processing incoming messages.
func (s *Service) FetchFacebookUserProfile(ctx context.Context, psID string, pageAccessToken string) (*FBUserProfile, error) {
	ctx, cancel := context.WithTimeout(ctx, 10*time.Second)
	defer cancel()

	resp, err := s.client.R().
		SetContext(ctx).
		SetQueryParams(map[string]string{
			"fields":       "id,name,first_name,last_name,profile_pic,locale,timezone,gender",
			"access_token": pageAccessToken,
		}).
		SetResult(&FBUserProfile{}).
		Get(fmt.Sprintf("%s/%s", s.graphAPIBase, psID))

	if err != nil {
		return nil, fmt.Errorf("facebook user profile fetch failed: %w", err)
	}

	if resp.StatusCode() != 200 {
		return nil, fmt.Errorf("facebook user profile fetch returned HTTP %d", resp.StatusCode())
	}

	return resp.Result().(*FBUserProfile), nil
}

// FetchInstagramUserProfile fetches an Instagram user profile via the Graph API.
func (s *Service) FetchInstagramUserProfile(ctx context.Context, igid string, pageAccessToken string) (*IGUserProfile, error) {
	ctx, cancel := context.WithTimeout(ctx, 10*time.Second)
	defer cancel()

	resp, err := s.client.R().
		SetContext(ctx).
		SetQueryParams(map[string]string{
			"fields":       "id,username,name,profile_picture_url,biography,followers_count",
			"access_token": pageAccessToken,
		}).
		SetResult(&IGUserProfile{}).
		Get(fmt.Sprintf("%s/%s", s.graphAPIBase, igid))

	if err != nil {
		return nil, fmt.Errorf("instagram user profile fetch failed: %w", err)
	}

	if resp.StatusCode() != 200 {
		return nil, fmt.Errorf("instagram user profile fetch returned HTTP %d", resp.StatusCode())
	}

	return resp.Result().(*IGUserProfile), nil
}

// === Webhook Verification ===

// VerifyWebhookToken checks if the provided verify token matches the stored one.
func (s *Service) VerifyWebhookToken(ctx context.Context, pageID string, providedToken string) (bool, error) {
	// Lookup channel by page_id to get stored verify token
	ch, err := s.repo.GetFacebookByPageID(ctx, pageID)
	if err != nil {
		return false, fmt.Errorf("failed to find ChannelFacebook by page_id: %w", err)
	}

	return ch.WebhookVerifyToken == providedToken, nil
}

// === Reauthorization Status ===

// MarkReauthorizationRequired flags a channel as needing token reauthorization.
// Reference: Chatwoot prompt_reauthorization! — sets reauthorization_required=true
func (s *Service) MarkReauthorizationRequired(ctx context.Context, channelID uint, channelType string, reason string) error {
	switch channelType {
	case "facebook":
		ch, err := s.repo.GetFacebookByID(ctx, channelID)
		if err != nil {
			return err
		}
		ch.ReauthorizationRequired = true
		return s.repo.UpdateFacebook(ctx, ch)

	case "instagram":
		ch, err := s.repo.GetInstagramByID(ctx, channelID)
		if err != nil {
			return err
		}
		ch.ReauthorizationRequired = true
		return s.repo.UpdateInstagram(ctx, ch)

	default:
		return fmt.Errorf("unsupported channel type: %s", channelType)
	}
}

// === Helper Functions ===

// getEnvOrDefault returns the value of an environment variable or a default value.
func getEnvOrDefault(key string, defaultValue string) string {
	if value := os.Getenv(key); value != "" {
		return value
	}
	return defaultValue
}

// === Inbox Resolution ===

// GetInboxForFacebookPage resolves an Inbox from a Facebook Page ID.
func (s *Service) GetInboxForFacebookPage(ctx context.Context, pageID string) (*model.Inbox, error) {
	ch, err := s.repo.GetFacebookByPageID(ctx, pageID)
	if err != nil {
		return nil, fmt.Errorf("no ChannelFacebook found for page_id=%s: %w", pageID, err)
	}

	// In production: query Inbox by channel_id + channel_type
	// Placeholder: return minimal Inbox with channel reference
	inbox := &model.Inbox{
		AccountID: ch.AccountID,
	}
	return inbox, nil
}

// GetInboxForInstagramAccount resolves an Inbox from an Instagram Account ID.
func (s *Service) GetInboxForInstagramAccount(ctx context.Context, igAccountID string) (*model.Inbox, error) {
	ch, err := s.repo.GetInstagramByAccountID(ctx, igAccountID)
	if err != nil {
		return nil, fmt.Errorf("no ChannelInstagram found for ig_account_id=%s: %w", igAccountID, err)
	}

	inbox := &model.Inbox{
		AccountID: ch.AccountID,
	}
	return inbox, nil
}