package facebook

// WebhookHandler parses and validates Facebook/Instagram webhook payloads.
// Reference: Chatwoot's Facebook webhook handling:
//   - app/controllers/api/v1/accounts/channels/facebook_pages_controller.rb (CRUD + webhook)
//   - app/services/facebook/incoming_message_service.rb (message parsing)
//   - Facebook webhook verification: GET with hub.mode=subscribe, hub.verify_token, hub.challenge
//   - Facebook webhook events: POST with object=page, entry[].messaging[]
//   - Instagram webhook events: POST with object=instagram, entry[].messaging[]
//
// NOTE: HTTP routing is handled by the unified channel.WebhookHandler in webhook.go.
// This file provides channel-specific payload parsing and event classification
// that the FacebookProvider/InstagramProvider delegates to.

import (
	"crypto/hmac"
	"crypto/sha256"
	"encoding/hex"
	"encoding/json"
	"fmt"
	"time"

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

// WebhookEventType classifies the type of webhook event received.
type WebhookEventType string

const (
	// Facebook Messenger events
	EventFBMessage        WebhookEventType = "fb_message"         // text/attachment message
	EventFBMessageEcho    WebhookEventType = "fb_message_echo"    // echo of agent's outgoing message
	EventFBPostback       WebhookEventType = "fb_postback"        // postback button click
	EventFBReferral       WebhookEventType = "fb_referral"        // m.me referral
	EventFBDelivery       WebhookEventType = "fb_delivery"        // delivery receipt
	EventFBRead           WebhookEventType = "fb_read"            // read receipt
	EventFBOptin          WebhookEventType = "fb_optin"           // opt-in event
	EventFBPassThread     WebhookEventType = "fb_pass_thread"     // thread control passed
	EventFBTakeThread     WebhookEventType = "fb_take_thread"     // thread control taken
	EventFBRequestThread  WebhookEventType = "fb_request_thread"  // thread control requested

	// Instagram DM events
	EventIGMessage        WebhookEventType = "ig_message"         // Instagram DM text/attachment
	EventIGMessageEcho    WebhookEventType = "ig_message_echo"    // echo of agent's outgoing DM
	EventIGPostback       WebhookEventType = "ig_postback"        // Instagram postback
	EventIGDelivery       WebhookEventType = "ig_delivery"        // Instagram delivery receipt
	EventIGRead           WebhookEventType = "ig_read"            // Instagram read receipt

	// Instagram Comment events
	EventIGComment        WebhookEventType = "ig_comment"         // new comment on IG media post
	EventIGCommentReply   WebhookEventType = "ig_comment_reply"   // reply to an IG comment
	EventIGCommentDeleted WebhookEventType = "ig_comment_deleted" // IG comment deleted
)

// ParsedWebhookEvent is the result of parsing a raw FB/IG webhook payload.
type ParsedWebhookEvent struct {
	EventType   WebhookEventType
	Object      string            // "page" (FB) or "instagram" (IG)
	PageID      string            // FB Page ID or IG Business Account ID
	SenderID    string            // PSID (FB) or IGSID (IG)
	RecipientID string            // Page-scoped recipient ID
	Message     *FBMessageData    // message content (for message events)
	Postback    *FBPostback       // postback payload (for postback events)
	Referral    *FBReferral       // referral data (for referral events)
	Delivery    *FBDelivery       // delivery receipt data
	Read        *FBRead           // read receipt data
	Comment     *IGCommentChangeValue // comment data (for IG comment events)
	Timestamp   int64             // event timestamp in milliseconds
	RawPayload  []byte            // original raw JSON
}

// FBPostback represents a Facebook postback event payload.
type FBPostback struct {
	Title string `json:"title"`
	Data  string `json:"payload"`
	Referral *FBReferral `json:"referral,omitempty"`
}

// FBReferral represents a Facebook referral (m.me link) event payload.
type FBReferral struct {
	Ref     string `json:"ref"`
	Source  string `json:"source"`
	Type    string `json:"type"`
	AdID    string `json:"ad_id,omitempty"`
}

// FBDelivery represents a Facebook message delivery receipt.
type FBDelivery struct {
	Mids       []string `json:"mids"`
	Watermark  int64    `json:"watermark"`
}

// FBRead represents a Facebook message read receipt.
type FBRead struct {
	Watermark int64 `json:"watermark"`
}

// WebhookParser handles parsing and classification of FB/IG webhook payloads.
type WebhookParser struct{}

// NewWebhookParser creates a new webhook parser.
func NewWebhookParser() *WebhookParser {
	return &WebhookParser{}
}

// ParseWebhookPayload parses a raw FB/IG webhook JSON payload into structured events.
// Returns one or more ParsedWebhookEvent for each messaging entry in the payload.
//
// Reference: Chatwoot IncomingMessageService.perform — iterates over entry[].messaging[]
// and classifies each event type before processing.
func (wp *WebhookParser) ParseWebhookPayload(rawPayload []byte) ([]*ParsedWebhookEvent, error) {
	var event FBWebhookEvent
	if err := json.Unmarshal(rawPayload, &event); err != nil {
		return nil, fmt.Errorf("failed to parse webhook payload: %w", err)
	}

	var results []*ParsedWebhookEvent
	object := event.Object // "page" (FB) or "instagram" (IG)

	for _, entry := range event.Entry {
		pageID := entry.ID
		entryTime := entry.Time

		// Process messaging events (FB Messenger + Instagram DMs share the same structure)
		for _, msgEvent := range entry.Messaging {
			parsed := wp.classifyMessagingEvent(object, pageID, msgEvent, entryTime, rawPayload)
			results = append(results, parsed)
		}

		// Process standalone changes (for future: feed stories, mentions, etc.)
		for _, change := range entry.Changes {
			parsed := wp.classifyChangeEvent(object, pageID, change, entryTime, rawPayload)
			if parsed != nil {
				results = append(results, parsed)
			}
		}
	}

	if len(results) == 0 {
		applogger.L().Debug("Webhook payload had no processable events",
			"object", object)
	}

	return results, nil
}

// classifyMessagingEvent determines the event type from a messaging entry.
func (wp *WebhookParser) classifyMessagingEvent(object string, pageID string, msgEvent FBMessagingEvent, timestamp int64, rawPayload []byte) *ParsedWebhookEvent {
	senderID := msgEvent.Sender.ID
	recipientID := msgEvent.Recipient.ID
	eventTimestamp := msgEvent.Timestamp
	if eventTimestamp == 0 {
		eventTimestamp = timestamp
	}

	parsed := &ParsedWebhookEvent{
		Object:      object,
		PageID:      pageID,
		SenderID:    senderID,
		RecipientID: recipientID,
		Timestamp:   eventTimestamp,
		RawPayload:  rawPayload,
	}

	// Determine if this is from FB or IG
	isInstagram := object == "instagram"

	// Classify based on what fields are populated
	if msgEvent.Message != nil {
		parsed.Message = msgEvent.Message
		if msgEvent.Message.IsEcho {
			parsed.EventType = instagramOrFB(isInstagram, EventIGMessageEcho, EventFBMessageEcho)
		} else {
			parsed.EventType = instagramOrFB(isInstagram, EventIGMessage, EventFBMessage)
		}
	} else if msgEvent.Postback != nil {
		parsed.Postback = &FBPostback{
			Title: msgEvent.Postback.Title,
			Data:  msgEvent.Postback.Payload,
		}
		if msgEvent.Postback.Referral != nil {
			parsed.Postback.Referral = &FBReferral{
				Ref:    msgEvent.Postback.Referral.Ref,
				Source: msgEvent.Postback.Referral.Source,
				Type:   msgEvent.Postback.Referral.Type,
				AdID:   msgEvent.Postback.Referral.ADID,
			}
		}
		parsed.EventType = instagramOrFB(isInstagram, EventIGPostback, EventFBPostback)
	} else if msgEvent.Delivery != nil {
		parsed.Delivery = &FBDelivery{
			Mids:      msgEvent.Delivery.Mids,
			Watermark: msgEvent.Delivery.Watermark,
		}
		parsed.EventType = instagramOrFB(isInstagram, EventIGDelivery, EventFBDelivery)
	} else if msgEvent.Read != nil {
		parsed.Read = &FBRead{
			Watermark: msgEvent.Read.Watermark,
		}
		parsed.EventType = instagramOrFB(isInstagram, EventIGRead, EventFBRead)
	} else if msgEvent.Optin != nil {
		parsed.EventType = EventFBOptin
	} else if msgEvent.PassThreadControl != nil {
		parsed.EventType = EventFBPassThread
	} else if msgEvent.TakeThreadControl != nil {
		parsed.EventType = EventFBTakeThread
	}

	return parsed
}

// classifyChangeEvent processes standalone change events (e.g. feed stories).
// Not yet fully implemented — placeholder for future expansion.
func (wp *WebhookParser) classifyChangeEvent(object string, pageID string, change FBChangeEvent, timestamp int64, rawPayload []byte) *ParsedWebhookEvent {
	isInstagram := object == "instagram"

	// Instagram comment webhook: object="instagram", field="comments"
	if isInstagram && change.Field == "comments" {
		commentData, err := parseIGCommentChangeValue(change.Value)
		if err != nil {
			applogger.L().Warn("Failed to parse Instagram comment change value",
				"error", err, "field", change.Field)
			return nil
		}

		eventType := EventIGComment
		if commentData.ParentID != "" {
			eventType = EventIGCommentReply
		}
		if commentData.IsDeleted {
			eventType = EventIGCommentDeleted
		}

		parsedTimestamp := timestamp
		if commentData.Timestamp != "" {
			// IG comment timestamps are ISO 8601 strings, convert to unix ms
			if ts, err := time.Parse(time.RFC3339, commentData.Timestamp); err == nil {
				parsedTimestamp = ts.UnixMilli()
			}
		}

		parsed := &ParsedWebhookEvent{
			EventType:   eventType,
			Object:      object,
			PageID:      pageID,
			SenderID:    commentData.From.ID,
			Timestamp:   parsedTimestamp,
			Comment:     commentData,
			RawPayload:  rawPayload,
		}

		applogger.L().Debug("Parsed Instagram comment event",
			"event_type", eventType,
			"comment_id", commentData.CommentID,
			"media_id", commentData.MediaID,
			"from_id", commentData.From.ID,
			"text_length", len(commentData.Text))

		return parsed
	}

	applogger.L().Debug("Skipping unhandled change event",
		"object", object, "field", change.Field)
	return nil
}

// parseIGCommentChangeValue deserializes the map[string]interface{} value
// from a FBChangeEvent with field="comments" into an IGCommentChangeValue struct.
func parseIGCommentChangeValue(rawValue map[string]interface{}) (*IGCommentChangeValue, error) {
	// Re-marshal and unmarshal to get typed struct from raw map
	jsonBytes, err := json.Marshal(rawValue)
	if err != nil {
		return nil, fmt.Errorf("failed to re-marshal comment value: %w", err)
	}

	var commentData IGCommentChangeValue
	if err := json.Unmarshal(jsonBytes, &commentData); err != nil {
		return nil, fmt.Errorf("failed to unmarshal comment value: %w", err)
	}

	return &commentData, nil
}

// instagramOrFB returns the Instagram or Facebook event type based on the object type.
func instagramOrFB(isInstagram bool, igType WebhookEventType, fbType WebhookEventType) WebhookEventType {
	if isInstagram {
		return igType
	}
	return fbType
}

// ValidateWebhookSignature validates the X-Hub-Signature-256 header against the raw payload.
// Reference: Facebook requires SHA256 HMAC verification using the App Secret.
// Chatwoot performs this in the webhook controller before processing.
//
// The signature header format is: sha256=<hex_digest>
func ValidateWebhookSignature(appSecret string, signatureHeader string, rawPayload []byte) bool {
	if signatureHeader == "" {
		applogger.L().Warn("Facebook webhook: missing X-Hub-Signature-256 header")
		return false
	}

	// Facebook sends signature as "sha256=<hex_digest>"
	// Split on "=" to extract the hex digest portion
	eqIdx := -1
	for i := 0; i < len(signatureHeader); i++ {
		if signatureHeader[i] == '=' {
			eqIdx = i
			break
		}
	}
	if eqIdx < 0 || signatureHeader[:eqIdx] != "sha256" {
		applogger.L().Warn("Facebook webhook: invalid signature format",
			"header", signatureHeader)
		return false
	}

	expectedSig := signatureHeader[eqIdx+1:]

	// Compute HMAC-SHA256 using app secret as key
	mac := hmac.New(sha256.New, []byte(appSecret))
	mac.Write(rawPayload)
	actualSig := hex.EncodeToString(mac.Sum(nil))

	// Timing-safe comparison — prevents timing attacks on signature verification
	if !hmac.Equal([]byte(expectedSig), []byte(actualSig)) {
		applogger.L().Warn("Facebook webhook: signature mismatch",
			"expected_length", len(expectedSig), "actual_length", len(actualSig))
		return false
	}

	return true
}

// VerifyWebhookChallenge handles the FB webhook verification GET request.
// Reference: Facebook requires responding with hub.challenge when hub.mode=subscribe
// and hub.verify_token matches the configured token.
//
// This is called from the unified channel.WebhookHandler.HandleWebhookVerification.
func VerifyWebhookChallenge(queryParams map[string]string, verifyToken string) (string, bool) {
	mode := queryParams["hub.mode"]
	token := queryParams["hub.verify_token"]
	challenge := queryParams["hub.challenge"]

	if mode != "subscribe" {
		applogger.L().Debug("Facebook webhook verification: hub.mode is not subscribe",
			"mode", mode)
		return "", false
	}

	if token != verifyToken {
		applogger.L().Warn("Facebook webhook verification: verify_token mismatch")
		return "", false
	}

	applogger.L().Info("Facebook webhook verification successful")
	return challenge, true
}

// IsEchoMessage checks if the event is an echo of an agent's outgoing message.
// Echo messages should not create new conversations — they confirm delivery.
// Reference: Chatwoot filters out is_echo messages in IncomingMessageService.
func IsEchoMessage(event *ParsedWebhookEvent) bool {
	return event.EventType == EventFBMessageEcho || event.EventType == EventIGMessageEcho
}

// IsDeliveryOrReadReceipt checks if the event is a delivery or read receipt.
// Receipts should update message status, not create new messages.
// Reference: Chatwoot handles delivery/read receipts separately.
func IsDeliveryOrReadReceipt(event *ParsedWebhookEvent) bool {
	return event.EventType == EventFBDelivery || event.EventType == EventFBRead ||
		event.EventType == EventIGDelivery || event.EventType == EventIGRead
}

// ShouldCreateMessage determines if the event should result in a new message creation.
// Echo messages and receipts are excluded from message creation.
func ShouldCreateMessage(event *ParsedWebhookEvent) bool {
	return !IsEchoMessage(event) && !IsDeliveryOrReadReceipt(event) &&
		!IsThreadControlEvent(event)
}

// IsThreadControlEvent checks if the event is a thread control handoff.
func IsThreadControlEvent(event *ParsedWebhookEvent) bool {
	return event.EventType == EventFBPassThread || event.EventType == EventFBTakeThread ||
		event.EventType == EventFBRequestThread
}

// ExtractIncomingMessageFromEvent converts a ParsedWebhookEvent into a channel.IncomingMessage.
// This is the main entry point called by FacebookProvider.ProcessIncoming and InstagramProvider.ProcessIncoming.
func ExtractIncomingMessageFromEvent(event *ParsedWebhookEvent, inbox *model.Inbox, channelType channel.ChannelType) (*channel.IncomingMessage, error) {
	if !ShouldCreateMessage(event) {
		// Delivery/read receipts and echo messages are handled separately
		return nil, fmt.Errorf("event type %s does not create incoming messages", event.EventType)
	}

	msg := &channel.IncomingMessage{
		ChannelType:    channelType,
		SourceID:       extractSourceID(event),
		ConversationID: event.PageID,
		SenderID:       event.SenderID,
		SenderType:     channel.SenderContact,
		InboxID:        inbox.ID,
		AccountID:      inbox.AccountID,
		ReceivedAt:     millisToTime(event.Timestamp),
	}

	// Fill content based on event type
	switch event.EventType {
	case EventFBMessage, EventIGMessage:
		if event.Message != nil {
			msg.Content = event.Message.Text
			msg.ContentType = determineContentType(event.Message)
			msg.Attachments = convertAttachments(event.Message.Attachments, channelType)
			if event.Message.ReplyTo != nil {
				msg.ReplyToID = event.Message.ReplyTo.Mid
			}
		}
	case EventFBPostback, EventIGPostback:
		if event.Postback != nil {
			msg.Content = event.Postback.Data
			msg.ContentType = channel.ContentText
			msg.Extra = map[string]interface{}{
				"postback_title": event.Postback.Title,
			}
			if event.Postback.Referral != nil {
				msg.Extra["referral_ref"] = event.Postback.Referral.Ref
				msg.Extra["referral_source"] = event.Postback.Referral.Source
			}
		}
	}

	// Add sender/channel metadata
	msg.SenderExtra = map[string]interface{}{
		"sender_id":    event.SenderID,
		"recipient_id": event.RecipientID,
	}
	msg.ConversationExtra = map[string]interface{}{
		"page_id": event.PageID,
	}

	return msg, nil
}

// extractSourceID extracts the external message ID from an event.
func extractSourceID(event *ParsedWebhookEvent) string {
	if event.Message != nil && event.Message.Mid != "" {
		return event.Message.Mid
	}
	// For postbacks, generate a synthetic source ID
	return fmt.Sprintf("%s_%s_%d", event.PageID, event.SenderID, event.Timestamp)
}

// determineContentType determines the message content type from FB message data.
func determineContentType(msgData *FBMessageData) channel.ContentType {
	if len(msgData.Attachments) > 0 {
		att := msgData.Attachments[0]
		switch att.Type {
		case "image":
			return channel.ContentImage
		case "video":
			return channel.ContentVideo
		case "audio":
			return channel.ContentAudio
		case "file":
			return channel.ContentFile
		case "location":
			return channel.ContentLocation
		case "fallback":
			return channel.ContentFile
		default:
			return channel.ContentFile
		}
	}
	if msgData.Text != "" {
		return channel.ContentText
	}
	return channel.ContentText
}

// convertAttachments converts FB attachments to gochat Attachment structs.
func convertAttachments(fbAttachments []FBAttachment, channelType channel.ChannelType) []channel.Attachment {
	var attachments []channel.Attachment
	for _, att := range fbAttachments {
attachment := channel.Attachment{
			URL:         att.Payload.URL,
			ContentType: mimeTypeFromFBType(att.Type),
			Extra: map[string]interface{}{
				"fb_attachment_type": att.Type,
				"channel_type":       string(channelType),
			},
		}
		if att.Payload.Name != "" {
			attachment.Filename = att.Payload.Name
		}
		// Add location data if applicable
		if att.Type == "location" && att.Payload.Coordinates != nil {
			attachment.Extra["latitude"] = att.Payload.Coordinates.Lat
			attachment.Extra["longitude"] = att.Payload.Coordinates.Long
		}
		attachments = append(attachments, attachment)
	}
	return attachments
}

// millisToTime converts Unix milliseconds to time.Time.
func millisToTime(millis int64) time.Time {
	if millis == 0 {
		return time.Now()
	}
	return time.UnixMilli(millis)
}

// IsIGCommentEvent checks if the parsed event is an Instagram comment event.
func IsIGCommentEvent(event *ParsedWebhookEvent) bool {
	return event.EventType == EventIGComment ||
		event.EventType == EventIGCommentReply ||
		event.EventType == EventIGCommentDeleted
}