app/facebook.py

import hmac
import hashlib
import json
from typing import Any, Dict, Optional
import httpx
from fastapi import HTTPException, Request
from loguru import logger

from .utils import timing_decorator

class FacebookClient:
    def __init__(self, app_secret: str):
        """
        Khởi tạo FacebookClient với app_secret.
        Input: app_secret (str) - Facebook App Secret.
        Output: FacebookClient instance.
        """
        self.app_secret = app_secret
        self._client = httpx.AsyncClient()

    async def verify_webhook(self, token: str, challenge: str, verify_token: str) -> int:
        """
        Xác thực webhook Facebook bằng verify_token và trả về challenge.
        Input: token (str), challenge (str), verify_token (str)
        Output: int (challenge nếu thành công, lỗi nếu thất bại)
        """
        if token != verify_token:
            raise HTTPException(status_code=403, detail="Invalid verify token")
        return int(challenge)

    def verify_signature(self, request: Request, payload: bytes) -> bool:
        """
        Kiểm tra chữ ký X-Hub-Signature-256 để xác thực request từ Facebook.
        Input: request (Request), payload (bytes)
        Output: bool (True nếu hợp lệ, False nếu không)
        """
        signature = request.headers.get("X-Hub-Signature-256", "")
        if not signature.startswith("sha256="):
            return False

        expected = hmac.new(
            self.app_secret.encode(),
            payload,
            hashlib.sha256
        ).hexdigest()
        
        return hmac.compare_digest(signature[7:], expected)

    @timing_decorator
    async def send_message(self, page_access_token: str, recipient_id: str, message: str) -> Dict[str, Any]:
        """
        Gửi message tới user qua Facebook Messenger API.
        Input: page_access_token (str), recipient_id (str), message (str)
        Output: dict (response từ Facebook API)
        """
        url = f"https://graph.facebook.com/v18.0/me/messages?access_token={page_access_token}"
        
        payload = {
            "recipient": {"id": recipient_id},
            "message": {"text": message}
        }

        try:
            async with self._client as client:
                response = await client.post(url, json=payload)
                response.raise_for_status()
                return response.json()
        except httpx.HTTPError as e:
            logger.error(f"Error sending message to Facebook: {e}")
            raise HTTPException(status_code=500, detail="Failed to send message to Facebook")

    def parse_message(self, body: Dict[str, Any]) -> Optional[Dict[str, Any]]:
        """
        Parse message từ payload Facebook webhook.
        Input: body (dict) - payload JSON từ Facebook.
        Output: dict chứa sender_id, page_id, timestamp, text, attachments hoặc None nếu lỗi.
        """
        try:
            entry = body["entry"][0]
            messaging = entry["messaging"][0]
            
            sender_id = messaging["sender"]["id"]
            recipient_id = messaging["recipient"]["id"]
            timestamp = messaging["timestamp"]
            
            message_data = {
                "sender_id": sender_id,
                "page_id": recipient_id,
                "timestamp": timestamp,
                "text": None,
                "attachments": []
            }

            if "message" in messaging:
                message = messaging["message"]
                if "text" in message:
                    message_data["text"] = message["text"]
                if "attachments" in message:
                    message_data["attachments"] = message["attachments"]

            return message_data
        except (KeyError, IndexError) as e:
            logger.error(f"Error parsing Facebook message: {e}")
            return None