import json
import os
from dotenv import load_dotenv
import firebase_admin
from firebase_admin import messaging, credentials
from google.oauth2.service_account import Credentials
from pydantic import BaseModel
from fastapi import HTTPException

load_dotenv()


class FcmRequest(BaseModel):
    token: str
    title: str
    body: str
    data: dict | None = None


class FcmService:
    """Singleton service for sending Firebase Cloud Messages."""

    _instance = None

    def __new__(cls):
        if cls._instance is None:
            cls._instance = super(FcmService, cls).__new__(cls)
            cls._instance._initialize()
        return cls._instance

    def _initialize(self):
        """Initialize Firebase Admin SDK once."""
        service_account_json = os.getenv("FIREBASE_SERVICE_ACCOUNT_JSON")

        if not service_account_json:
            raise RuntimeError(
                "FIREBASE_SERVICE_ACCOUNT_JSON not found in environment variables"
            )

        # Load service account credentials from env JSON
        cred_info = json.loads(service_account_json)

        # Initialize Firebase only once
        if not firebase_admin._apps:
            cred = credentials.Certificate(cred_info)
            firebase_admin.initialize_app(cred)

        self.admin_key = os.getenv("FIREBASE_API_ADMIN_KEY", "super-secret-admin-key")

    async def send_fcm(self, request: FcmRequest):
        """Send an FCM notification to a specific device."""
        try:
            message = messaging.Message(
                notification=messaging.Notification(
                    title=request.title,
                    body=request.body,
                ),
                data=request.data or {},
                token=request.token,
                android=messaging.AndroidConfig(
                    priority="high",
                    notification=messaging.AndroidNotification(
                        sound="default",
                        channel_id="feedback_notifications",  # optional but recommended
                    ),
                ),
                apns=messaging.APNSConfig(
                    payload=messaging.APNSPayload(
                        aps=messaging.Aps(
                            sound="default",
                            content_available=True,
                        )
                    ),
                    headers={
                        "apns-priority": "10",  # 10 = immediate
                    },
                ),
            )

            response = messaging.send(message)
            return {"status": "success", "message_id": response}
        except Exception as e:
            raise HTTPException(status_code=500, detail=str(e))
    
    async def send_to_topic(self, title: str, body: str, topic: str = "work_updates", data: dict | None = None):
        """Send an FCM notification to all users subscribed to a topic."""
        try:
            message = messaging.Message(
                notification=messaging.Notification(
                    title=title,
                    body=body,
                ),
                data=data or {},
                topic=topic,  # 👈 send to everyone subscribed to this topic
                android=messaging.AndroidConfig(
                    priority="high",
                    notification=messaging.AndroidNotification(
                        sound="default",
                        channel_id="feedback_notifications",
                    ),
                ),
                apns=messaging.APNSConfig(
                    payload=messaging.APNSPayload(
                        aps=messaging.Aps(
                            sound="default",
                            content_available=True,
                        )
                    ),
                    headers={"apns-priority": "10"},
                ),
            )

            response = messaging.send(message)
            return {"status": "success", "message_id": response}
        except Exception as e:
            raise HTTPException(status_code=500, detail=str(e))
        


# ✅ Singleton instance
fcm_service = FcmService()