# backend/push.py
# Push Notifications — Web Push API with VAPID authentication
# ROADMAP #67

import base64
import json
import logging
import os
from datetime import datetime, timezone
from pathlib import Path
from typing import Any

from fastapi import APIRouter, Depends, HTTPException
from pydantic import BaseModel, Field

from backend.auth.middleware import require_auth

logger = logging.getLogger("obsigate.push")

router = APIRouter(prefix="/api/push", tags=["push"])

# VAPID keys storage
VAPID_KEYS_FILE = Path(os.environ.get("OBSIGATE_DATA_DIR", "data")) / "vapid_keys.json"
PUSH_SUBSCRIPTIONS_FILE = Path(os.environ.get("OBSIGATE_DATA_DIR", "data")) / "push_subscriptions.json"

# In-memory cache
_vapid_keys: dict[str, str] = {}
_push_subscriptions: list[dict[str, Any]] = []


def load_vapid_keys() -> dict[str, str]:
    """Load VAPID keys from file or generate new ones."""
    global _vapid_keys
    if _vapid_keys:
        return _vapid_keys
    
    try:
        if VAPID_KEYS_FILE.exists():
            with open(VAPID_KEYS_FILE, "r") as f:
                _vapid_keys = json.load(f)
        else:
            # Generate new VAPID keys
            from cryptography.hazmat.primitives import serialization
            from cryptography.hazmat.primitives.asymmetric import ec
            
            private_key = ec.generate_private_key(ec.SECP256R1())
            public_key = private_key.public_key()
            
            private_pem = private_key.private_bytes(
                encoding=serialization.Encoding.PEM,
                format=serialization.PrivateFormat.PKCS8,
                encryption_algorithm=serialization.NoEncryption()
            ).decode('utf-8')
            
            public_pem = public_key.public_bytes(
                encoding=serialization.Encoding.PEM,
                format=serialization.PublicFormat.SubjectPublicKeyInfo
            ).decode('utf-8')
            
            # Convert to base64url for Web Push
            public_numbers = public_key.public_numbers()
            
            def int_to_base64url(n: int) -> str:
                byte_len = (n.bit_length() + 7) // 8
                return base64.urlsafe_b64encode(n.to_bytes(byte_len, 'big')).decode('utf-8').rstrip('=')
            
            _vapid_keys = {
                "private_key": private_pem,
                "public_key": public_pem,
                "public_key_base64url": int_to_base64url(public_numbers.x) + "." + int_to_base64url(public_numbers.y)
            }
            
            VAPID_KEYS_FILE.parent.mkdir(parents=True, exist_ok=True)
            with open(VAPID_KEYS_FILE, "w") as f:
                json.dump(_vapid_keys, f)
    except Exception as e:
        logger.error(f"Failed to load/generate VAPID keys: {e}")
        # Fallback: return empty (will use demo keys if needed)
        _vapid_keys = {}
    
    return _vapid_keys


def get_vapid_public_key() -> str:
    """Get VAPID public key in base64url format for client."""
    keys = load_vapid_keys()
    return keys.get("public_key_base64url", "")


def load_push_subscriptions() -> list[dict[str, Any]]:
    """Load push subscriptions from file."""
    global _push_subscriptions
    if _push_subscriptions:
        return _push_subscriptions
    
    try:
        if PUSH_SUBSCRIPTIONS_FILE.exists():
            with open(PUSH_SUBSCRIPTIONS_FILE, "r") as f:
                _push_subscriptions = json.load(f)
    except Exception as e:
        logger.error(f"Failed to load push subscriptions: {e}")
        _push_subscriptions = []
    return _push_subscriptions


def save_push_subscriptions() -> None:
    """Save push subscriptions to file."""
    try:
        PUSH_SUBSCRIPTIONS_FILE.parent.mkdir(parents=True, exist_ok=True)
        with open(PUSH_SUBSCRIPTIONS_FILE, "w") as f:
            json.dump(_push_subscriptions, f, indent=2)
    except Exception as e:
        logger.error(f"Failed to save push subscriptions: {e}")


# ── Models ──────────────────────────────────────────────────────────────────

class PushSubscription(BaseModel):
    """Push subscription from client (matches Push API)."""
    endpoint: str
    keys: dict[str, str]  # { p256dh, auth }


class SubscribeRequest(BaseModel):
    """Request to subscribe to push notifications."""
    subscription: PushSubscription
    vault: str = Field(description="Vault name this subscription is for")


class SubscribeResponse(BaseModel):
    """Response to subscription request."""
    success: bool
    subscription_id: str | None = None


class VapidPublicKeyResponse(BaseModel):
    """VAPID public key for client."""
    public_key: str


class PushPayload(BaseModel):
    """Payload for sending a push notification."""
    vault: str
    title: str
    body: str
    data: dict[str, Any] = Field(default_factory=dict)
    tag: str = "obsigate-notification"


# ── Endpoints ───────────────────────────────────────────────────────────────

@router.get("/vapid-public-key", response_model=VapidPublicKeyResponse)
async def get_vapid_public_key_endpoint():
    """Get VAPID public key for client subscription."""
    public_key = get_vapid_public_key()
    if not public_key:
        # Return a demo key if generation failed (for testing)
        return {"public_key": "demo-key-for-testing"}
    return {"public_key": public_key}


@router.post("/subscribe", response_model=SubscribeResponse)
async def subscribe_push(
    request: SubscribeRequest,
    current_user=Depends(require_auth)
):
    """Subscribe to push notifications for a vault."""
    username = current_user.get("username", "unknown")
    
    # Check if user has access to this vault
    user_vaults = current_user.get("_token_vaults") or current_user.get("vaults", [])
    if "*" not in user_vaults and request.vault not in user_vaults:
        raise HTTPException(status_code=403, detail="No access to this vault")
    
    # Check if subscription already exists
    for sub in _push_subscriptions:
        if sub["endpoint"] == request.subscription.endpoint and sub["username"] == username:
            return SubscribeResponse(success=True, subscription_id=sub.get("id"))
    
    # Add new subscription
    sub_id = base64.urlsafe_b64encode(os.urandom(16)).decode('utf-8').rstrip('=')
    subscription = {
        "id": sub_id,
        "endpoint": request.subscription.endpoint,
        "keys": request.subscription.keys,
        "vault": request.vault,
        "username": username,
        "created_at": datetime.now(timezone.utc).isoformat()
    }
    
    _push_subscriptions.append(subscription)
    save_push_subscriptions()
    
    logger.info(f"Push subscription added for user={username}, vault={request.vault}")
    return SubscribeResponse(success=True, subscription_id=sub_id)


@router.delete("/subscribe")
async def unsubscribe_push(
    endpoint: str,
    current_user=Depends(require_auth)
):
    """Unsubscribe from push notifications."""
    username = current_user.get("username", "unknown")
    
    global _push_subscriptions
    original_len = len(_push_subscriptions)
    _push_subscriptions = [
        s for s in _push_subscriptions
        if not (s["endpoint"] == endpoint and s["username"] == username)
    ]
    
    if len(_push_subscriptions) < original_len:
        save_push_subscriptions()
        return {"success": True, "message": "Unsubscribed"}
    
    return {"success": False, "message": "Subscription not found"}


@router.get("/subscriptions")
async def list_subscriptions(current_user=Depends(require_auth)):
    """List current user's push subscriptions."""
    username = current_user.get("username", "unknown")
    user_subs = [
        {
            "id": s["id"],
            "vault": s["vault"],
            "created_at": s["created_at"],
            "endpoint": s["endpoint"][:50] + "..."  # Truncate for privacy
        }
        for s in _push_subscriptions if s["username"] == username
    ]
    return {"subscriptions": user_subs}


# ── Internal: Send push notification ────────────────────────────────────────

async def send_push_notification(vault: str, title: str, body: str, data: dict | None = None, tag: str = "obsigate-notification") -> int:
    """Send push notification to all subscribers of a vault. Returns count of sent notifications."""
    subscriptions = [s for s in _push_subscriptions if s["vault"] == vault]
    
    if not subscriptions:
        return 0
    
    payload = {
        "title": title,
        "body": body,
        "data": data or {},
        "tag": tag
    }
    
    # Import here to avoid circular dependency
    from pywebpush import WebPushException, webpush
    
    keys = load_vapid_keys()
    vapid_private_key = keys.get("private_key")
    vapid_claims = {
        "sub": "mailto:admin@obsigate.local"
    }
    
    sent = 0
    for sub in subscriptions:
        try:
            webpush(
                subscription_info={
                    "endpoint": sub["endpoint"],
                    "keys": sub["keys"]
                },
                data=json.dumps(payload),
                vapid_private_key=vapid_private_key,
                vapid_claims=vapid_claims
            )
            sent += 1
        except WebPushException as e:
            logger.warning(f"Push failed for subscription {sub['id']}: {e}")
            # If subscription expired/invalid, remove it
            if e.response and e.response.status_code in (404, 410):
                _push_subscriptions.remove(sub)
        except Exception as e:
            logger.error(f"Push error for {sub['id']}: {e}")
    
    if sent < len(subscriptions):
        save_push_subscriptions()
    
    return sent