import json
import os
import threading
import urllib.request
import urllib.parse
import boto3

# Cache bot token (fetched once at Lambda init)
_bot_token: str | None = None
_token_lock = threading.Lock()


def get_bot_token() -> str:
    global _bot_token
    if _bot_token is None:
        with _token_lock:
            if _bot_token is None:
                sm = boto3.client('secretsmanager')
                _bot_token = sm.get_secret_value(
                    SecretId=os.environ['TELEGRAM_BOT_TOKEN_SECRET_ARN']
                )['SecretString']
    return _bot_token


def send_typing(chat_id: str) -> None:
    """Fire-and-forget typing action (does not raise on failure)."""
    try:
        token = get_bot_token()
        data = json.dumps({'chat_id': chat_id, 'action': 'typing'}).encode()
        req = urllib.request.Request(
            f'https://api.telegram.org/bot{token}/sendChatAction',
            data=data,
            headers={'Content-Type': 'application/json'},
        )
        urllib.request.urlopen(req, timeout=3)
    except Exception:
        pass  # typing is best-effort


def handler(event, context):
    # ── Validate Telegram webhook secret ──────────────────────────────────
    expected_secret = os.environ.get('TELEGRAM_WEBHOOK_SECRET', '')
    if expected_secret:
        headers = event.get('headers') or {}
        received = headers.get('x-telegram-bot-api-secret-token', '')
        if received != expected_secret:
            return {'statusCode': 403, 'body': 'Forbidden'}

    # ── Parse Telegram Update ─────────────────────────────────────────────
    try:
        body = json.loads(event.get('body', '{}'))
    except json.JSONDecodeError:
        return {'statusCode': 400, 'body': 'Bad Request'}

    update_id = body.get('update_id')

    # Support regular messages and edited messages
    message = body.get('message') or body.get('edited_message')
    if not message:
        # Not a message update (could be channel_post, callback_query, etc.)
        return {'statusCode': 200, 'body': 'ok'}

    chat_id = str(message.get('chat', {}).get('id', ''))
    text = message.get('text', '')
    from_user = message.get('from', {})
    timestamp = message.get('date', 0)

    if not chat_id or not text:
        return {'statusCode': 200, 'body': 'ok'}

    # ── Send typing action (non-blocking, background thread) ──────────────
    t = threading.Thread(target=send_typing, args=(chat_id,))
    t.daemon = True
    t.start()

    # ── Enqueue to SQS FIFO ───────────────────────────────────────────────
    sqs = boto3.client('sqs')
    sqs.send_message(
        QueueUrl=os.environ['MESSAGE_QUEUE_URL'],
        MessageGroupId=chat_id,
        MessageDeduplicationId=str(update_id),
        MessageBody=json.dumps({
            'channel': 'telegram',
            'chat_id': chat_id,
            'messages': [{
                'text': text,
                'from_id': str(from_user.get('id', '')),
                'from_username': from_user.get('username', ''),
                'from_name': f"{from_user.get('first_name', '')} {from_user.get('last_name', '')}".strip(),
            }],
            'update_id': update_id,
            'timestamp': timestamp,
        }),
    )

    return {'statusCode': 200, 'body': 'ok'}