"""
Email authentication logic with crypto-secure code generation
"""
import secrets
import re
import logging
from datetime import datetime, timedelta
from typing import Optional, Dict
from collections import defaultdict

logger = logging.getLogger(__name__)

# ============================================================================
# RATE LIMITING (In-Memory)
# ============================================================================
# NOTE: For production with multiple bot instances, migrate to Redis
# See "Optional Future Enhancements" section in plan

_rate_limit_store: Dict[str, list] = defaultdict(list)


async def check_rate_limit(
    identifier: str,
    max_attempts: int = 3,
    window_minutes: int = 60
) -> bool:
    """
    Check if identifier is within rate limit

    Args:
        identifier: Email or telegram_user_id (as string)
        max_attempts: Maximum attempts allowed
        window_minutes: Time window in minutes

    Returns:
        True if within limit (can proceed), False if exceeded

    NOTE: In-memory implementation - resets on bot restart
    """
    now = datetime.now()
    cutoff = now - timedelta(minutes=window_minutes)

    # Clean old attempts
    _rate_limit_store[identifier] = [
        attempt for attempt in _rate_limit_store[identifier]
        if attempt > cutoff
    ]

    # Check limit
    if len(_rate_limit_store[identifier]) >= max_attempts:
        logger.warning(f"Rate limit exceeded for {identifier}")
        return False

    # Add new attempt
    _rate_limit_store[identifier].append(now)
    return True


def clear_rate_limit(identifier: str) -> None:
    """Clear rate limit for identifier (e.g., after successful auth)"""
    if identifier in _rate_limit_store:
        del _rate_limit_store[identifier]
        logger.debug(f"Rate limit cleared for {identifier}")


# ============================================================================
# CODE GENERATION (Crypto-Secure)
# ============================================================================

def generate_email_code() -> str:
    """
    Generate crypto-secure 6-digit code

    Uses secrets module (not random) for cryptographic security

    Returns:
        6-digit string (000000 - 999999)
    """
    # Generate 6-digit code using secrets (crypto-secure)
    code = ''.join(secrets.choice('0123456789') for _ in range(6))

    logger.debug(f"Generated email auth code (length: {len(code)})")
    return code


# ============================================================================
# EMAIL VALIDATION
# ============================================================================

def is_valid_email_format(email: str) -> bool:
    """
    Validate email format (basic regex)

    Args:
        email: Email address to validate

    Returns:
        True if format is valid
    """
    pattern = r'^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$'
    return bool(re.match(pattern, email))


async def verify_email_in_oracle(email: str) -> Optional[str]:
    """
    Verify email exists in Oracle UTILIZATORI table via backend API

    Args:
        email: Email address to check

    Returns:
        Oracle username if found and active, None otherwise

    NOTE: Uses backend API endpoint /api/telegram/auth/verify-email
    """
    try:
        from app.api.client import get_backend_client

        backend_client = get_backend_client()

        # Call backend API to verify email
        response = await backend_client.verify_email(email)

        if response.get('success'):
            username = response.get('username')
            logger.info(f"Email verified via backend: {email} -> {username}")
            return username
        else:
            logger.warning(f"Email not found or inactive: {email}")
            return None

    except Exception as e:
        logger.error(f"Error verifying email via backend: {e}", exc_info=True)
        return None


# ============================================================================
# SESSION TOKEN GENERATION (Prevent User ID Spoofing)
# ============================================================================

def generate_session_token(telegram_user_id: int, email: str) -> str:
    """
    Generate signed session token for backend verification

    This prevents user ID spoofing attacks where malicious clients
    could impersonate Telegram users by sending arbitrary user IDs

    Args:
        telegram_user_id: Telegram user ID
        email: Verified email address

    Returns:
        Signed token (simple implementation - upgrade to JWT in future)

    NOTE: For production, use proper JWT signing with shared secret
    """
    import hashlib
    import os

    # Get secret from env (should match backend)
    secret = os.getenv("AUTH_SESSION_SECRET", "change-me-in-production")

    # Create signature: HMAC-like hash
    payload = f"{telegram_user_id}:{email}:{secret}"
    signature = hashlib.sha256(payload.encode()).hexdigest()[:16]

    # Token format: user_id:email:signature
    token = f"{telegram_user_id}:{email}:{signature}"

    logger.debug(f"Generated session token for user {telegram_user_id}")
    return token