"""
Stateless HMAC-signed confirmation tokens.

Token format: base64url( email : unix_timestamp : hmac_sha256 )
No database storage needed — the signature proves authenticity.
"""

import base64
import hashlib
import hmac
import time

from app.config import settings


def generate_token(email: str) -> str:
    """Create a URL-safe confirmation token for the given email."""
    timestamp = str(int(time.time()))
    payload = f"{email}:{timestamp}"
    sig = hmac.new(
        settings.CONFIRM_SECRET.encode(),
        payload.encode(),
        hashlib.sha256,
    ).hexdigest()
    return base64.urlsafe_b64encode(f"{payload}:{sig}".encode()).decode()


def verify_token(token: str) -> str | None:
    """
    Verify a confirmation token. Returns the email if valid, None otherwise.
    Checks both HMAC signature and expiry.
    """
    try:
        decoded = base64.urlsafe_b64decode(token.encode()).decode()
        # rsplit from the right: email may contain colons (unlikely but safe)
        parts = decoded.rsplit(":", 2)
        if len(parts) != 3:
            return None

        email, timestamp, sig = parts

        # Verify HMAC
        expected = hmac.new(
            settings.CONFIRM_SECRET.encode(),
            f"{email}:{timestamp}".encode(),
            hashlib.sha256,
        ).hexdigest()
        if not hmac.compare_digest(sig, expected):
            return None

        # Check expiry
        age_seconds = time.time() - int(timestamp)
        if age_seconds > settings.CONFIRM_TOKEN_EXPIRY_HOURS * 3600:
            return None
        if age_seconds < 0:
            return None  # future timestamp — tampered

        return email
    except Exception:
        return None