"""RoutingKeyGenerator — date-based routing key derivation for Kademlia.

Ported from net.i2p.data.RoutingKeyGenerator.

Routing keys rotate daily at midnight UTC. The routing key for a given
database key is SHA-256(key + YYYY-MM-DD_UTF8).
"""

from __future__ import annotations

import hashlib
import time
from datetime import datetime, timezone


class RoutingKeyGenerator:
    """Generate date-based routing keys for NetDB lookups."""

    def __init__(self) -> None:
        self._mod_data: bytes = b""
        self._last_changed: float = 0.0
        self.generate_date_based_mod_data()

    def get_routing_key(self, orig_key: bytes) -> bytes:
        """Compute the routing key: SHA-256(orig_key + mod_data)."""
        return hashlib.sha256(orig_key + self._mod_data).digest()

    def generate_date_based_mod_data(self) -> bool:
        """Update mod_data if the date has changed.

        Returns True if mod_data was updated.
        """
        now = datetime.now(timezone.utc)
        new_mod = now.strftime("%Y-%m-%d").encode("ascii")
        if new_mod != self._mod_data:
            self._mod_data = new_mod
            self._last_changed = time.monotonic()
            return True
        return False

    def get_time_till_midnight_utc(self) -> float:
        """Seconds until the next UTC midnight."""
        now = datetime.now(timezone.utc)
        tomorrow = now.replace(
            hour=0, minute=0, second=0, microsecond=0
        )
        # Move to next day
        from datetime import timedelta
        tomorrow += timedelta(days=1)
        return (tomorrow - now).total_seconds()

    @property
    def mod_data(self) -> bytes:
        return self._mod_data

    @property
    def last_changed(self) -> float:
        return self._last_changed