"""MessageValidator — reject expired, far-future, and duplicate I2NP messages.

Ported from net.i2p.router.MessageValidator.

Uses a DecayingBloomFilter to detect duplicate messages. Messages are
identified by their (message_id XOR truncated_expiration) fingerprint.
"""

from __future__ import annotations

import struct
import time

from i2p_router.bloom_filter import DecayingBloomFilter


class MessageValidator:
    """Validate inbound I2NP messages for expiration and duplicates."""

    # Java I2P uses 65 seconds of clock fudge
    CLOCK_FUDGE_FACTOR_MS = 65_000

    def __init__(self, bloom_filter: DecayingBloomFilter | None = None) -> None:
        if bloom_filter is None:
            bloom_filter = DecayingBloomFilter(
                "msg-validator", duration_seconds=600, expected_entries=50000
            )
        self._bloom = bloom_filter

    def validate_message(
        self, message_id: int, expiration_ms: int, now_ms: int | None = None
    ) -> bool:
        """Return True if the message should be accepted.

        Rejects expired, far-future, and duplicate messages.
        """
        if now_ms is None:
            now_ms = int(time.time() * 1000)

        if self._is_expired(expiration_ms, now_ms):
            return False
        if self._is_too_far_future(expiration_ms, now_ms):
            return False
        if self._is_duplicate(message_id, expiration_ms):
            return False
        return True

    def _is_expired(self, expiration_ms: int, now_ms: int) -> bool:
        """True if message has expired (with 1.5x fudge)."""
        return now_ms > expiration_ms + int(self.CLOCK_FUDGE_FACTOR_MS * 1.5)

    def _is_too_far_future(self, expiration_ms: int, now_ms: int) -> bool:
        """True if expiration is unreasonably far in the future."""
        return expiration_ms > now_ms + self.CLOCK_FUDGE_FACTOR_MS * 4

    def _is_duplicate(self, message_id: int, expiration_ms: int) -> bool:
        """True if we've already seen this message."""
        # Fingerprint: XOR message_id with truncated expiration
        exp_trunc = expiration_ms & 0xFFFFFFFF
        fingerprint = struct.pack("!I", message_id ^ exp_trunc)
        return self._bloom.add(fingerprint)