"""Multicast DNS Service Discovery for Python, v0.14-wmcbrine
Copyright 2003 Paul Scott-Murphy, 2014 William McBrine

This module provides a framework for the use of DNS Service Discovery
using IP multicast.

This library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.

This library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.

You should have received a copy of the GNU Lesser General Public
License along with this library; if not, write to the Free Software
Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301
USA
"""

from __future__ import annotations

import asyncio
import logging
import random
from functools import partial
from typing import TYPE_CHECKING, cast

from ._logger import QuietLogger, log
from ._protocol.incoming import DNSIncoming
from ._transport import _WrappedTransport, make_wrapped_transport
from ._utils.time import current_time_millis, millis_to_seconds
from .const import (
    _DUPLICATE_PACKET_SUPPRESSION_INTERVAL,
    _MAX_DEFERRED_ADDRS,
    _MAX_DEFERRED_PER_ADDR,
    _MAX_MSG_ABSOLUTE,
    _RECENT_PACKETS_MAX,
)

if TYPE_CHECKING:
    from ._core import Zeroconf

_TC_DELAY_RANDOM_INTERVAL = (400, 500)


_bytes = bytes
_str = str
_int = int
_float = float

DEBUG_ENABLED = partial(log.isEnabledFor, logging.DEBUG)


class AsyncListener:
    """A Listener is used by this module to listen on the multicast
    group to which DNS messages are sent, allowing the implementation
    to cache information as it arrives.

    It requires registration with an Engine object in order to have
    the read() method called when a socket is available for reading."""

    __slots__ = (
        "_deferred",
        "_deferred_deadlines",
        "_query_handler",
        "_recent_packets",
        "_record_manager",
        "_registry",
        "_timers",
        "data",
        "last_message",
        "last_time",
        "sock_description",
        "transport",
        "zc",
    )

    def __init__(self, zc: Zeroconf) -> None:
        self.zc = zc
        self._registry = zc.registry
        self._record_manager = zc.record_manager
        self._query_handler = zc.query_handler
        self.data: bytes | None = None
        self.last_time: float = 0
        self.last_message: DNSIncoming | None = None
        self.transport: _WrappedTransport | None = None
        self.sock_description: str | None = None
        self._deferred: dict[str, list[DNSIncoming]] = {}
        self._timers: dict[str, asyncio.TimerHandle] = {}
        self._deferred_deadlines: dict[str, float] = {}
        # Bounded recency window so an alternating (A, B, A, B, ...)
        # flood cannot defeat single-slot dedup; relies on dict insertion
        # order so the oldest entry is evicted first. Only payloads
        # without a QU question are cached so unicast replies still go
        # out on every receipt.
        self._recent_packets: dict[bytes, float] = {}
        super().__init__()

    def datagram_received(self, data: _bytes, addrs: tuple[str, int] | tuple[str, int, int, int]) -> None:
        data_len = len(data)
        debug = DEBUG_ENABLED()

        if data_len > _MAX_MSG_ABSOLUTE:
            # Guard against oversized packets to ensure bad implementations cannot overwhelm
            # the system.
            if debug:
                log.debug(
                    "Discarding incoming packet with length %s, which is larger "
                    "than the absolute maximum size of %s",
                    data_len,
                    _MAX_MSG_ABSOLUTE,
                )
            return
        now = current_time_millis()
        self._process_datagram_at_time(debug, data_len, now, data, addrs)

    def _process_datagram_at_time(
        self,
        debug: bool,
        data_len: _int,
        now: _float,
        data: _bytes,
        addrs: tuple[str, int] | tuple[str, int, int, int],
    ) -> None:
        if (
            self.data == data
            and (now - _DUPLICATE_PACKET_SUPPRESSION_INTERVAL) < self.last_time
            and self.last_message is not None
            and not self.last_message.has_qu_question()
        ):
            # Guard against duplicate packets
            if debug:
                log.debug(
                    "Ignoring duplicate message with no unicast questions"
                    " received from %s [socket %s] (%d bytes) as [%r]",
                    addrs,
                    self.sock_description,
                    data_len,
                    data,
                )
            return

        # `get(data, -1e30)` keeps the suppression compare a single C
        # double compare; the sentinel is far below any real `now -
        # _DUPLICATE_PACKET_SUPPRESSION_INTERVAL` so a cache miss never
        # triggers the branch even when `now` is small (time.monotonic
        # is allowed to start near zero, leaving `now - INTERVAL`
        # negative for the first ~1s after boot). Only non-QU payloads
        # are cached, so any hit here is safe to suppress without re-
        # checking has_qu_question.
        recent_time = self._recent_packets.get(data, -1e30)
        if (now - _DUPLICATE_PACKET_SUPPRESSION_INTERVAL) < recent_time:
            # No timestamp refresh on hit so the suppression window
            # ends at first-observation + interval; one parse-and-
            # dispatch fires per payload per interval, capping the
            # CPU cost under a sustained alternating flood.
            if debug:
                log.debug(
                    "Ignoring duplicate message with no unicast questions"
                    " received from %s [socket %s] (%d bytes) as [%r]",
                    addrs,
                    self.sock_description,
                    data_len,
                    data,
                )
            return

        if len(addrs) == 2:
            v6_flow_scope: tuple[()] | tuple[int, int] = ()
            # https://github.com/python/mypy/issues/1178
            addr, port = addrs
            addr_port = addrs
            if TYPE_CHECKING:
                addr_port = cast(tuple[str, int], addr_port)
            scope = None
        else:
            # https://github.com/python/mypy/issues/1178
            addr, port, flow, scope = addrs
            if debug:  # pragma: no branch
                log.debug("IPv6 scope_id %d associated to the receiving interface", scope)
            v6_flow_scope = (flow, scope)
            addr_port = (addr, port)

        msg = DNSIncoming(data, addr_port, scope, now)
        self.data = data
        self.last_time = now
        self.last_message = msg
        if not msg.has_qu_question():
            # Refresh LRU position when an entry exists but the
            # suppression window has expired; otherwise evict the oldest
            # entry once the window is full.
            if data in self._recent_packets:
                del self._recent_packets[data]
            elif len(self._recent_packets) >= _RECENT_PACKETS_MAX:
                del self._recent_packets[next(iter(self._recent_packets))]
            self._recent_packets[data] = now
        if msg.valid is True:
            if debug:
                log.debug(
                    "Received from %r:%r [socket %s]: %r (%d bytes) as [%r]",
                    addr,
                    port,
                    self.sock_description,
                    msg,
                    data_len,
                    data,
                )
        else:
            if debug:
                log.debug(
                    "Received from %r:%r [socket %s]: (%d bytes) [%r]",
                    addr,
                    port,
                    self.sock_description,
                    data_len,
                    data,
                )
            return

        if not msg.is_query():
            self._record_manager.async_updates_from_response(msg)
            return

        if not self._registry.has_entries:
            # If the registry is empty, we have no answers to give.
            return

        if TYPE_CHECKING:
            assert self.transport is not None
        self.handle_query_or_defer(msg, addr, port, self.transport, v6_flow_scope)

    def handle_query_or_defer(
        self,
        msg: DNSIncoming,
        addr: _str,
        port: _int,
        transport: _WrappedTransport,
        v6_flow_scope: tuple[()] | tuple[int, int],
    ) -> None:
        """Deal with incoming query packets.  Provides a response if
        possible."""
        if not msg.truncated:
            self._respond_query(msg, addr, port, transport, v6_flow_scope)
            return

        if addr not in self._deferred and len(self._deferred) >= _MAX_DEFERRED_ADDRS:
            # Bound total deferred addrs so a spoofed-source flood
            # cannot keep adding distinct entries; evict the oldest
            # (insertion-order) entry and discard its in-flight queue.
            self._evict_oldest_deferred()

        deferred = self._deferred.setdefault(addr, [])
        if len(deferred) >= _MAX_DEFERRED_PER_ADDR:
            # Bound per-addr queue length; further fragments from the
            # same source are dropped until the timer flushes.
            return
        # If we get the same packet we ignore it
        for incoming in reversed(deferred):
            if incoming.data == msg.data:
                return
        deferred.append(msg)
        loop = self.zc.loop
        assert loop is not None
        now = loop.time()
        delay = millis_to_seconds(random.randint(*_TC_DELAY_RANDOM_INTERVAL))  # noqa: S311
        fire_at = self._compute_deferred_fire_at(addr, now, delay)
        if fire_at < 0.0:
            # Sentinel: a new reset would push the flush past the
            # per-addr reassembly deadline, so leave the existing
            # TimerHandle in place rather than re-arming it.
            return
        self._cancel_any_timers_for_addr(addr)
        self._timers[addr] = loop.call_at(
            fire_at,
            self._respond_query,
            None,
            addr,
            port,
            transport,
            v6_flow_scope,
        )

    def _compute_deferred_fire_at(self, addr: _str, now: _float, delay: _float) -> _float:
        """Return the bounded call_at time for a TC-deferred flush, or -1.0 to keep the existing timer."""
        # RFC 6762 §18.5 frames the random delay as a fixed reassembly budget
        # starting at first arrival, not a sliding heartbeat.
        deadline = self._deferred_deadlines.get(addr)
        if deadline is None:
            deadline = now + millis_to_seconds(_TC_DELAY_RANDOM_INTERVAL[1])
            self._deferred_deadlines[addr] = deadline
        fire_at = now + delay
        if fire_at >= deadline:
            if addr in self._timers:
                # Existing timer already fires at or before the deadline;
                # signal the caller to leave it alone rather than reset it.
                return -1.0
            # First packet for this addr already proposes a fire-time at
            # or past the deadline — clamp to the deadline so the flush
            # still happens within the reassembly budget.
            return deadline
        # Within budget: schedule at the proposed fire-time.
        return fire_at

    def _cancel_any_timers_for_addr(self, addr: _str) -> None:
        """Cancel any future truncated packet timers for the address."""
        if addr in self._timers:
            self._timers.pop(addr).cancel()

    def _drop_deferred(self, addr: _str) -> None:
        """Cancel an address's timer and discard its reassembly state."""
        self._cancel_any_timers_for_addr(addr)
        self._deferred_deadlines.pop(addr, None)
        self._deferred.pop(addr, None)

    def cancel_pending_timers(self) -> None:
        """Cancel all pending TC-reassembly timers and drop deferred state.

        Called when this listener's transport is removed so a timer cannot
        fire a response against an already-closed transport. Every timer's
        addr also has a deferred entry, so dropping each deferred addr
        cancels its timer too.
        """
        for addr in list(self._deferred):
            self._drop_deferred(addr)

    def _evict_oldest_deferred(self) -> None:
        """Discard the oldest deferred addr's reassembly state.

        Used when ``_MAX_DEFERRED_ADDRS`` would be exceeded; the
        evicted addr's queue and timer are dropped without firing, so
        the bound holds even when an attacker rotates source IPs.
        Eviction is FIFO (oldest by first-seen, via dict insertion
        order) rather than LRU so an active flooder cannot pin its
        slots by re-sending into the same addr.
        """
        self._drop_deferred(next(iter(self._deferred)))

    def _respond_query(
        self,
        msg: DNSIncoming | None,
        addr: _str,
        port: _int,
        transport: _WrappedTransport,
        v6_flow_scope: tuple[()] | tuple[int, int],
    ) -> None:
        """Respond to a query and reassemble any truncated deferred packets."""
        self._cancel_any_timers_for_addr(addr)
        self._deferred_deadlines.pop(addr, None)
        packets = self._deferred.pop(addr, [])
        if msg:
            packets.append(msg)

        self._query_handler.handle_assembled_query(packets, addr, port, transport, v6_flow_scope)

    def error_received(self, exc: Exception) -> None:
        """Likely socket closed or IPv6."""
        # We preformat the message string with the socket as we want
        # log_exception_once to log a warning message once PER EACH
        # different socket in case there are problems with multiple
        # sockets
        msg_str = f"Error with socket {self.sock_description}): %s"
        QuietLogger.log_exception_once(exc, msg_str, exc)

    def connection_made(self, transport: asyncio.BaseTransport) -> None:
        wrapped_transport = make_wrapped_transport(cast(asyncio.DatagramTransport, transport))
        self.transport = wrapped_transport
        self.sock_description = f"{wrapped_transport.fileno} ({wrapped_transport.sock_name})"

    def connection_lost(self, exc: Exception | None) -> None:
        """Handle connection lost."""
