"""IRC server tunnel — exposes local IRC server as I2P destination.

Extends ServerTunnelTask with USER command mangling to replace
the connecting user's identity with an I2P-derived cloak,
preventing real hostname/IP leakage.

Ported from net.i2p.i2ptunnel.I2PTunnelIRCServer.
"""

from __future__ import annotations

import hashlib
import logging

from i2p_apps.i2ptunnel.config import TunnelDefinition, TunnelType
from i2p_apps.i2ptunnel.tasks import ServerTunnelTask

logger = logging.getLogger(__name__)


class IRCServerTask(ServerTunnelTask):
    """IRC server tunnel with USER command mangling.

    Accepts I2P connections and forwards to a local IRC server,
    replacing the USER command's username/hostname with an I2P-derived
    cloak so the real identity is never exposed.
    """

    def __init__(self, config: TunnelDefinition, session) -> None:
        super().__init__(config, session)

    def _compute_cloak(self, remote_dest: str) -> str:
        """Compute a deterministic .b32.i2p cloak from a destination.

        Uses SHA-256 of the destination to produce a stable,
        privacy-preserving identifier.
        """
        h = hashlib.sha256(remote_dest.encode("utf-8")).hexdigest()[:16]
        return f"{h}.b32.i2p"

    def _mangle_user(self, line: str, remote_dest: str) -> str:
        """Mangle a USER command, replacing the username with a cloak.

        If the line is not a USER command, returns it unchanged.
        Format: USER <username> <mode> <unused> :<realname>
        """
        if not line.upper().startswith("USER "):
            return line

        parts = line.split(" ", 4)
        if len(parts) < 5:
            return line

        cloak = self._compute_cloak(remote_dest)
        # Replace username (parts[1]) with cloak, preserve realname
        parts[1] = cloak
        return " ".join(parts)