BanGUI/backend/app/services/server_service.py

"""Server-level settings service.

Provides methods to read and update fail2ban server-level settings
(log level, log target, database configuration) via the Unix domain socket.
Also exposes the ``flushlogs`` command for use after log rotation.

Architecture note: this module is a pure service — it contains **no**
HTTP/FastAPI concerns.
"""

from __future__ import annotations

from typing import cast

import structlog

from app.models.server import ServerSettings, ServerSettingsResponse, ServerSettingsUpdate
from app.utils.fail2ban_client import Fail2BanClient, Fail2BanCommand, Fail2BanResponse

# ---------------------------------------------------------------------------
# Types
# ---------------------------------------------------------------------------

type Fail2BanSettingValue = str | int | bool
"""Allowed values for server settings commands."""

log: structlog.stdlib.BoundLogger = structlog.get_logger()

_SOCKET_TIMEOUT: float = 10.0


def _to_int(value: object | None, default: int) -> int:
    """Convert a raw value to an int, falling back to a default.

    The fail2ban control socket can return either int or str values for some
    settings, so we normalise them here in a type-safe way.
    """
    if isinstance(value, int):
        return value
    if isinstance(value, float):
        return int(value)
    if isinstance(value, str):
        try:
            return int(value)
        except ValueError:
            return default
    return default


def _to_str(value: object | None, default: str) -> str:
    """Convert a raw value to a string, falling back to a default."""
    if value is None:
        return default
    return str(value)


# ---------------------------------------------------------------------------
# Custom exceptions
# ---------------------------------------------------------------------------


class ServerOperationError(Exception):
    """Raised when a server-level set command fails."""


# ---------------------------------------------------------------------------
# Internal helpers
# ---------------------------------------------------------------------------


def _ok(response: Fail2BanResponse) -> object:
    """Extract payload from a fail2ban ``(code, data)`` response.

    Args:
        response: Raw value returned by :meth:`~Fail2BanClient.send`.

    Returns:
        The payload ``data`` portion of the response.

    Raises:
        ValueError: If the return code indicates an error.
    """
    try:
        code, data = response
    except (TypeError, ValueError) as exc:
        raise ValueError(f"Unexpected response shape: {response!r}") from exc
    if code != 0:
        raise ValueError(f"fail2ban error {code}: {data!r}")
    return data


async def _safe_get(
    client: Fail2BanClient,
    command: Fail2BanCommand,
    default: object | None = None,
) -> object | None:
    """Send a command and silently return *default* on any error.

    Args:
        client: The :class:`~app.utils.fail2ban_client.Fail2BanClient` to use.
        command: Command list to send.
        default: Fallback value.

    Returns:
        The successful response, or *default*.
    """
    try:
        response = await client.send(command)
        return _ok(cast("Fail2BanResponse", response))
    except Exception:
        return default


# ---------------------------------------------------------------------------
# Public API
# ---------------------------------------------------------------------------


async def get_settings(socket_path: str) -> ServerSettingsResponse:
    """Return current fail2ban server-level settings.

    Fetches log level, log target, syslog socket, database file path, purge
    age, and max matches in a single round-trip batch.

    Args:
        socket_path: Path to the fail2ban Unix domain socket.

    Returns:
        :class:`~app.models.server.ServerSettingsResponse`.

    Raises:
        ~app.utils.fail2ban_client.Fail2BanConnectionError: Socket unreachable.
    """
    import asyncio

    client = Fail2BanClient(socket_path=socket_path, timeout=_SOCKET_TIMEOUT)

    (
        log_level_raw,
        log_target_raw,
        syslog_socket_raw,
        db_path_raw,
        db_purge_age_raw,
        db_max_matches_raw,
    ) = await asyncio.gather(
        _safe_get(client, ["get", "loglevel"], "INFO"),
        _safe_get(client, ["get", "logtarget"], "STDOUT"),
        _safe_get(client, ["get", "syslogsocket"], None),
        _safe_get(client, ["get", "dbfile"], "/var/lib/fail2ban/fail2ban.sqlite3"),
        _safe_get(client, ["get", "dbpurgeage"], 86400),
        _safe_get(client, ["get", "dbmaxmatches"], 10),
    )

    log_level = _to_str(log_level_raw, "INFO").upper()
    log_target = _to_str(log_target_raw, "STDOUT")
    syslog_socket = _to_str(syslog_socket_raw, "") or None
    db_path = _to_str(db_path_raw, "/var/lib/fail2ban/fail2ban.sqlite3")
    db_purge_age = _to_int(db_purge_age_raw, 86400)
    db_max_matches = _to_int(db_max_matches_raw, 10)

    settings = ServerSettings(
        log_level=log_level,
        log_target=log_target,
        syslog_socket=syslog_socket,
        db_path=db_path,
        db_purge_age=db_purge_age,
        db_max_matches=db_max_matches,
    )

    log.info("server_settings_fetched")
    return ServerSettingsResponse(settings=settings)


async def update_settings(socket_path: str, update: ServerSettingsUpdate) -> None:
    """Apply *update* to fail2ban server-level settings.

    Only non-None fields in *update* are sent.

    Args:
        socket_path: Path to the fail2ban Unix domain socket.
        update: Partial update payload.

    Raises:
        ServerOperationError: If any ``set`` command is rejected.
        ~app.utils.fail2ban_client.Fail2BanConnectionError: Socket unreachable.
    """
    client = Fail2BanClient(socket_path=socket_path, timeout=_SOCKET_TIMEOUT)

    async def _set(key: str, value: Fail2BanSettingValue) -> None:
        try:
            response = await client.send(["set", key, value])
            _ok(cast("Fail2BanResponse", response))
        except ValueError as exc:
            raise ServerOperationError(f"Failed to set {key!r} = {value!r}: {exc}") from exc

    if update.log_level is not None:
        await _set("loglevel", update.log_level.upper())
    if update.log_target is not None:
        await _set("logtarget", update.log_target)
    if update.db_purge_age is not None:
        await _set("dbpurgeage", update.db_purge_age)
    if update.db_max_matches is not None:
        await _set("dbmaxmatches", update.db_max_matches)

    log.info("server_settings_updated")


async def flush_logs(socket_path: str) -> str:
    """Flush and re-open fail2ban log files.

    Useful after log rotation so the daemon starts writing to the newly
    created file rather than the old rotated one.

    Args:
        socket_path: Path to the fail2ban Unix domain socket.

    Returns:
        The response message from fail2ban (e.g. ``"OK"``) as a string.

    Raises:
        ServerOperationError: If the command is rejected.
        ~app.utils.fail2ban_client.Fail2BanConnectionError: Socket unreachable.
    """
    client = Fail2BanClient(socket_path=socket_path, timeout=_SOCKET_TIMEOUT)
    try:
        response = await client.send(["flushlogs"])
        result = _ok(cast("Fail2BanResponse", response))
        log.info("logs_flushed", result=result)
        return str(result)
    except ValueError as exc:
        raise ServerOperationError(f"flushlogs failed: {exc}") from exc