languard-servers-manager/backend/core/threads/log_tail.py

"""
LogTailThread — tails a server's log file, parses lines via LogParser,
and persists parsed entries to the logs table.

Design notes:
- Opens the log file in text mode with errors="replace" to handle encoding issues
- Detects log rotation by checking if the inode changes (Unix) or file shrinks (Windows)
- On rotation: closes old handle, reopens from position 0
- Flushes inserts in batches of up to LOG_BATCH_SIZE per loop iteration
"""
from __future__ import annotations

import logging
import os
import queue
from pathlib import Path
from typing import Callable, Optional

from core.dal.log_repository import LogRepository
from core.threads.base_thread import BaseServerThread

logger = logging.getLogger(__name__)

_LOG_BATCH_SIZE = 50
_POLL_INTERVAL = 1.0
_REOPEN_DELAY = 2.0


class LogTailThread(BaseServerThread):
    """
    Tails a log file for a specific server.

    Args:
        server_id: The database server ID.
        log_path: Absolute path to the log file to tail.
        log_parser: LogParser adapter instance for this game type.
        broadcast_queue: Optional queue.Queue to push parsed events to BroadcastThread.
    """

    def __init__(
        self,
        server_id: int,
        log_path: str,
        log_parser,
        broadcast_queue=None,
    ) -> None:
        super().__init__(server_id, "LogTail")
        self._log_path = log_path
        self._log_parser = log_parser
        self._broadcast_queue = broadcast_queue
        self._file_handle = None
        self._last_inode = None
        self._last_size = 0

    # ── Lifecycle ──

    def _on_start(self) -> None:
        self._open_log_file()

    def _on_stop(self) -> None:
        self._close_file()

    # ── Main loop ──

    def _run_loop(self) -> None:
        if self._file_handle is None:
            self._stop_event.wait(timeout=_POLL_INTERVAL)
            self._open_log_file()
            return

        if self._detect_rotation():
            logger.info("[%s] Log rotation detected, reopening", self.name)
            self._close_file()
            self._stop_event.wait(timeout=_REOPEN_DELAY)
            self._open_log_file()
            return

        lines_read = 0
        entries_to_insert = []

        while lines_read < _LOG_BATCH_SIZE:
            line = self._file_handle.readline()
            if not line:
                break
            lines_read += 1
            line = line.rstrip("\n").rstrip("\r")
            if not line:
                continue

            parsed = self._log_parser.parse_line(line)
            if parsed is not None:
                entries_to_insert.append(parsed)

        if entries_to_insert and self._db is not None:
            log_repo = LogRepository(self._db)
            for entry in entries_to_insert:
                log_repo.insert(server_id=self.server_id, entry=entry)
            try:
                self._db.commit()
            except Exception as exc:
                logger.error("[%s] DB commit failed: %s", self.name, exc)
                self._db.rollback()

            if self._broadcast_queue is not None:
                for entry in entries_to_insert:
                    try:
                        self._broadcast_queue.put_nowait({
                            "type": "log",
                            "server_id": self.server_id,
                            "data": entry,
                        })
                    except queue.Full:
                        logger.debug("[%s] Broadcast queue full, dropping log event", self.name)

        if lines_read == 0:
            self._stop_event.wait(timeout=_POLL_INTERVAL)

    # ── File management ──

    def _open_log_file(self) -> None:
        if not os.path.exists(self._log_path):
            return
        try:
            self._file_handle = open(
                self._log_path, "r", encoding="utf-8", errors="replace"
            )
            # Start tailing from the end of the file
            self._file_handle.seek(0, 2)
            self._last_size = self._file_handle.tell()
            stat = os.stat(self._log_path)
            self._last_inode = getattr(stat, "st_ino", None)
            logger.debug("[%s] Opened log file: %s", self.name, self._log_path)
        except OSError as exc:
            logger.warning("[%s] Cannot open log file %s: %s", self.name, self._log_path, exc)
            self._file_handle = None

    def _close_file(self) -> None:
        if self._file_handle is not None:
            try:
                self._file_handle.close()
            except OSError as exc:
                logger.debug("[%s] Error closing log file: %s", self.name, exc)
            self._file_handle = None
            self._last_inode = None
            self._last_size = 0

    def _detect_rotation(self) -> bool:
        """Returns True if the log file has been rotated."""
        try:
            stat = os.stat(self._log_path)
        except OSError:
            return True

        current_inode = getattr(stat, "st_ino", None)
        if current_inode is not None and self._last_inode is not None:
            if current_inode != self._last_inode:
                return True

        # Windows fallback: file shrunk
        current_size = stat.st_size
        if self._file_handle is not None:
            current_pos = self._file_handle.tell()
            if current_size < current_pos:
                return True
            self._last_size = current_size

        return False