/**
* Logger utility for Back-Agent MCP Server
*
* IMPORTANT: All logs must go to stderr to avoid interfering with
* the MCP stdio communication (which uses stdout for JSON-RPC messages).
*
* Logs are written to both stderr and optionally to a file.
*/
import { appendFileSync, existsSync, mkdirSync } from 'fs';
import { dirname, resolve } from 'path';
export enum LogLevel {
DEBUG = 0,
INFO = 1,
WARN = 2,
ERROR = 3,
}
let currentLogLevel: LogLevel = LogLevel.INFO;
let logFilePath: string | null = null;
/**
* Initialize file logging
* @param filePath Path to the log file. If relative, resolves from current working directory
*/
export function initLogFile(filePath?: string): void {
const path = filePath || process.env.LOG_FILE;
if (!path) {
return;
}
// Resolve relative paths from current working directory
logFilePath = resolve(process.cwd(), path);
// Create directory if it doesn't exist
const logDir = dirname(logFilePath);
if (!existsSync(logDir)) {
mkdirSync(logDir, { recursive: true });
}
// Write startup marker
const separator = '='.repeat(60);
const startMsg = `${separator}\n[Back-Agent MCP] Logging started at ${new Date().toISOString()}\n${separator}\n`;
appendFileSync(logFilePath, startMsg);
}
/**
* Set the current log level
*/
export function setLogLevel(level: LogLevel): void {
currentLogLevel = level;
}
/**
* Format timestamp for log messages
*/
function getTimestamp(): string {
return new Date().toISOString();
}
/**
* Write log message to file
*/
function writeToFile(message: string): void {
if (!logFilePath) {
return;
}
try {
appendFileSync(logFilePath, message + '\n');
} catch (error) {
// Silently fail to avoid infinite loop if logging fails
// The error will still be visible in stderr
}
}
/**
* Write log message to stderr
*/
function log(level: LogLevel, message: string, ...args: unknown[]): void {
if (level < currentLogLevel) {
return;
}
const levelName = LogLevel[level];
const timestamp = getTimestamp();
const prefix = `[${timestamp}] [${levelName}]`;
const output = args.length > 0
? `${prefix} ${message} ${args.map(String).join(' ')}`
: `${prefix} ${message}`;
// Always write to stderr to avoid interfering with MCP stdio communication
console.error(output);
// Also write to file if enabled
writeToFile(output);
}
export const logger = {
debug: (message: string, ...args: unknown[]) => log(LogLevel.DEBUG, message, ...args),
info: (message: string, ...args: unknown[]) => log(LogLevel.INFO, message, ...args),
warn: (message: string, ...args: unknown[]) => log(LogLevel.WARN, message, ...args),
error: (message: string, ...args: unknown[]) => log(LogLevel.ERROR, message, ...args),
};
