super-productivity/packages/super-sync-server/src/logger.ts

import * as fs from 'fs';
import * as path from 'path';

const getTimestamp = (): string => new Date().toISOString();

let logFileStream: fs.WriteStream | null = null;

if (process.env.LOG_TO_FILE === 'true') {
  const logDir = path.join(process.cwd(), 'logs');
  if (!fs.existsSync(logDir)) {
    fs.mkdirSync(logDir);
  }
  logFileStream = fs.createWriteStream(path.join(logDir, 'app.log'), { flags: 'a' });
}

const writeToFile = (level: string, message: string, ...args: unknown[]) => {
  if (logFileStream) {
    const logEntry = JSON.stringify({
      timestamp: getTimestamp(),
      level,
      message,
      args: args.length ? args : undefined,
    });
    logFileStream.write(logEntry + '\n');
  }
};

export interface AuditLogEntry {
  event: string;
  userId: number;
  clientId?: string;
  opId?: string;
  entityType?: string;
  entityId?: string;
  errorCode?: string;
  reason?: string;
  ip?: string;
  [key: string]: unknown;
}

export const Logger = {
  debug: (message: string, ...args: unknown[]): void => {
    if (process.env.LOG_LEVEL === 'debug') {
      console.log(`${getTimestamp()} [DEBUG] ${message}`, ...args);
      writeToFile('DEBUG', message, ...args);
    }
  },
  info: (message: string, ...args: unknown[]): void => {
    console.log(`${getTimestamp()} [INFO] ${message}`, ...args);
    writeToFile('INFO', message, ...args);
  },
  warn: (message: string, ...args: unknown[]): void => {
    console.warn(`${getTimestamp()} [WARN] ${message}`, ...args);
    writeToFile('WARN', message, ...args);
  },
  error: (message: string, ...args: unknown[]): void => {
    console.error(`${getTimestamp()} [ERROR] ${message}`, ...args);
    writeToFile('ERROR', message, ...args);
  },

  /**
   * Structured audit log for security-relevant events.
   * Outputs JSON for easy parsing by log aggregation tools.
   *
   * Events:
   * - OP_REJECTED: Operation was rejected (validation, conflict, etc.)
   * - RATE_LIMITED: User hit rate limit
   * - AUTH_FAILED: Authentication attempt failed
   * - SUSPICIOUS_REQUEST: Request contained suspicious data
   */
  audit: (entry: AuditLogEntry): void => {
    const logEntry = {
      timestamp: getTimestamp(),
      level: 'AUDIT',
      ...entry,
    };
    console.log(JSON.stringify(logEntry));
    if (logFileStream) {
      logFileStream.write(JSON.stringify(logEntry) + '\n');
    }
  },
};