logger.ts

import winston from 'winston';
import DailyRotateFile from 'winston-daily-rotate-file';

const isDev = process.env['NODE_ENV'] !== 'production';

const devPrintf = winston.format.printf((info) => {
  const { timestamp, level, message, ...meta } = info as Record<string, unknown>;
  const metaStr = Object.keys(meta).length ? '\n' + JSON.stringify(meta, null, 2) : '';
  return `${timestamp} [${level}] ${message}${metaStr}`;
});

/** Format for the Console transport — colorized in dev for readability. */
const consoleFormat = isDev
  ? winston.format.combine(
      winston.format.colorize(),
      winston.format.timestamp({ format: 'HH:mm:ss' }),
      devPrintf,
    )
  : winston.format.combine(winston.format.timestamp(), winston.format.json());

/** Format for file transports — no ANSI escape codes, safe for log parsers. */
const fileFormat = isDev
  ? winston.format.combine(winston.format.timestamp({ format: 'HH:mm:ss' }), devPrintf)
  : winston.format.combine(winston.format.timestamp(), winston.format.json());

/**
 * Creates a console-only fallback logger used as the initial singleton value
 * before {@link createLogger} is called by main.ts.
 */
function createConsoleOnlyLogger(): winston.Logger {
  return winston.createLogger({
    level: isDev ? 'debug' : 'info',
    format: consoleFormat,
    transports: [new winston.transports.Console()],
  });
}

/**
 * Module-level logger singleton.  Initially console-only; reassigned (as a
 * live ESM binding) when {@link createLogger} is called from main.ts so that
 * all existing importers automatically see the upgraded instance.
 */
export let logger: winston.Logger = createConsoleOnlyLogger();

/**
 * Creates a full winston logger with both a Console transport and a
 * DailyRotateFile transport that writes to `logDir`.  Also reassigns the
 * exported {@link logger} singleton so that modules that imported it before
 * `main.ts` started still get the upgraded instance.
 *
 * @param logDir - Directory in which daily log files will be written.
 * @returns The newly created {@link winston.Logger} instance.
 */
export function createLogger(logDir: string): winston.Logger {
  const newLogger = winston.createLogger({
    level: isDev ? 'debug' : 'info',
    transports: [
      new winston.transports.Console({ format: consoleFormat }),
      new DailyRotateFile({
        format: fileFormat,
        dirname: logDir,
        filename: 'main-%DATE%.log',
        datePattern: 'YYYY-MM-DD',
        maxFiles: '14d',
      }),
    ],
  });

  // Reassign the live ESM binding so importers see the upgraded instance.
  logger = newLogger;
  return newLogger;
}