golfgame/tests/soak/core/logger.ts

/**
 * Structured JSONL logger for the soak harness.
 *
 * One JSON line per call, written to stdout by default. Child loggers
 * inherit parent meta so scenarios can bind room/game context once and
 * every subsequent call carries it automatically.
 */

import type { Logger, LogLevel } from './types';

const LEVEL_ORDER: Record<LogLevel, number> = {
  debug: 0,
  info: 1,
  warn: 2,
  error: 3,
};

export interface LoggerOptions {
  runId: string;
  minLevel?: LogLevel;
  /** Defaults to process.stdout.write bound to stdout. Override for tests. */
  write?: (line: string) => boolean;
  baseMeta?: Record<string, unknown>;
}

export function createLogger(opts: LoggerOptions): Logger {
  const minLevel = opts.minLevel ?? 'info';
  const write = opts.write ?? ((s: string) => process.stdout.write(s));
  const baseMeta = opts.baseMeta ?? {};

  function emit(level: LogLevel, msg: string, meta?: object): void {
    if (LEVEL_ORDER[level] < LEVEL_ORDER[minLevel]) return;
    const line = JSON.stringify({
      timestamp: new Date().toISOString(),
      level,
      msg,
      runId: opts.runId,
      ...baseMeta,
      ...(meta ?? {}),
    }) + '\n';
    write(line);
  }

  const logger: Logger = {
    debug: (msg, meta) => emit('debug', msg, meta),
    info: (msg, meta) => emit('info', msg, meta),
    warn: (msg, meta) => emit('warn', msg, meta),
    error: (msg, meta) => emit('error', msg, meta),
    child: (meta) =>
      createLogger({
        runId: opts.runId,
        minLevel,
        write,
        baseMeta: { ...baseMeta, ...meta },
      }),
  };

  return logger;
}