/** Minimal structured logger: one JSON line per entry in production, readable lines in dev. */
type Level = 'debug' | 'info' | 'warn' | 'error';

const LEVELS: Record<Level, number> = { debug: 10, info: 20, warn: 30, error: 40 };
const minLevel: Level = (process.env.LOG_LEVEL as Level | undefined) ?? (process.env.NODE_ENV === 'test' ? 'warn' : 'info');
const json = process.env.NODE_ENV === 'production';

function write(level: Level, msg: string, fields?: Record<string, unknown>) {
  if (LEVELS[level] < LEVELS[minLevel]) return;
  if (json) {
    const line = JSON.stringify({ t: new Date().toISOString(), level, msg, ...fields });
    (level === 'error' || level === 'warn' ? process.stderr : process.stdout).write(line + '\n');
    return;
  }
  const extra = fields && Object.keys(fields).length > 0 ? ' ' + JSON.stringify(fields, errorReplacer) : '';
  const out = `[game ${level}] ${msg}${extra}`;
  if (level === 'error') console.error(out);
  else if (level === 'warn') console.warn(out);
  else console.log(out);
}

function errorReplacer(_key: string, value: unknown) {
  if (value instanceof Error) return { name: value.name, message: value.message, stack: value.stack };
  return value;
}

export const log = {
  debug: (msg: string, fields?: Record<string, unknown>) => write('debug', msg, fields),
  info: (msg: string, fields?: Record<string, unknown>) => write('info', msg, fields),
  warn: (msg: string, fields?: Record<string, unknown>) => write('warn', msg, fields),
  error: (msg: string, fields?: Record<string, unknown>) => write('error', msg, fields),
};