/**
 * MCP servers communicate over stdio, so ALL logs must go to stderr.
 * Never write logs to stdout — it corrupts the JSON-RPC stream.
 */
type Level = 'debug' | 'info' | 'warn' | 'error';

const LEVELS: Record<Level, number> = { debug: 10, info: 20, warn: 30, error: 40 };

function currentThreshold(): number {
  const env = (process.env.NEXUS_LOG_LEVEL || 'info').toLowerCase() as Level;
  return LEVELS[env] ?? LEVELS.info;
}

function emit(level: Level, scope: string, message: string, extra?: unknown): void {
  if (LEVELS[level] < currentThreshold()) return;
  const ts = new Date().toISOString();
  let line = `[${ts}] ${level.toUpperCase()} (${scope}) ${message}`;
  if (extra !== undefined) {
    try {
      line += ` ${typeof extra === 'string' ? extra : JSON.stringify(extra)}`;
    } catch {
      line += ' [unserializable extra]';
    }
  }
  process.stderr.write(line + '\n');
}

export interface Logger {
  debug(message: string, extra?: unknown): void;
  info(message: string, extra?: unknown): void;
  warn(message: string, extra?: unknown): void;
  error(message: string, extra?: unknown): void;
}

export function createLogger(scope: string): Logger {
  return {
    debug: (m, e) => emit('debug', scope, m, e),
    info: (m, e) => emit('info', scope, m, e),
    warn: (m, e) => emit('warn', scope, m, e),
    error: (m, e) => emit('error', scope, m, e),
  };
}