/**
 * IPC Layer - stdin/stdout JSON-line communication
 */

import { createInterface } from 'node:readline';
import type { FrontendMessage, BackendMessage } from '@tiny-workshop/ipc-types';

/**
 * Emit a message to the frontend via stdout
 *
 * Uses process.stdout.write directly to bypass stdout protection.
 * This is the ONLY place that should write to stdout!
 */
export function emit(msg: BackendMessage): void {
  process.stdout.write(JSON.stringify(msg) + '\n');
}

/**
 * Start listening for messages from frontend via stdin
 *
 * @param handler - Async function to handle each message
 */
export function startIpcListener(
  handler: (msg: FrontendMessage) => void | Promise<void>
): void {
  const rl = createInterface({
    input: process.stdin,
    crlfDelay: Infinity,
  });

  rl.on('line', async (line) => {
    // Skip empty lines
    if (!line.trim()) return;

    try {
      const msg = JSON.parse(line) as FrontendMessage;
      await handler(msg);
    } catch (error) {
      emit({
        type: 'error',
        code: 'PARSE_ERROR',
        message: `Failed to parse message: ${error}`,
        recoverable: true,
      });
    }
  });

  rl.on('close', () => {
    // Frontend closed stdin, exit gracefully
    process.exit(0);
  });
}