import { describe, it, expect } from 'vitest';
import { readStdinAsUtf8 } from './router-stdin-helper.mjs';

async function* fromBuffers(buffers) {
  for (const b of buffers) yield b;
}

describe('readStdinAsUtf8', () => {
  it('decodes UTF-8 cyrillic correctly across chunk boundaries', async () => {
    const text = 'посмотри сторожа достаточно ему информации?';
    const buf = Buffer.from(text, 'utf-8');
    // Split across multi-byte boundary (UTF-8 cyrillic = 2 bytes per char)
    const mid = 9; // mid-byte split for 'посмо|три...'
    const result = await readStdinAsUtf8(fromBuffers([buf.subarray(0, mid), buf.subarray(mid)]));
    expect(result).toBe(text);
  });

  it('handles ASCII without modification', async () => {
    const text = 'hello world';
    const result = await readStdinAsUtf8(fromBuffers([Buffer.from(text)]));
    expect(result).toBe(text);
  });

  it('returns empty string on empty stream', async () => {
    const result = await readStdinAsUtf8(fromBuffers([]));
    expect(result).toBe('');
  });

  it('does NOT mangle byte-level concatenation (regression guard)', async () => {
    // The bug: `for await (const c of stdin) input += c` interprets Buffer
    // via Buffer.prototype.toString() = 'utf-8' by default in Node, BUT
    // concatenation across chunks at multi-byte boundary fails.
    // Our helper must use a StringDecoder to handle the boundary.
    const cyrillic = 'тест';
    const buf = Buffer.from(cyrillic, 'utf-8');
    // Split exactly in the middle of 'т' (2-byte char)
    const result = await readStdinAsUtf8(fromBuffers([buf.subarray(0, 1), buf.subarray(1)]));
    expect(result).toBe(cyrillic);
  });
});