// src/lib/serial/serial.service.ts
// Web Serial API implementation
// Requires: @types/w3c-web-serial

/**
 * 内部IO资源
 */
let reader: ReadableStreamDefaultReader<Uint8Array> | null = null;
let writer: WritableStreamDefaultWriter<Uint8Array> | null = null;

let isOpen = false;

/**
 * 判断当前环境是否支持Web Serial API
 */
export function isWebSerialSupported(): boolean {
  return typeof navigator !== 'undefined' && 'serial' in navigator;
}

/**
 * 请求用户选择串口设备
 */
export async function requestPort(
  filters?: SerialPortRequestOptions['filters']
): Promise<SerialPort | null> {
  if (!isWebSerialSupported()) {
    throw new Error('Web Serial API is not supported in this environment.');
  }

  const port = await navigator.serial.requestPort(
    filters ? { filters } : undefined
  );

  return port ?? null;
}

/**
 * 打开串口
 */
export async function openPort(
  port: SerialPort,
  options: SerialOptions
): Promise<void> {
  if (isOpen) {
    // 串口已经打开，直接返回
    return;
  }

  await port.open(options);
  isOpen = true;

  // 初始化reader和writer
  reader = port.readable?.getReader() ?? null;
  writer = port.writable?.getWriter() ?? null;
}

/**
 * 关闭串口
 */
export async function closePort(port: SerialPort) {
  if (!isOpen) {
    // 串口未打开，直接返回
    return;
  }

  await reader?.cancel();
  reader?.releaseLock();
  await writer?.close();
  writer?.releaseLock();

  reader = null;
  writer = null;
  isOpen = false;

  await port.close();
}

/**
 * 向串口写入数据
 */
export async function write(data: Uint8Array): Promise<void> {
  if (!writer) {
    throw new Error('Serial port is not writable.');
  }
  await writer.write(data);
}

/**
 * 开始读取串口数据循环
 */
export async function startReadLoop(
  onData: (chunk: Uint8Array) => void,
  onError?: (err: unknown) => void
): Promise<void> {
  if (!reader) {
    throw new Error('Serial port is not readable.');
  }

  try {
    while (true) {
      const { value, done } = await reader.read();
      if (done) break;
      if (value) onData(value);
    }
  } catch (err) {
    onError?.(err);
  }
}