/**
 * WijiBoard – BLE Singleton
 * web/js/ble.js
 *
 * Provides a singleton BLE object with:
 *   BLE.connect()         → connects to device, gets characteristics
 *   BLE.disconnect()      → disconnects
 *   BLE.write(cmd)        → writes ASCII command (write-without-response)
 *   BLE.isConnected()     → boolean
 *   BLE.on(event, cb)     → subscribe to 'connected' | 'disconnected' | 'status'
 *   BLE.off(event, cb)    → unsubscribe
 *
 * Command characteristic (WRITE_NR):
 *   S1+<n>  → step motor 1 clockwise n steps
 *   S1-<n>  → step motor 1 counter-clockwise n steps
 *   S2+<n>  → step motor 2 clockwise n steps
 *   S2-<n>  → step motor 2 counter-clockwise n steps
 *   SPD:<n> → set max speed (steps/sec)
 *   ACC:<n> → set acceleration (steps/sec²)
 *   HOME    → zero both steppers
 *   POS     → request position report
 *
 * Status characteristic (NOTIFY):
 *   P:<s1>,<s2>  → current step positions for motor 1 & 2
 */

// ── UUIDs – must match src/main.cpp exactly ──────────────────────
const SERVICE_UUID = '18f3b235-9831-4c75-8ec0-210469b820a0';
const CMD_UUID = 'cd083b06-4447-4cf3-a7c3-322ecf802ce4';
const STATUS_UUID = '82e38c5b-d3ab-41d1-861c-b84dc6bb1e03';
const DEVICE_NAME = 'WijiBoard';

const BLE = (() => {
  // ── Internal state ──────────────────────────────────────────
  let device = null;
  let server = null;
  let cmdChar = null;
  let statusChar = null;
  const encoder = new TextEncoder();

  // ── Tiny event emitter ──────────────────────────────────────
  const listeners = {};

  function emit(event, ...args) {
    (listeners[event] || []).forEach(cb => {
      try { cb(...args); } catch (e) { console.error('[BLE] listener error', e); }
    });
  }

  function on(event, cb) {
    if (!listeners[event]) listeners[event] = [];
    listeners[event].push(cb);
  }

  function off(event, cb) {
    if (!listeners[event]) return;
    listeners[event] = listeners[event].filter(fn => fn !== cb);
  }

  // ── Disconnect handler ──────────────────────────────────────
  function onDisconnected() {
    console.log('[BLE] Device disconnected');
    device = null;
    server = null;
    cmdChar = null;
    statusChar = null;
    emit('disconnected');
  }

  // ── Status notification handler ─────────────────────────────
  function onStatusNotification(event) {
    const value = new TextDecoder().decode(event.target.value);
    emit('status', value.trim());
  }

  // ── connect() ───────────────────────────────────────────────
  async function connect() {
    console.log('[BLE] connect() called');
    if (!navigator.bluetooth) {
      throw new Error('Web Bluetooth API not available. Use Chrome/Edge over HTTPS or localhost.');
    }

    emit('connecting');

    console.log('[BLE] Requesting device...');
    device = await navigator.bluetooth.requestDevice({
      filters: [{ name: DEVICE_NAME }],
      optionalServices: [SERVICE_UUID],
    });
    console.log('[BLE] Device selected:', device.name);

    device.addEventListener('gattserverdisconnected', onDisconnected);

    console.log('[BLE] Connecting to GATT server...');
    server = await device.gatt.connect();
    console.log('[BLE] GATT server connected');

    console.log('[BLE] Getting primary service:', SERVICE_UUID);
    const service = await server.getPrimaryService(SERVICE_UUID);
    console.log('[BLE] Primary service found');

    console.log('[BLE] Getting command characteristic:', CMD_UUID);
    cmdChar = await service.getCharacteristic(CMD_UUID);
    console.log('[BLE] Command characteristic found');

    // Status notifications (optional – firmware may not have this char yet)
    try {
      console.log('[BLE] Getting status characteristic:', STATUS_UUID);
      statusChar = await service.getCharacteristic(STATUS_UUID);
      console.log('[BLE] Starting notifications...');
      await statusChar.startNotifications();
      statusChar.addEventListener('characteristicvaluechanged', onStatusNotification);
      console.log('[BLE] Notifications started');
    } catch (err) {
      console.warn('[BLE] Status characteristic not available – notifications disabled', err);
    }

    console.log('[BLE] Connection fully established, emitting connected');
    emit('connected', device.name);
  }

  // ── disconnect() ────────────────────────────────────────────
  async function disconnect() {
    if (device?.gatt?.connected) {
      device.gatt.disconnect();
    }
  }

  // ── write() ─────────────────────────────────────────────────
  async function write(cmd) {
    if (!cmdChar) throw new Error('BLE not connected');
    await cmdChar.writeValueWithoutResponse(encoder.encode(cmd));
    emit('sent', cmd);
  }

  // ── isConnected() ───────────────────────────────────────────
  function isConnected() {
    return !!(device?.gatt?.connected && cmdChar);
  }

  // ── getDeviceName() ─────────────────────────────────────────
  function getDeviceName() {
    return device?.name ?? null;
  }

  return {
    on, off, connect, disconnect, write, isConnected, getDeviceName,
    SERVICE_UUID, CMD_UUID, STATUS_UUID, DEVICE_NAME,
  };
})();

export default BLE;