// ble.js — Web Bluetooth client for the BabyMobile XIAO firmware.
//
// Protocol (see baby_mobile_v2.ino):
//   Service 12340001-…
//   Cmd  char 12340002 (write):           0x02 <track>  start upload to slot
//                                          0x03          finish upload + reload tracks
//                                          0x04 <track>  play slot
//                                          0x05          stop playback
//   Data char 12340003 (write-w/o-resp):  raw WAV bytes (header included)
//   Stat char 12340004 (read/notify):     uint32 BE = cumulative bytes written
//
// The firmware stores the WAV intact and parses bit-depth / sample-rate from the
// header at load time, so we just stream a conformant WAV file as-is.

export const SVC_UUID  = '12340001-0000-1000-8000-00805f9b34fb';
export const CMD_UUID  = '12340002-0000-1000-8000-00805f9b34fb';
export const DATA_UUID = '12340003-0000-1000-8000-00805f9b34fb';
export const STAT_UUID = '12340004-0000-1000-8000-00805f9b34fb';

export const CMD_UPLOAD_START = 0x02;
export const CMD_UPLOAD_END   = 0x03;
export const CMD_PLAY         = 0x04;
export const CMD_STOP         = 0x05;
export const CMD_LIST         = 0x06;
export const CMD_DELETE       = 0x07;
export const CMD_SET_VOL      = 0x08;
export const CMD_GET_VOL      = 0x09;

// Status-notification tags in byte 0 (see firmware):
//   0x00      → upload progress: whole packet is uint32 BE byte count (files <16 MB)
//   0x80|idx  → list entry:  [0x80|idx, bits, rate_kHz, duration_s]
//   0xC0      → volume reply: [0xC0, percent, 0, 0]
//   0xD0      → delete reply: [0xD0, idx, success, 0]
//   0xFF      → list end:    [0xFF, num_tracks, 0, 0]
const TAG_LIST_END = 0xff;
const TAG_DELETE   = 0xd0;
const TAG_VOLUME   = 0xc0;

export const MAX_TRACKS = 32;

// ATT MTU is negotiated to 247 (firmware requests via requestMtuExchange(247)).
// Write-without-response payload = MTU - 3 = 244 bytes.
const DATA_CHUNK = 244;

export function isSupported() {
  return typeof navigator !== 'undefined' && !!navigator.bluetooth;
}

export class BabyMobile extends EventTarget {
  constructor() {
    super();
    this.device = null;
    this.server = null;
    this.cmd = null;
    this.data = null;
    this.stat = null;
    this._statBytes = 0;
    this._onStat = this._onStat.bind(this);
    this._onDisconnect = this._onDisconnect.bind(this);
    this._connecting = false;
  }

  get connected() {
    return !!(this.device && this.device.gatt && this.device.gatt.connected);
  }

  _log(msg) {
    this.dispatchEvent(new CustomEvent('log', { detail: msg }));
  }

  _emit(type, detail) {
    this.dispatchEvent(new CustomEvent(type, { detail }));
  }

  async connect() {
    if (!isSupported()) {
      throw new Error('Web Bluetooth is not available in this browser. On iOS use the Bluefy browser; on desktop/Android use Chrome or Edge.');
    }
    if (this._connecting) throw new Error('Already connecting…');
    this._connecting = true;
    try {
      // Tear down any stale device/handle from a previous session so reconnects
      // don't trip over a half-open GATT or duplicate event listeners.
      this._teardown();

      this._log('Requesting device…');
      // Primary match is the 128-bit service UUID (rock solid). The name filter is
      // a loose prefix because the advertised name may be radio-truncated.
      this.device = await navigator.bluetooth.requestDevice({
        filters: [{ services: [SVC_UUID] }, { namePrefix: 'Baby' }],
        optionalServices: [SVC_UUID],
      });
      this.device.addEventListener('gattserverdisconnected', this._onDisconnect);

      await this._connectGatt(3);
      this._log('Connected.');
      this._emit('connected', { name: this.device.name });
      return this.device.name;
    } finally {
      this._connecting = false;
    }
  }

  // Connect + discover with retries. A freshly-disconnected peripheral often
  // leaves the link half-open for a moment; the first attempt then fails with
  // "Connection failed"/"GATT operation failed" until a browser refresh. Retrying
  // after an explicit disconnect + short backoff recovers without a refresh.
  async _connectGatt(attempts) {
    let lastErr;
    for (let i = 0; i < attempts; i++) {
      try {
        if (this.device.gatt.connected) this.device.gatt.disconnect();
        this._log(`Connecting${i ? ` (retry ${i})` : ''} to ${this.device.name || 'device'}…`);
        this.server = await this.device.gatt.connect();
        const svc = await this.server.getPrimaryService(SVC_UUID);
        this.cmd  = await svc.getCharacteristic(CMD_UUID);
        this.data = await svc.getCharacteristic(DATA_UUID);
        this.stat = await svc.getCharacteristic(STAT_UUID);
        await this.stat.startNotifications();
        this.stat.addEventListener('characteristicvaluechanged', this._onStat);
        return;
      } catch (err) {
        lastErr = err;
        this._log(`Connect attempt ${i + 1} failed: ${err.message || err}`);
        try { this.device.gatt.disconnect(); } catch {}
        if (i < attempts - 1) await new Promise((r) => setTimeout(r, 600));
      }
    }
    throw lastErr;
  }

  async disconnect() {
    if (this.device && this.device.gatt && this.device.gatt.connected) {
      this.device.gatt.disconnect();
    }
  }

  // Fully detach the current device + listeners (used before a fresh connect).
  _teardown() {
    if (this.stat) {
      try { this.stat.removeEventListener('characteristicvaluechanged', this._onStat); } catch {}
    }
    if (this.device) {
      try { this.device.removeEventListener('gattserverdisconnected', this._onDisconnect); } catch {}
      try { if (this.device.gatt.connected) this.device.gatt.disconnect(); } catch {}
    }
    this.device = this.server = this.cmd = this.data = this.stat = null;
  }

  _onDisconnect() {
    this._log('Disconnected.');
    if (this.stat) {
      try { this.stat.removeEventListener('characteristicvaluechanged', this._onStat); } catch {}
    }
    this.server = this.cmd = this.data = this.stat = null;
    this._emit('disconnected', {});
  }

  _onStat(ev) {
    const dv = ev.target.value;
    if (dv.byteLength < 1) return;
    const tag = dv.getUint8(0);

    if (tag === TAG_LIST_END && dv.byteLength >= 2) {
      this._emit('list-end', { numTracks: dv.getUint8(1) });
    } else if (tag === TAG_VOLUME && dv.byteLength >= 2) {
      this._emit('volume', { percent: dv.getUint8(1) });
    } else if (tag === TAG_DELETE && dv.byteLength >= 3) {
      this._emit('deleted', { idx: dv.getUint8(1), success: dv.getUint8(2) === 1 });
    } else if ((tag & 0x80) && (tag & 0x7f) < MAX_TRACKS && dv.byteLength >= 4) {
      this._emit('list-entry', {
        idx: tag & 0x7f,
        bits: dv.getUint8(1),
        rate: dv.getUint8(2) * 1000,
        durationSec: dv.getUint8(3),
      });
    } else if (dv.byteLength >= 4) {
      this._statBytes = dv.getUint32(0, false); // big-endian byte count
      this._emit('progress', { bytes: this._statBytes });
    }
  }

  _requireConnected() {
    if (!this.connected) throw new Error('Not connected.');
  }

  async _writeCmd(bytes) {
    this._requireConnected();
    await this.cmd.writeValue(Uint8Array.from(bytes));
  }

  async play(track) {
    await this._writeCmd([CMD_PLAY, track & 0xff]);
    this._log(`▶ Play slot ${track}`);
  }

  async stop() {
    await this._writeCmd([CMD_STOP]);
    this._log('⏹ Stop');
  }

  // Set the persistent global volume (0–255 % of unity). The device echoes the
  // applied value via a 'volume' event.
  async setVolume(percent) {
    const p = Math.max(0, Math.min(255, Math.round(percent)));
    await this._writeCmd([CMD_SET_VOL, p]);
  }

  // Ask the device for its current global volume; resolves to the percent.
  async getVolume(timeoutMs = 3000) {
    this._requireConnected();
    return new Promise((resolve, reject) => {
      const onVol = (e) => { cleanup(); resolve(e.detail.percent); };
      const cleanup = () => { clearTimeout(timer); this.removeEventListener('volume', onVol); };
      const timer = setTimeout(() => { cleanup(); reject(new Error('Volume read timed out')); }, timeoutMs);
      this.addEventListener('volume', onVol);
      this._writeCmd([CMD_GET_VOL]).catch((err) => { cleanup(); reject(err); });
    });
  }

  // Returns [{ idx, bits, rate, durationSec }], sorted by slot.
  async listTracks(timeoutMs = 4000) {
    this._requireConnected();
    return new Promise((resolve, reject) => {
      const entries = [];
      const onEntry = (e) => entries.push(e.detail);
      const finish = () => {
        cleanup();
        resolve(entries.sort((a, b) => a.idx - b.idx));
      };
      const cleanup = () => {
        clearTimeout(timer);
        this.removeEventListener('list-entry', onEntry);
        this.removeEventListener('list-end', finish);
      };
      const timer = setTimeout(finish, timeoutMs); // resolve with whatever arrived
      this.addEventListener('list-entry', onEntry);
      this.addEventListener('list-end', finish);
      this._writeCmd([CMD_LIST]).catch((err) => { cleanup(); reject(err); });
    });
  }

  // Resolves { idx, success }.
  async deleteTrack(track, timeoutMs = 4000) {
    this._requireConnected();
    return new Promise((resolve, reject) => {
      const onDel = (e) => {
        if (e.detail.idx !== (track & 0xff)) return; // ignore replies for other slots
        cleanup();
        resolve(e.detail);
      };
      const cleanup = () => { clearTimeout(timer); this.removeEventListener('deleted', onDel); };
      const timer = setTimeout(() => { cleanup(); reject(new Error('Delete timed out')); }, timeoutMs);
      this.addEventListener('deleted', onDel);
      this._writeCmd([CMD_DELETE, track & 0xff]).catch((err) => { cleanup(); reject(err); });
    });
  }

  // Stream a complete WAV file to a slot. `onProgress(shown, total)` reports a
  // single monotonic value combining the locally-sent count and the device's
  // acknowledged count.
  async upload(track, wavBytes, onProgress) {
    this._requireConnected();
    const total = wavBytes.byteLength;
    this._statBytes = 0;
    let acked = 0;

    // The optimistic local "sent" count races ahead of the device's ack
    // notifications, and the two arrive interleaved (and acks can lag badly over
    // a slow mobile link). Reporting both directly makes the bar jump forward then
    // snap backward. Clamp to a high-water mark so progress only ever advances.
    let shown = 0;
    const report = (n) => {
      const v = Math.min(Math.max(0, n), total);
      if (v > shown) { shown = v; if (onProgress) onProgress(shown, total); }
    };

    const progressHandler = (ev) => { acked = ev.detail.bytes; report(acked); };
    this.addEventListener('progress', progressHandler);

    try {
      this._log(`Starting upload of ${total} bytes to slot ${track}…`);
      await this._writeCmd([CMD_UPLOAD_START, track & 0xff]);

      // Send all data chunks using write-with-response.  Each writeValue() call
      // blocks until the SoftDevice sends an ATT Write Response, which only happens
      // after it has delivered the packet to the firmware's write callback.  This
      // provides natural per-packet flow control: CMD_UPLOAD_END cannot be sent until
      // every data packet has been confirmed received, eliminating all OS TX-queue
      // race conditions without any byte-counting hacks.
      for (let off = 0; off < total; off += DATA_CHUNK) {
        await this.data.writeValue(
          wavBytes.subarray(off, Math.min(off + DATA_CHUNK, total)));
        // Cap the optimistic local count at 99%; the final 1% is filled only when
        // the device's finalize ack confirms the bytes actually landed in flash.
        report(Math.min(off + DATA_CHUNK, Math.floor(total * 0.99)));
      }

      // All data confirmed received — finalize.
      await this._writeCmd([CMD_UPLOAD_END]);

      // Wait for that single finalize notification.  Allow up to 60 s: at 300 ms/sector
      // worst-case, a 1.4 MB file has ~350 sectors = 105 s of erase time.  In practice
      // most sectors erase in ~30 ms so finalization completes in well under 60 s.
      await this._waitForAck(total, 60000);
      const ok = acked >= total;
      if (ok) {
        this._log(`✅ Upload complete: ${acked}/${total} bytes acknowledged.`);
      } else {
        this._log(`⚠ Upload finished but device acknowledged only ${acked}/${total} bytes (flash full?).`);
      }
      this._emit('uploaded', { track, total, acked, ok });
      return { total, acked, ok };
    } finally {
      this.removeEventListener('progress', progressHandler);
    }
  }

  _waitForAck(target, timeoutMs) {
    return new Promise((resolve) => {
      if (this._statBytes >= target) return resolve();
      const deadline = Date.now() + timeoutMs;
      const cleanup = () => {
        clearInterval(poll);
        this.removeEventListener('progress', tick);
        this.removeEventListener('disconnected', onDisconnect);
      };
      const tick = () => {
        if (this._statBytes >= target || Date.now() > deadline) { cleanup(); resolve(); }
      };
      // Resolve on a real disconnect rather than polling .connected, which can
      // return false momentarily on some BLE stacks even when still connected.
      const onDisconnect = () => { cleanup(); resolve(); };
      this.addEventListener('progress', tick);
      this.addEventListener('disconnected', onDisconnect);
      // Fallback poll for timeout and when no further notifications arrive.
      const poll = setInterval(() => {
        if (this._statBytes >= target || Date.now() > deadline) { cleanup(); resolve(); }
      }, 200);
    });
  }
}