background.js

let creatingOffscreen = null;

async function ensureOffscreenDocument() {
  const offscreenUrl = chrome.runtime.getURL('offscreen.html');
  const existingContexts = await chrome.runtime.getContexts({
    contextTypes: ['OFFSCREEN_DOCUMENT'],
    documentUrls: [offscreenUrl]
  });

  if (existingContexts.length > 0) return;

  if (creatingOffscreen) {
    await creatingOffscreen;
  } else {
    creatingOffscreen = chrome.offscreen.createDocument({
      url: 'offscreen.html',
      reasons: ['AUDIO_PLAYBACK'],
      justification: 'Route tab audio to specific hardware output devices'
    });
    await creatingOffscreen;
    creatingOffscreen = null;
  }
}

chrome.runtime.onMessage.addListener((message, sender, sendResponse) => {
  if (message.action === 'ROUTE_TAB_AUDIO') {
    handleAudioRouting(message.tabId, message.deviceId, message.volume);
  }
});

async function handleAudioRouting(tabId, deviceId, volume) {
  // Ensure the offscreen document is alive
  await ensureOffscreenDocument();

  let streamId;
  try {
    // 1. Try to get a media stream ID for the target tab
    streamId = await chrome.tabCapture.getMediaStreamId({
      targetTabId: tabId
    });
  } catch (error) {
    // If it fails because the stream is already active, we can just change the sink
    if (error.message && (error.message.includes('active stream') || error.message.includes('already being captured'))) {
      console.log('Tab already captured, changing sink instead.');
      chrome.runtime.sendMessage({
        action: 'CHANGE_SINK',
        tabId: tabId,
        deviceId: deviceId
      });
      return;
    } else {
      console.error('Error capturing tab:', error);
      return;
    }
  }

  // 2. If we got a new streamId, send it to offscreen.js to play
  chrome.runtime.sendMessage({
    action: 'PLAY_STREAM_ON_DEVICE',
    streamId: streamId,
    tabId: tabId,
    deviceId: deviceId,
    volume: volume
  });
}