background.js

'use strict';

const kTST_ID = 'treestyletab@piro.sakura.ne.jp';

async function registerToTST() {
  try {
    const self = await browser.management.getSelf();

    let success = await browser.runtime.sendMessage(kTST_ID, {
      type: 'register-self',
      name: self.id,
    });

    return success;
  } catch (e) {
    // TST is not available
  }
}

browser.runtime.onMessageExternal.addListener((aMessage, aSender) => {
  switch (aSender.id) {
    case kTST_ID:
      switch (aMessage.type) {
        case 'ready':
          registerToTST();
          break;
      }
      break;
  }
});

registerToTST().then(res => {
  browser.tabs.onActivated.addListener(callback);
  browser.tabs.onCreated.addListener(callback);
  browser.tabs.onRemoved.addListener(callback);
});

async function getSortedWinTabs() {
  const tabs = await browser.tabs.query({ currentWindow: true });
  tabs.sort((a, b) => (a.lastAccessed < b.lastAccessed ? 1 : -1));
  return tabs;
}

async function wait(ms) {
  return new Promise(resolve => {
    setTimeout(resolve, ms);
  });
}

async function callback() {
  await wait(300);

  const sortedTabs = await getSortedWinTabs();

  const allTabsIDs = sortedTabs.reduce((allIDs, currentTab) => {
    allIDs.push(currentTab.id);
    return allIDs;
  }, []);

  browser.runtime.sendMessage(kTST_ID, {
    type: 'remove-tab-state',
    tabs: allTabsIDs,
    state: 'last-active',
  });

  browser.runtime.sendMessage(kTST_ID, {
    type: 'add-tab-state',
    tabs: [sortedTabs[1].id],
    state: 'last-active',
  });
}