background.js

// MV3 service worker background script

// In MV3, the service worker can be suspended at any time, so we keep a small
// in-memory cache AND persist per-tab icon state in storage.session (if available).

const ICON_DEFAULT = 'icons/inactive.png';

// Prefer storage.session (not persisted across browser restarts) for tab state.
// Fallback to storage.local if session isn't available in the current environment.
const tabStateStorage = (chrome.storage && chrome.storage.session) ? chrome.storage.session : chrome.storage.local;

const iconCache = new Map(); // tabId -> icon filename, e.g. 'next.png'

function setTabIcon(tabId, iconFile) {
  const path = 'icons/' + iconFile;
  chrome.action.setIcon({ tabId, path });
}

async function rememberTabIcon(tabId, iconFile) {
  iconCache.set(tabId, iconFile);
  await tabStateStorage.set({ ['page_turner_icon_' + tabId]: iconFile });
}

async function recallTabIcon(tabId) {
  if (iconCache.has(tabId)) return iconCache.get(tabId);

  const key = 'page_turner_icon_' + tabId;
  const data = await tabStateStorage.get(key);
  const iconFile = data[key];
  if (iconFile) iconCache.set(tabId, iconFile);
  return iconFile;
}

// Messages from the content script tell us what icon to show for the current tab.
chrome.runtime.onMessage.addListener((request, sender, sendResponse) => {
  if (!request || !request.icon) return;

  const tabId = sender && sender.tab && sender.tab.id;
  if (typeof tabId !== 'number') return;

  // Don't change extension icon when pages are prerendered.
  // In MV3, sender.tab.active is usually available; if not, we still remember state.
  const isActive = sender.tab && sender.tab.active === true;

  (async () => {
    if (isActive) setTabIcon(tabId, request.icon);
    await rememberTabIcon(tabId, request.icon);
  })();

  // No async response needed.
});

// When user switches tabs, restore the last-known icon for that tab (or default).
chrome.tabs.onActivated.addListener(({ tabId }) => {
  (async () => {
    const iconFile = await recallTabIcon(tabId);
    if (iconFile) {
      setTabIcon(tabId, iconFile);
    } else {
      chrome.action.setIcon({ tabId, path: ICON_DEFAULT });
    }
  })();
});

// Avoid storing icon data for closed tabs.
chrome.tabs.onRemoved.addListener((tabId) => {
  iconCache.delete(tabId);
  tabStateStorage.remove('page_turner_icon_' + tabId);
});