background.js

/*
 * background.js — MV3 service worker.
 *
 * Sole job: inject the in-page overlay on demand (from the popup) and report
 * its visibility. Injection is triggered only by an explicit user action and
 * targets the tab the user is looking at (activeTab), so the extension touches
 * a page only when asked.
 */
'use strict';

const OVERLAY_FILES = ['lib/format.js', 'lib/priority.js', 'content/overlay.js'];

/** Read the overlay's current visibility flag from the page (isolated world). */
function readOverlayVisible() {
  return typeof window.__wfiOverlayVisible === 'boolean' ? window.__wfiOverlayVisible : false;
}

async function injectAndToggle(tabId) {
  // Re-running overlay.js is idempotent: it toggles if already present.
  await chrome.scripting.executeScript({ target: { tabId }, files: OVERLAY_FILES });
  const res = await chrome.scripting.executeScript({
    target: { tabId },
    func: readOverlayVisible,
  });
  return !!(res && res[0] && res[0].result);
}

async function readState(tabId) {
  try {
    const res = await chrome.scripting.executeScript({
      target: { tabId },
      func: readOverlayVisible,
    });
    return !!(res && res[0] && res[0].result);
  } catch (e) {
    return false;
  }
}

chrome.runtime.onMessage.addListener((msg, sender, sendResponse) => {
  if (!msg || !msg.type) return false;

  if (msg.type === 'WFI_TOGGLE_OVERLAY') {
    injectAndToggle(msg.tabId)
      .then((visible) => sendResponse({ ok: true, visible }))
      .catch((err) => sendResponse({ ok: false, error: String(err && err.message ? err.message : err) }));
    return true; // async response
  }

  if (msg.type === 'WFI_OVERLAY_STATE') {
    readState(msg.tabId)
      .then((visible) => sendResponse({ ok: true, visible }))
      .catch(() => sendResponse({ ok: true, visible: false }));
    return true;
  }

  return false;
});