search-with-chatgpt-powered-by-openai-extension/background/background.js

import { load } from "../lib/settings.js";
import { buildChatGptUrl } from "../lib/build-url.js";

const MENU_ID = "ask-chatgpt-selection";
const COMMAND_ID = "ask-chatgpt";

// Reads the user's selection for the keyboard-shortcut path. The context menu
// does not need this — it receives info.selectionText directly.
//
// A commands invocation confers activeTab (ext-commands.js grants it before
// firing onCommand), so executeScript works with no host permission.
//
// Every frame keeps its own independent Selection, and a selection made in a
// non-focused frame is not cleared when the user selects elsewhere. Without a
// filter, a stale selection in an unfocused (possibly cross-origin) iframe
// could win over — or be pulled alongside — the selection the user actually
// made, with the winner among multiple non-empty results decided by an
// executeScript ordering that isn't specified. The injected snippet is
// therefore gated on document.hasFocus(), which is true for the focused
// document and all of its ancestors: the top frame wins when the user
// selected there, and an iframe's selection is only picked up when it is
// itself the focused frame.
//
// Failure has three measured shapes, all handled here: a thrown
// "Missing host permission for the tab", a thrown variant naming frames, and a
// SILENT resolution to [null] on parent-process about: pages. Never index into
// a result without a null check.
async function readSelection() {
  let tabs;
  try {
    tabs = await browser.tabs.query({ active: true, currentWindow: true });
  } catch {
    return "";
  }

  // Only tab.id may be read. Reading tab.url or tab.title would require the
  // "tabs" permission, which does add an install-prompt warning line.
  const tabId = tabs?.[0]?.id;
  if (typeof tabId !== "number") {
    return "";
  }

  let results;
  try {
    results = await browser.tabs.executeScript(tabId, {
      code: "document.hasFocus() ? window.getSelection().toString() : ''",
      allFrames: true,
      matchAboutBlank: true,
    });
  } catch {
    return "";
  }

  if (!Array.isArray(results)) {
    return "";
  }
  for (const result of results) {
    if (typeof result === "string" && result.trim() !== "") {
      return result;
    }
  }
  return "";
}

async function openChatGpt(query) {
  try {
    const settings = await load();
    const url = buildChatGptUrl(settings, query);

    if (settings.openIn === "new-window") {
      try {
        await browser.windows.create({ url });
        return;
      } catch {
        // Fall through to a tab rather than doing nothing.
      }
    }

    await browser.tabs.create({ url, active: settings.openIn !== "background-tab" });
  } catch {
    // Nothing useful to say and nowhere useful to say it: the user expects a
    // tab or nothing at all. Both call sites invoke this without awaiting, so
    // without this catch a failure would log an unhandled rejection.
  }
}

// removeAll() first, so a background event page waking up and re-running this
// module cannot throw on a duplicate menu id.
async function registerMenu() {
  await browser.menus.removeAll();
  browser.menus.create({
    id: MENU_ID,
    title: 'Ask ChatGPT about "%s"',
    contexts: ["selection"],
  });
}

browser.menus.onClicked.addListener((info) => {
  if (info.menuItemId !== MENU_ID) {
    return;
  }
  openChatGpt(info.selectionText ?? "");
});

// browser.commands does not exist on Firefox for Android. This extension is
// desktop-only, but guard rather than throwing at startup.
if (browser.commands) {
  browser.commands.onCommand.addListener(async (command) => {
    if (command !== COMMAND_ID) {
      return;
    }
    openChatGpt(await readSelection());
  });
}

registerMenu().catch(() => {
  // menus.removeAll() is promise-based and can reject; a failed re-registration
  // cannot be retried usefully from here. (menus.create() is callback-based and
  // cannot reject, so it needs no guard.)
});