background.js

/**
 * Freedom PDF Viewer — Background Service Worker
 *
 * Intercepts navigations to PDF files and redirects them to the
 * built-in PDF.js viewer. This covers:
 *   • Clicking a PDF link (http / https)
 *   • Typing / pasting a PDF URL into the address bar
 *   • Opening a local PDF via File → Open (file://)
 *   • Dragging and dropping a PDF file onto a Chrome tab (file://)
 *
 * Embedded PDFs (lazy-loaded iframes, <object>, etc.) must NOT be
 * redirected — only full-tab navigations to a .pdf URL.
 */

const VIEWER = chrome.runtime.getURL('pdfjs/web/viewer.html');

/**
 * Returns true if the URL looks like a PDF and is not already
 * being handled by our viewer.
 */
function isPdfNavigation(url) {
  if (!url || typeof url !== 'string' || url.startsWith(VIEWER)) return false;
  try {
    const { pathname } = new URL(url);
    return pathname.toLowerCase().endsWith('.pdf');
  } catch {
    // Fallback for malformed URLs
    return /\.pdf($|\?|#)/i.test(url);
  }
}

/**
 * True only for a user-visible tab navigation to a PDF — not an iframe,
 * fenced frame, or prerendered document.
 * Chrome 106+ exposes `frameType`; older builds fall back to frameId/parentFrameId.
 */
function isTopLevelUserTabNavigation(details) {
  if (details.documentLifecycle === 'prerender') {
    return false;
  }

  const { frameType, frameId, parentFrameId } = details;

  if (frameType === 'sub_frame' || frameType === 'fenced_frame') {
    return false;
  }
  if (frameType === 'outermost_frame') {
    return true;
  }

  // Chrome < 106: frameType may be undefined — use frame hierarchy only
  if (frameType === undefined) {
    if (frameId !== 0) {
      return false;
    }
    if (parentFrameId === undefined || parentFrameId === null) {
      return true;
    }
    return parentFrameId === -1;
  }

  return false;
}

/**
 * Redirect the tab to our PDF viewer with the original URL
 * encoded as the `file` query parameter that PDF.js expects.
 */
function openInViewer(tabId, url) {
  // If the URL has a fragment (e.g. #page=2), keep it outside the 'file' param
  // so that PDF.js can parse it correctly for its own navigation.
  const [baseUrl, fragment] = url.split('#');
  const redirectUrl = `${VIEWER}?file=${encodeURIComponent(baseUrl)}${fragment ? '#' + fragment : ''}`;
  chrome.tabs.update(tabId, { url: redirectUrl });
}

// ── Intercept navigations ────────────────────────────────────────────────────

// onBeforeNavigate fires early — before Chrome's built-in PDF renderer
// has a chance to claim the navigation — making it ideal for interception.
chrome.webNavigation.onBeforeNavigate.addListener(
  (details) => {
    if (!isPdfNavigation(details.url)) {
      return;
    }
    if (!isTopLevelUserTabNavigation(details)) {
      return;
    }
    openInViewer(details.tabId, details.url);
  },
  {
    url: [
      // HTTP / HTTPS PDFs (web links and web drag-and-drop)
      { schemes: ['http'], urlMatches: '\\.pdf($|\\?|#)' },
      { schemes: ['https'], urlMatches: '\\.pdf($|\\?|#)' },
      // Local file PDFs (file → open OR drag-and-drop from file manager)
      { schemes: ['file'], urlMatches: '\\.pdf($|\\?|#)' },
    ],
  }
);