import type { Page, Frame, BrowserContext, Download } from 'playwright';
import * as fs from 'fs';
import { logger } from '../../utils/logger';
import { SELECTORS, deepClickByText } from '../selectors';

type Scope = Page | Frame;

async function clickFirstVisible(
  page: Scope,
  selector: string,
  limit = 20,
): Promise<boolean> {
  const locator = page.locator(selector);
  const count = Math.min(await locator.count().catch(() => 0), limit);

  for (let index = 0; index < count; index++) {
    const candidate = locator.nth(index);
    if (!(await candidate.isVisible({ timeout: 800 }).catch(() => false))) {
      continue;
    }
    await candidate.click({ force: true });
    return true;
  }

  return false;
}

// ---------------------------------------------------------------------------
// Context-level download listener
// ---------------------------------------------------------------------------

/**
 * Wait for a download event across all pages in the context.
 * Turnitin may open/close temporary pages during export, so we listen at the
 * context level rather than on a single page.
 */
function waitForAnyDownload(
  context: BrowserContext,
  timeoutMs: number,
): Promise<Download> {
  return new Promise((resolve, reject) => {
    const timer = setTimeout(
      () => cleanup(new Error(`Timed out waiting ${timeoutMs}ms for download`)),
      timeoutMs,
    );
    const pageListeners = new Map<Page, (d: Download) => void>();

    const onDownload = (download: Download) => cleanup(null, download);
    const onPage = (p: Page) => attach(p);

    function attach(p: Page) {
      p.on('download', onDownload);
      pageListeners.set(p, onDownload);
    }

    function cleanup(error: Error | null, download?: Download) {
      clearTimeout(timer);
      context.off('page', onPage);
      for (const [p, listener] of pageListeners) {
        p.off('download', listener);
      }
      if (error) reject(error);
      else resolve(download!);
    }

    for (const p of context.pages()) attach(p);
    context.on('page', onPage);
  });
}

// ---------------------------------------------------------------------------
// Public API
// ---------------------------------------------------------------------------

/**
 * Download the Turnitin report as a PDF from the viewer page.
 *
 * Steps:
 * 1. Set up context-level download listener (not page-level)
 * 2. Click download menu
 * 3. Select Current View / Similarity Report
 * 4. Wait for download to complete
 * 5. Save to outputPath
 *
 * @returns The actual file path where the PDF was saved.
 */
export async function downloadPdf(
  page: Scope,
  context: BrowserContext,
  outputPath: string,
): Promise<string> {
  const ownerPage =
    typeof (page as any).page === 'function'
      ? (page as Frame).page()
      : (page as Page);

  // Validate that we are on the correct viewer URL.
  // Check both the scope URL (Frame or Page) and the owner page URL —
  // the report domain may only appear on one of them.
  const scopeUrl = page.url();
  const ownerUrl = ownerPage.url();
  const isValidViewerUrl = (url: string) =>
    url.includes('reports.integrity.turnitin.com') &&
    /submission-viewer|\/submission\//i.test(url);

  if (!isValidViewerUrl(scopeUrl) && !isValidViewerUrl(ownerUrl)) {
    throw new Error(
      `Cannot download report because viewer page is not active. ` +
      `scope URL: ${scopeUrl}, owner URL: ${ownerUrl}`,
    );
  }

  // ── BUG-5 FIX: Attach download listener BEFORE clicking any menu ──
  // Previously the listener was set up after a 1-second wait post-click.
  // If the browser starts the download faster than 1s the event was missed
  // and the job timed out after 120 seconds.
  const downloadPromise = waitForAnyDownload(context, 120000);

  // Click download menu
  let clickedDownloadMenu = false;
  const downloadMenuDeadline = Date.now() + 30_000;
  while (Date.now() < downloadMenuDeadline && !clickedDownloadMenu) {
    clickedDownloadMenu = await clickFirstVisible(
      page,
      SELECTORS.download.downloadMenu,
      20,
    );
    if (!clickedDownloadMenu) {
      await ownerPage.waitForTimeout(1000);
    }
  }
  if (!clickedDownloadMenu) {
    const clicked = await deepClickByText(page, ['download']);
    if (!clicked) {
      throw new Error('Download menu button was not found in report viewer');
    }
  }
  await ownerPage.waitForTimeout(1000);

  const optionSelectors = [
    SELECTORS.download.currentViewOption,
    '[with-data-px="DownloadOptionCurrentViewClicked"]',
    '[data-px="DownloadOptionCurrentViewClicked"]',
    'button:has-text("Current View")',
    'tdl-button:has-text("Current View")',
    '[role="menuitem"]:has-text("Current View")',
    'button:has-text("Similarity Report")',
    'tdl-button:has-text("Similarity Report")',
    '[role="menuitem"]:has-text("Similarity Report")',
  ];

  let clickedOption = false;
  for (const selector of optionSelectors) {
    if (await clickFirstVisible(page, selector, 10)) {
      clickedOption = true;
      break;
    }
  }

  if (!clickedOption) {
    clickedOption = await deepClickByText(page, [
      'current view',
      'download current view',
      'similarity report',
      'download similarity report',
    ]);
  }

  if (!clickedOption) {
    throw new Error('Download option was not found after opening download menu');
  }

  const download = await downloadPromise;
  await download.saveAs(outputPath);

  const stat = fs.statSync(outputPath);
  if (stat.size <= 0) {
    // BUG-12 FIX: Remove the empty file so it doesn't accumulate in tmpDir
    try { fs.unlinkSync(outputPath); } catch { /* ignore */ }
    throw new Error(`Downloaded PDF is empty: ${outputPath}`);
  }

  logger.info('PDF downloaded', {
    outputPath,
    suggestedFilename: download.suggestedFilename(),
    size: stat.size,
  });

  return outputPath;
}