/**
 * exportPdf.ts
 * Combines all slide PNGs into a single multi-page PDF using pdf-lib.
 * Each PNG becomes one page at the original 1080x1080 dimensions.
 *
 * Approach: PNG → PDF embedding (not HTML→PDF) for pixel-perfect output.
 * This avoids cross-page layout bleed and ensures each slide is exactly one page.
 */

import fs from 'fs';
import path from 'path';

import type { SlideContent } from '../schema/carouselSchema';
import type { Theme } from '../render/themes';
import { exportToPngs } from './exportPng';

// Points per pixel at 72 DPI (PDF's native unit)
// 1080px at 96 DPI screen = 810pt at 72 DPI
// We preserve 1:1 mapping for now (1px = 1pt) which gives ~15" square at 72dpi
// For LinkedIn, pixel dimensions are more important than physical size
const PX_TO_PT = 1.0; // 1080px slides → 1080pt pages

/**
 * Export all slides to a single PDF file.
 * First renders PNGs (if not already done), then combines them.
 *
 * @param slides     - Ordered array of SlideContent
 * @param theme      - Visual theme
 * @param outputDir  - Base output directory
 * @param existingPngs - Optional: pre-rendered PNG paths to skip re-render
 * @returns          - Absolute path to generated PDF
 */
export async function exportToPdf(
  slides: SlideContent[],
  theme: Theme,
  outputDir: string,
  existingPngs?: string[]
): Promise<string> {
  // Lazy-import pdf-lib
  let PDFDocument: typeof import('pdf-lib').PDFDocument;
  let pdfLib: typeof import('pdf-lib');
  try {
    pdfLib = await import('pdf-lib');
    PDFDocument = pdfLib.PDFDocument;
  } catch (err) {
    throw new Error(
      'pdf-lib is not installed. Run: npm install pdf-lib\n' +
      'If you cannot install it, PNG exports are still available in slides_preview/.'
    );
  }

  // Render PNGs if not provided
  const pngPaths = existingPngs ?? (await exportToPngs(slides, theme, outputDir));

  if (pngPaths.length === 0) {
    throw new Error('No PNG files available to combine into PDF.');
  }

  // Create PDF
  const pdfDoc = await PDFDocument.create();

  for (const pngPath of pngPaths) {
    const pngBytes = fs.readFileSync(pngPath);
    const pngImage = await pdfDoc.embedPng(pngBytes);

    // Use the actual image dimensions for the page
    const { width, height } = pngImage;
    const page = pdfDoc.addPage([width * PX_TO_PT, height * PX_TO_PT]);

    page.drawImage(pngImage, {
      x: 0,
      y: 0,
      width: width * PX_TO_PT,
      height: height * PX_TO_PT,
    });
  }

  // Set PDF metadata
  pdfDoc.setTitle('LinkedIn Career Carousel');
  pdfDoc.setAuthor('Generated by job-carousel skill');
  pdfDoc.setCreationDate(new Date());

  const pdfBytes = await pdfDoc.save();
  const pdfPath = path.join(outputDir, 'linkedin_carousel.pdf');
  fs.writeFileSync(pdfPath, pdfBytes);

  console.log(`  ✓ PDF exported: linkedin_carousel.pdf (${pngPaths.length} slides)`);
  return pdfPath;
}