import puppeteer from 'puppeteer';
import { readFile, writeFile, stat, rename, unlink, access } from 'fs/promises';
import { resolve, dirname } from 'path';
import { fileURLToPath } from 'url';
import { execFile } from 'child_process';
import { promisify } from 'util';
import nunjucks from 'nunjucks';
import matter from 'gray-matter';

const execFileAsync = promisify(execFile);
const __dir = dirname(fileURLToPath(import.meta.url));
const root = resolve(__dir, '..');

// KDP constants — Premium Color paper, 8.5×8.5 in trim
const BLEED_IN        = 0.125;
const TRIM_W_IN       = 8.5;
const TRIM_H_IN       = 8.5;
const SPINE_PER_PAGE  = 0.002347;   // inches per page, Premium Color
const SAFE_IN         = 0.125;      // safe zone inset from trim edge (front/back)
const SPINE_SAFE_IN   = 0.0625;     // safe zone inset from spine fold (each side)
const MIN_SPINE_TEXT  = 79;         // KDP minimum pages for spine text

async function fileExists(p) {
  try { await access(p); return true; } catch { return false; }
}

// Encode a JS string as UTF-16BE hex for PostScript pdfmarks (handles umlauts etc.)
function toUtf16BeHex(str) {
  const hex = [];
  for (let i = 0; i < str.length; i++) {
    const cp = str.charCodeAt(i);
    hex.push(((cp >> 8) & 0xff).toString(16).padStart(2, '0'));
    hex.push((cp & 0xff).toString(16).padStart(2, '0'));
  }
  return 'FEFF' + hex.join('').toUpperCase();
}

function buildPdfmarks({ title, author }) {
  return [
    '[ /Title <' + toUtf16BeHex(title)  + '>',
    '  /Author <' + toUtf16BeHex(author) + '>',
    '  /Creator (Puppeteer + Ghostscript)',
    '  /DOCINFO pdfmark',
  ].join('\n');
}

async function runGhostscript({ rawPath, outputPath, marksPath, title, author, totalWidth, totalHeight }) {
  await writeFile(marksPath, buildPdfmarks({ title, author }), 'utf-8');

  const args = [
    '-dBATCH', '-dNOPAUSE', '-dQUIET',
    '-sDEVICE=pdfwrite',
    '-dCompatibilityLevel=1.3',
    '-dPDFSETTINGS=/prepress',
    '-dEmbedAllFonts=true',
    '-dSubsetFonts=false',
    '-dDownsampleColorImages=false',
    '-dDownsampleGrayImages=false',
    '-dDownsampleMonoImages=false',
    // RGB → CMYK conversion
    '-sColorConversionStrategy=CMYK',
    '-dProcessColorModel=/DeviceCMYK',
    `-sOutputFile=${outputPath}`,
    marksPath,
    rawPath,
  ];

  try {
    await execFileAsync('gs', args);
  } catch (err) {
    console.error('Ghostscript failed:', err.message);
    await rename(rawPath, outputPath);
    console.warn('Falling back to raw Puppeteer PDF (RGB, no GS post-processing).');
    return false;
  }
  return true;
}

async function generate() {
  // Read page count produced by build.js
  const metaPath = resolve(root, 'output', 'book-meta.json');
  let pageCount = 100;

  if (await fileExists(metaPath)) {
    const meta = JSON.parse(await readFile(metaPath, 'utf-8'));
    pageCount = meta.pageCount;
    console.log(`Page count: ${pageCount}  (from output/book-meta.json)`);
  } else {
    console.warn(`book-meta.json not found — using default page count ${pageCount}`);
    console.warn('Run `pnpm build` first for an accurate spine width.\n');
  }

  // Amazon rounds odd page counts up to even before computing spine width
  const effectivePageCount = pageCount % 2 === 0 ? pageCount : pageCount + 1;
  const spineWidth  = effectivePageCount * SPINE_PER_PAGE;
  const totalWidth  = BLEED_IN + TRIM_W_IN + spineWidth + TRIM_W_IN + BLEED_IN;
  const totalHeight = BLEED_IN + TRIM_H_IN + BLEED_IN;

  console.log(`Spine width : ${spineWidth.toFixed(4)} in`);
  console.log(`Cover canvas: ${totalWidth.toFixed(4)} × ${totalHeight.toFixed(4)} in\n`);

  // Check for optional artwork files
  const frontImage = await fileExists(resolve(root, 'images/cover/front.png'))
    ? '../images/cover/front.png' : null;
  const backImage  = await fileExists(resolve(root, 'images/cover/back.png'))
    ? '../images/cover/back.png' : null;

  // Load author / title from front matter
  const fmRaw = await readFile(resolve(root, 'content', '00-front-matter.md'), 'utf-8');
  const { data: fm } = matter(fmRaw);
  const title  = fm.title  || 'Das Kaleidoskop der Schlummerwelten';
  const author = fm.author || '';

  // Render HTML from template
  const env = nunjucks.configure(resolve(root, 'templates'), { autoescape: false });
  const html = env.render('cover.html', {
    pageCount,
    spineWidth:   spineWidth.toFixed(4),
    totalWidth:   totalWidth.toFixed(4),
    totalHeight:  totalHeight.toFixed(4),
    bleed:        BLEED_IN,
    trimW:        TRIM_W_IN,
    trimH:        TRIM_H_IN,
    safe:         SAFE_IN,
    spineSafe:    SPINE_SAFE_IN,
    hasSpineText: pageCount >= MIN_SPINE_TEXT,
    frontImage,
    backImage,
    author,
    title,
    subtitle: fm.subtitle || '',
  });

  const htmlOut  = resolve(root, 'output', 'cover.html');
  const rawPath  = resolve(root, 'output', 'cover-raw.pdf');
  const marksPath = resolve(root, 'output', 'cover-pdfmarks.ps');
  const pdfOut   = resolve(root, 'output', 'cover.pdf');

  await writeFile(htmlOut, html, 'utf-8');

  // Generate raw PDF with Puppeteer
  const systemChromium = '/usr/bin/chromium';
  const useSystem = await fileExists(systemChromium);
  console.log(`Launching Puppeteer (${useSystem ? 'system Chromium' : 'bundled Chrome'})…`);

  const browser = await puppeteer.launch({
    headless: true,
    ...(useSystem ? { executablePath: systemChromium } : {}),
  });

  const page = await browser.newPage();
  await page.goto(`file://${htmlOut}`, { waitUntil: 'networkidle0' });

  await page.pdf({
    path: rawPath,
    width:  `${totalWidth}in`,
    height: `${totalHeight}in`,
    printBackground: true,
    margin: { top: 0, bottom: 0, left: 0, right: 0 },
  });

  await browser.close();

  const rawSize = (await stat(rawPath)).size;
  console.log(`Raw PDF: ${(rawSize / 1_048_576).toFixed(1)} MB`);

  console.log('Running Ghostscript (CMYK conversion + font embedding + metadata)…');
  const gsOk = await runGhostscript({ rawPath, outputPath: pdfOut, marksPath, title, author, totalWidth, totalHeight });

  if (gsOk) {
    const finalSize = (await stat(pdfOut)).size;
    console.log(`Final PDF: ${(finalSize / 1_048_576).toFixed(1)} MB  (CMYK)`);
    await unlink(rawPath).catch(() => {});
    await unlink(marksPath).catch(() => {});
    console.log('Cover PDF written to output/cover.pdf');
  }
}

generate().catch(err => { console.error(err); process.exit(1); });