import { readdir, readFile, writeFile, access, mkdir } from 'fs/promises';
import { join, resolve, dirname } from 'path';
import { fileURLToPath } from 'url';
import matter from 'gray-matter';
import { marked } from 'marked';
import nunjucks from 'nunjucks';
import sharp from 'sharp';

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

// Nunjucks: load templates relative to project root
const env = nunjucks.configure(join(root, 'templates'), { autoescape: true });

const PRINT_PX = 2550; // 8.5 in × 300 DPI

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

// Resize image to PRINT_PX on the long side, write to output/resized/ tree.
// Returns the resized file path (absolute). Skips resize if already ≤ PRINT_PX.
async function resizeForPrint(srcAbs, resizedDir) {
  const rel   = srcAbs.replace(root + '/', '');            // e.g. images/01/scene-1.png
  const dest  = join(resizedDir, rel);
  const destDir = dirname(dest);

  await mkdir(destDir, { recursive: true });

  const meta = await sharp(srcAbs).metadata();
  const maxDim = Math.max(meta.width || 0, meta.height || 0);

  if (maxDim <= PRINT_PX) {
    // Already small enough — copy as-is
    await sharp(srcAbs).toFile(dest);
  } else {
    await sharp(srcAbs)
      .resize(PRINT_PX, PRINT_PX, { fit: 'inside', withoutEnlargement: true })
      .png({ compressionLevel: 6 })
      .toFile(dest);
  }
  return dest;
}

async function loadStories() {
  const contentDir  = join(root, 'content');
  const resizedDir  = join(root, 'output', 'resized');
  const files = (await readdir(contentDir)).filter(f => f.endsWith('.md')).sort();

  const stories = [];

  for (const file of files) {
    const raw = await readFile(join(contentDir, file), 'utf-8');
    const { data, content } = matter(raw);

    if (data.type === 'front-matter') continue;

    const sceneTexts = content.split(/\n---\n/).map(t => t.trim()).filter(Boolean);

    const scenes = await Promise.all(
      (data.scenes || []).map(async (scene, i) => {
        const srcAbs = join(root, scene.image);
        const imageExists = await fileExists(srcAbs);

        let imageSrc = `../${scene.image}`;
        if (imageExists) {
          await resizeForPrint(srcAbs, resizedDir);
          // Relative path from output/book.html to output/resized/
          imageSrc = `resized/${scene.image}`;
        }

        return {
          ...scene,
          imageExists,
          image: imageSrc,
          html: marked.parse(sceneTexts[i] || ''),
        };
      })
    );

    stories.push({ ...data, scenes });
  }

  return stories;
}

async function loadFrontMatter() {
  const raw = await readFile(join(root, 'content', '00-front-matter.md'), 'utf-8');
  return matter(raw).data;
}

async function build() {
  const [stories, frontMatter] = await Promise.all([loadStories(), loadFrontMatter()]);

  const html = env.render('book.html', { stories, frontMatter });

  const outPath = join(root, 'output', 'book.html');
  await writeFile(outPath, html, 'utf-8');

  // imprint + title page + TOC + (4 scenes × 2 pages per story)
  const pageCount = 3 + stories.reduce((acc, s) => acc + s.scenes.length * 2, 0);
  await writeFile(
    join(root, 'output', 'book-meta.json'),
    JSON.stringify({ pageCount, storyCount: stories.length, builtAt: new Date().toISOString() }, null, 2),
    'utf-8'
  );
  console.log(`Built output/book.html — ${stories.length} stories, ${pageCount} pages`);
}

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