// Self-hosted UI fonts (research 07 §8): Bender (numerals/HUD) and Novecento
// Wide (Latin headers), from TimWangZi/The-font-of-Arknights. Downloaded next
// to the site as public/fonts/*.{otf,ttf}, converted to .woff2 (tools/assets/
// woff2.mjs) and exposed through public/fonts/fonts.css. Noto Sans/Serif SC are
// NOT self-hosted (Google Fonts with system fallback, see DESIGN §10).

import { readFile, writeFile, mkdir, rename, stat } from 'node:fs/promises';
import { join } from 'node:path';
import { RAW, joinUrl } from './sources.mjs';
import { encodeWoff2, decodeWoff2Tables, readSfnt } from './woff2.mjs';

/** Font files: family, weight, source path in the font repo, local base name. */
export const FONTS = Object.freeze([
  { family: 'Bender', weight: 400, style: 'normal', src: 'Bender/BENDER.OTF', name: 'bender-regular', ext: 'otf', bytes: 52536 },
  { family: 'Bender', weight: 300, style: 'normal', src: 'Bender/BenderLight.woff.ttf', name: 'bender-light', ext: 'ttf', bytes: 68256 },
  { family: 'Novecento Wide', weight: 400, style: 'normal', src: 'Novecento-Wide-Normal-2.otf', name: 'novecento-wide-normal', ext: 'otf', bytes: 45356 },
]);

/**
 * Download jobs for the font files (rel paths are relative to public/fonts).
 * @returns {{rel:string, urls:string[], kind:string, bytes:number}[]}
 */
export function fontJobs() {
  return FONTS.map((f) => ({ rel: `${f.name}.${f.ext}`, urls: [joinUrl(RAW.fonts, f.src)], kind: 'font', bytes: f.bytes }));
}

async function exists(p) { try { return (await stat(p)).isFile(); } catch { return false; } }

/**
 * Convert downloaded fonts to WOFF2 (skipping up-to-date outputs) and write fonts.css.
 * @param {string} fontsDir absolute public/fonts directory
 * @param {(m:string)=>void} log
 * @returns {Promise<{ files: Record<string, {family:string, weight:number, woff2?:string, original?:string}>, css: string|null, errors: string[] }>}
 */
export async function buildFonts(fontsDir, log = console.log) {
  await mkdir(fontsDir, { recursive: true });
  const files = {};
  const errors = [];
  const faces = [];
  for (const f of FONTS) {
    const orig = join(fontsDir, `${f.name}.${f.ext}`);
    const woff2 = join(fontsDir, `${f.name}.woff2`);
    if (!(await exists(orig))) { errors.push(`missing font ${f.name}.${f.ext}`); continue; }
    const entry = { family: f.family, weight: f.weight, original: `/fonts/${f.name}.${f.ext}` };
    try {
      const src = await readFile(orig);
      readSfnt(src); // validate
      let ok = false;
      if (await exists(woff2)) {
        // Up to date when it decodes to exactly the source tables.
        try {
          const dec = decodeWoff2Tables(await readFile(woff2));
          const s = readSfnt(src);
          ok = dec.tables.length === s.tables.length && s.tables.every((t) => dec.tables.find((d) => d.tag === t.tag)?.data.equals(t.data));
        } catch { ok = false; }
      }
      if (!ok) {
        const out = encodeWoff2(src);
        const tmp = woff2 + '.tmp';
        await writeFile(tmp, out);
        await rename(tmp, woff2);
        log(`[fonts] ${f.name}.woff2 ${src.length} → ${out.length} B`);
      }
      entry.woff2 = `/fonts/${f.name}.woff2`;
    } catch (e) {
      errors.push(`${f.name}: ${e.message}`);
    }
    files[f.name] = entry;
    const srcs = [];
    if (entry.woff2) srcs.push(`url('${entry.woff2}') format('woff2')`);
    srcs.push(`url('${entry.original}') format('${f.ext === 'ttf' ? 'truetype' : 'opentype'}')`);
    faces.push(`@font-face {\n  font-family: '${f.family}';\n  font-style: ${f.style};\n  font-weight: ${f.weight};\n` +
      `  font-display: swap;\n  src: ${srcs.join(',\n       ')};\n}`);
  }
  let css = null;
  if (faces.length) {
    css = `/* Generated by tools/fetch-assets.mjs — do not edit.\n` +
      ` * Bender (c) Jovanny Lemonad / Oleg Zhuravlev, Gladkikh Ivan — free font.\n` +
      ` * Novecento Wide (c) Jan Tonellato / Synthview — free font.\n` +
      ` * Usage: font-family: Bender, Rajdhani, 'Noto Sans SC', sans-serif;\n` +
      ` *        font-family: 'Novecento Wide', 'Saira Condensed', 'Noto Sans SC', sans-serif; */\n\n` +
      faces.join('\n\n') + '\n';
    await writeFile(join(fontsDir, 'fonts.css'), css);
  }
  return { files, css, errors };
}