/* ============================================================
   build.mjs — zero-dependency bundler + inliner.
   Walks the ES-module graph from src/main.js, wraps each module
   in a tiny require() shim (constrained to the named-import /
   named-export subset this project uses), inlines the CSS, and
   writes a single self-contained, file://-openable
   bubble_chamber.html.

   Run:  node build.mjs
   ============================================================ */
import { readFileSync, writeFileSync } from 'node:fs';
import path from 'node:path';

const ROOT = path.dirname(new URL(import.meta.url).pathname);
const ENTRY = 'src/main.js';

const IMPORT_RE = /^\s*import\s*\{([^}]*)\}\s*from\s*['"]([^'"]+)['"]\s*;?\s*$/;
const EXPORT_RE = /^\s*export\s+(function|const|let|var|class)\s+([A-Za-z0-9_$]+)/;

const modules = new Map();   // id -> { code }
const order = [];

function resolve(fromId, spec) {
  const dir = path.posix.dirname(fromId);
  let id = path.posix.normalize(path.posix.join(dir, spec));
  if (!id.endsWith('.js')) id += '.js';
  return id;
}

function load(id) {
  if (modules.has(id)) return;
  const src = readFileSync(path.join(ROOT, id), 'utf8');
  const exports = [];
  const deps = [];
  const lines = src.split('\n').map((line) => {
    const imp = line.match(IMPORT_RE);
    if (imp) {
      const names = imp[1].split(',').map(s => s.trim()).filter(Boolean);
      const depId = resolve(id, imp[2]);
      deps.push(depId);
      return `const { ${names.join(', ')} } = __require(${JSON.stringify(depId)});`;
    }
    const exp = line.match(EXPORT_RE);
    if (exp) {
      exports.push(exp[2]);
      return line.replace(/^\s*export\s+/, '');
    }
    return line;
  });
  let code = lines.join('\n');
  if (exports.length) code += `\nObject.assign(exports, { ${exports.join(', ')} });\n`;
  modules.set(id, { code });
  for (const d of deps) load(d);   // depth-first; registry handles cycles/order
  order.push(id);
}

load(ENTRY);

let bundle = `(function () {\n`;
bundle += `  const __cache = {};\n  const __reg = {};\n`;
bundle += `  function __require(id) {\n    if (__cache[id]) return __cache[id].exports;\n` +
          `    const module = { exports: {} }; __cache[id] = module;\n` +
          `    __reg[id](module, module.exports, __require);\n    return module.exports;\n  }\n`;
for (const id of [...modules.keys()]) {
  bundle += `  __reg[${JSON.stringify(id)}] = function (module, exports, __require) {\n`;
  bundle += modules.get(id).code + '\n';
  bundle += `  };\n`;
}
bundle += `  __require(${JSON.stringify(ENTRY)});\n})();\n`;

// inline into index.html
let html = readFileSync(path.join(ROOT, 'index.html'), 'utf8');
const css = readFileSync(path.join(ROOT, 'src/style.css'), 'utf8');
html = html.replace(
  /<link rel="stylesheet" href="src\/style\.css">/,
  `<style>\n${css}\n</style>`
);
html = html.replace(
  /<script type="module" src="src\/main\.js"><\/script>/,
  `<script>\n${bundle}</script>`
);
html = html.replace('Parametric Generator · v3', 'Parametric Generator · v3 (built)');

writeFileSync(path.join(ROOT, 'bubble_chamber.html'), html);
console.log(`built bubble_chamber.html — ${modules.size} modules, ${(html.length / 1024).toFixed(1)} KB`);