const path = require('path');
const { rollup } = require('rollup');
const virtual = require('@rollup/plugin-virtual');
const fs = require('fs');

function main() {
  const input = process.argv[2] || get_input();
  check(input).then((result) => {
    const relative = path.relative(process.cwd(), input);

    if (result.shaken) {
      console.error(`Success! ${relative} is fully tree-shakeable`);
    } else {
      error(`Failed to tree-shake ${relative}`);
    }
  });
}

function error(msg) {
  console.error(msg);
  process.exit(1);
}

function get_input() {
  if (!fs.existsSync('package.json')) {
    error(`Could not find package.json`);
  }

  const pkg = JSON.parse(fs.readFileSync('package.json'), 'utf-8');

  const unresolved = pkg.module || pkg.main || 'index';
  const resolved = resolve(unresolved);

  if (!resolved) {
    error(`Could not resolve entry point`);
  }

  return resolved;
}

function resolve(file) {
  if (is_directory(file)) {
    return if_exists(`${file}/index.mjs`) || if_exists(`${file}/index.js`);
  }

  return if_exists(file) || if_exists(`${file}.mjs`) || if_exists(`${file}.js`);
}

function is_directory(file) {
  try {
    const stats = fs.statSync(file);
    return stats.isDirectory();
  } catch (err) {
    return false;
  }
}

function if_exists(file) {
  return fs.existsSync(file) ? file : null;
}

const check = (input) => {
  const resolved = path.resolve(input);

  return rollup({
    input: '__agadoo__',
    plugins: [
      virtual({
        __agadoo__: `import ${JSON.stringify(resolved)}`,
      }),
      {
        resolveId(id) {
          if (!id.startsWith('.') && !id.startsWith('/')) {
            return { id: id, external: true, moduleSideEffects: false };
          }
          return null;
        },
      },
    ],
    onwarn: (warning, handle) => {
      if (warning.code !== 'EMPTY_BUNDLE') handle(warning);
    },
  })
    .then((bundle) =>
      bundle.generate({
        format: 'es',
      })
    )
    .then((o) => {
      const output = o.output;
      console.log(output);
      return {
        shaken: output.length === 1 && output[0].code.trim() === '',
      };
    });
};

main();
