import { promisify } from 'util';
import { writeFile, mkdir, exists } from 'fs';
import { Namespaces } from './generate';
import { generateNamespaceTs, Mirrors } from './generateNamespaceTs';
import { resolve } from 'path';

const fsWriteFile = promisify(writeFile);
const fsExists = promisify(exists);
const fsMkdir = promisify(mkdir);

export async function generateFiles(
  namespacesToGenerate: Namespaces,
  {
    targetDir = resolve(__dirname, '../dist'),
    mirrors = {} as Mirrors,
  } = {},
) {
  if (!(await fsExists(targetDir))) {
    await fsMkdir(targetDir);
  }
  const generatedFilenames = await Promise.all(
    Object.entries(namespacesToGenerate)
    .map(([filename, namespace]) => generateFile(filename, namespace, { targetDir, mirrors }))
  );
  const indexContents = Object.keys(namespacesToGenerate)
    // This is a somewhat hackish workaround to this proposal not being ratified for Ecmascript yet:
    // https://github.com/tc39/proposal-export-ns-from
    .map((filename) => {
      const exportLine = `import * as ${filename}Import from './${filename}'; export const ${filename} = ${filename}Import;`
      return generatedFilenames.includes(filename)
        ? exportLine
        : `// This vocabulary was unavailable when this file was generated:\n// ${exportLine}`;
    })
    .join('\n');
  return fsWriteFile(resolve(targetDir, 'index.ts'), indexContents);
}

async function generateFile(
  filename: string,
  namespace: string,
  {
    targetDir = resolve(__dirname, '../dist'),
    mirrors = {} as Mirrors,
  } = {},
) {
  try {
    const contents = await generateNamespaceTs(namespace, { mirrors });
    await fsWriteFile(resolve(targetDir, `${filename}.ts`), contents);
    return filename;
  } catch(e) {
    console.error(`Error generating constants for namespace <${namespace}>:`, e);
    return null;
  }
}