// Babel transformed "helloworld.js" into "transformed.js"
const transformedMap = JSON.stringify({
  file: 'transformed.js',
  // 1st column of 2nd line of output file translates into the 1st source
  // file, line 3, column 2
  mappings: ';CAEE',
  sources: ['helloworld.js'],
  version: 3,
});

// Uglify minified "transformed.js" into "transformed.min.js"
const minifiedTransformedMap = JSON.stringify({
  file: 'transformed.min.js',
  // 0th column of 1st line of output file translates into the 1st source
  // file, line 2, column 1.
  mappings: 'AACC',
  names: [],
  sources: ['transformed.js'],
  version: 3,
});

const remapped = remapping(
  minifiedTransformedMap,
  (file, ctx) => {

    // The "transformed.js" file is an transformed file.
    if (file === 'transformed.js') {
      // The root importer is empty.
      console.assert(ctx.importer === '');
      // The depth in the sourcemap tree we're currently loading.
      // The root `minifiedTransformedMap` is depth 0, and its source children are depth 1, etc.
      console.assert(ctx.depth === 1);

      return transformedMap;
    }

    // Loader will be called to load transformedMap's source file pointers as well.
    console.assert(file === 'helloworld.js');
    // `transformed.js`'s sourcemap points into `helloworld.js`.
    console.assert(ctx.importer === 'transformed.js');
    // This is a source child of `transformed`, which is a source child of `minifiedTransformedMap`.
    console.assert(ctx.depth === 2);
    return null;
  }
);

console.log(remapped);
// {
//   file: 'transpiled.min.js',
//   mappings: 'AAEE',
//   sources: ['helloworld.js'],
//   version: 3,
// };

const remapped = remapping(
  [minifiedTransformedMap, transformedMap],
  () => null
);

console.log(remapped);
// {
//   file: 'transpiled.min.js',
//   mappings: 'AAEE',
//   sources: ['helloworld.js'],
//   version: 3,
// };

const remapped = remapping(
  minifiedTransformedMap,
  (file, ctx) => {

    if (file === 'transformed.js') {
      // We pretend the transformed.js file actually exists in the 'src/' directory. When the nested
      // source files are loaded, they will now be relative to `src/`.
      ctx.source = 'src/transformed.js';
      return transformedMap;
    }

    console.assert(file === 'src/helloworld.js');
    // We could futher change the source of this original file, eg, to be inside a nested directory
    // itself. This will be reflected in the remapped sourcemap.
    ctx.source = 'src/nested/transformed.js';
    return null;
  }
);

console.log(remapped);
// {
//   …,
//   sources: ['src/nested/helloworld.js'],
// };

const remapped = remapping(
  minifiedTransformedMap,
  (file, ctx) => {

    if (file === 'transformed.js') {
      // transformedMap does not include a `sourcesContent` field, so usually the remapped sourcemap
      // would not include any `sourcesContent` values.
      return transformedMap;
    }

    console.assert(file === 'helloworld.js');
    // We can read the file to provide the source content.
    ctx.content = fs.readFileSync(file, 'utf8');
    return null;
  }
);

console.log(remapped);
// {
//   …,
//   sourcesContent: [
//     'console.log("Hello world!")',
//   ],
// };