/**
 * utils around working with DOM file lists
 *
 * @module
 */

export const fromArray = (files: File[]): FileList => {
  const dt = new DataTransfer();
  for (const file of files) {
    dt.items.add(file);
  }
  return dt.files;
};

export const reduce = <T>(
  fileList: FileList,
  reduceFn: (current: T, file: File, index: number) => T,
  seed: T,
): T => Array.from(fileList).reduce(reduceFn, seed);

export const map = (
  fileList: FileList,
  mapFn: (file: File, index: number) => File,
): FileList =>
  reduce(
    fileList,
    (dt, file, i) => {
      dt.items.add(mapFn(file, i));
      return dt;
    },
    new DataTransfer(),
  ).files;

export const remove = (fileList: FileList, index: number): FileList =>
  reduce(
    fileList,
    (dt, file, i) => {
      if (i === index) {
        return dt;
      }
      dt.items.add(file);
      return dt;
    },
    new DataTransfer(),
  ).files;

export const update = (
  fileList: FileList,
  index: number,
  updateFn: (file: File) => File,
): FileList =>
  map(fileList, (file, i) => (i !== index ? file : updateFn(file)));

export const rename = (
  fileList: FileList,
  index: number,
  newName: string,
): FileList =>
  update(fileList, index, (file) => new File([file.slice()], newName));

export const concat = (a: FileList, b: FileList): FileList => {
  const dt = new DataTransfer();

  for (const aFile of a) {
    dt.items.add(aFile);
  }

  for (const bFile of b) {
    dt.items.add(bFile);
  }

  return dt.files;
};

export const at = (fileList: FileList, index: number): File | undefined =>
  Array.from(fileList).at(index);