/// <reference no-default-lib="true" />
/// <reference lib="esnext" />
/// <reference lib="dom" />

export interface UploadInit {
  /** uploadできるファイルの種類 */
  accept: string;
  /** 複数個ファイルをuploadできるかどうか */
  multiple?: boolean;
}

export function upload(
  init: Omit<UploadInit, "multiple"> & { multiple?: false },
): Promise<File | undefined>;
export function upload(
  init: Omit<UploadInit, "multiple"> & { multiple: true },
): Promise<FileList | undefined>;
export function upload(init: UploadInit): Promise<FileList | File | undefined> {
  return new Promise((resolve, reject) => {
    const input = document.createElement("input");
    input.type = "file";
    input.accept = init.accept;
    input.multiple = init.multiple ?? false;
    input.addEventListener("change", () => {
      resolve(
        init.multiple === true
          ? (!input.files ? undefined : input.files.length === 0 ? undefined : input.files)
          : (input.files?.[0] ?? undefined),
      );
    });
    input.addEventListener("error", reject);
    input.click();
  });
}