export type OnFileCallback = (file: File, path: string) => Promise<void>;

export async function traverseDirectoryTreeWrapper(fileList: DataTransferItemList, onFileCallback: OnFileCallback) {
  for (const dtItem of fileList) {
    if (dtItem) {
      await traverseDirectoryTree(dtItem.webkitGetAsEntry(), onFileCallback);
    }
  }
}
async function traverseDirectoryTree(item: FileSystemEntry | null, onFileCallback: OnFileCallback, path: string = '') {
  if (item?.isFile) {
    const fileItem = item as FileSystemFileEntry;
    await getFileEntriesFromReader(fileItem, onFileCallback, path);
  } else if (item?.isDirectory) {
    const directoryItem = item as FileSystemDirectoryEntry;
    const directoryReader = directoryItem.createReader();
    let entries: Array<FileSystemEntry> = [];
    let lastAdditions = 0;
    do {
      const entrySet = await getDirectoryEntriesFromReader(directoryReader);
      lastAdditions = entrySet.length;
      entries = entries.concat(entrySet);
    } while (lastAdditions > 0);
    for (const element of entries) {
      await traverseDirectoryTree(element, onFileCallback, path + directoryItem.name + '/');
    }
  }
}

async function getDirectoryEntriesFromReader(
  directoryReader: FileSystemDirectoryReader
): Promise<Array<FileSystemEntry>> {
  return await new Promise((resolve, reject) => {
    directoryReader.readEntries((entries: Array<FileSystemEntry>) => {
      resolve(entries);
    }, reject);
  });
}

async function getFileEntriesFromReader(item: FileSystemFileEntry, onFileCallback: OnFileCallback, path: string) {
  return await new Promise<void>((resolve, _reject) => {
    item.file(async (file: File) => {
      await onFileCallback(file, path);
      resolve();
    });
  });
}