src/types/file-system.d.ts

interface FileSystemWritableFileStream extends WritableStream {
  write(data: BufferSource | Blob | string): Promise<void>;
  seek(position: number): Promise<void>;
  truncate(size: number): Promise<void>;
}

interface FileSystemFileHandle {
  kind: "file";
  name: string;
  getFile(): Promise<File>;
  createWritable(options?: {
    keepExistingData?: boolean;
  }): Promise<FileSystemWritableFileStream>;
}

interface FileSystemDirectoryHandle {
  kind: "directory";
  name: string;
  getDirectoryHandle(
    name: string,
    options?: { create?: boolean },
  ): Promise<FileSystemDirectoryHandle>;
  getFileHandle(
    name: string,
    options?: { create?: boolean },
  ): Promise<FileSystemFileHandle>;
}

interface SaveFilePickerOptions {
  suggestedName?: string;
  types?: Array<{
    description?: string;
    accept: Record<string, string[]>;
  }>;
  excludeAcceptAllOption?: boolean;
}

interface Window {
  showDirectoryPicker(): Promise<FileSystemDirectoryHandle>;
  showSaveFilePicker(
    options?: SaveFilePickerOptions,
  ): Promise<FileSystemFileHandle>;
}