// Project utility files retain their directory structure in OPFS.
export async function writeProjectUtilityFiles(directory: string,
  files: Array<{ filename: string; contentsBase64: string }>): Promise<void> {
  if (!directory.trim() || /[\\/]/.test(directory) || [".", ".."].includes(directory))
    throw new Error("Choose a project folder name");
  const root = await navigator.storage.getDirectory();
  const projects = await root.getDirectoryHandle("freecad-project-utility", { create: true });
  const destination = await projects.getDirectoryHandle(directory, { create: true });
  for (const file of files) {
    const parts = file.filename.split("/");
    if (parts.some(part => !part || part === "." || part === ".." || part.includes("\\")))
      throw new Error("Invalid project file path");
    let parent = destination;
    for (const part of parts.slice(0, -1)) parent = await parent.getDirectoryHandle(part, { create: true });
    const handle = await parent.getFileHandle(parts[parts.length - 1], { create: true });
    const writer = await handle.createWritable();
    try {
      await writer.write(Uint8Array.from(atob(file.contentsBase64), char => char.charCodeAt(0)));
      await writer.close();
    } catch (error) { await writer.abort().catch(() => undefined); throw error; }
  }
}

export async function readProjectUtilityFiles(directory: string): Promise<Array<{ filename: string; contentsBase64: string }>> {
  if (!directory.trim() || /[\\/]/.test(directory) || [".", ".."].includes(directory))
    throw new Error("Choose a project folder name");
  const root = await navigator.storage.getDirectory();
  const projects = await root.getDirectoryHandle("freecad-project-utility");
  const source = await projects.getDirectoryHandle(directory);
  const files: Array<{ filename: string; contentsBase64: string }> = [];
  async function visit(handle: FileSystemDirectoryHandle, prefix: string): Promise<void> {
    // The iterable DOM declaration is not available in every TypeScript DOM lib.
    const iterable = handle as FileSystemDirectoryHandle & {
      entries(): AsyncIterableIterator<[string, FileSystemHandle]>;
    };
    for await (const [name, entry] of iterable.entries()) {
      if (entry.kind === "directory") await visit(entry as FileSystemDirectoryHandle, prefix + name + "/");
      else files.push({ filename: prefix + name,
        contentsBase64: await encodeProjectFile(await (entry as FileSystemFileHandle).getFile()) });
    }
  }
  await visit(source, "");
  return files;
}

export async function encodeProjectFile(file: Blob): Promise<string> {
  const bytes = new Uint8Array(await file.arrayBuffer());
  let binary = "";
  for (let offset = 0; offset < bytes.length; offset += 8192)
    binary += String.fromCharCode(...bytes.subarray(offset, offset + 8192));
  return btoa(binary);
}