function splitPath(path) {
  if (typeof path !== "string" || path.length === 0) {
    throw new Error("OPFS path must be a non-empty relative path.");
  }
  if (path.startsWith("/") || path.includes("//")) {
    throw new Error(`Invalid OPFS path: ${path}`);
  }

  const parts = path.split("/");
  if (parts.some((part) => part === "." || part === ".." || part === "")) {
    throw new Error(`Invalid OPFS path: ${path}`);
  }
  return parts;
}

export async function getOpfsRoot(storage = globalThis.navigator?.storage) {
  if (!storage?.getDirectory) {
    throw new Error("OPFS is not available in this browser.");
  }
  return storage.getDirectory();
}

export async function ensureParentDir(root, path) {
  const parts = splitPath(path);
  let current = root;
  for (const part of parts.slice(0, -1)) {
    current = await current.getDirectoryHandle(part, { create: true });
  }
  return current;
}

export async function saveTextFile(path, text, storage) {
  const root = await getOpfsRoot(storage);
  const dir = await ensureParentDir(root, path);
  const filename = splitPath(path).at(-1);
  const fileHandle = await dir.getFileHandle(filename, { create: true });
  const writable = await fileHandle.createWritable();
  await writable.write(text);
  await writable.close();
}

export async function loadTextFile(path, storage) {
  const root = await getOpfsRoot(storage);
  const parts = splitPath(path);
  let current = root;
  for (const part of parts.slice(0, -1)) {
    current = await current.getDirectoryHandle(part);
  }
  const fileHandle = await current.getFileHandle(parts.at(-1));
  const file = await fileHandle.getFile();
  return file.text();
}