// Google Drive helpers. Files written to the appDataFolder space are invisible
// to the user in the regular Drive UI and only readable by this app's Google
// Cloud project.
//
// Docs: https://developers.google.com/drive/api/guides/appdata

const DRIVE = "https://www.googleapis.com/drive/v3";
const UPLOAD = "https://www.googleapis.com/upload/drive/v3";

async function driveFetch(token, url, init = {}) {
  const res = await fetch(url, {
    ...init,
    headers: {
      Authorization: `Bearer ${token}`,
      ...(init.headers || {}),
    },
  });
  if (!res.ok) {
    const text = await res.text();
    throw new Error(`Drive API ${res.status}: ${text.slice(0, 300)}`);
  }
  return res;
}

// Find a file by exact name inside the appDataFolder. Returns the file id, or
// null if not found. If several exist (two devices signed up at the same
// moment), the OLDEST wins, so every device converges on the same key.
export async function findAppDataFile(token, name) {
  const url =
    `${DRIVE}/files?spaces=appDataFolder` +
    `&q=${encodeURIComponent(`name = '${name.replace(/'/g, "\\'")}'`)}` +
    `&fields=files(id,createdTime)`;
  const res = await driveFetch(token, url);
  const { files } = await res.json();
  if (!files || files.length === 0) return null;
  files.sort((a, b) => (a.createdTime || "").localeCompare(b.createdTime || ""));
  return files[0].id;
}

export async function downloadFile(token, fileId) {
  const res = await driveFetch(token, `${DRIVE}/files/${fileId}?alt=media`);
  return res.text();
}

// Multipart upload of a small text blob. If fileId is given, replaces that
// file's content; otherwise creates a new file under `parents`
// (["appDataFolder"] for the hidden key file, omit for My Drive).
export async function uploadFile(token, { name, content, mimeType = "application/json", parents, fileId = null }) {
  const boundary = "goostr-" + Math.random().toString(36).slice(2);
  const metadata = fileId ? { name } : { name, mimeType, ...(parents ? { parents } : {}) };

  const body =
    `--${boundary}\r\n` +
    `Content-Type: application/json; charset=UTF-8\r\n\r\n` +
    `${JSON.stringify(metadata)}\r\n` +
    `--${boundary}\r\n` +
    `Content-Type: ${mimeType}\r\n\r\n` +
    `${content}\r\n` +
    `--${boundary}--`;

  const url = fileId
    ? `${UPLOAD}/files/${fileId}?uploadType=multipart`
    : `${UPLOAD}/files?uploadType=multipart&fields=id,webViewLink`;

  const res = await driveFetch(token, url, {
    method: fileId ? "PATCH" : "POST",
    headers: { "Content-Type": `multipart/related; boundary=${boundary}` },
    body,
  });
  return res.json();
}

export async function fetchUserInfo(token) {
  const res = await driveFetch(token, "https://www.googleapis.com/oauth2/v3/userinfo");
  return res.json(); // { sub, name, picture, email, ... }
}