/**
 * Attachment plumbing for the editor.
 *
 * An `<img>` tag cannot carry an Authorization header, so attachment bytes are
 * fetched with an authenticated request, kept in IndexedDB and handed to the
 * DOM as a blob URL. That also means images render offline, and each one is
 * downloaded at most once per device.
 */

import * as sync from "../syncEngine";
import * as db from "../offlineStore";

const _urls = new Map(); // attachmentId -> object URL
const _inflight = new Map(); // attachmentId -> Promise<string>

export const MAX_ATTACHMENT_BYTES = 15 * 1024 * 1024;
export const ACCEPTED_TYPES = ["image/png", "image/jpeg", "image/webp", "image/gif", "image/avif"];

const readAsDataUrl = (file) =>
  new Promise((resolve, reject) => {
    const r = new FileReader();
    r.onload = () => resolve(r.result);
    r.onerror = () => reject(r.error || new Error("Could not read file"));
    r.readAsDataURL(file);
  });

/** Uploads a pasted or dropped image and returns its attachment id. */
export async function uploadImage(file) {
  if (!ACCEPTED_TYPES.includes(file.type))
    throw new Error(`Unsupported image type: ${file.type || "unknown"}`);
  if (file.size > MAX_ATTACHMENT_BYTES) throw new Error("Image is larger than 15 MB");

  const dataUrl = await readAsDataUrl(file);
  const { id } = await sync.uploadAttachment(dataUrl, file.name);

  // Seed the cache from the bytes already in hand — no round trip to display it.
  try {
    await db.putAttachmentBlob(id, file);
  } catch {
    /* cache is best-effort */
  }
  return id;
}

/** A displayable URL for an attachment, from cache when possible. */
export function resolveUrl(id) {
  if (!id) return Promise.resolve(null);
  const cached = _urls.get(id);
  if (cached) return Promise.resolve(cached);
  if (_inflight.has(id)) return _inflight.get(id);

  const job = (async () => {
    let blob = await db.getAttachmentBlob(id).catch(() => null);
    if (!blob) {
      blob = await sync.fetchAttachmentBlob(id);
      db.putAttachmentBlob(id, blob).catch(() => {});
    }
    const url = URL.createObjectURL(blob);
    _urls.set(id, url);
    return url;
  })().finally(() => _inflight.delete(id));

  _inflight.set(id, job);
  return job;
}

/* Object URLs live as long as the page does. They are a few dozen bytes of
 * bookkeeping each and the same image usually reappears as the user moves
 * between notes, so they are kept rather than revoked per unmount. */
export function releaseAll() {
  for (const url of _urls.values()) URL.revokeObjectURL(url);
  _urls.clear();
}