import { accounts } from "$lib/stores/accounts.svelte";
import { auth } from "$lib/stores/auth.svelte";

const BASE = import.meta.env.VITE_API_BASE ?? "/api";
const RETRY_DELAY = 2500;

export interface CustomEmojiAsset {
  mime: string;
  url: string;
}

const ready = new Map<string, CustomEmojiAsset>();
const missing = new Set<string>();
const inflight = new Map<string, Promise<CustomEmojiAsset | null>>();

function authHeaders(): Record<string, string> {
  return auth.token ? { Authorization: `Bearer ${auth.token}` } : {};
}

function delay(ms: number): Promise<void> {
  return new Promise((resolve) => {
    setTimeout(resolve, ms);
  });
}

async function fetchEmoji(
  account: number,
  id: string,
  key: string,
  retry: boolean
): Promise<CustomEmojiAsset | null> {
  const url = `${BASE}/custom-emoji/${id}?account_id=${account}`;
  const response = await fetch(url, { headers: authHeaders() });
  if (response.ok) {
    const blob = await response.blob();
    const asset = { url: URL.createObjectURL(blob), mime: blob.type };
    ready.set(key, asset);
    return asset;
  }
  if (response.status === 409 && retry) {
    await delay(RETRY_DELAY);
    return fetchEmoji(account, id, key, false);
  }
  missing.add(key);
  return null;
}

export function loadCustomEmoji(id: string): Promise<CustomEmojiAsset | null> {
  const account = accounts.selectedId;
  if (account === null) {
    return Promise.resolve(null);
  }
  const key = `${account}:${id}`;
  const cached = ready.get(key);
  if (cached) {
    return Promise.resolve(cached);
  }
  if (missing.has(key)) {
    return Promise.resolve(null);
  }
  const existing = inflight.get(key);
  if (existing) {
    return existing;
  }
  const promise = fetchEmoji(account, id, key, true).finally(() => {
    inflight.delete(key);
  });
  inflight.set(key, promise);
  return promise;
}