import { accounts } from "#lib/stores/accounts.svelte.js";
import { auth } from "#lib/stores/auth.svelte.js";
import { PUBLIC_API_BASE_URL } from "$app/env/public";

const BASE = PUBLIC_API_BASE_URL;

const MAX_CACHED = 100;

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

function remember(key: string, url: string) {
  ready.set(key, url);
  while (ready.size > MAX_CACHED) {
    const oldest = ready.keys().next();
    if (oldest.done) {
      return;
    }
    const stale = ready.get(oldest.value);
    ready.delete(oldest.value);
    if (stale) {
      URL.revokeObjectURL(stale);
    }
  }
}

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

async function fetchStoryMedia(
  account: number,
  peerId: number,
  storyId: number,
  key: string
): Promise<string | null> {
  const url = `${BASE}/stories/${peerId}/${storyId}/media?account_id=${account}`;
  const response = await fetch(url, { headers: authHeaders() });
  if (response.ok) {
    const objectUrl = URL.createObjectURL(await response.blob());
    remember(key, objectUrl);
    return objectUrl;
  }
  missing.add(key);
  return null;
}

export function loadStoryMedia(
  peerId: number,
  storyId: number
): Promise<string | null> {
  const account = accounts.selectedId;
  if (account === null) {
    return Promise.resolve(null);
  }
  const key = `${account}:${peerId}:${storyId}`;
  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 = fetchStoryMedia(account, peerId, storyId, key).finally(() => {
    inflight.delete(key);
  });
  inflight.set(key, promise);
  return promise;
}