import { Task } from '@lit-labs/task';
import { ReactiveControllerHost } from '@lit/reactive-element';
import { HomeAssistant } from 'custom-card-helpers';

/**
 * Fetch a thumbnail URL and return a data URL.
 * @param hass Home Assistant object.
 * @param thumbnailURL The thumbnail URL.
 * @returns A base64 encoded data URL for the thumbnail.
 */
export const fetchThumbnail = async (
  hass: HomeAssistant,
  thumbnailURL: string,
): Promise<string | null> => {
  if (!hass) {
    return null;
  }
  if (thumbnailURL?.startsWith('data:')) {
    return thumbnailURL;
  }
  return new Promise((resolve, reject) => {
    if (!hass) {
      reject();
      return;
    }
    hass
      .fetchWithAuth(thumbnailURL)
      // Since we are fetching with an authorization header, we cannot just put the
      // URL directly into the document; we need to embed the image. We could do this
      // using blob URLs, but then we would need to keep track of them in order to
      // release them properly. Instead, we embed the thumbnail using base64.
      .then((response) => response.blob())
      .then((blob) => {
        const reader = new FileReader();
        reader.onload = () => {
          const result = reader.result;
          resolve(typeof result === 'string' ? result : null);
        };
        reader.onerror = (e) => reject(e);
        reader.readAsDataURL(blob);
      });
  });
};

type FetchThumbnailTaskArgs = [boolean, string | undefined];

/**
 * Create a Lit task to fetch a thumbnail.
 * @param host The Lit Element.
 * @param getHASS A function to get the Home Assistant object.
 * @param getThumbnail A function to get the Thumbnail URL.
 * @returns A new Lit Task.
 */
export const createFetchThumbnailTask = (
  host: ReactiveControllerHost,
  getHASS: () => HomeAssistant | undefined,
  getThumbnailURL: () => string | undefined,
  autoRun = true,
): Task<FetchThumbnailTaskArgs, string | null> => {
  return new Task(
    host,
    {
      // Do not re-run the task if hass changes, unless it was previously undefined.
      args: (): FetchThumbnailTaskArgs => [!!getHASS(), getThumbnailURL()],
      task: async ([haveHASS, thumbnailURL]: FetchThumbnailTaskArgs): Promise<
        string | null
      > => {
        const hass = getHASS();
        if (!haveHASS || !hass || !thumbnailURL) {
          return null;
        }
        return fetchThumbnail(hass, thumbnailURL);
      },
      autoRun: autoRun,
    },
  );
};