import defined from "../Core/defined.js";

/**
 * A policy for discarding tile images that contain no data (and so aren't actually images).
 * This policy discards {@link DiscardEmptyTileImagePolicy.EMPTY_IMAGE}, which is
 * expected to be used in place of any empty tile images by the image loading code.
 *
 * @alias DiscardEmptyTileImagePolicy
 * @constructor
 *
 * @see DiscardMissingTileImagePolicy
 */
function DiscardEmptyTileImagePolicy(options) {}

/**
 * Determines if the discard policy is ready to process images.
 * @returns {Boolean} True if the discard policy is ready to process images; otherwise, false.
 */
DiscardEmptyTileImagePolicy.prototype.isReady = function () {
  return true;
};

/**
 * Given a tile image, decide whether to discard that image.
 *
 * @param {HTMLImageElement} image An image to test.
 * @returns {Boolean} True if the image should be discarded; otherwise, false.
 */
DiscardEmptyTileImagePolicy.prototype.shouldDiscardImage = function (image) {
  return DiscardEmptyTileImagePolicy.EMPTY_IMAGE === image;
};

let emptyImage;

Object.defineProperties(DiscardEmptyTileImagePolicy, {
  /**
   * Default value for representing an empty image.
   * @type {HTMLImageElement}
   * @readonly
   * @memberof DiscardEmptyTileImagePolicy
   */
  EMPTY_IMAGE: {
    get: function () {
      if (!defined(emptyImage)) {
        emptyImage = new Image();
        // load a blank data URI with a 1x1 transparent pixel.
        emptyImage.src =
          "data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAQAAAC1HAwCAAAAC0lEQVR42mNkYAAAAAYAAjCB0C8AAAAASUVORK5CYII=";
      }
      return emptyImage;
    },
  },
});
export default DiscardEmptyTileImagePolicy;