/**
 * @module ol/TileQueue
 */
import {inherits} from './index.js';
import TileState from './TileState.js';
import {listen, unlisten} from './events.js';
import EventType from './events/EventType.js';
import PriorityQueue from './structs/PriorityQueue.js';


/**
 * @typedef {function(module:ol/Tile~Tile, string, module:ol/coordinate~Coordinate, number): number} PriorityFunction
 */


/**
 * @constructor
 * @extends {module:ol/structs/PriorityQueue~PriorityQueue.<Array>}
 * @param {module:ol/TileQueue~PriorityFunction} tilePriorityFunction
 *     Tile priority function.
 * @param {function(): ?} tileChangeCallback
 *     Function called on each tile change event.
 * @struct
 */
const TileQueue = function(tilePriorityFunction, tileChangeCallback) {

  PriorityQueue.call(
    this,
    /**
       * @param {Array} element Element.
       * @return {number} Priority.
       */
    function(element) {
      return tilePriorityFunction.apply(null, element);
    },
    /**
       * @param {Array} element Element.
       * @return {string} Key.
       */
    function(element) {
      return /** @type {module:ol/Tile~Tile} */ (element[0]).getKey();
    });

  /**
   * @private
   * @type {function(): ?}
   */
  this.tileChangeCallback_ = tileChangeCallback;

  /**
   * @private
   * @type {number}
   */
  this.tilesLoading_ = 0;

  /**
   * @private
   * @type {!Object.<string,boolean>}
   */
  this.tilesLoadingKeys_ = {};

};

inherits(TileQueue, PriorityQueue);


/**
 * @inheritDoc
 */
TileQueue.prototype.enqueue = function(element) {
  const added = PriorityQueue.prototype.enqueue.call(this, element);
  if (added) {
    const tile = element[0];
    listen(tile, EventType.CHANGE,
      this.handleTileChange, this);
  }
  return added;
};


/**
 * @return {number} Number of tiles loading.
 */
TileQueue.prototype.getTilesLoading = function() {
  return this.tilesLoading_;
};


/**
 * @param {module:ol/events/Event~Event} event Event.
 * @protected
 */
TileQueue.prototype.handleTileChange = function(event) {
  const tile = /** @type {module:ol/Tile~Tile} */ (event.target);
  const state = tile.getState();
  if (state === TileState.LOADED || state === TileState.ERROR ||
      state === TileState.EMPTY || state === TileState.ABORT) {
    unlisten(tile, EventType.CHANGE,
      this.handleTileChange, this);
    const tileKey = tile.getKey();
    if (tileKey in this.tilesLoadingKeys_) {
      delete this.tilesLoadingKeys_[tileKey];
      --this.tilesLoading_;
    }
    this.tileChangeCallback_();
  }
};


/**
 * @param {number} maxTotalLoading Maximum number tiles to load simultaneously.
 * @param {number} maxNewLoads Maximum number of new tiles to load.
 */
TileQueue.prototype.loadMoreTiles = function(maxTotalLoading, maxNewLoads) {
  let newLoads = 0;
  let abortedTiles = false;
  let state, tile, tileKey;
  while (this.tilesLoading_ < maxTotalLoading && newLoads < maxNewLoads &&
         this.getCount() > 0) {
    tile = /** @type {module:ol/Tile~Tile} */ (this.dequeue()[0]);
    tileKey = tile.getKey();
    state = tile.getState();
    if (state === TileState.ABORT) {
      abortedTiles = true;
    } else if (state === TileState.IDLE && !(tileKey in this.tilesLoadingKeys_)) {
      this.tilesLoadingKeys_[tileKey] = true;
      ++this.tilesLoading_;
      ++newLoads;
      tile.load();
    }
  }
  if (newLoads === 0 && abortedTiles) {
    // Do not stop the render loop when all wanted tiles were aborted due to
    // a small, saturated tile cache.
    this.tileChangeCallback_();
  }
};
export default TileQueue;