import {
  isArray,
  forEach
} from 'min-dash';


/**
 * A service that offers the current selection in a diagram.
 * Offers the api to control the selection, too.
 *
 * @class
 *
 * @param {EventBus} eventBus the event bus
 */
export default function Selection(eventBus) {

  this._eventBus = eventBus;

  this._selectedElements = [];

  var self = this;

  eventBus.on([ 'shape.remove', 'connection.remove' ], function(e) {
    var element = e.element;
    self.deselect(element);
  });

  eventBus.on([ 'diagram.clear' ], function(e) {
    self.select(null);
  });
}

Selection.$inject = [ 'eventBus' ];


Selection.prototype.deselect = function(element) {
  var selectedElements = this._selectedElements;

  var idx = selectedElements.indexOf(element);

  if (idx !== -1) {
    var oldSelection = selectedElements.slice();

    selectedElements.splice(idx, 1);

    this._eventBus.fire('selection.changed', { oldSelection: oldSelection, newSelection: selectedElements });
  }
};


Selection.prototype.get = function() {
  return this._selectedElements;
};

Selection.prototype.isSelected = function(element) {
  return this._selectedElements.indexOf(element) !== -1;
};


/**
 * This method selects one or more elements on the diagram.
 *
 * By passing an additional add parameter you can decide whether or not the element(s)
 * should be added to the already existing selection or not.
 *
 * @method Selection#select
 *
 * @param  {Object|Object[]} elements element or array of elements to be selected
 * @param  {boolean} [add] whether the element(s) should be appended to the current selection, defaults to false
 */
Selection.prototype.select = function(elements, add) {
  var selectedElements = this._selectedElements,
      oldSelection = selectedElements.slice();

  if (!isArray(elements)) {
    elements = elements ? [ elements ] : [];
  }

  // selection may be cleared by passing an empty array or null
  // to the method
  if (add) {
    forEach(elements, function(element) {
      if (selectedElements.indexOf(element) !== -1) {
        // already selected
        return;
      } else {
        selectedElements.push(element);
      }
    });
  } else {
    this._selectedElements = selectedElements = elements.slice();
  }

  this._eventBus.fire('selection.changed', { oldSelection: oldSelection, newSelection: selectedElements });
};