var ELEMENT_ID = 'data-element-id';

import { attr as svgAttr } from 'tiny-svg';


/**
 * @class
 *
 * A registry that keeps track of all shapes in the diagram.
 */
export default function ElementRegistry(eventBus) {
  this._elements = {};

  this._eventBus = eventBus;
}

ElementRegistry.$inject = [ 'eventBus' ];

/**
 * Register a pair of (element, gfx, (secondaryGfx)).
 *
 * @param {djs.model.Base} element
 * @param {SVGElement} gfx
 * @param {SVGElement} [secondaryGfx] optional other element to register, too
 */
ElementRegistry.prototype.add = function(element, gfx, secondaryGfx) {

  var id = element.id;

  this._validateId(id);

  // associate dom node with element
  svgAttr(gfx, ELEMENT_ID, id);

  if (secondaryGfx) {
    svgAttr(secondaryGfx, ELEMENT_ID, id);
  }

  this._elements[id] = { element: element, gfx: gfx, secondaryGfx: secondaryGfx };
};

/**
 * Removes an element from the registry.
 *
 * @param {djs.model.Base} element
 */
ElementRegistry.prototype.remove = function(element) {
  var elements = this._elements,
      id = element.id || element,
      container = id && elements[id];

  if (container) {

    // unset element id on gfx
    svgAttr(container.gfx, ELEMENT_ID, '');

    if (container.secondaryGfx) {
      svgAttr(container.secondaryGfx, ELEMENT_ID, '');
    }

    delete elements[id];
  }
};

/**
 * Update the id of an element
 *
 * @param {djs.model.Base} element
 * @param {String} newId
 */
ElementRegistry.prototype.updateId = function(element, newId) {

  this._validateId(newId);

  if (typeof element === 'string') {
    element = this.get(element);
  }

  this._eventBus.fire('element.updateId', {
    element: element,
    newId: newId
  });

  var gfx = this.getGraphics(element),
      secondaryGfx = this.getGraphics(element, true);

  this.remove(element);

  element.id = newId;

  this.add(element, gfx, secondaryGfx);
};

/**
 * Return the model element for a given id or graphics.
 *
 * @example
 *
 * elementRegistry.get('SomeElementId_1');
 * elementRegistry.get(gfx);
 *
 *
 * @param {String|SVGElement} filter for selecting the element
 *
 * @return {djs.model.Base}
 */
ElementRegistry.prototype.get = function(filter) {
  var id;

  if (typeof filter === 'string') {
    id = filter;
  } else {
    id = filter && svgAttr(filter, ELEMENT_ID);
  }

  var container = this._elements[id];
  return container && container.element;
};

/**
 * Return all elements that match a given filter function.
 *
 * @param {Function} fn
 *
 * @return {Array<djs.model.Base>}
 */
ElementRegistry.prototype.filter = function(fn) {

  var filtered = [];

  this.forEach(function(element, gfx) {
    if (fn(element, gfx)) {
      filtered.push(element);
    }
  });

  return filtered;
};

/**
 * Return all rendered model elements.
 *
 * @return {Array<djs.model.Base>}
 */
ElementRegistry.prototype.getAll = function() {
  return this.filter(function(e) { return e; });
};

/**
 * Iterate over all diagram elements.
 *
 * @param {Function} fn
 */
ElementRegistry.prototype.forEach = function(fn) {

  var map = this._elements;

  Object.keys(map).forEach(function(id) {
    var container = map[id],
        element = container.element,
        gfx = container.gfx;

    return fn(element, gfx);
  });
};

/**
 * Return the graphical representation of an element or its id.
 *
 * @example
 * elementRegistry.getGraphics('SomeElementId_1');
 * elementRegistry.getGraphics(rootElement); // <g ...>
 *
 * elementRegistry.getGraphics(rootElement, true); // <svg ...>
 *
 *
 * @param {String|djs.model.Base} filter
 * @param {Boolean} [secondary=false] whether to return the secondary connected element
 *
 * @return {SVGElement}
 */
ElementRegistry.prototype.getGraphics = function(filter, secondary) {
  var id = filter.id || filter;

  var container = this._elements[id];
  return container && (secondary ? container.secondaryGfx : container.gfx);
};

/**
 * Validate the suitability of the given id and signals a problem
 * with an exception.
 *
 * @param {String} id
 *
 * @throws {Error} if id is empty or already assigned
 */
ElementRegistry.prototype._validateId = function(id) {
  if (!id) {
    throw new Error('element must have an id');
  }

  if (this._elements[id]) {
    throw new Error('element with id ' + id + ' already added');
  }
};