"use strict";
// https://heycam.github.io/webidl/#idl-named-properties

const IS_NAMED_PROPERTY = Symbol();
const TRACKER = Symbol();

/**
 * Create a new NamedPropertiesTracker for the given `object`.
 *
 * Named properties are used in DOM to let you lookup (for example) a Node by accessing a property on another object.
 * For example `window.foo` might resolve to an image element with id "foo".
 *
 * This tracker is a workaround because the ES6 Proxy feature is not yet available.
 *
 * @param {Object} object
 * @param {Function} resolverFunc Each time a property is accessed, this function is called to determine the value of
 *        the property. The function is passed 3 arguments: (object, name, values).
 *        `object` is identical to the `object` parameter of this `create` function.
 *        `name` is the name of the property.
 *        `values` is a function that returns a Set with all the tracked values for this name. The order of these
 *        values is undefined.
 *
 * @returns {NamedPropertiesTracker}
 */
exports.create = function (object, resolverFunc) {
  if (object[TRACKER]) {
    throw Error("A NamedPropertiesTracker has already been created for this object");
  }

  const tracker = new NamedPropertiesTracker(object, resolverFunc);
  object[TRACKER] = tracker;
  return tracker;
};

exports.get = function (object) {
  if (!object) {
    return null;
  }

  return object[TRACKER] || null;
};

function NamedPropertiesTracker(object, resolverFunc) {
  this.object = object;
  this.resolverFunc = resolverFunc;
  this.trackedValues = new Map(); // Map<Set<value>>
}

function newPropertyDescriptor(tracker, name) {
  const emptySet = new Set();

  function getValues() {
    return tracker.trackedValues.get(name) || emptySet;
  }

  const descriptor = {
    enumerable: true,
    configurable: true,
    get() {
      return tracker.resolverFunc(tracker.object, name, getValues);
    },
    set(value) {
      Object.defineProperty(tracker.object, name, {
        enumerable: true,
        configurable: true,
        writable: true,
        value
      });
    }
  };

  descriptor.get[IS_NAMED_PROPERTY] = true;
  descriptor.set[IS_NAMED_PROPERTY] = true;
  return descriptor;
}

/**
 * Track a value (e.g. a Node) for a specified name.
 *
 * Values can be tracked eagerly, which means that not all tracked values *have* to appear in the output. The resolver
 * function that was passed to the output may filter the value.
 *
 * Tracking the same `name` and `value` pair multiple times has no effect
 *
 * @param {String} name
 * @param {*} value
 */
NamedPropertiesTracker.prototype.track = function (name, value) {
  if (name === undefined || name === null || name === "") {
    return;
  }

  let valueSet = this.trackedValues.get(name);
  if (!valueSet) {
    valueSet = new Set();
    this.trackedValues.set(name, valueSet);
  }

  valueSet.add(value);

  if (name in this.object) {
    // already added our getter or it is not a named property (e.g. "addEventListener")
    return;
  }

  const descriptor = newPropertyDescriptor(this, name);
  Object.defineProperty(this.object, name, descriptor);
};

/**
 * Stop tracking a previously tracked `name` & `value` pair, see track().
 *
 * Untracking the same `name` and `value` pair multiple times has no effect
 *
 * @param {String} name
 * @param {*} value
 */
NamedPropertiesTracker.prototype.untrack = function (name, value) {
  if (name === undefined || name === null || name === "") {
    return;
  }

  const valueSet = this.trackedValues.get(name);
  if (!valueSet) {
    // the value is not present
    return;
  }

  if (!valueSet.delete(value)) {
    // the value was not present
    return;
  }

  if (valueSet.size === 0) {
    this.trackedValues.delete(name);
  }

  if (valueSet.size > 0) {
    // other values for this name are still present
    return;
  }

  // at this point there are no more values, delete the property

  const descriptor = Object.getOwnPropertyDescriptor(this.object, name);

  if (!descriptor || !descriptor.get || descriptor.get[IS_NAMED_PROPERTY] !== true) {
    // Not defined by NamedPropertyTracker
    return;
  }

  // note: delete puts the object in dictionary mode.
  // if this turns out to be a performance issue, maybe add:
  // https://github.com/petkaantonov/bluebird/blob/3e36fc861ac5795193ba37935333eb6ef3716390/src/util.js#L177
  delete this.object[name];
};