// Copyright 2007 The Closure Library Authors. All Rights Reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS-IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

/**
 * @fileoverview Datastructure: Pool.
 *
 *
 * A generic class for handling pools of objects that is more efficient than
 * goog.structs.Pool because it doesn't maintain a list of objects that are in
 * use. See constructor comment.
 */


goog.provide('goog.structs.SimplePool');

goog.require('goog.Disposable');



/**
 * A generic pool class. Simpler and more efficient than goog.structs.Pool
 * because it doesn't maintain a list of objects that are in use. This class
 * has constant overhead and doesn't create any additional objects as part of
 * the pool management after construction time.
 *
 * IMPORTANT: If the objects being pooled are arrays or maps that can have
 * unlimited number of properties, they need to be cleaned before being
 * returned to the pool.
 *
 * Also note that {@see goog.object.clean} actually allocates an array to clean
 * the object passed to it, so simply using this function would defy the
 * purpose of using the pool.
 *
 * @param {number} initialCount Initial number of objects to populate the free
 *     pool at construction time.
 * @param {number} maxCount Maximum number of objects to keep in the free pool.
 * @constructor
 * @extends {goog.Disposable}
 * @template T
 */
goog.structs.SimplePool = function(initialCount, maxCount) {
  goog.Disposable.call(this);

  /**
   * Function for overriding createObject. The avoids a common case requiring
   * subclassing this class.
   * @private {Function}
   */
  this.createObjectFn_ = null;

  /**
   * Function for overriding disposeObject. The avoids a common case requiring
   * subclassing this class.
   * @private {Function}
   */
  this.disposeObjectFn_ = null;

  /**
   * Maximum number of objects allowed
   * @private {number}
   */
  this.maxCount_ = maxCount;

  /**
   * Queue used to store objects that are currently in the pool and available
   * to be used.
   * @private {Array.<T>}
   */
  this.freeQueue_ = [];

  this.createInitial_(initialCount);
};
goog.inherits(goog.structs.SimplePool, goog.Disposable);


/**
 * Sets the {@code createObject} function which is used for creating a new
 * object in the pool.
 * @param {Function} createObjectFn Create object function which returns the
 *     newly created object.
 */
goog.structs.SimplePool.prototype.setCreateObjectFn = function(createObjectFn) {
  this.createObjectFn_ = createObjectFn;
};


/**
 * Sets the {@code disposeObject} function which is used for disposing of an
 * object in the pool.
 * @param {Function} disposeObjectFn Dispose object function which takes the
 *     object to dispose as a parameter.
 */
goog.structs.SimplePool.prototype.setDisposeObjectFn = function(
    disposeObjectFn) {
  this.disposeObjectFn_ = disposeObjectFn;
};


/**
 * Gets an unused object from the the pool, if there is one available,
 * otherwise creates a new one.
 * @return {T} An object from the pool or a new one if necessary.
 */
goog.structs.SimplePool.prototype.getObject = function() {
  if (this.freeQueue_.length) {
    return this.freeQueue_.pop();
  }
  return this.createObject();
};


/**
 * Returns an object to the pool so that it can be reused. If the pool is
 * already full, the object is disposed instead.
 * @param {T} obj The object to release.
 */
goog.structs.SimplePool.prototype.releaseObject = function(obj) {
  if (this.freeQueue_.length < this.maxCount_) {
    this.freeQueue_.push(obj);
  } else {
    this.disposeObject(obj);
  }
};


/**
 * Populates the pool with initialCount objects.
 * @param {number} initialCount The number of objects to add to the pool.
 * @private
 */
goog.structs.SimplePool.prototype.createInitial_ = function(initialCount) {
  if (initialCount > this.maxCount_) {
    throw Error('[goog.structs.SimplePool] Initial cannot be greater than max');
  }
  for (var i = 0; i < initialCount; i++) {
    this.freeQueue_.push(this.createObject());
  }
};


/**
 * Should be overridden by sub-classes to return an instance of the object type
 * that is expected in the pool.
 * @return {T} The created object.
 */
goog.structs.SimplePool.prototype.createObject = function() {
  if (this.createObjectFn_) {
    return this.createObjectFn_();
  } else {
    return {};
  }
};


/**
 * Should be overrideen to dispose of an object. Default implementation is to
 * remove all of the object's members, which should render it useless. Calls the
 *  object's dispose method, if available.
 * @param {T} obj The object to dispose.
 */
goog.structs.SimplePool.prototype.disposeObject = function(obj) {
  if (this.disposeObjectFn_) {
    this.disposeObjectFn_(obj);
  } else if (goog.isObject(obj)) {
    if (goog.isFunction(obj.dispose)) {
      obj.dispose();
    } else {
      for (var i in obj) {
        delete obj[i];
      }
    }
  }
};


/**
 * Disposes of the pool and all objects currently held in the pool.
 * @override
 * @protected
 */
goog.structs.SimplePool.prototype.disposeInternal = function() {
  goog.structs.SimplePool.superClass_.disposeInternal.call(this);
  // Call disposeObject on each object held by the pool.
  var freeQueue = this.freeQueue_;
  while (freeQueue.length) {
    this.disposeObject(freeQueue.pop());
  }
  delete this.freeQueue_;
};
