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+// 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 A LinkedMap data structure that is accessed using key/value
+ * pairs like an ordinary Map, but which guarantees a consistent iteration
+ * order over its entries. The iteration order is either insertion order (the
+ * default) or ordered from most recent to least recent use. By setting a fixed
+ * size, the LRU version of the LinkedMap makes an effective object cache. This
+ * data structure is similar to Java's LinkedHashMap.
+ *
+ * @author brenneman@google.com (Shawn Brenneman)
+ */
+
+
+goog.provide('goog.structs.LinkedMap');
+
+goog.require('goog.structs.Map');
+
+
+
+/**
+ * Class for a LinkedMap datastructure, which combines O(1) map access for
+ * key/value pairs with a linked list for a consistent iteration order. Sample
+ * usage:
+ *
+ * <pre>
+ * var m = new LinkedMap();
+ * m.set('param1', 'A');
+ * m.set('param2', 'B');
+ * m.set('param3', 'C');
+ * alert(m.getKeys()); // param1, param2, param3
+ *
+ * var c = new LinkedMap(5, true);
+ * for (var i = 0; i < 10; i++) {
+ *   c.set('entry' + i, false);
+ * }
+ * alert(c.getKeys()); // entry9, entry8, entry7, entry6, entry5
+ *
+ * c.set('entry5', true);
+ * c.set('entry1', false);
+ * alert(c.getKeys()); // entry1, entry5, entry9, entry8, entry7
+ * </pre>
+ *
+ * @param {number=} opt_maxCount The maximum number of objects to store in the
+ *     LinkedMap. If unspecified or 0, there is no maximum.
+ * @param {boolean=} opt_cache When set, the LinkedMap stores items in order
+ *     from most recently used to least recently used, instead of insertion
+ *     order.
+ * @constructor
+ */
+goog.structs.LinkedMap = function(opt_maxCount, opt_cache) {
+  /**
+   * The maximum number of entries to allow, or null if there is no limit.
+   * @type {?number}
+   * @private
+   */
+  this.maxCount_ = opt_maxCount || null;
+
+  /**
+   * @type {boolean}
+   * @private
+   */
+  this.cache_ = !!opt_cache;
+
+  this.map_ = new goog.structs.Map();
+
+  this.head_ = new goog.structs.LinkedMap.Node_('', undefined);
+  this.head_.next = this.head_.prev = this.head_;
+};
+
+
+/**
+ * Finds a node and updates it to be the most recently used.
+ * @param {string} key The key of the node.
+ * @return {goog.structs.LinkedMap.Node_} The node or null if not found.
+ * @private
+ */
+goog.structs.LinkedMap.prototype.findAndMoveToTop_ = function(key) {
+  var node = /** @type {goog.structs.LinkedMap.Node_} */ (this.map_.get(key));
+  if (node) {
+    if (this.cache_) {
+      node.remove();
+      this.insert_(node);
+    }
+  }
+  return node;
+};
+
+
+/**
+ * Retrieves the value for a given key. If this is a caching LinkedMap, the
+ * entry will become the most recently used.
+ * @param {string} key The key to retrieve the value for.
+ * @param {*=} opt_val A default value that will be returned if the key is
+ *     not found, defaults to undefined.
+ * @return {*} The retrieved value.
+ */
+goog.structs.LinkedMap.prototype.get = function(key, opt_val) {
+  var node = this.findAndMoveToTop_(key);
+  return node ? node.value : opt_val;
+};
+
+
+/**
+ * Retrieves the value for a given key without updating the entry to be the
+ * most recently used.
+ * @param {string} key The key to retrieve the value for.
+ * @param {*=} opt_val A default value that will be returned if the key is
+ *     not found.
+ * @return {*} The retrieved value.
+ */
+goog.structs.LinkedMap.prototype.peekValue = function(key, opt_val) {
+  var node = this.map_.get(key);
+  return node ? node.value : opt_val;
+};
+
+
+/**
+ * Sets a value for a given key. If this is a caching LinkedMap, this entry
+ * will become the most recently used.
+ * @param {string} key The key to retrieve the value for.
+ * @param {*} value A default value that will be returned if the key is
+ *     not found.
+ */
+goog.structs.LinkedMap.prototype.set = function(key, value) {
+  var node = this.findAndMoveToTop_(key);
+  if (node) {
+    node.value = value;
+  } else {
+    node = new goog.structs.LinkedMap.Node_(key, value);
+    this.map_.set(key, node);
+    this.insert_(node);
+  }
+};
+
+
+/**
+ * Returns the value of the first node without making any modifications.
+ * @return {*} The value of the first node or undefined if the map is empty.
+ */
+goog.structs.LinkedMap.prototype.peek = function() {
+  return this.head_.next.value;
+};
+
+
+/**
+ * Returns the value of the last node without making any modifications.
+ * @return {*} The value of the last node or undefined if the map is empty.
+ */
+goog.structs.LinkedMap.prototype.peekLast = function() {
+  return this.head_.prev.value;
+};
+
+
+/**
+ * Removes the first node from the list and returns its value.
+ * @return {*} The value of the popped node, or undefined if the map was empty.
+ */
+goog.structs.LinkedMap.prototype.shift = function() {
+  return this.popNode_(this.head_.next);
+};
+
+
+/**
+ * Removes the last node from the list and returns its value.
+ * @return {*} The value of the popped node, or undefined if the map was empty.
+ */
+goog.structs.LinkedMap.prototype.pop = function() {
+  return this.popNode_(this.head_.prev);
+};
+
+
+/**
+ * Removes a value from the LinkedMap based on its key.
+ * @param {string} key The key to remove.
+ * @return {boolean} True if the entry was removed, false if the key was not
+ *     found.
+ */
+goog.structs.LinkedMap.prototype.remove = function(key) {
+  var node = /** @type {goog.structs.LinkedMap.Node_} */ (this.map_.get(key));
+  if (node) {
+    this.removeNode(node);
+    return true;
+  }
+  return false;
+};
+
+
+/**
+ * Removes a node from the {@code LinkedMap}. It can be overridden to do
+ * further cleanup such as disposing of the node value.
+ * @param {!goog.structs.LinkedMap.Node_} node The node to remove.
+ * @protected
+ */
+goog.structs.LinkedMap.prototype.removeNode = function(node) {
+  node.remove();
+  this.map_.remove(node.key);
+};
+
+
+/**
+ * @return {number} The number of items currently in the LinkedMap.
+ */
+goog.structs.LinkedMap.prototype.getCount = function() {
+  return this.map_.getCount();
+};
+
+
+/**
+ * @return {boolean} True if the cache is empty, false if it contains any items.
+ */
+goog.structs.LinkedMap.prototype.isEmpty = function() {
+  return this.map_.isEmpty();
+};
+
+
+/**
+ * Sets the maximum number of entries allowed in this object, truncating any
+ * excess objects if necessary.
+ * @param {number} maxCount The new maximum number of entries to allow.
+ */
+goog.structs.LinkedMap.prototype.setMaxCount = function(maxCount) {
+  this.maxCount_ = maxCount || null;
+  if (this.maxCount_ != null) {
+    this.truncate_(this.maxCount_);
+  }
+};
+
+
+/**
+ * @return {!Array.<string>} The list of the keys in the appropriate order for
+ *     this LinkedMap.
+ */
+goog.structs.LinkedMap.prototype.getKeys = function() {
+  return this.map(function(val, key) {
+    return key;
+  });
+};
+
+
+/**
+ * @return {!Array} The list of the values in the appropriate order for
+ *     this LinkedMap.
+ */
+goog.structs.LinkedMap.prototype.getValues = function() {
+  return this.map(function(val, key) {
+    return val;
+  });
+};
+
+
+/**
+ * Tests whether a provided value is currently in the LinkedMap. This does not
+ * affect item ordering in cache-style LinkedMaps.
+ * @param {Object} value The value to check for.
+ * @return {boolean} Whether the value is in the LinkedMap.
+ */
+goog.structs.LinkedMap.prototype.contains = function(value) {
+  return this.some(function(el) {
+    return el == value;
+  });
+};
+
+
+/**
+ * Tests whether a provided key is currently in the LinkedMap. This does not
+ * affect item ordering in cache-style LinkedMaps.
+ * @param {string} key The key to check for.
+ * @return {boolean} Whether the key is in the LinkedMap.
+ */
+goog.structs.LinkedMap.prototype.containsKey = function(key) {
+  return this.map_.containsKey(key);
+};
+
+
+/**
+ * Removes all entries in this object.
+ */
+goog.structs.LinkedMap.prototype.clear = function() {
+  this.truncate_(0);
+};
+
+
+/**
+ * Calls a function on each item in the LinkedMap.
+ *
+ * @see goog.structs.forEach
+ * @param {Function} f The function to call for each item. The function takes
+ *     three arguments: the value, the key, and the LinkedMap.
+ * @param {Object=} opt_obj The object context to use as "this" for the
+ *     function.
+ */
+goog.structs.LinkedMap.prototype.forEach = function(f, opt_obj) {
+  for (var n = this.head_.next; n != this.head_; n = n.next) {
+    f.call(opt_obj, n.value, n.key, this);
+  }
+};
+
+
+/**
+ * Calls a function on each item in the LinkedMap and returns the results of
+ * those calls in an array.
+ *
+ * @see goog.structs.map
+ * @param {!Function} f The function to call for each item. The function takes
+ *     three arguments: the value, the key, and the LinkedMap.
+ * @param {Object=} opt_obj The object context to use as "this" for the
+ *     function.
+ * @return {!Array} The results of the function calls for each item in the
+ *     LinkedMap.
+ */
+goog.structs.LinkedMap.prototype.map = function(f, opt_obj) {
+  var rv = [];
+  for (var n = this.head_.next; n != this.head_; n = n.next) {
+    rv.push(f.call(opt_obj, n.value, n.key, this));
+  }
+  return rv;
+};
+
+
+/**
+ * Calls a function on each item in the LinkedMap and returns true if any of
+ * those function calls returns a true-like value.
+ *
+ * @see goog.structs.some
+ * @param {Function} f The function to call for each item. The function takes
+ *     three arguments: the value, the key, and the LinkedMap, and returns a
+ *     boolean.
+ * @param {Object=} opt_obj The object context to use as "this" for the
+ *     function.
+ * @return {boolean} Whether f evaluates to true for at least one item in the
+ *     LinkedMap.
+ */
+goog.structs.LinkedMap.prototype.some = function(f, opt_obj) {
+  for (var n = this.head_.next; n != this.head_; n = n.next) {
+    if (f.call(opt_obj, n.value, n.key, this)) {
+      return true;
+    }
+  }
+  return false;
+};
+
+
+/**
+ * Calls a function on each item in the LinkedMap and returns true only if every
+ * function call returns a true-like value.
+ *
+ * @see goog.structs.some
+ * @param {Function} f The function to call for each item. The function takes
+ *     three arguments: the value, the key, and the Cache, and returns a
+ *     boolean.
+ * @param {Object=} opt_obj The object context to use as "this" for the
+ *     function.
+ * @return {boolean} Whether f evaluates to true for every item in the Cache.
+ */
+goog.structs.LinkedMap.prototype.every = function(f, opt_obj) {
+  for (var n = this.head_.next; n != this.head_; n = n.next) {
+    if (!f.call(opt_obj, n.value, n.key, this)) {
+      return false;
+    }
+  }
+  return true;
+};
+
+
+/**
+ * Appends a node to the list. LinkedMap in cache mode adds new nodes to
+ * the head of the list, otherwise they are appended to the tail. If there is a
+ * maximum size, the list will be truncated if necessary.
+ *
+ * @param {goog.structs.LinkedMap.Node_} node The item to insert.
+ * @private
+ */
+goog.structs.LinkedMap.prototype.insert_ = function(node) {
+  if (this.cache_) {
+    node.next = this.head_.next;
+    node.prev = this.head_;
+
+    this.head_.next = node;
+    node.next.prev = node;
+  } else {
+    node.prev = this.head_.prev;
+    node.next = this.head_;
+
+    this.head_.prev = node;
+    node.prev.next = node;
+  }
+
+  if (this.maxCount_ != null) {
+    this.truncate_(this.maxCount_);
+  }
+};
+
+
+/**
+ * Removes elements from the LinkedMap if the given count has been exceeded.
+ * In cache mode removes nodes from the tail of the list. Otherwise removes
+ * nodes from the head.
+ * @param {number} count Number of elements to keep.
+ * @private
+ */
+goog.structs.LinkedMap.prototype.truncate_ = function(count) {
+  for (var i = this.map_.getCount(); i > count; i--) {
+    this.removeNode(this.cache_ ? this.head_.prev : this.head_.next);
+  }
+};
+
+
+/**
+ * Removes the node from the LinkedMap if it is not the head, and returns
+ * the node's value.
+ * @param {!goog.structs.LinkedMap.Node_} node The item to remove.
+ * @return {*} The value of the popped node.
+ * @private
+ */
+goog.structs.LinkedMap.prototype.popNode_ = function(node) {
+  if (this.head_ != node) {
+    this.removeNode(node);
+  }
+  return node.value;
+};
+
+
+
+/**
+ * Internal class for a doubly-linked list node containing a key/value pair.
+ * @param {string} key The key.
+ * @param {*} value The value.
+ * @constructor
+ * @private
+ */
+goog.structs.LinkedMap.Node_ = function(key, value) {
+  this.key = key;
+  this.value = value;
+};
+
+
+/**
+ * The next node in the list.
+ * @type {!goog.structs.LinkedMap.Node_}
+ */
+goog.structs.LinkedMap.Node_.prototype.next;
+
+
+/**
+ * The previous node in the list.
+ * @type {!goog.structs.LinkedMap.Node_}
+ */
+goog.structs.LinkedMap.Node_.prototype.prev;
+
+
+/**
+ * Causes this node to remove itself from the list.
+ */
+goog.structs.LinkedMap.Node_.prototype.remove = function() {
+  this.prev.next = this.next;
+  this.next.prev = this.prev;
+
+  delete this.prev;
+  delete this.next;
+};