/*
 * Copyright 2012, Mozilla Foundation and contributors
 *
 * 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.
 */

define(function(require, exports, module) {

'use strict';

/**
 * A History object remembers commands that have been entered in the past and
 * provides an API for accessing them again.
 * See Bug 681340: Search through history (like C-r in bash)?
 */
function History() {
  // This is the actual buffer where previous commands are kept.
  // 'this._buffer[0]' should always be equal the empty string. This is so
  // that when you try to go in to the "future", you will just get an empty
  // command.
  this._buffer = [''];

  // This is an index in to the history buffer which points to where we
  // currently are in the history.
  this._current = 0;
}

/**
 * Avoid memory leaks
 */
History.prototype.destroy = function() {
  delete this._buffer;
};

/**
 * Record and save a new command in the history.
 */
History.prototype.add = function(command) {
  this._buffer.splice(1, 0, command);
  this._current = 0;
};

/**
 * Get the next (newer) command from history.
 */
History.prototype.forward = function() {
  if (this._current > 0 ) {
    this._current--;
  }
  return this._buffer[this._current];
};

/**
 * Get the previous (older) item from history.
 */
History.prototype.backward = function() {
  if (this._current < this._buffer.length - 1) {
    this._current++;
  }
  return this._buffer[this._current];
};

exports.History = History;

});
