"use strict";

( function ( NS ) {


var UndoManager = NS.Class({

 Extends: NS.Object,

 init: function ( mixin ) {
   this._undoStack = [];
   this._redoStack = [];

   this._isInUndoState = false;

   this.canUndo = false;
   this.canRedo = false;

   this.maxUndoCount = 1;

   UndoManager.parent.init.call( this, mixin );
 },

 _pushState: function ( stack, data ) {
   stack.push( data );
   while ( stack.length > this.maxUndoCount ) {
     stack.shift();
   }
   this._isInUndoState = true;
 },

 dataDidChange: function () {
   this._isInUndoState = false;
   this._redoStack.length = 0;
   this.set( 'canRedo', false )
     .set( 'canUndo', true );
   return this;
 },

 saveUndoCheckpoint: function () {
   if ( !this._isInUndoState ) {
     var data = this.getUndoData();
     if ( data !== null ) {
       this._pushState( this._undoStack, data );
     } else {
       this._isInUndoState = true;
       this.set( 'canUndo', !!this._undoStack.length );
     }
   }
   return this;
 },

 undo: function () {
   if ( this.get( 'canUndo' ) ) {
     if ( !this._isInUndoState ) {
       this.saveUndoCheckpoint();
       return this.undo();
     } else {
       this._pushState( this._redoStack,
         this.applyChange( this._undoStack.pop(), false )
       );
       this.set( 'canUndo', !!this._undoStack.length )
         .set( 'canRedo', true );
     }
   }
   return this;
 },

 redo: function () {
   if ( this.get( 'canRedo' ) ) {
     this._pushState( this._undoStack,
       this.applyChange( this._redoStack.pop(), true )
     );
     this.set( 'canUndo', true )
       .set( 'canRedo', !!this._redoStack.length );
   }
   return this;
 },

 getUndoData: function () {},

 applyChange: function (/* data, isRedo */) {}
});

var StoreUndoManager = NS.Class({

 Extends: UndoManager,

 init: function ( mixin ) {
   var store = mixin.store;
   store.on( 'willCommit', this, 'saveUndoCheckpoint' )
      .on( 'record:user:create', this, 'dataDidChange' )
      .on( 'record:user:update', this, 'dataDidChange' )
      .on( 'record:user:destroy', this, 'dataDidChange' );
   StoreUndoManager.parent.init.call( this, mixin );
 },

 destroy: function () {
   this.store.off( 'willCommit', this, 'saveUndoCheckpoint' )
          .off( 'record:user:create', this, 'dataDidChange' )
          .off( 'record:user:update', this, 'dataDidChange' )
          .off( 'record:user:destroy', this, 'dataDidChange' );
   StoreUndoManager.parent.destroy.call( this );
 },

 getUndoData: function () {
   var store = this.store;
   return store.hasChanges() ? store.getInverseChanges() : null;
 },

 applyChange: function ( data ) {
   var store = this.store,
     inverse;
   store.applyChanges( data );
   inverse = store.getInverseChanges();
   store.commitChanges();
   return inverse;
 }
});

NS.UndoManager = UndoManager;
NS.StoreUndoManager = StoreUndoManager;

}( O ) );