dojo.provide("dojo.undo.Manager");
dojo.require("dojo.lang");

dojo.undo.Manager = function(parent) {
	this.clear();
	this._parent = parent;
};
dojo.lang.extend(dojo.undo.Manager, {
	_parent: null,
	_undoStack: null,
	_redoStack: null,
	_currentManager: null,

	canUndo: false,
	canRedo: false,

	isUndoing: false,
	isRedoing: false,

	// these events allow you to hook in and update your code (UI?) as necessary
	onUndo: function(manager, item) {},
	onRedo: function(manager, item) {},

	// fired when you do *any* undo action, which means you'll have one for every item
	// in a transaction. this is usually only useful for debugging
	onUndoAny: function(manager, item) {},
	onRedoAny: function(manager, item) {},

	_updateStatus: function() {
		this.canUndo = this._undoStack.length > 0;
		this.canRedo = this._redoStack.length > 0;
	},

	clear: function() {
		this._undoStack = [];
		this._redoStack = [];
		this._currentManager = this;

		this.isUndoing = false;
		this.isRedoing = false;

		this._updateStatus();
	},

	undo: function() {
		if(!this.canUndo) { return false; }

		this.endAllTransactions();

		this.isUndoing = true;
		var top = this._undoStack.pop();
		if(top instanceof dojo.undo.Manager){
			top.undoAll();
		}else{
			top.undo();
		}
		if(top.redo){
			this._redoStack.push(top);
		}
		this.isUndoing = false;

		this._updateStatus();
		this.onUndo(this, top);
		if(!(top instanceof dojo.undo.Manager)){
			this.getTop().onUndoAny(this, top);
		}
		return true;
	},

	redo: function() {
		if(!this.canRedo){ return false; }

		this.isRedoing = true;
		var top = this._redoStack.pop();
		if(top instanceof dojo.undo.Manager){
			top.redoAll();
		}else{
			top.redo();
		}
		this._undoStack.push(top);
		this.isRedoing = false;

		this._updateStatus();
		this.onRedo(this, top);
		if(!(top instanceof dojo.undo.Manager)){
			this.getTop().onRedoAny(this, top);
		}
		return true;
	},

	undoAll: function() {
		while(this._undoStack.length > 0) {
			this.undo();
		}
	},

	redoAll: function() {
		while(this._redoStack.length > 0) {
			this.redo();
		}
	},

	push: function(undo, redo /* optional */, description /* optional */) {
		if(!undo) { return; }

		if(this._currentManager == this) {
			this._undoStack.push({
				undo: undo,
				redo: redo,
				description: description
			});
		} else {
			this._currentManager.push.apply(this._currentManager, arguments);
		}
		// adding a new undo-able item clears out the redo stack
		this._redoStack = [];
		this._updateStatus();
	},

	concat: function(manager) {
		if ( !manager ) { return; }

		if (this._currentManager == this ) {
			for(var x=0; x < manager._undoStack.length; x++) {
				this._undoStack.push(manager._undoStack[x]);
			}
			// adding a new undo-able item clears out the redo stack
			if (manager._undoStack.length > 0) {
				this._redoStack = [];
			}
			this._updateStatus();
		} else {
			this._currentManager.concat.apply(this._currentManager, arguments);
		}
	},

	beginTransaction: function(description /* optional */) {
		if(this._currentManager == this) {
			var mgr = new dojo.undo.Manager(this);
			mgr.description = description ? description : "";
			this._undoStack.push(mgr);
			this._currentManager = mgr;
			return mgr;
		} else {
			//for nested transactions need to make sure the top level _currentManager is set
			this._currentManager = this._currentManager.beginTransaction.apply(this._currentManager, arguments);
		}
	},

	endTransaction: function(flatten /* optional */) {
		if(this._currentManager == this) {
			if(this._parent) {
				this._parent._currentManager = this._parent;
				// don't leave empty transactions hangin' around
				if(this._undoStack.length == 0 || flatten) {
					var idx = dojo.lang.find(this._parent._undoStack, this);
					if (idx >= 0) {
						this._parent._undoStack.splice(idx, 1);
						//add the current transaction to parents undo stack
						if (flatten) {
							for(var x=0; x < this._undoStack.length; x++){
								this._parent._undoStack.splice(idx++, 0, this._undoStack[x]);
							}
							this._updateStatus();
						}
					}
				}
				return this._parent;
			}
		} else {
			//for nested transactions need to make sure the top level _currentManager is set
			this._currentManager = this._currentManager.endTransaction.apply(this._currentManager, arguments);
		}
	},

	endAllTransactions: function() {
		while(this._currentManager != this) {
			this.endTransaction();
		}
	},

	// find the top parent of an undo manager
	getTop: function() {
		if(this._parent) {
			return this._parent.getTop();
		} else {
			return this;
		}
	}
});
