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(function() {
        
'use strict';

/**
 * SimpleUndo is a very basic javascript undo/redo stack for managing histories of basically anything.
 * 
 * options are: {
 *      * `provider` : required. a function to call on `save`, which should provide the current state of the historized object through the given "done" callback
 *      * `maxLength` : the maximum number of items in history
 *      * `opUpdate` : a function to call to notify of changes in history. Will be called on `save`, `undo`, `redo` and `clear`
 * }
 * 
 */
var SimpleUndo = function(options) {
        
        var settings = options ? options : {};
        var defaultOptions = {
                provider: function() {
                        throw new Error("No provider!");
                },
                maxLength: 30,
                onUpdate: function() {}
        };
        
        this.provider = (typeof settings.provider != 'undefined') ? settings.provider : defaultOptions.provider;
        this.maxLength = (typeof settings.maxLength != 'undefined') ? settings.maxLength : defaultOptions.maxLength;
        this.onUpdate = (typeof settings.onUpdate != 'undefined') ? settings.onUpdate : defaultOptions.onUpdate;
        
        this.initialItem = null;
        this.clear();
};

function truncate (stack, limit) {
        while (stack.length > limit) {
                stack.shift();
        }
}

SimpleUndo.prototype.initialize = function(initialItem) {
        this.stack[0] = initialItem;
        this.initialItem = initialItem;
};


SimpleUndo.prototype.clear = function() {
        this.stack = [this.initialItem];
        this.position = 0;
        this.onUpdate();
};

SimpleUndo.prototype.save = function() {
        this.provider(function(current) {
                truncate(this.stack, this.maxLength);
                this.position = Math.min(this.position,this.stack.length - 1);
                
                this.stack = this.stack.slice(0, this.position + 1);
                this.stack.push(current);
                this.position++;
                this.onUpdate();
        }.bind(this));
};

SimpleUndo.prototype.undo = function(callback) {
        if (this.canUndo()) {
                var item =  this.stack[--this.position];
                this.onUpdate();
                
                if (callback) {
                        callback(item);
                }
        }
};

SimpleUndo.prototype.redo = function(callback) {
        if (this.canRedo()) {
                var item = this.stack[++this.position];
                this.onUpdate();
                
                if (callback) {
                        callback(item);
                }
        }
};

SimpleUndo.prototype.canUndo = function() {
        return this.position > 0;
};

SimpleUndo.prototype.canRedo = function() {
        return this.position < this.count();
};

SimpleUndo.prototype.count = function() {
        return this.stack.length - 1; // -1 because of initial item
};





//exports
// node module
if (typeof module != 'undefined') {
        module.exports = SimpleUndo;
}

// browser global
if (typeof window != 'undefined') {
        window.SimpleUndo = SimpleUndo;
}

})();

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