if(typeof($) == 'function') {

    /*
     *  Like constructor for jQuery plugin.
     */
    jQuery.makePresentation = function(settings) {
        
        settings = jQuery.extend({
            aSlidesLength   : 0,
            onShowSlide     : null,
            onSwitchMode    : null,
            canGo           : null
        }, settings);
        
        /*
         *  Presentation plugin
         */
        jQuery.presentation = {
            
            settings: settings,
            
            isSlides: false,
            aCounter: 0,
                
            /*
             *  Base
             */
            switchMode: function () {
                this.isSlides = !this.isSlides;
                
                if(typeof(this.settings.onSwitchMode) == 'function') {
                    this.settings.onSwitchMode(this.isSlides);
                }
            },
            
            /*
             *  Navigation
             */ 
            canGo: function() {
                return this.settings.aSlidesLength > 0;
            },
            
            canGoNext: function() {
                return this.canGo && (this.aCounter + 1) < this.settings.aSlidesLength;
            },
            
            canGoPrev: function() {
                return this.canGo && this.aCounter > 0;
            },
            
            goNext: function() {
                if(this.aCounter < 0) this.aCounter = 0;
                if(this.canGoNext() && (typeof(this.settings.canGo) != 'function' || this.settings.canGo(true))) this.goTo(++this.aCounter);
            },
            
            goPrev: function() {
                if(this.aCounter >= this.settings.aSlidesLenght) this.aCounter = this.settings.aSlidesLenght - 1;
                if(this.canGoPrev() && (typeof(this.settings.canGo) != 'function' || this.settings.canGo(false))) this.goTo(--this.aCounter);
            },
            
            goTo: function(aSlide) {
                if(aSlide >= 0 && aSlide < this.settings.aSlidesLength) {
                    if(typeof(this.settings.onShowSlide) == 'function') this.settings.onShowSlide(aSlide);
                } else {
                    console.error('Out of bounds');                // REMOVE THIS LINE! MAYBE LATER...
                }
            },
            
            goToFirst: function () {
                this.aCounter = 0;
                this.goTo(this.aCounter);
            },
            
            goToLast: function() {
                this.aCounter = this.settings.aSlidesLength - 1;
                this.goTo(this.aCounter);
            },
            
            isFirstSlide: function() {
                return this.aCounter == 0;
            },
            
            isLastSlide: function() {
                return this.aCounter == this.settings.aSlidesLength - 1;
            }
            
        }
        
        /*
         *  Events
         */
        $(document).keyup(function(e) {

            if(typeof($.presentation) == 'object' && $.presentation.isSlides) {
                
                switch(e.keyCode) {
                    case 13: case 32: case 34: case 39: case 40:
                        if($.presentation.canGoNext()) $.presentation.goNext();
                        break;
                    case 33: case 37: case 38:
                        if($.presentation.canGoPrev()) $.presentation.goPrev();
                        break;
                    case 36:
                        if($.presentation.canGo()) $.presentation.goToFirst();
                        break;
                    case 35:
                        if($.presentation.canGo()) $.presentation.goToLast();
                        break;
                    case 27:
                        $.presentation.switchMode();
                        break;
                }
                
                return false;
                        
            }
            
            if(typeof($.presentation) == 'object' && !$.presentation.isSlides) {
                
                if(e.keyCode == 13) {
                    $.presentation.switchMode();
                    return false;
                }
            }

        });
        
        $(document).mouseup(function(e) {
            if (typeof($.presentation) == 'object' && $.presentation.isSlides) {
                switch(e.keyCode) {
                    case 13: case 32: case 34: case 39: case 40:
                        if($.presentation.canGoNext()) $.presentation.goNext();
                        break;
                    case 33: case 37: case 38:
                        if($.presentation.canGoPrev()) $.presentation.goPrev();
                        break;
                    case 36:
                        if($.presentation.canGo()) $.presentation.goToFirst();
                        break;
                    case 35:
                        if($.presentation.canGo()) $.presentation.goToLast();
                        break;
                    case 27:
                        $.presentation.switchMode();
                        break;
                }

                return false;
            }
        });

        return true;
        
    }
    
}