var image = 1;

window.addEvent('domready', function() {

    $$('body').setStyle('background-position','0 -30px');
    
    $$('.switch.nr' + image).addClass('active');     
    $('image_back').addEvent('click', function(){
        if(image != 1) {
            image--;
            var pos = (image - 1) * 179;
            $$('.image').setStyle('background-position', '0 -' + pos + 'px');
            $$('.desc').hide();
            $$('.desc.nr' + image).show();
            $$('.switch').removeClass('active');
            $$('.switch.nr' + image).addClass('active');    
        }
    });
    
    $('image_forward').addEvent('click', function(){
        if(image != 3) {
            image++;
            var pos = (image - 1) * 179;
            $$('.image').setStyle('background-position', '0 -' + pos + 'px');
            $$('.desc').hide();
            $$('.desc.nr' + image).show();
            $$('.switch').removeClass('active');
            $$('.switch.nr' + image).addClass('active');   
        }
    });
});

function changeImage(nr) {
    image = nr;
    var pos = (image - 1) * 179;
    $$('.image').setStyle('background-position', '0 -' + pos + 'px');
    $$('.desc').hide();
    $$('.desc.nr' + image).show();
    $$('.switch').removeClass('active');
    $$('.switch.nr' + image).addClass('active');   
}