$(document).ready( function() {
    function init_sliders() {
        $('#sliders .werkzaamheden').each( function() {
           $(this).hide(); 
        });
        
        for( var i=1; i <= 3; i++) {
            $('#'+i).show();
        }
        
    }    
    function show_slider( id ) {
        $('#'+id).slideDown(1000);
    }
    function next_slides( i ) {
        $('#sliders .werkzaamheden').each( function() {
           $(this).slideUp(600); 
        });
        
        if( i >= 9 ) {
            i = 1;
        }
        
        var old_i = i;
        for( i; i <= old_i+2; i++) {
            show_slider(i);
        }
        return i;
    }
    function previous_slides( i ) {
        $('#sliders .werkzaamheden').each( function() {
           $(this).slideUp(600); 
        });
        
        if( i <= 1 ) {
            i = 9;
        }
        
        var old_i = i;
        for( i; i >= old_i-2; i--) {
            show_slider(i);
        }
        return i;
    }
    
    init_sliders(); //Verberg alles.
    current_slide = 4;
    
    var slider_left = $('#but_slider_left');
    var slider_right = $('#but_slider_right');
    
    slider_left.click( function (event) {
           event.preventDefault(); 
           current_slide = previous_slides( current_slide );
    });
    
    slider_right.click( function (event) {
            event.preventDefault();
            current_slide = next_slides( current_slide );
    });
    
});