$(document).ready(function(){

    var show_per_page = 4;
    var number_of_items = $('#content').children().size();
    var number_of_pages = Math.ceil(number_of_items/show_per_page);
    var end = number_of_pages -1;

    $('#current_page').val(0);
    $('#show_per_page').val(show_per_page);

    var navigation_html = '<a href="javascript:go_to_page(0);"><<</a>';
    navigation_html += '<a href="javascript:nav(-1);"><</a>';
    var current_link = 0;
    while(number_of_pages > current_link){
        navigation_html += '<a class="page_link" href="javascript:go_to_page(' + current_link +')" longdesc="' + current_link +'">'+ (current_link + 1) +'</a>';
        current_link++;
    }
    navigation_html += '<a href="javascript:nav(+1);">></a>';
    navigation_html += '<a href="javascript:go_to_page(' + end +')"">>></a>';

    $('.page_navigation').html(navigation_html);
    $('.page_navigation .page_link:first').addClass('active_page');

    $('#content').children().css('display', 'none');
    $('#content').children().slice(0, show_per_page).css('display', 'block');

});

function nav(dir){
    if(dir==+1){
        new_page = parseInt($('#current_page').val()) + 1;
        if($('.active_page').next('.page_link').length==true){
            go_to_page(new_page);
        }
    }else if(dir==-1){
        new_page = parseInt($('#current_page').val()) - 1;
        if($('.active_page').prev('.page_link').length==true){
            go_to_page(new_page);
        }
    }
}

function go_to_page(page_num){
    var show_per_page = parseInt($('#show_per_page').val());
    start_from = page_num * show_per_page;
    end_on = start_from + show_per_page;
    $('#content').children().css('display', 'none').slice(start_from, end_on).css('display', 'block');
    $('.page_link[longdesc=' + page_num +']').addClass('active_page').siblings('.active_page').removeClass('active_page');
    $('#current_page').val(page_num);
}