function start_long_task() {
    // create a progress bar
    var nanobar = new Nanobar({
        bg: '#88f'
    });

    // send ajax POST request to start background job
    $.ajax({
        type: 'POST',
        url: '/longtask',
        success: function(data, status, request) {
            status_url = request.getResponseHeader('Location');
            update_progress(status_url, nanobar);
        },
        error: function() {
            alert('Unexpected dumb error');
        }
    });
}
function update_progress(status_url, nanobar) {
    // send GET request to status URL
    $.getJSON(status_url, function(data) {
        // update UI
        percent = parseInt(data['current'] * 100 / data['total']);
        nanobar.go(percent);
        if (data['state'] == 'PENDING' || data['state'] == 'PROGRESS') {
            // rerun in 2 seconds
            setTimeout(function() {
                update_progress(status_url, nanobar);
            }, 100);
        }
    });
}
$(function() {
    $('#start-bg-job').click(start_long_task);
});