function solve() {
        let departButton = $('#depart');
        let arriveButton = $('#arrive');
        let nextStopID = 'depot';
        let infoElement = $('.info');
        let currentStopName = '';

        return {
            depart,
            arrive
        };

        function depart() {
            let url = `https://judgetests.firebaseio.com/schedule/${nextStopID}.json`;
            $.ajax({
                url: url,
                success: onDepart,
                error: onDepartError
            });
        }

        function arrive() {
            infoElement.text(`Arriving at ${currentStopName}`);
            departButton.prop('disabled', false);
            arriveButton.prop('disabled', true);
        }

        function onDepart(data) {
            if (data === null) {
                onDepartError();
                return;
            }

            nextStopID = data.next;
            infoElement.text(`Next stop ${data.name}`);
            currentStopName = data.name;
            departButton.prop('disabled', true);
            arriveButton.prop('disabled', false);
        }

        function onDepartError() {
            infoElement.text('Error');
            departButton.prop('disabled', true);
            arriveButton.prop('disabled', true);
        }
    }