exports.at = at;

function at(hours, minutes) {
    let hr = hours;
    let min = 0;

    if (minutes) {
        hr += Math.floor(minutes / 60);
        min = minutes;
    }
    // overflow calculations for hours and minutes
    hr = (hr >= 0 ? hr % 24 : 24 + hr % 24);
    min = (min >= 0 ? min % 60 : 60 + min % 60);

    return formatTime(hr) + ':' + formatTime(min);
}

function formatTime(time) { // used to format both hours and minutes
    if (time < 10) { // if hours/minutes is a single digit number, prepend 0
        return '0' + time.toString();
    } else {
        return time.toString();
    }
}

String.prototype.plus = function(minutes) {
    let time = this.split(':');
    let hr = parseInt(time[0]);
    let min = parseInt(time[1]);

    min += minutes;
    hr += Math.floor(min / 60);
    min %= 60;
    hr %= 24;

    return formatTime(hr) + ':' + formatTime(min);
};

String.prototype.minus = function(minutes) {
    let time = this.split(':');
    let hr = parseInt(time[0]);
    let min = parseInt(time[1]);

    min -= minutes;
    hr += Math.floor(min / 60);

    min = (min >= 0 ? min % 60 : 60 + min % 60);
    hr = (hr >= 0 ? hr % 24 : 24 + hr % 24);
    if (hr % 24 === 0) hr %= 24; // handles negative integer multiples 24

    return formatTime(hr) + ':' + formatTime(min);
};

String.prototype.equals = function(time2) {
    return this === time2;
};