traffic-light-with-possible-invalid-states.ts

interface TrafficLight {
    red: boolean;
    yellow: boolean;
    green: boolean;
}

function nextTrafficLightState(
    trafficLight: TrafficLight): TrafficLight {
        
    if (trafficLight.red && trafficLight.yellow) {
        return { red: false, yellow: false, green: true };
    } else if (trafficLight.red) {
        return { red: true, yellow: true, green: false };
    } else if (trafficLight.yellow) {
        return { red: true, yellow: false, green: false };
    } else if (trafficLight.green) {
        return { red: false, yellow: true, green: false };
    }
}