/**
 * 🎄 Challenge: 
 * 1. The Christmas tree's lights should switch 
 *    on and off every 800 miliseconds.
 * 
 * Stretch Goal:
 *    Make the blue and red lights flash alternately.
 **/ 

function switchLights() {
    setInterval(function() {
        let redLights = document.getElementsByClassName("red")
        let blueLights = document.getElementsByClassName("blue")

        // turn on red lights
        for (let i = 0; i < redLights.length; i++) {
            redLights[i].style.filter = "none"
        }

        // turn off red lights after 1.5 seconds
        setTimeout(function() {
            for (let i = 0; i < redLights.length; i++) {
                redLights[i].style.filter = "grayscale(100%)"
            }
        }, 1500)

        // turn on blue lights after 1.5 seconds
        setTimeout(function() {
            for (let i = 0; i < blueLights.length; i++) {
                blueLights[i].style.filter = "none"
            }
        }, 1500)

        // turn off blue lights after 1.5 seconds
        setTimeout(function() {
            for (let i = 0; i < blueLights.length; i++) {
                blueLights[i].style.filter = "grayscale(100%)"
            }
        }, 3000)
    }, 3000) // total interval for switching lights
}

switchLights()