function updateTheme(a){
    console.log("a");
    // delTheme();
    // if(currentTheme=="today"){
    //     link.href = "styles/today/main.css";
    // }else if(themeName=="2000"){
    // setTheme(themeName);
}

function delTheme(){
    let themeNode = document.getElementById("theme");
    themeNode.parentNode.removeChild(themeNode);
}

function setTheme(themeName){

    let head = document.getElementsByTagName("HEAD")[0]; 
    let link = document.createElement("link");

    // set the attributes for link element 
    link.rel = "stylesheet"; 
    link.type = "text/css";
    link.id = "theme";
    if(themeName=="today"){
        link.href = "styles/today/main.css";
    }else if(themeName=="2000"){
        link.href = "styles/2000/main.css";
    }else throw new Error("invalid theme : "+themeName);
    head.appendChild(link);
}

var currentTheme = "today";
setTheme(currentTheme);