/**
 * Produces a function which uses template strings to do simple interpolation from objects.
 * 
 * Usage:
 *    var makeMeKing = generateTemplateString('${name} is now the king of ${country}!');
 * 
 *    console.log(makeMeKing({ name: 'Bryan', country: 'Scotland'}));
 *    // Logs 'Bryan is now the king of Scotland!'
 */
var generateTemplateString = (function(){
    var cache = {};

    function generateTemplate(template){

    var fn = cache[template];

    if (!fn){
        
    // Replace ${expressions} (etc) with ${map.expressions}.

    var sanitized = template
        .replace(/\$\{([\s]*[^;\s\{]+[\s]*)\}/g, function(_, match){
            return `\$\{map.${match.trim()}\}`;
            })
        // Afterwards, replace anything that's not ${map.expressions}' (etc) with a blank string.
        .replace(/(\$\{(?!map\.)[^}]+\})/g, '');
    
    fn = Function('map', `return \`${sanitized}\``);

    }

    return fn;
};

return generateTemplate;
})();