minify-lit-elt-template-literal-loader/minifyTemplate.js

var U2 = require("uglify-js");
let htmlMinify = require('html-minifier').minify;
var CleanCSS = require('clean-css');

defaultOptions = {
  collapseWhitespace: true,
  minifyCSS:true,
}
module.exports = function (code, options){
  let mergedOptions = {...defaultOptions, ...options}
  const ast = U2.parse(code)
  let cssOptions = false;
  if (mergedOptions.minifyCSS){
    cssOptions = typeof mergedOptions.minifyCSS == 'object' ? mergedOptions.minifyCSS:{}
  } 
  // Accumulate lit-html tempaltes nodes in this array
  const lit_html_templates = [];
  ast.walk(new U2.TreeWalker( (node)=>{
    if (node instanceof U2.AST_Template && node.tag && ['html','css','svg'].includes(node.tag.name)){
      lit_html_templates.push(node);
    }
  }))

  for (let i = lit_html_templates.length; --i >= 0 ;) {
    var node = lit_html_templates[i];
    const templateContent = node.strings.map(s=>s.replace(/[\n|\r]/gm, ' ')).join('${}')
    let output
    if(node.tag.name =="html"){
      output = htmlMinify(templateContent, mergedOptions);
    } else if(node.tag.name == "css" && cssOptions){
      output = new CleanCSS(cssOptions).minify(templateContent).styles;
    } else if(node.tag.name == "svg"){
      // Todo implement svgo optimisation
      output = htmlMinify(templateContent, mergedOptions);
    } 
    node.strings = output.split("${}");
  }

  return ast.print_to_string({ beautify: false });;
}