/* Note: there would be comments in each portion of the file to guide the user. Need to add them still*/

const crypto = require('crypto');
const csstree = require('css-tree');

const styleInjectionCode = (rawCss) => `
 var styleTag = document.createElement('style');
 var stylesTextNode = document.createTextNode('${rawCss}');
 styleTag.appendChild(stylesTextNode);
 var head = document.getElementsByTagName('head')[0];
 head.appendChild(styleTag);
`;

const localIdsExportCode = (localIds) => {
 const classExportsString = Object.keys(localIds).map((className) => {
   return `'${className}': '${localIds[className]}'`;
 }).join(',');
 return `
  module.exports = {
    ${classExportsString}
  };
 `;
};

function loader(filename, content){

  const localIds = {};

  const ast = csstree.parse(content);

  csstree.walk(ast, function(node){
    if(node.type === 'ClassSelector'){
      const hash = crypto.createHash('sha256');
      hash.update(`${filename}-${node.name}`);
      localIds[node.name] = hash.digest('base64');
      node.name = localIds[node.name];
    }
  });

  const transformedCss = csstree.generate(ast);

  const result =  `
    ${styleInjectionCode(transformedCss)}
    ${localIdsExportCode(localIds)}
  `;
  return result;
};

module.exports = loader;