const postcss = require('postcss');

module.exports = postcss.plugin('postcss-partial-process', ({
  startComment = 'postcss-partial-process start',
  endComment = 'postcss-partial-process end',
  removeComments = 'auto',
  plugins = []
} = {}) => {
  return root => {
    let processing = false;
    let partialRoot = null;
    const promises = [];

    const end = (callback) => {
      promises.push(
        postcss(plugins).process(partialRoot, {
          from: undefined
        }).then(callback)
      );
    };

    root.each(node => {
      let starting = false;
      let ending = false;
      let removeComment = false;

      if (node.type === 'comment') {
        let comment = node.toString();
        let matches = comment.match(/\/\*!?\s*(.*?)\s*\*\//, '');
        matches = matches || [];
        if (matches.length > 1) {
          starting = !processing && matches[1] === startComment;
          ending = processing && matches[1] === endComment;
          removeComment = removeComments === true || (removeComments === 'auto' && !comment.startsWith('/*!'));
        }
      }

      if (ending) {
        end(result => {
          node.before(result.root);
          if (removeComment) {
            node.remove();
          }
        });
        processing = false;
      }

      if (processing) {
        partialRoot.append(node);
      }

      if (starting) {
        partialRoot = postcss.root();
        if (removeComment) {
          node.remove();
        }
        processing = true;
      }
    });

    if (processing) {
      end(result => {
        root.append(result.root);
      });
    }

    return Promise.all(promises);
  };
});