text: // handles different types of whitespace
  const unified = require("unified");
  const html = require("rehype-parse");
  const visit = require("unist-util-visit");
  
  const NEWLINE = "\n";
  
  // natively supported types
  const types = {
    // aliases for infima color names
    secondary: "note",
    info: "important",
    success: "tip",
    danger: "warning",
    // base types
    note: {
      ifmClass: "secondary",
      keyword: "note",
      emoji: "ℹ️", // '&#x2139;'
      svg:
        '<svg xmlns="http://www.w3.org/2000/svg" width="14" height="16" viewBox="0 0 14 16"><path fill-rule="evenodd" d="M6.3 5.69a.942.942 0 0 1-.28-.7c0-.28.09-.52.28-.7.19-.18.42-.28.7-.28.28 0 .52.09.7.28.18.19.28.42.28.7 0 .28-.09.52-.28.7a1 1 0 0 1-.7.3c-.28 0-.52-.11-.7-.3zM8 7.99c-.02-.25-.11-.48-.31-.69-.2-.19-.42-.3-.69-.31H6c-.27.02-.48.13-.69.31-.2.2-.3.44-.31.69h1v3c.02.27.11.5.31.69.2.2.42.31.69.31h1c.27 0 .48-.11.69-.31.2-.19.3-.42.31-.69H8V7.98v.01zM7 2.3c-3.14 0-5.7 2.54-5.7 5.68 0 3.14 2.56 5.7 5.7 5.7s5.7-2.55 5.7-5.7c0-3.15-2.56-5.69-5.7-5.69v.01zM7 .98c3.86 0 7 3.14 7 7s-3.14 7-7 7-7-3.12-7-7 3.14-7 7-7z"/></svg>'
    },
    tip: {
      ifmClass: "success",
      keyword: "tip",
      emoji: "💡", //'&#x1F4A1;'
      svg:
        '<svg xmlns="http://www.w3.org/2000/svg" width="12" height="16" viewBox="0 0 12 16"><path fill-rule="evenodd" d="M6.5 0C3.48 0 1 2.19 1 5c0 .92.55 2.25 1 3 1.34 2.25 1.78 2.78 2 4v1h5v-1c.22-1.22.66-1.75 2-4 .45-.75 1-2.08 1-3 0-2.81-2.48-5-5.5-5zm3.64 7.48c-.25.44-.47.8-.67 1.11-.86 1.41-1.25 2.06-1.45 3.23-.02.05-.02.11-.02.17H5c0-.06 0-.13-.02-.17-.2-1.17-.59-1.83-1.45-3.23-.2-.31-.42-.67-.67-1.11C2.44 6.78 2 5.65 2 5c0-2.2 2.02-4 4.5-4 1.22 0 2.36.42 3.22 1.19C10.55 2.94 11 3.94 11 5c0 .66-.44 1.78-.86 2.48zM4 14h5c-.23 1.14-1.3 2-2.5 2s-2.27-.86-2.5-2z"/></svg>'
    },
    warning: {
      ifmClass: "danger",
      keyword: "warning",
      emoji: "🔥", //'&#x1F525;'
      svg:
        '<svg xmlns="http://www.w3.org/2000/svg" width="12" height="16" viewBox="0 0 12 16"><path fill-rule="evenodd" d="M5.05.31c.81 2.17.41 3.38-.52 4.31C3.55 5.67 1.98 6.45.9 7.98c-1.45 2.05-1.7 6.53 3.53 7.7-2.2-1.16-2.67-4.52-.3-6.61-.61 2.03.53 3.33 1.94 2.86 1.39-.47 2.3.53 2.27 1.67-.02.78-.31 1.44-1.13 1.81 3.42-.59 4.78-3.42 4.78-5.56 0-2.84-2.53-3.22-1.25-5.61-1.52.13-2.03 1.13-1.89 2.75.09 1.08-1.02 1.8-1.86 1.33-.67-.41-.66-1.19-.06-1.78C8.18 5.31 8.68 2.45 5.05.32L5.03.3l.02.01z"/></svg>'
    },
    important: {
      ifmClass: "info",
      keyword: "important",
      emoji: "❗️", //'&#x2757;'
      svg:
        '<svg xmlns="http://www.w3.org/2000/svg" width="14" height="16" viewBox="0 0 14 16"><path fill-rule="evenodd" d="M7 2.3c3.14 0 5.7 2.56 5.7 5.7s-2.56 5.7-5.7 5.7A5.71 5.71 0 0 1 1.3 8c0-3.14 2.56-5.7 5.7-5.7zM7 1C3.14 1 0 4.14 0 8s3.14 7 7 7 7-3.14 7-7-3.14-7-7-7zm1 3H6v5h2V4zm0 6H6v2h2v-2z"/></svg>'
    },
    caution: {
      ifmClass: "warning",
      keyword: "caution",
      emoji: "⚠️", // '&#x26A0;&#xFE0F;'
      svg:
        '<svg xmlns="http://www.w3.org/2000/svg" width="16" height="16" viewBox="0 0 16 16"><path fill-rule="evenodd" d="M8.893 1.5c-.183-.31-.52-.5-.887-.5s-.703.19-.886.5L.138 13.499a.98.98 0 0 0 0 1.001c.193.31.53.501.886.501h13.964c.367 0 .704-.19.877-.5a1.03 1.03 0 0 0 .01-1.002L8.893 1.5zm.133 11.497H6.987v-2.003h2.039v2.003zm0-3.004H6.987V5.987h2.039v4.006z"/></svg>'
    }
  };
  
  // default options for plugin
  const defaultOptions = {
    customTypes: [],
    useDefaultTypes: true,
    infima: true,
    tag: ":::",
    icons: "svg"
  };
  
  // override default options
  const configure = options => {
    const { customTypes, ...baseOptions } = {
      ...defaultOptions,
      ...options
    };
  
    return {
      ...baseOptions,
      types: { ...types, ...customTypes }
    };
  };
  
  // escape regex special characters
  function escapeRegExp(s) {
    return s.replace(new RegExp(`[-[\\]{}()*+?.\\\\^$|/]`, "g"), "\\$&");
  }
  
  // helper: recursively replace nodes
  const _nodes = ({
    tagName: hName,
    properties: hProperties,
    position,
    children
  }) => {
    return {
      type: "admonitionHTML",
      data: {
        hName,
        hProperties
      },
      position,
      children: children.map(_nodes)
    };
  };
  
  // convert HTML to MDAST (must be a single root element)
  const nodes = markup => {
    return _nodes(
      unified()
        .use(html)
        .parse(markup).children[0].children[1].children[0]
    );
  };
  
  // create a simple text node
  const text = value => {
    return {
      type: "text",
      value
    };
  };
  
  // create a node that will compile to HTML
  const element = (tagName, classes = [], children = []) => {
    return {
      type: "admonitionHTML",
      data: {
        hName: tagName,
        hProperties: classes.length
          ? {
              className: classes
            }
          : {}
      },
      children
    };
  };
  
  // passed to unified.use()
  // you have to use a named function for access to `this` :(
  module.exports = function attacher(options) {
    const config = configure(options);
  
    // match to determine if the line is an opening tag
    const keywords = Object.keys(config.types)
      .map(escapeRegExp)
      .join("|");
    const tag = escapeRegExp(config.tag);
    const regex = new RegExp(`${tag}(${keywords})(?: *(.*))?\n`);
    const escapeTag = new RegExp(escapeRegExp(`\\${config.tag}`), "g");
  
    // the tokenizer is called on blocks to determine if there is an admonition present and create tags for it
    function blockTokenizer(eat, value, silent) {
      // stop if no match or match does not start at beginning of line
      const match = regex.exec(value);
      if (!match || match.index !== 0) return false;
      // if silent return the match
      if (silent) return true;
  
      const now = eat.now();
      const [opening, keyword, title] = match;
      const food = [];
      const content = [];
  
      // consume lines until a closing tag
      let idx = 0;
      while ((idx = value.indexOf(NEWLINE)) !== -1) {
        // grab this line and eat it
        const next = value.indexOf(NEWLINE, idx + 1);
        const line =
          next !== -1 ? value.slice(idx + 1, next) : value.slice(idx + 1);
        food.push(line);
        value = value.slice(idx + 1);
        // the closing tag is NOT part of the content
        if (line.startsWith(config.tag)) break;
        content.push(line);
      }
  
      // consume the processed tag and replace escape sequences
      const contentString = content.join(NEWLINE).replace(escapeTag, config.tag);
      const add = eat(opening + food.join(NEWLINE));
  
      // parse the content in block mode
      const exit = this.enterBlock();
      const contentNodes = element(
        "div",
        "admonition-content",
        this.tokenizeBlock(contentString, now)
      );
      exit();
      // parse the title in inline mode
      const titleNodes = this.tokenizeInline(title || keyword, now);
      // create the nodes for the icon
      const entry = config.types[keyword];
      const settings = typeof entry === "string" ? config.types[entry] : entry;
      const iconNodes =
        config.icons === "svg" ? nodes(settings.svg) : text(settings.emoji);
      const iconContainerNodes =
        config.icons === "none"
          ? []
          : [element("span", "admonition-icon", [iconNodes])];
  
      // build the nodes for the full markup
      const admonition = element(
        "div",
        ["admonition", `admonition-${keyword}`].concat(
          settings.ifmClass ? ["alert", `alert--${settings.ifmClass}`] : []
        ),
        [
          element("div", "admonition-heading", [
            element("h5", "", iconContainerNodes.concat(titleNodes))
          ]),
          contentNodes
        ]
      );
  
      return add(admonition);
    }
  
    // add tokenizer to parser after fenced code blocks
    const Parser = this.Parser.prototype;
    Parser.blockTokenizers.admonition = blockTokenizer;
    Parser.blockMethods.splice(
      Parser.blockMethods.indexOf("fencedCode") + 1,
      0,
      "admonition"
    );
    Parser.interruptParagraph.splice(
      Parser.interruptParagraph.indexOf("fencedCode") + 1,
      0,
      ["admonition"]
    );
    Parser.interruptList.splice(
      Parser.interruptList.indexOf("fencedCode") + 1,
      0,
      ["admonition"]
    );
    Parser.interruptBlockquote.splice(
      Parser.interruptBlockquote.indexOf("fencedCode") + 1,
      0,
      ["admonition"]
    );
  
    // TODO: add compiler rules for converting back to markdown
  
    return function transformer(tree) {
      // escape everything except admonitionHTML nodes
      visit(
        tree,
        node => {
          return node.type !== "admonitionHTML";
        },
        function visitor(node) {
          if (node.value) node.value = node.value.replace(escapeTag, config.tag);
          return node;
        }
      );
    };
  };
  