Convert textile files into markdown files

convert-textile.js

const { promises: fs } = require("fs");
const textile = require("textile-js");
const prettier = require("prettier");
const path = require("path");

async function main() {
  const postsDir = path.resolve("source", "_posts");
  const files = (await fs.readdir(postsDir)).filter(file =>
    file.endsWith(".textile")
  );
  for (const file of files) {
    // Read textile file.
    const filePath = path.resolve(postsDir, file);
    const content = await fs.readFile(filePath, "utf8");
    console.log(file, content.length);

    // Extract frontmatter if exists.
    let frontmatter = "";
    let body = content;
    if (content.startsWith("---")) {
      const start = content.indexOf("---", 3) + 4;
      frontmatter = content.slice(0, start);
      body = content.slice(start);
    }

    // Convert textile into markdown.
    const parsed = textile.jsonml(body, { breaks: false });
    await fs.writeFile(
      path.resolve(postsDir, file.replace(/\.textile$/, ".json")),
      JSON.stringify(parsed, null, 2)
    );
    const markdown = frontmatter + renderMarkdown(parsed);
    // Format with prettier.
    const formatted = prettier.format(markdown, {
      parser: "markdown"
    });
    await fs.writeFile(
      path.resolve(postsDir, file.replace(/\.textile$/, ".markdown")),
      formatted
    );
  }
}

const KNOWN_PROPS = {
  a: ["href", "title"],
  img: ["src", "alt", "width", "height"],
  span: ["class"],
  pre: ["class"]
};

const KNOWN_CLASSES = {
  span: ["caps"],
  pre: ["prettyprint"]
};

function arePropsKnown(tag, props) {
  const propsCount = Object.keys(props).length;
  if (propsCount === 0) {
    return true;
  }
  const knownProps = KNOWN_PROPS[tag] || [];
  if (Object.keys(props).some(p => !knownProps.includes(p))) {
    return false;
  }
  const knownClasses = KNOWN_CLASSES[tag] || [];
  if (props.class && !knownClasses.includes(props.class)) {
    return false;
  }
  return true;
}

function renderMarkdown(jsonml) {
  if (typeof jsonml === "string") {
    if (jsonml === "\n") {
      // Remove unnecessary line breaks.
      return "";
    }
    // textile-js inserts tabs before each list item.
    if (jsonml === "\n\t") {
      return "";
    }
    if (jsonml === "\n\t\t") {
      // Nested list
      return "  ";
    }
    if (jsonml === "\n\t\t\t") {
      // Nested list
      return "    ";
    }
    if (jsonml === "\n\t\t\t\t") {
      // Nested list
      return "      ";
    }
    return jsonml;
  }

  if (!Array.isArray(jsonml)) {
    throw new Error("Unexpected element: " + jsonml);
  }

  const [tag, ...elements] = jsonml;
  let props = {};
  if (typeof elements[0] === "object" && !Array.isArray(elements[0])) {
    props = elements[0];
    elements.splice(0, 1);
    if (!arePropsKnown(tag, props)) {
      console.log("   ", tag, props);
    }
  }

  switch (tag) {
    case "html":
      return elements.map(renderMarkdown).join("");
    case "p":
      return elements.map(renderMarkdown).join("") + "\n\n";
    case "h2":
    case "h3":
      return "## " + elements.map(renderMarkdown).join("") + "\n\n";
    case "h4":
      return "### " + elements.map(renderMarkdown).join("") + "\n\n";
    case "pre":
      return (
        "```\n" +
        makeSureNewLine(elements.map(renderMarkdown).join("")) +
        "```\n\n"
      );
    case "blockquote":
      return "> " + elements.map(renderMarkdown).join("") + "\n\n";
    case "ul": {
      const nested = elements[0].startsWith("\n\t\t");
      return (
        (nested ? "\n" : "") + elements.map(renderMarkdown).join("") + "\n"
      );
    }
    case "li":
      return makeSureNewLine("- " + elements.map(renderMarkdown).join(""));
    // Convert <dl> to <ul>
    case "dl":
      return elements.map(renderMarkdown).join("") + "\n";
    case "dt":
      return "- " + elements.map(renderMarkdown).join("") + ": ";
    case "dd":
      return makeSureNewLine(elements.map(renderMarkdown).join(""));
    // -- Inline elements
    case "span":
      return elements.map(renderMarkdown).join("");
    case "code":
      return "`" + elements.map(renderMarkdown).join("") + "`";
    case "del":
      return "~" + elements.map(renderMarkdown).join("") + "~";
    case "ins":
      return "<ins>" + elements.map(renderMarkdown).join("") + "</ins>";
    case "strong":
      return "**" + elements.map(renderMarkdown).join("") + "**";
    case "a": {
      // Check if elements has only text.
      if (!(elements.length === 1 && typeof elements[0] === "string")) {
        console.error("Unexpected elements for <a>", elements);
      }
      const text = elements.map(renderMarkdown).join("");
      const title = props.title ? ` "${props.title}"` : "";
      return `[${text}](${props.href}${title})`;
    }
    case "img": {
      const { src, alt, width, height } = props;
      // Markdown doesn't have syntax for image size.
      // Encode size at the end of title so that it can be used in post processing.
      // Ideas from https://github.com/markedjs/marked/issues/339
      const title = width && height ? ` "=${width}x${height}"` : "";
      return `![${alt}](${src}${title})`;
    }
    case "br":
      return "";
    default:
      throw new Error("Unexpected tag: " + tag);
  }
}

function makeSureNewLine(str) {
  if (str.endsWith("\n")) {
    return str;
  }
  return str + "\n";
}

main().then(console.log, console.log);