const fm = require("front-matter");
const fs = require("fs");
const hljs = require("highlight.js");
const katex = require("katex");
const makeTweetUrl = require("./make-tweet-url.js");
const marked = require("marked");
const strftime = require("strftime");

marked.setOptions({
  gfm: true,
  highlight: (code, lang) => {
    return lang
      ? hljs.highlight(lang, code).value
      : hljs.highlightAuto(code).value;
  },
});

function loadArticle(filename) {
  return new Promise((resolve, reject) => {
    fs.readFile(filename, (err, data) => {
      if (err) { return reject(err); }

      const article = fm(data.toString());
      const body = marked(
        article.body.replace(/\$\$([^$]*)\$\$/g, (_, tex) =>
          katex.renderToString(tex, { displayMode: true })
        )
      );

      let summary = article.attributes.description;
      if (!summary) {
        const paragraphBreak = article.body.match(/\r?\n\r?\n/);
        if (paragraphBreak) {
          summary = marked(article.body.slice(0, paragraphBreak.index));
        } else {
          summary = article.body;
        }
      }

      const rawDate = article.attributes.date;
      let date = null;

      if (rawDate) {
        ;["FullYear", "Month", "Date", "Hours"].forEach(field => {
          rawDate["set" + field](rawDate["getUTC" + field]());
        });

        // date = strftime("%B %d, %Y", rawDate);
        date = strftime("%Y. %B. %d.", rawDate);
      }

      const tweetUrl = makeTweetUrl(article);
      const defaults = { hidden: false, timeless: false };

      const tags = article.attributes.tags
        ? article.attributes.tags.split(", ")
        : [];

      resolve(
        Object.assign({}, defaults, article.attributes, {
          filename,
          summary,
          date,
          rawDate,
          tweetUrl,
          tags,
          rawBody: article.body,
          body,
        })
      );
    });
  });
}

module.exports = loadArticle;