text: const { DateTime } = require('luxon');
  const fs = require('fs');
  const pluginRss = require('@11ty/eleventy-plugin-rss');
  const pluginSyntaxHighlight = require('@11ty/eleventy-plugin-syntaxhighlight');
  const pluginNavigation = require('@11ty/eleventy-navigation');
  const markdownIt = require('markdown-it');
  const markdownItAnchor = require('markdown-it-anchor');
  const markdownItKatex = require('@iktakahiro/markdown-it-katex');
  const markdownItNomnoml = require('@ospatil/markdown-it-nomnoml');
  
  module.exports = function (eleventyConfig) {
    eleventyConfig.addPlugin(pluginRss);
    eleventyConfig.addPlugin(pluginSyntaxHighlight);
    eleventyConfig.addPlugin(pluginNavigation);
  
    eleventyConfig.setDataDeepMerge(true);
  
    eleventyConfig.addLayoutAlias('post', 'layouts/post.njk');
  
    eleventyConfig.addFilter('readableDate', (dateObj) => {
      return DateTime.fromJSDate(dateObj, { zone: 'utc' }).toFormat(
        'dd LLL yyyy'
      );
    });
  
    // https://html.spec.whatwg.org/multipage/common-microsyntaxes.html#valid-date-string
    eleventyConfig.addFilter('htmlDateString', (dateObj) => {
      return DateTime.fromJSDate(dateObj, { zone: 'utc' }).toFormat('yyyy-LL-dd');
    });
  
    // Get the first `n` elements of a collection.
    eleventyConfig.addFilter('head', (array, n) => {
      if (n < 0) {
        return array.slice(n);
      }
  
      return array.slice(0, n);
    });
  
    eleventyConfig.addFilter('min', (...numbers) => {
      return Math.min.apply(null, numbers);
    });
  
    eleventyConfig.addCollection('tagList', function (collection) {
      let tagSet = new Set();
      collection.getAll().forEach(function (item) {
        if ('tags' in item.data) {
          let tags = item.data.tags;
  
          tags = tags.filter(function (item) {
            switch (item) {
              // this list should match the `filter` list in tags.njk
              case 'all':
              case 'nav':
              case 'post':
              case 'posts':
                return false;
            }
  
            return true;
          });
  
          for (const tag of tags) {
            tagSet.add(tag);
          }
        }
      });
  
      // returning an array in addCollection works in Eleventy 0.5.3
      return [...tagSet];
    });
  
    eleventyConfig.addPassthroughCopy('src/img');
    eleventyConfig.addPassthroughCopy('src/css');
    eleventyConfig.addPassthroughCopy({
      'node_modules/terminal.css/dist/*.min.css': 'css',
    });
  
    /* Markdown Overrides */
    let markdownLibrary = markdownIt({
      html: true,
      breaks: true,
      linkify: true,
    })
      .use(markdownItAnchor, {
        permalink: true,
        permalinkClass: 'direct-link',
        permalinkSymbol: '#',
      })
      .use(markdownItKatex)
      .use(markdownItNomnoml);
    eleventyConfig.setLibrary('md', markdownLibrary);
  
    // Browsersync Overrides
    eleventyConfig.setBrowserSyncConfig({
      open: true,
      callbacks: {
        ready: function (err, browserSync) {
          const content_404 = fs.readFileSync('_site/404.html');
  
          browserSync.addMiddleware('*', (req, res) => {
            // Provides the 404 content without redirect.
            res.write(content_404);
            res.end();
          });
        },
      },
      ui: false,
      ghostMode: false,
    });
  
    // eleventyConfig.addFilter("filterHomeNavItem", function(nav) {
    //   return nav.filter(navItem => navItem.key !== 'Home');
    // });
  
    return {
      templateFormats: ['md', 'njk', 'html'],
  
      // If your site lives in a different subdirectory, change this.
      // Leading or trailing slashes are all normalized away, so don’t worry about those.
  
      // If you don’t have a subdirectory, use "" or "/" (they do the same thing)
      // This is only used for link URLs (it does not affect your file structure)
      // Best paired with the `url` filter: https://www.11ty.dev/docs/filters/url/
  
      // You can also pass this in on the command line using `--pathprefix`
      // pathPrefix: "/",
  
      markdownTemplateEngine: 'njk',
      htmlTemplateEngine: 'njk',
      dataTemplateEngine: 'njk',
  
      dir: {
        input: 'src',
        // These are all optional, defaults are shown below:
        // includes: '_includes',
        // data: '_data',
        // output: '_site',
      },
    };
  };
  