.eleventy.js

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");
require("dotenv").config();
const THRESHOLD = 0.5

module.exports = function(eleventyConfig) {

  let env = process.env.ELEVENTY_ENV;

  eleventyConfig.addPlugin(pluginRss);
  eleventyConfig.addPlugin(pluginSyntaxHighlight);
  eleventyConfig.addPlugin(pluginNavigation);

  eleventyConfig.setDataDeepMerge(true);

  eleventyConfig.addLayoutAlias("post", "./src/layouts/post.njk");

  eleventyConfig.addFilter("readableDate", dateObj => {
    return DateTime.fromJSDate(dateObj, {zone: 'utc'}).toFormat("dd LLL yyyy");
  });

  eleventyConfig.addFilter('prefetchNextURL', (entry, url) => {
    // check threshold //
    if (entry.nextPageCertainty > 0.4) {
      return entry.nextPagePath.replace("-", "")
    }
  })

  // 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.addCollection("tagList", require("./src/_11ty/getTagList"));

  eleventyConfig.addPassthroughCopy("src/img");
  eleventyConfig.addPassthroughCopy("src/css");

  /* Markdown Overrides */
  let markdownLibrary = markdownIt({
    html: true,
    breaks: true,
    linkify: true
  }).use(markdownItAnchor, {
    permalink: true,
    permalinkClass: "direct-link",
    permalinkSymbol: "#"
  });
  eleventyConfig.setLibrary("md", markdownLibrary);

  // Browsersync Overrides
  eleventyConfig.setBrowserSyncConfig({
    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();
        });
      }
    }
  });

  return {
    templateFormats: [
      "md",
      "njk",
      "html",
      "liquid"
    ],

    // 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)
    // You can also pass this in on the command line using `--pathprefix`

    // pathPrefix: "/",

    markdownTemplateEngine: "liquid",
    htmlTemplateEngine: "njk",
    dataTemplateEngine: "njk",

    // These are all optional, defaults are shown:
    dir: {
      input: "src",
      includes: "_includes",
      data: "_data",
      output: "_site"
    }
  };
};