.eleventy.js

const fs = require('fs')

const { DateTime } = require('luxon')
const markdownIt = require('markdown-it')
const markdownItAnchor = require('markdown-it-anchor')

const pluginRss = require('@11ty/eleventy-plugin-rss')
const pluginSyntaxHighlight = require('@11ty/eleventy-plugin-syntaxhighlight')
const pluginNavigation = require('@11ty/eleventy-navigation')

module.exports = function (eleventyConfig) {
  // Copy the `img` and `css` folders to the output
  eleventyConfig.addPassthroughCopy('src/img')
  eleventyConfig.addPassthroughCopy('src/css')

  // Add plugins
  eleventyConfig.addPlugin(pluginRss)
  eleventyConfig.addPlugin(pluginSyntaxHighlight)
  eleventyConfig.addPlugin(pluginNavigation)

  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 (!Array.isArray(array) || array.length === 0) {
      return []
    }
    if (n < 0) {
      return array.slice(n)
    }

    return array.slice(0, n)
  })

  // Return the smallest number argument
  eleventyConfig.addFilter('min', (...numbers) => {
    return Math.min.apply(null, numbers)
  })

  function filterTagList(tags) {
    return (tags || []).filter(
      (tag) => ['all', 'nav', 'post', 'posts'].indexOf(tag) === -1
    )
  }

  eleventyConfig.addFilter('filterTagList', filterTagList)

  // Create an array of all tags
  eleventyConfig.addCollection('tagList', function (collection) {
    let tagSet = new Set()
    collection.getAll().forEach((item) => {
      ;(item.data.tags || []).forEach((tag) => tagSet.add(tag))
    })

    return filterTagList([...tagSet])
  })

  // Customize Markdown library and settings:
  let markdownLibrary = markdownIt({
    html: true,
    breaks: true,
    linkify: true,
  }).use(markdownItAnchor, {
    slugify: eleventyConfig.getFilter('slug'),
  })
  
  eleventyConfig.setLibrary('md', markdownLibrary)

  // Override Browsersync defaults (used only with --serve)
  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.writeHead(404, { 'Content-Type': 'text/html; charset=UTF-8' })
          res.write(content_404)
          res.end()
        })
      },
    },
    ui: false,
    ghostMode: false,
  })

  return {
    templateFormats: ['md', 'njk', 'html'],
    markdownTemplateEngine: 'njk',
    htmlTemplateEngine: 'njk',
    dir: {
      input: 'src',
      includes: '_includes',
      data: '_data',
      output: '_site',
    },
  }
}