From b82a3fc69f51da71ea57ece7cc6b41b604fe4a28 Mon Sep 17 00:00:00 2001
From: Shawn Allen <shawn.allen@github.com>
Date: Mon, 22 Jul 2019 14:57:11 -0700
Subject: [PATCH] use ERB converts for octicon() and avatar_for()

---
 lib/erb-to-html.js | 84 ++++++++++++++++++++++++++++++++++++++++++++++
 lib/mdx-loader.js  | 19 ++++++++++-
 2 files changed, 102 insertions(+), 1 deletion(-)
 create mode 100644 lib/erb-to-html.js

diff --git a/lib/erb-to-html.js b/lib/erb-to-html.js
new file mode 100644
index 00000000..6c8519bc
--- /dev/null
+++ b/lib/erb-to-html.js
@@ -0,0 +1,84 @@
+const visit = require('unist-util-visit')
+const cache = new Map()
+
+module.exports = options => {
+  const convert = converter(options)
+  return tree => {
+    visit(tree, 'code', (node, parent, index) => {
+      const match = node.lang ? node.lang.match(/^[a-z]+/) : null
+      const lang = match ? match[0] : null
+      if (lang === 'erb' || lang === 'html') {
+        const erb = node.value
+        const html = convert(node.value)
+
+        if (html && !html.includes('<%')) {
+          node.value = html
+          node.lang = node.lang.replace(/^erb/, 'html')
+        }
+      } else {
+        // console.warn(`Unknown code block lang: ${node.lang}`)
+      }
+    })
+  }
+}
+
+function converter({converters = {}}) {
+  return erb => {
+    const blocks = erb.match(/<%=[^%]+%>/g)
+    if (blocks && blocks.length) {
+      let html = erb
+      console.warn(`Replacing ${blocks.length} ERB block(s)...`)
+      for (const input of blocks) {
+        const output = convert(input)
+        if (output !== input) {
+          html = replaceAll(html, input, output)
+        }
+      }
+      return html
+    }
+  }
+
+  function convert(block) {
+    if (cache.has(block)) {
+      return cache.get(block)
+    }
+
+    const [_, method, argString] = block.match(/<%= *(\w+)[ \(]([^\)]+)\)? *%>/)
+    const parts = argString.split(/, */)
+    const args = []
+    const kwargs = {}
+    for (const part of parts) {
+      let match
+      if (match = part.match(/^:(.+) => (.+)$/)) {
+        kwargs[unquote(match[1])] = unquote(match[2])
+      } else if (match = part.match(/^(.+): (.+)$/)) {
+        kwargs[unquote(match[1])] = unquote(match[2])
+      } else {
+        args.push(unquote(part))
+      }
+    }
+
+    if (typeof converters[method] === 'function') {
+      let output = converters[method](args, kwargs)
+      output = `<!-- ${block} -->\n${output}`
+      cache.set(block, output)
+      return output
+    } else {
+      console.warn(`Unable to convert: ${block}`)
+      return block
+    }
+  }
+}
+
+function replaceAll(str, input, output) {
+  let result = str
+  while (result.includes(input)) {
+    result = result.replace(input, output)
+  }
+  return result
+}
+
+
+function unquote(str) {
+  return str.replace(/^\s*"([^"]+)"\s*$/, (_, value) => value)
+}
diff --git a/lib/mdx-loader.js b/lib/mdx-loader.js
index 835c8434..7fa1f723 100644
--- a/lib/mdx-loader.js
+++ b/lib/mdx-loader.js
@@ -1,11 +1,13 @@
 const {getOptions} = require('loader-utils')
 const mdx = require('@mdx-js/mdx')
+const octicons = require('@primer/octicons')
 
 const emoji = require('remark-emoji')
 const images = require('remark-images')
 const rehypePrism = require('./rehype-prism')
 const textr = require('remark-textr')
 const toc = require('remark-toc')
+const erbToHTML = require('./erb-to-html')
 
 const mdxExportJSONByDefault = require('mdx-constant')
 const grayMatter = require('gray-matter')
@@ -22,7 +24,22 @@ module.exports = async function(source) {
         [toc, {heading: '(table of|section)? contents'}],
         images,
         emoji,
-        [textr, {plugins: [typographicBase]}]
+        [textr, {plugins: [typographicBase]}],
+        [erbToHTML, {
+          converters: {
+            octicon: ([icon], attrs) => {
+              if (octicons[icon]) {
+                return octicons[icon].toSVG(attrs)
+              } else {
+                throw new Error(`No such octicon: "${icon}"`)
+              }
+            },
+            avatar_for: ([username, size], kwargs) => {
+              const attrs = Object.entries(kwargs).map(([key, value]) => ` ${key}="${value}"`).join(' ')
+              return `<img src="https://github.com/github.png?s=${size * 2}" width="${size}" height="${size}"${attrs}>`
+            }
+          }
+        }]
       ],
       hastPlugins: [rehypePrism],
       compilers: [mdxExportJSONByDefault('frontMatter', data)]