From e29220313b8e7f2ce9ff669293b00b8a31e32996 Mon Sep 17 00:00:00 2001
From: Christopher Biscardi <biscarch@sketcht.com>
Date: Sun, 5 Aug 2018 21:57:12 -0700
Subject: [PATCH] add headings from #31

---
 .../gatsby-plugin-mdx/extend-node-type.js     | 52 +++++++++++++++++++
 packages/gatsby-plugin-mdx/package.json       |  1 +
 2 files changed, 53 insertions(+)

diff --git a/packages/gatsby-plugin-mdx/extend-node-type.js b/packages/gatsby-plugin-mdx/extend-node-type.js
index d670148c325eb..608e727787843 100644
--- a/packages/gatsby-plugin-mdx/extend-node-type.js
+++ b/packages/gatsby-plugin-mdx/extend-node-type.js
@@ -11,6 +11,7 @@ const remark = require("remark");
 const retext = require("retext");
 const visit = require("unist-util-visit");
 const remove = require("unist-util-remove");
+const toString = require("mdast-util-to-string");
 const stripMarkdown = require("strip-markdown");
 const grayMatter = require("gray-matter");
 const { createMdxAstCompiler } = require("@mdx-js/mdx");
@@ -62,6 +63,35 @@ import { MDXTag } from '@mdx-js/tag'
 ${code}`;
     }
 
+    const HeadingType = new GraphQLObjectType({
+      name: `MdxHeading`,
+      fields: {
+        value: {
+          type: GraphQLString,
+          resolve(heading) {
+            return heading.value;
+          }
+        },
+        depth: {
+          type: GraphQLInt,
+          resolve(heading) {
+            return heading.depth;
+          }
+        }
+      }
+    });
+    const Headings = new GraphQLEnumType({
+      name: `Headings`,
+      values: {
+        h1: { value: 1 },
+        h2: { value: 2 },
+        h3: { value: 3 },
+        h4: { value: 4 },
+        h5: { value: 5 },
+        h6: { value: 6 }
+      }
+    });
+
     return resolve({
       code: {
         type: GraphQLString,
@@ -94,6 +124,28 @@ ${code}`;
           return prune(excerptNodes.join(" "), pruneLength, "…");
         }
       },
+      headings: {
+        type: new GraphQLList(HeadingType),
+        args: {
+          depth: {
+            type: Headings
+          }
+        },
+        async resolve(mdxNode, { depth }) {
+          const ast = await getAST(mdxNode);
+          let headings = [];
+          visit(ast, "heading", heading => {
+            headings.push({
+              value: toString(heading),
+              depth: heading.depth
+            });
+          });
+          if (typeof depth === `number`) {
+            headings = headings.filter(heading => heading.depth === depth);
+          }
+          return headings;
+        }
+      },
       timeToRead: {
         type: GraphQLInt,
         async resolve(mdxNode) {
diff --git a/packages/gatsby-plugin-mdx/package.json b/packages/gatsby-plugin-mdx/package.json
index 86026f11cd7b4..5dd7572d76a58 100644
--- a/packages/gatsby-plugin-mdx/package.json
+++ b/packages/gatsby-plugin-mdx/package.json
@@ -16,6 +16,7 @@
     "gray-matter": "^4.0.1",
     "json5": "^1.0.1",
     "lodash": "^4.17.10",
+    "mdast-util-to-string": "^1.0.4",
     "remark": "^9.0.0",
     "retext": "^5.0.0",
     "strip-markdown": "^3.0.1",