fix(client): handle challenge creation (#42272)

This lets us create new challenges/steps without having to restart the
client

client/plugins/fcc-source-challenges/gatsby-node.js

@@ -1,4 +1,6 @@
+const path = require('path');
 const chokidar = require('chokidar');
+const readdirp = require('readdirp');
 
 const { createChallengeNode } = require('./create-challenge-nodes');
 
@@ -28,6 +30,7 @@ exports.sourceNodes = function sourceChallengesSourceNodes(
   const { createNode } = actions;
   const watcher = chokidar.watch(curriculumPath, {
     ignored: /(^|[\/\\])\../,
+    ignoreInitial: true,
     persistent: true,
     usePolling: true,
     cwd: curriculumPath
@@ -55,6 +58,43 @@ File changed at ${filePath}, replacing challengeNode id ${challenge.id}
       : null
   );
 
+  // if a file is added, that might change the order of the challenges in the
+  // containing block, so we recreate them all
+  watcher.on('add', filePath => {
+    if (/\.md?$/.test(filePath)) {
+      const blockPath = path.dirname(filePath);
+      const fullBlockPath = path.join(
+        __dirname,
+        '../../../curriculum/challenges/english/',
+        blockPath
+      );
+      readdirp(fullBlockPath, { fileFilter: '*.md' })
+        .on('data', entry => {
+          const { path: siblingPath } = entry;
+          const relativePath = path.join(blockPath, siblingPath);
+          onSourceChange(relativePath)
+            .then(challenge => {
+              reporter.info(
+                `
+File changed at ${relativePath}, replacing challengeNode id ${challenge.id}
+            `
+              );
+              createVisibleChallenge(challenge);
+            })
+            .catch(e =>
+              reporter.error(`fcc-replace-challenge
+attempting to replace ${relativePath}
+
+${e.message}
+
+`)
+            );
+        })
+        .on('warn', error => console.error('non-fatal error', error))
+        .on('error', error => console.error('fatal error', error));
+    }
+  });
+
   function sourceAndCreateNodes() {
     return source()
       .then(challenges => Promise.all(challenges))