Pick top N tags from posts

src/Nav.js

@@ -69,33 +69,82 @@ class TagNav extends Component {
   constructor (props) {
     super(props);
 
+    // TODO: fetch this number from config
+    // Number of top tags to display
+    this.numTop = 5;
+
     this.state = {
-      topTags: [
+      topTags: [],
-        'Tag 1',
-        'Tag 2',
-        'Really long tag',
-        'Really really really long tag',
-        'Another tag',
-      ],
     }
   }
 
-  topTags () {
+  fetchTopTags () {
+    fetch('/site.json')
+      .then(resp => resp.json())
+      .then(blob => {
+        let counts = new Map();
+
+        // Count up the tags
+        blob.posts.forEach(post => {
+          post.tags.forEach(tag => {
+            let count = counts.get(tag);
+            if (count === undefined) {
+              count = 0;
+            }
+
+            counts.set(tag, count + 1);
+          });
+        });
+
+        // Sort the tags
+        let tags = [...counts.entries()];
+        tags.sort(function(t1, t2) {
+          let tag1 = t1[0];
+          let tag2 = t2[0];
+          let count1 = t1[1];
+          let count2 = t2[1]
+
+          let diff = count2 - count1;
+
+          if (diff !== 0) {
+            return diff
+          } else {
+            // We have a tie, sort by the strings
+            return tag1.localeCompare(tag2);
+          }
+        });
+
+        // Get just the tag names
+        tags = tags.map(t => t[0]);
+
+        // Get top N
+        tags = tags.slice(0, this.numTop);
+
+        this.setState({topTags: tags});
+      });
+  }
+
+  componentDidMount() {
+    this.fetchTopTags();
   }
 
   render() {
-    // TODO: Populate these tags from the top tags in the post
+    let tags = "";
-    let tags = (
+    if (this.state.topTags.length > 0) {
+      tags = (
+        <div>
+          <h5 className="nav-header">Top Tags</h5>
           <ul>
             {this.state.topTags.map(tag => (
               <ListLink icon="tag" key={tag} name={tag} href={"/tag/" + tag} />
             ))}
           </ul>
+        </div>
       );
+    }
 
     return (
       <Row>
-        <h5 className="nav-header">Top Tags</h5>
         { tags }
       </Row>
     );