feat: Adds sidebar to articles view.

Sources/Docs/Extensions.swift

@@ -54,6 +54,29 @@ extension Item where M == ArticleMetadata {
   }
 }
 
+extension Array where Element == Item<ArticleMetadata> {
+
+  func years() -> Set<String> {
+    let dateFormatter = DateFormatter()
+    dateFormatter.dateFormat = "yyyy"
+    return reduce(into: Set()) { set, item in
+      let date = dateFormatter.string(from: item.getDate())
+      set.insert(date)
+      if let updatedDate = item.getUpdatedDate() {
+        set.insert(dateFormatter.string(from: updatedDate))
+      }
+    }
+  }
+
+  func uniqueTags() -> Set<String> {
+    reduce(into: Set()) { set, item in
+      for tag in item.metadata.tags {
+        set.insert(tag)
+      }
+    }
+  }
+}
+
 // NOTE: Most of these are taken from https://github.com/loopwerk/loopwerk.io
 
 extension String {