Improve api oembed controller (#3450)

* Add StreamEntryFinder class to parse URLs

* Use StreamEntryFinder and clean up api/oembed controller

app/lib/stream_entry_finder.rb

@@ -0,0 +1,34 @@
+# frozen_string_literal: true
+
+class StreamEntryFinder
+  attr_reader :url
+
+  def initialize(url)
+    @url = url
+  end
+
+  def stream_entry
+    verify_action!
+
+    case recognized_params[:controller]
+    when 'stream_entries'
+      StreamEntry.find(recognized_params[:id])
+    when 'statuses'
+      Status.find(recognized_params[:id]).stream_entry
+    else
+      raise ActiveRecord::RecordNotFound
+    end
+  end
+
+  private
+
+  def recognized_params
+    Rails.application.routes.recognize_path(url)
+  end
+
+  def verify_action!
+    unless recognized_params[:action] == 'show'
+      raise ActiveRecord::RecordNotFound
+    end
+  end
+end