Improve api oembed controller (#3450)

* Add StreamEntryFinder class to parse URLs

* Use StreamEntryFinder and clean up api/oembed controller

spec/lib/stream_entry_finder_spec.rb

@@ -0,0 +1,47 @@
+# frozen_string_literal: true
+
+require 'rails_helper'
+
+describe StreamEntryFinder do
+  include RoutingHelper
+
+  describe '#stream_entry' do
+    context 'with a status url' do
+      let(:status) { Fabricate(:status) }
+      let(:url) { short_account_status_url(account_username: status.account.username, id: status.id) }
+      subject { described_class.new(url) }
+
+      it 'finds the stream entry' do
+        expect(subject.stream_entry).to eq(status.stream_entry)
+      end
+    end
+
+    context 'with a stream entry url' do
+      let(:stream_entry) { Fabricate(:stream_entry) }
+      let(:url) { account_stream_entry_url(stream_entry.account, stream_entry) }
+      subject { described_class.new(url) }
+
+      it 'finds the stream entry' do
+        expect(subject.stream_entry).to eq(stream_entry)
+      end
+    end
+
+    context 'with a plausible url' do
+      let(:url) { 'https://example.com/users/test/updates/123/embed' }
+      subject { described_class.new(url) }
+
+      it 'raises an error' do
+        expect { subject.stream_entry }.to raise_error(ActiveRecord::RecordNotFound)
+      end
+    end
+
+    context 'with an unrecognized url' do
+      let(:url) { 'https://example.com/about' }
+      subject { described_class.new(url) }
+
+      it 'raises an error' do
+        expect { subject.stream_entry }.to raise_error(ActiveRecord::RecordNotFound)
+      end
+    end
+  end
+end