DEV: separates preferred-chat-mode service (#18883)

Also adds end to end system tests to ensure navigation scenarios are working correctly. This separation will make it easier to implement state in/out from chat.

plugins/chat/spec/system/navigation_spec.rb

@@ -1,22 +1,26 @@
 # frozen_string_literal: true
 
 RSpec.describe "Navigation", type: :system, js: true do
-  fab!(:user) { Fabricate(:user) }
+  fab!(:category) { Fabricate(:category) }
+  fab!(:topic) { Fabricate(:topic) }
+  fab!(:post) { Fabricate(:post, topic: topic) }
+  fab!(:user) { Fabricate(:admin) }
   fab!(:category_channel) { Fabricate(:category_channel) }
   fab!(:message) { Fabricate(:chat_message, chat_channel: category_channel) }
 
   before do
+    # ensures we have one valid registered admin
+    user.activate
+
     SiteSetting.chat_enabled = true
     SiteSetting.chat_allowed_groups = Group::AUTO_GROUPS[:everyone]
+    category_channel.add(user)
+
+    sign_in(user)
   end
 
   context "when visiting /chat" do
-    before do
-      category_channel.add(user)
-      sign_in(user)
-    end
-
-    it "it opens full page" do
+    it "opens full page" do
       visit("/chat")
 
       expect(page).to have_current_path(
@@ -26,4 +30,46 @@ RSpec.describe "Navigation", type: :system, js: true do
       expect(page).to have_css(".chat-message-container[data-id='#{message.id}']")
     end
   end
+
+  context "when opening chat" do
+    it "opens the drawer by default" do
+      visit("/")
+      find(".open-chat").click
+
+      expect(page).to have_css(".topic-chat-container.expanded.visible")
+    end
+  end
+
+  context "when opening chat with full page as preferred mode" do
+    it "opens the full page" do
+      visit("/")
+      find(".open-chat").click
+      find(".topic-chat-drawer-header__full-screen-btn").click
+
+      expect(page).to have_current_path(
+        chat.channel_path(category_channel.id, category_channel.slug),
+      )
+
+      visit("/")
+      find(".open-chat").click
+
+      expect(page).to have_current_path(
+        chat.channel_path(category_channel.id, category_channel.slug),
+      )
+    end
+  end
+
+  context "when opening chat with drawer as preferred mode" do
+    it "opens the full page" do
+      visit("/chat")
+      find(".chat-full-screen-button").click
+
+      expect(page).to have_css(".topic-chat-container.expanded.visible")
+
+      visit("/")
+      find(".open-chat").click
+
+      expect(page).to have_css(".topic-chat-container.expanded.visible")
+    end
+  end
 end