FEATURE: Track last_viewed_at datetime for channel members (#22294)

Whenever a user opens a channel or marks it read, we now
update the last_viewed_at datetime for that channel membership
record. This is so we will be able to show thread unread indicators
in the channel sidebar that clear independently of the main thread
unread indicators. This unread functionality will follow in another
PR.

plugins/chat/app/models/chat/user_chat_channel_membership.rb

@@ -32,6 +32,7 @@ end
 #  updated_at                          :datetime         not null
 #  last_unread_mention_when_emailed_id :integer
 #  join_mode                           :integer          default("manual"), not null
+#  last_viewed_at                      :datetime         not null
 #
 # Indexes
 #

plugins/chat/app/services/chat/channel_view_builder.rb

@@ -39,6 +39,7 @@ module Chat
     step :fetch_tracking
     step :fetch_thread_memberships
     step :fetch_thread_participants
+    step :update_channel_last_viewed_at
     step :build_view
 
     class Contract
@@ -226,6 +227,10 @@ module Chat
         ::Chat::ThreadParticipantQuery.call(thread_ids: threads.map(&:id))
     end
 
+    def update_channel_last_viewed_at(channel:, guardian:, **)
+      channel.membership_for(guardian.user)&.update!(last_viewed_at: Time.zone.now)
+    end
+
     def build_view(
       guardian:,
       channel:,

plugins/chat/app/services/chat/update_user_last_read.rb

@@ -21,8 +21,10 @@ module Chat
     policy :invalid_access
     model :message
     policy :ensure_message_id_recency
-    step :update_last_read_message_id
+    transaction do
-    step :mark_associated_mentions_as_read
+      step :update_membership_state
+      step :mark_associated_mentions_as_read
+    end
     step :publish_new_last_read_to_clients
 
     # @!visibility private
@@ -56,8 +58,8 @@ module Chat
         message.id >= active_membership.last_read_message_id
     end
 
-    def update_last_read_message_id(message:, active_membership:, **)
+    def update_membership_state(message:, active_membership:, **)
-      active_membership.update!(last_read_message_id: message.id)
+      active_membership.update!(last_read_message_id: message.id, last_viewed_at: Time.zone.now)
     end
 
     def mark_associated_mentions_as_read(active_membership:, message:, **)

plugins/chat/db/migrate/20230627044755_add_last_viewed_at_to_user_chat_channel_memberships.rb

@@ -0,0 +1,11 @@
+# frozen_string_literal: true
+
+class AddLastViewedAtToUserChatChannelMemberships < ActiveRecord::Migration[7.0]
+  def change
+    add_column :user_chat_channel_memberships,
+               :last_viewed_at,
+               :datetime,
+               null: false,
+               default: -> { "CURRENT_TIMESTAMP" }
+  end
+end

plugins/chat/spec/services/chat/channel_view_builder_spec.rb

@@ -37,6 +37,8 @@ RSpec.describe Chat::ChannelViewBuilder do
       }
     end
 
+    before { channel.add(current_user) }
+
     it "threads_enabled is false by default" do
       expect(result.threads_enabled).to eq(false)
     end
@@ -76,6 +78,14 @@ RSpec.describe Chat::ChannelViewBuilder do
       )
     end
 
+    it "updates the channel membership last_viewed_at" do
+      membership = channel.membership_for(current_user)
+      membership.update!(last_viewed_at: 1.day.ago)
+      old_last_viewed_at = membership.last_viewed_at
+      result
+      expect(membership.reload.last_viewed_at).not_to eq_time(old_last_viewed_at)
+    end
+
     it "does not query thread tracking overview or state by default" do
       Chat::TrackingStateReportQuery.expects(:call).never
       result

plugins/chat/spec/services/chat/update_user_last_read_spec.rb

@@ -109,6 +109,13 @@ RSpec.describe Chat::UpdateUserLastRead do
         it "publishes new last read to clients" do
           expect(messages.map(&:channel)).to include("/chat/user-tracking-state/#{current_user.id}")
         end
+
+        it "updates the channel membership last_viewed_at datetime" do
+          membership.update!(last_viewed_at: 1.day.ago)
+          old_last_viewed_at = membership.last_viewed_at
+          result
+          expect(membership.reload.last_viewed_at).not_to eq_time(old_last_viewed_at)
+        end
       end
     end
   end