DEV: Add last_message_id to channel and thread (#22488)

Initial migration and changes to models as well as
changing the following services to update last_message_id:

* Chat::MessageCreator
* Chat::RestoreMessage
* Chat::TrashMessage

The data migration will set the `last_message_id` for all existing
threads and channels in the database.

When we query the thread list as well as the channel,
we look at the last message ID for the following:

* Channel - Sorting DM channels, and channel metadata for the list of channels
* Thread - Last reply details for thread indicators and thread list

plugins/chat/db/migrate/20230707025733_add_last_message_id_to_channel_and_thread.rb

@@ -0,0 +1,11 @@
+# frozen_string_literal: true
+
+class AddLastMessageIdToChannelAndThread < ActiveRecord::Migration[7.0]
+  def change
+    add_column :chat_channels, :last_message_id, :bigint, null: true
+    add_column :chat_threads, :last_message_id, :bigint, null: true
+
+    add_index :chat_channels, :last_message_id
+    add_index :chat_threads, :last_message_id
+  end
+end

plugins/chat/db/migrate/20230707082645_backfill_chat_channel_and_thread_last_message_ids.rb

@@ -0,0 +1,35 @@
+# frozen_string_literal: true
+
+class BackfillChatChannelAndThreadLastMessageIds < ActiveRecord::Migration[7.0]
+  def up
+    execute <<-SQL
+      UPDATE chat_channels
+      SET last_message_id = (
+        SELECT cm.id
+        FROM chat_messages cm
+        LEFT JOIN chat_threads ON chat_threads.original_message_id = cm.id
+        WHERE cm.chat_channel_id = chat_channels.id
+          AND cm.deleted_at IS NULL
+          AND (cm.thread_id IS NULL OR chat_threads.id IS NOT NULL)
+        ORDER BY cm.created_at DESC, cm.id DESC
+        LIMIT 1
+      );
+    SQL
+
+    execute <<-SQL
+      UPDATE chat_threads
+      SET last_message_id = (
+        SELECT cm.id
+        FROM chat_messages cm
+        WHERE cm.thread_id = chat_threads.id
+          AND cm.deleted_at IS NULL
+        ORDER BY cm.created_at DESC, cm.id DESC
+        LIMIT 1
+      );
+    SQL
+  end
+
+  def down
+    raise ActiveRecord::IrreversibleMigration
+  end
+end

plugins/chat/db/post_migrate/20230710040640_backfill_chat_channel_and_thread_last_message_ids_post_migrate.rb

@@ -0,0 +1,29 @@
+# frozen_string_literal: true
+
+class BackfillChatChannelAndThreadLastMessageIdsPostMigrate < ActiveRecord::Migration[7.0]
+  execute <<-SQL
+    UPDATE chat_channels
+    SET last_message_id = (
+      SELECT cm.id
+      FROM chat_messages cm
+      LEFT JOIN chat_threads ON chat_threads.original_message_id = cm.id
+      WHERE cm.chat_channel_id = chat_channels.id
+        AND cm.deleted_at IS NULL
+        AND (cm.thread_id IS NULL OR chat_threads.id IS NOT NULL)
+      ORDER BY cm.created_at DESC, cm.id DESC
+      LIMIT 1
+    );
+  SQL
+
+  execute <<-SQL
+    UPDATE chat_threads
+    SET last_message_id = (
+      SELECT cm.id
+      FROM chat_messages cm
+      WHERE cm.thread_id = chat_threads.id
+        AND cm.deleted_at IS NULL
+      ORDER BY cm.created_at DESC, cm.id DESC
+      LIMIT 1
+    );
+  SQL
+end