DEV: extract the logic for extracting and expanding mentions from ChatNotifier (#20290)

Initially, the ChatMention model / db table was introduced to better support notifications (see discourse/discourse-chat@0801d10). That means that currently, we create a new chat_mention record only if a user will be notified about the mention.

Now we plan to start using the ChatMention model in other scenarios (for example for implementing user status on mentions) so we need to always create a new record in the chat_mention table. This PR does the first step into that direction by decoupling the logic for extracting and expanding mentions from the code related to notifications.

This doesn't change any behavior, only extracts code from ChatNotifier.

plugins/chat/spec/lib/chat_message_mentions_spec.rb

@@ -0,0 +1,154 @@
+# frozen_string_literal: true
+
+require "rails_helper"
+
+RSpec.describe Chat::ChatMessageMentions do
+  fab!(:channel_member_1) { Fabricate(:user) }
+  fab!(:channel_member_2) { Fabricate(:user) }
+  fab!(:channel_member_3) { Fabricate(:user) }
+  fab!(:not_a_channel_member) { Fabricate(:user) }
+  fab!(:chat_channel) { Fabricate(:chat_channel) }
+
+  before do
+    chat_channel.add(channel_member_1)
+    chat_channel.add(channel_member_2)
+    chat_channel.add(channel_member_3)
+  end
+
+  describe "#global_mentions" do
+    it "returns all members of the channel" do
+      message = create_message("mentioning @all")
+
+      mentions = Chat::ChatMessageMentions.new(message)
+      result = mentions.global_mentions.pluck(:username)
+
+      expect(result).to contain_exactly(
+        channel_member_1.username,
+        channel_member_2.username,
+        channel_member_3.username,
+      )
+    end
+
+    it "doesn't include users that were also mentioned directly" do
+      message = create_message("mentioning @all and @#{channel_member_1.username}")
+
+      mentions = Chat::ChatMessageMentions.new(message)
+      result = mentions.global_mentions.pluck(:username)
+
+      expect(result).to contain_exactly(channel_member_2.username, channel_member_3.username)
+    end
+
+    it "returns an empty list if there are no global mentions" do
+      message = create_message("not mentioning anybody")
+
+      mentions = Chat::ChatMessageMentions.new(message)
+      result = mentions.global_mentions.pluck(:username)
+
+      expect(result).to be_empty
+    end
+  end
+
+  describe "#here_mentions" do
+    before do
+      freeze_time
+      channel_member_1.update(last_seen_at: 2.minutes.ago)
+      channel_member_2.update(last_seen_at: 2.minutes.ago)
+      channel_member_3.update(last_seen_at: 5.minutes.ago)
+    end
+
+    it "returns all members of the channel who were online in the last 5 minutes" do
+      message = create_message("mentioning @here")
+
+      mentions = Chat::ChatMessageMentions.new(message)
+      result = mentions.here_mentions.pluck(:username)
+
+      expect(result).to contain_exactly(channel_member_1.username, channel_member_2.username)
+    end
+
+    it "doesn't include users that were also mentioned directly" do
+      message = create_message("mentioning @here and @#{channel_member_1.username}")
+
+      mentions = Chat::ChatMessageMentions.new(message)
+      result = mentions.here_mentions.pluck(:username)
+
+      expect(result).to contain_exactly(channel_member_2.username)
+    end
+
+    it "returns an empty list if there are no here mentions" do
+      message = create_message("not mentioning anybody")
+
+      mentions = Chat::ChatMessageMentions.new(message)
+      result = mentions.here_mentions.pluck(:username)
+
+      expect(result).to be_empty
+    end
+  end
+
+  describe "#direct_mentions" do
+    it "returns users who were mentioned directly" do
+      message =
+        create_message("mentioning @#{channel_member_1.username} and @#{channel_member_2.username}")
+
+      mentions = Chat::ChatMessageMentions.new(message)
+      result = mentions.direct_mentions.pluck(:username)
+
+      expect(result).to contain_exactly(channel_member_1.username, channel_member_2.username)
+    end
+
+    it "returns a mentioned user even if he's not a member of the channel" do
+      message = create_message("mentioning @#{not_a_channel_member.username}")
+
+      mentions = Chat::ChatMessageMentions.new(message)
+      result = mentions.direct_mentions.pluck(:username)
+
+      expect(result).to contain_exactly(not_a_channel_member.username)
+    end
+
+    it "returns an empty list if no one was mentioned directly" do
+      message = create_message("not mentioning anybody")
+
+      mentions = Chat::ChatMessageMentions.new(message)
+      result = mentions.direct_mentions.pluck(:username)
+
+      expect(result).to be_empty
+    end
+  end
+
+  describe "#group_mentions" do
+    fab!(:group1) { Fabricate(:group, mentionable_level: Group::ALIAS_LEVELS[:everyone]) }
+    fab!(:group_member_1) { Fabricate(:user, group_ids: [group1.id]) }
+    fab!(:group_member_2) { Fabricate(:user, group_ids: [group1.id]) }
+    fab!(:group_member_3) { Fabricate(:user, group_ids: [group1.id]) }
+
+    before do
+      chat_channel.add(group_member_1)
+      chat_channel.add(group_member_2)
+    end
+
+    it "returns members of a mentioned group even if some of them is not members of the channel" do
+      message = create_message("mentioning @#{group1.name}")
+
+      mentions = Chat::ChatMessageMentions.new(message)
+      result = mentions.group_mentions.pluck(:username)
+
+      expect(result).to contain_exactly(
+        group_member_1.username,
+        group_member_2.username,
+        group_member_3.username,
+      )
+    end
+
+    it "returns an empty list if no group was mentioned" do
+      message = create_message("not mentioning anybody")
+
+      mentions = Chat::ChatMessageMentions.new(message)
+      result = mentions.group_mentions.pluck(:username)
+
+      expect(result).to be_empty
+    end
+  end
+
+  def create_message(text)
+    Fabricate(:chat_message, chat_channel: chat_channel, message: text)
+  end
+end