Revert "DEV: Delete dead Topic#incoming_email_addresses code (#19970)" (#20037)

This reverts commit 88a972c61b.

It's actually used in some plugins.

app/models/topic.rb

@@ -1892,6 +1892,46 @@ class Topic < ActiveRecord::Base
       .first
   end
 
+  def incoming_email_addresses(group: nil, received_before: Time.zone.now)
+    email_addresses = Set.new
+
+    # TODO(martin) Look at improving this N1, it will just get slower the
+    # more replies/incoming emails there are for the topic.
+    self
+      .incoming_email
+      .where("created_at <= ?", received_before)
+      .each do |incoming_email|
+        to_addresses = incoming_email.to_addresses_split
+        cc_addresses = incoming_email.cc_addresses_split
+        combined_addresses = [to_addresses, cc_addresses].flatten
+
+        # We only care about the emails addressed to the group or CC'd to the
+        # group if the group is present. If combined addresses is empty we do
+        # not need to do this check, and instead can proceed on to adding the
+        # from address.
+        #
+        # Will not include test1@gmail.com if the only IncomingEmail
+        # is:
+        #
+        # from: test1@gmail.com
+        # to: test+support@discoursemail.com
+        #
+        # Because we don't care about the from addresses and also the to address
+        # is not the email_username, which will be something like test1@gmail.com.
+        if group.present? && combined_addresses.any?
+          next if combined_addresses.none? { |address| address =~ group.email_username_regex }
+        end
+
+        email_addresses.add(incoming_email.from_address)
+        email_addresses.merge(combined_addresses)
+      end
+
+    email_addresses.subtract([nil, ""])
+    email_addresses.delete(group.email_username) if group.present?
+
+    email_addresses.to_a
+  end
+
   def create_invite_notification!(target_user, notification_type, invited_by, post_number: 1)
     if UserCommScreener.new(
          acting_user: invited_by,

spec/lib/email/receiver_spec.rb

@@ -1550,12 +1550,10 @@ RSpec.describe Email::Receiver do
       handler_calls = 0
       handler =
         proc do |topic|
-          expect(
+          expect(topic.incoming_email_addresses).to contain_exactly(
-            [
+            "discourse@bar.com",
-              topic.incoming_email.first.from_address,
+            "category@foo.com",
-              topic.incoming_email.first.to_addresses_split,
+          )
-            ].flatten,
-          ).to contain_exactly("discourse@bar.com", "category@foo.com")
           handler_calls += 1
         end
 

spec/models/topic_spec.rb

@@ -3271,6 +3271,85 @@ RSpec.describe Topic do
     end
   end
 
+  describe "#incoming_email_addresses" do
+    fab!(:group) do
+      Fabricate(
+        :group,
+        smtp_server: "imap.gmail.com",
+        smtp_port: 587,
+        email_username: "discourse@example.com",
+        email_password: "discourse@example.com",
+      )
+    end
+
+    fab!(:topic) do
+      Fabricate(
+        :private_message_topic,
+        topic_allowed_groups: [Fabricate.build(:topic_allowed_group, group: group)],
+      )
+    end
+
+    let!(:incoming1) do
+      Fabricate(
+        :incoming_email,
+        to_addresses: "discourse@example.com",
+        from_address: "johnsmith@user.com",
+        topic: topic,
+        post: topic.posts.first,
+        created_at: 20.minutes.ago,
+      )
+    end
+    let!(:incoming2) do
+      Fabricate(
+        :incoming_email,
+        from_address: "discourse@example.com",
+        to_addresses: "johnsmith@user.com",
+        topic: topic,
+        post: Fabricate(:post, topic: topic),
+        created_at: 10.minutes.ago,
+      )
+    end
+    let!(:incoming3) do
+      Fabricate(
+        :incoming_email,
+        to_addresses: "discourse@example.com",
+        from_address: "johnsmith@user.com",
+        topic: topic,
+        post: topic.posts.first,
+        cc_addresses: "otherguy@user.com",
+        created_at: 2.minutes.ago,
+      )
+    end
+    let!(:incoming4) do
+      Fabricate(
+        :incoming_email,
+        to_addresses: "unrelated@test.com",
+        from_address: "discourse@example.com",
+        topic: topic,
+        post: topic.posts.first,
+        created_at: 1.minutes.ago,
+      )
+    end
+
+    it "returns an array of all the incoming email addresses" do
+      expect(topic.incoming_email_addresses).to match_array(
+        %w[discourse@example.com johnsmith@user.com otherguy@user.com unrelated@test.com],
+      )
+    end
+
+    it "returns an array of all the incoming email addresses where incoming was received before X" do
+      expect(topic.incoming_email_addresses(received_before: 5.minutes.ago)).to match_array(
+        %w[discourse@example.com johnsmith@user.com],
+      )
+    end
+
+    context "when the group is present" do
+      it "excludes incoming emails that are not to or CCd to the group" do
+        expect(topic.incoming_email_addresses(group: group)).not_to include("unrelated@test.com")
+      end
+    end
+  end
+
   describe "#cannot_permanently_delete_reason" do
     fab!(:post) { Fabricate(:post) }
     let!(:topic) { post.topic }