Paginate through users

If there are/have been over 1000 users in an organization, the
eligible_user_ids method in loads_slack_channel_members would only
retrieve the first 1000.

This change adds a method to follow any pagination cursors and combine
user pages together to ensure we have a complete user list to compare
to when intersecting with the channel member list.

This change also adds a limit of 200 for user retrievable, as
recommended by Slack's API guide.

Author: sej3506

app/services/slack/loads_slack_channel_members.rb

@@ -14,10 +14,21 @@ def call(channel:)
 
     def eligible_user_ids
       response = retry_when_rate_limited do
-        ClientWrapper.client.users_list
+        ClientWrapper.client.users_list(limit: 200)
       end
 
-      (response&.members || []).reject { |u| u.is_bot }.map(&:id)
+      members = get_paged_members(cursor: response&.response_metadata&.next_cursor, members: response&.members || [])
+      (members || []).reject { |u| u.is_bot }.map(&:id)
+    end
+
+    def get_paged_members(cursor:, members:)
+      while cursor.present?
+        response = ClientWrapper.client.users_list(cursor: cursor, limit: 200)
+        members.append(response.members)
+        cursor = response.response_metadata&.next_cursor
+      end
+
+      members.flatten
     end
   end
 end

spec/lib/slack/loads_slack_channel_members_spec.rb

@@ -35,6 +35,33 @@
     expect(members).to eq(slack_members)
   end
 
+  it "loads members found in a channel when pagination is required" do
+    all_slack_users = (0..205).map do |id|
+      Slack::Messages::Message.new(id: "USER_ID_#{id}")
+    end
+
+    slack_members = [
+      "USER_ID_1",
+      "USER_ID_3",
+      "USER_ID_205"
+    ]
+
+    response_metadata = Slack::Messages::Message.new(next_cursor: "cursor")
+    expect(@slack_client).to receive(:users_list).with(limit: 200) {
+      Slack::Messages::Message.new(ok: true, members: all_slack_users[0..199], response_metadata: response_metadata)
+    }
+    expect(@slack_client).to receive(:users_list).with(cursor: response_metadata.next_cursor, limit: 200) {
+      Slack::Messages::Message.new(ok: true, members: all_slack_users[200..])
+    }
+    expect(@slack_client).to receive(:conversations_members).with(channel: "CHANNEL_ID", limit: 1000) {
+      Slack::Messages::Message.new(ok: true, members: slack_members)
+    }
+
+    members = subject.call(channel: "CHANNEL_ID")
+
+    expect(members).to eq(slack_members)
+  end
+
   it "excludes bots from the returned users" do
     slack_user = Slack::Messages::Message.new(id: "USER_ID", is_bot: false)
     slack_app = Slack::Messages::Message.new(id: "APP_ID", is_bot: true)