fix: downcase email before finding (#8921)

* fix: downcase email when finding

* feat: add `from_email` class

* refactor: use `from_email`

* feat: add rule to disallow find_by email directly

* chore:  remove redundant test

Since the previous imlpmentation didn't do a case-insentive search, a new user would be created, and the error would be raised at the DB layer. With the new changes, this test case is redundant

* refactor: use from_email

lib/integrations/slack/slack_message_helper.rb

@@ -69,7 +69,7 @@ module Integrations::Slack::SlackMessageHelper
 
   def sender
     user_email = slack_client.users_info(user: params[:event][:user])[:user][:profile][:email]
-    conversation.account.users.find_by(email: user_email)
+    conversation.account.users.from_email(user_email)
   end
 
   def private_note?

lib/rubocop/user_find_by.rb

@@ -0,0 +1,16 @@
+require 'rubocop'
+
+# Enforces use of from_email for email attribute lookups
+class UseFromEmail < RuboCop::Cop::Cop
+  MSG = 'Use `from_email` for email lookups to ensure case insensitivity.'.freeze
+
+  def_node_matcher :find_by_email?, <<~PATTERN
+    (send _ :find_by (hash (pair (sym :email) _)))
+  PATTERN
+
+  def on_send(node)
+    return unless find_by_email?(node)
+
+    add_offense(node, message: MSG)
+  end
+end

lib/seeders/account_seeder.rb

@@ -88,7 +88,7 @@ class Seeders::AccountSeeder
   end
 
   def create_conversation(contact_inbox:, conversation_data:)
-    assignee = User.find_by(email: conversation_data['assignee']) if conversation_data['assignee'].present?
+    assignee = User.from_email(conversation_data['assignee']) if conversation_data['assignee'].present?
     conversation = contact_inbox.conversations.create!(account: contact_inbox.inbox.account, contact: contact_inbox.contact,
                                                        inbox: contact_inbox.inbox, assignee: assignee)
     create_messages(conversation: conversation, messages: conversation_data['messages'])
@@ -111,7 +111,7 @@ class Seeders::AccountSeeder
     if message_data['message_type'] == 'incoming'
       conversation.contact
     elsif message_data['sender'].present?
-      User.find_by(email: message_data['sender'])
+      User.from_email(message_data['sender'])
     end
   end