Add before save callback to truncate email if > 255 chars

What does this MR do and why?

Relates to #409653 (closed)

In cases where email length is > 255 chars, we modify the email to set it within limit and allow the note creation.

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Related to #409653 (closed)

app/models/notes/note_metadata.rb

@@ -4,9 +4,27 @@ module Notes
   class NoteMetadata < ApplicationRecord
     self.table_name = :note_metadata
 
+    EMAIL_PARTICIPANT_LENGTH = 255
+
     belongs_to :note, inverse_of: :note_metadata
-    validates :email_participant, length: { maximum: 255 }
 
     alias_attribute :external_author, :email_participant
+
+    before_save :ensure_email_participant_length
+
+    private
+
+    def ensure_email_participant_length
+      return unless email_participant.present?
+      return unless email_participant.length > EMAIL_PARTICIPANT_LENGTH
+
+      email_prefix, email_suffix = email_participant.split('@')
+
+      email_suffix_length = email_suffix ? email_suffix.length : 0
+
+      allowed_prefix_length = EMAIL_PARTICIPANT_LENGTH - email_suffix_length - 1 # 1 is for '@'
+
+      self.email_participant = "#{email_prefix[0...allowed_prefix_length]}@#{email_suffix}"
+    end
   end
 end