Format UK school postcodes

app/models/school.rb

@@ -30,6 +30,8 @@ class School < ApplicationRecord
 
   before_validation :normalize_reference
 
+  before_save :format_uk_postal_code, if: :should_format_uk_postal_code?
+
   def self.find_for_user!(user)
     school = Role.find_by(user_id: user.id)&.school || find_by(creator_id: user.id)
     raise ActiveRecord::RecordNotFound unless school
@@ -65,6 +67,10 @@ def reject
     update(rejected_at: Time.zone.now)
   end
 
+  def postal_code=(str)
+    super(str.to_s.upcase)
+  end
+
   private
 
   # Ensure the reference is nil, not an empty string
@@ -83,4 +89,15 @@ def rejected_at_cannot_be_changed
   def code_cannot_be_changed
     errors.add(:code, 'cannot be changed after verification') if code_was.present? && code_changed?
   end
+
+  def should_format_uk_postal_code?
+    country_code == 'GB' && postal_code.to_s.length >= 5
+  end
+
+  def format_uk_postal_code
+    cleaned_postal_code = postal_code.delete(' ')
+    # insert a space as the third-from-last character in the postcode, eg. SW1A1AA -> SW1A 1AA
+    # ensures UK postcodes are always formatted correctly (as the inward code is always 3 chars long)
+    self.postal_code = "#{cleaned_postal_code[0..-4]} #{cleaned_postal_code[-3..]}"
+  end
 end

spec/models/school_spec.rb

@@ -331,6 +331,51 @@
     end
   end
 
+  describe '#format_uk_postal_code' do
+    it 'retains correctly formatted UK postal_code' do
+      school.country_code = 'GB'
+      school.postal_code = 'SW1A 1AA'
+      school.save
+      expect(school.postal_code).to eq('SW1A 1AA')
+    end
+
+    it 'corrects incorrectly formatted UK postal_code' do
+      school.country_code = 'GB'
+      school.postal_code = 'SW1 A1AA'
+      expect { school.save }.to change(school, :postal_code).to('SW1A 1AA')
+    end
+
+    it 'formats UK postal_code with 4 char outcode' do
+      school.country_code = 'GB'
+      school.postal_code = 'SW1A1AA'
+      expect { school.save }.to change(school, :postal_code).to('SW1A 1AA')
+    end
+
+    it 'formats UK postal_code with 3 char outcode' do
+      school.country_code = 'GB'
+      school.postal_code = 'SW11AA'
+      expect { school.save }.to change(school, :postal_code).to('SW1 1AA')
+    end
+
+    it 'formats UK postal_code with 2 char outcode' do
+      school.country_code = 'GB'
+      school.postal_code = 'SW1AA'
+      expect { school.save }.to change(school, :postal_code).to('SW 1AA')
+    end
+
+    it 'does not format UK postal_code for short / invalid codes' do
+      school.country_code = 'GB'
+      school.postal_code = 'SW1A'
+      expect { school.save }.not_to change(school, :postal_code)
+    end
+
+    it 'does not format postal_code for non-UK countries' do
+      school.country_code = 'FR'
+      school.postal_code = '123456'
+      expect { school.save }.not_to change(school, :postal_code)
+    end
+  end
+
   describe '#reject' do
     it 'sets rejected_at to the current time' do
       school.reject