Add API for states by country

Add an API route for fetching states by country

config/routes.rb

@@ -118,6 +118,7 @@ Rails.application.routes.draw do
       draw :trial
       draw :trial_registration
       draw :country
+      draw :country_state
     end
 
     Gitlab.ee do

ee/app/controllers/countries_controller.rb

@@ -2,7 +2,10 @@
 
 class CountriesController < ActionController::Metal
   include AbstractController::Rendering
-  include ActionController::Renderers::All
+  include ActionController::ApiRendering
+  include ActionController::Renderers
+
+  use_renderers :json
 
   def index
     countries = World.countries_for_select

ee/app/controllers/country_states_controller.rb

+# frozen_string_literal: true
+
+class CountryStatesController < ActionController::Metal
+  include AbstractController::Rendering
+  include ActionController::ApiRendering
+  include ActionController::Renderers
+
+  use_renderers :json
+
+  def index
+    country = params[:country]
+    states = World.states_for_country(country)
+
+    render json: states, status: (states ? :ok : :not_found)
+  end
+end

ee/changelogs/unreleased/growth-87-states-api.yml

+---
+title: Add API for states by country
+merge_request: 21417
+author:
+type: added

ee/config/routes/country_state.rb

+# frozen_string_literal: true
+
+resources :country_states, only: [:index]

ee/lib/world.rb

@@ -10,6 +10,18 @@ module World
     strong_memoize(:countries_for_select) { all_countries.sort_by(&:name).map { |c| [c.name, c.alpha2] } }
   end
 
+  def states_for_country(country_code)
+    strong_memoize("states_for_country_#{country_code}") do
+      country = ISO3166::Country.find_country_by_alpha2(country_code)
+      next unless country
+
+      country.states
+        &.reject { |_, state| state.name.nil? }
+        &.sort_by { |_, state| state.name }
+        &.map { |code, state| [state.name, code] }.to_h
+    end
+  end
+
   def all_countries
     strong_memoize(:all_countries) { ISO3166::Country.all.reject {|item| DENYLIST.include?(item.name) } }
   end

ee/spec/controllers/country_states_controller_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe CountryStatesController do
+  describe 'GET #index' do
+    it 'returns a list of states as json' do
+      country = 'NL'
+      get :index, params: { country: country }
+
+      expected_json = World.states_for_country(country).to_json
+
+      expect(response.status).to eq(200)
+      expect(response.body).to eq(expected_json)
+    end
+
+    it 'returns "null" when the provided country is not found' do
+      country = 'NLX'
+      get :index, params: { country: country }
+
+      expect(response.status).to eq(404)
+      expect(response.body).to eq("null")
+    end
+  end
+end

ee/spec/lib/world_spec.rb

@@ -18,4 +18,18 @@ describe World do
       expect(result.first).to eq(%w[Afghanistan AF])
     end
   end
+
+  describe '.states_for_country' do
+    it 'returns a list of state names for a country in alphabetical order' do
+      result = described_class.states_for_country('NL')
+
+      expect(result.first).to eq(%w[Drenthe DR])
+    end
+
+    it 'returns nil when given country cannot be found' do
+      result = described_class.states_for_country('NLX')
+
+      expect(result).to be_nil
+    end
+  end
 end