Fix Italy state seed generation

Previously, Italy was using the top-level `subregions` - `regions`
in Carmen to generate states, however for a mailing address this
is incorrect, and it instead needs to use `provinces`, which is
nested as the second level of `subregions` in Carmen. This fixes the
seed generation, allowing for more countries to make this switch
as necessary (there are a handful of other countries that need this)

Also, adds a `state:regenerate` rake task that updates states for
countries that were generated incorrectly, like Italy. This is so
people updgrading from v2.10 to v2.11 can easily update to the
correct state list.

core/db/default/spree/states.rb

@@ -1,14 +1,24 @@
 # frozen_string_literal: true
 
+countries_that_use_nested_subregions = %w(IT)
+
+def create_states(subregions, country)
+  subregions.each do |subregion|
+    Spree::State.where(abbr: subregion.code, country: country).first_or_create!(
+      name: subregion.name
+    )
+  end
+end
+
 ActiveRecord::Base.transaction do
   Spree::Country.all.each do |country|
     carmen_country = Carmen::Country.coded(country.iso)
     next unless carmen_country.subregions?
 
-    carmen_country.subregions.each do |subregion|
-      Spree::State.where(abbr: subregion.code, country: country).first_or_create!(
-        name: subregion.name
-      )
+    if countries_that_use_nested_subregions.include? country.iso
+      create_states(carmen_country.subregions.flat_map(&:subregions), country)
+    else
+      create_states(carmen_country.subregions, country)
     end
   end
 end

core/lib/tasks/states.rake

@@ -0,0 +1,57 @@
+# frozen_string_literal: true
+
+def get_carmen_states(iso)
+  carmen_country = Carmen::Country.coded(iso)
+  return false unless carmen_country&.subregions?
+
+  if %w(IT).include? iso
+    return carmen_country.subregions.flat_map(&:subregions)
+  else
+    return carmen_country.subregions
+  end
+end
+
+def user_agrees(destroy_states, create_states, country)
+  puts "\e[31mStates for #{country.name} are incorrect. If you proceed, the following changes will happen:\e[0m"
+  puts "\e[31mThese states will be destroyed:\e[0m #{destroy_states}"
+  puts "\e[31mThese states will be created:\e[0m #{create_states}"
+  puts "\e[31mDo you want to proceed? [y/n]\e[0m "
+  ["y", "yes"].include? STDIN.gets.strip.downcase
+end
+
+def delete_states(country, carmen_names)
+  country.states.where.not(name: carmen_names).destroy_all
+end
+
+def create_states(country, carmen_states, state_names)
+  carmen_states.each do |state|
+    unless state_names.include? state.name
+      Spree::State.where(abbr: state.code, country: country).first_or_create!(
+        name: state.name
+      )
+    end
+  end
+end
+
+namespace :states do
+  desc "Regenerates states in cases where previous Solidus versions generated incorrect states"
+  task regenerate: :environment do
+    Spree::Country.all.each do |country|
+      if carmen_states = get_carmen_states(country.iso)
+        if (state_names = country.states.pluck(:name)) != (carmen_names = carmen_states.map(&:name).sort)
+          if user_agrees(
+            (state_names - carmen_names),
+            (carmen_names - state_names),
+            country
+          )
+            delete_states(country, carmen_names)
+            create_states(country, carmen_states, state_names)
+            puts "#{country} states have been regenerated"
+          else
+            puts "Skipping #{country}"
+          end
+        end
+      end
+    end
+  end
+end