feat(products): add attached_to_plan_or_subscription? to catalog models

## Context

Structural catalog fields (code, product attachment, filter values) must
stop being editable once an item is in use. An item is in use as soon as it
is part of a plan, not only when a subscription exists.

## Description

Add attached_to_plan_or_subscription? to Product, ProductItem and
ProductItemFilter. A product item is attached when a plan_product_item or a
subscription_product_item references it; a product when it belongs to a plan
or any of its items is on a subscription; a filter delegates to its item.

Author: rsempe

app/models/product.rb

@@ -26,6 +26,12 @@ def self.ransackable_attributes(_auth_object = nil)
   def invoice_name
     invoice_display_name.presence || name
   end
+
+  def attached_to_plan_or_subscription?
+    return true if plan_products.exists?
+
+    SubscriptionProductItem.where(product_item_id: product_items.select(:id)).exists?
+  end
 end
 
 # == Schema Information

app/models/product_item.rb

@@ -41,6 +41,10 @@ def invoice_name
     invoice_display_name.presence || name
   end
 
+  def attached_to_plan_or_subscription?
+    plan_product_items.exists? || subscription_product_items.exists?
+  end
+
   private
 
   def validate_billable_metric_presence

app/models/product_item_filter.rb

@@ -12,6 +12,8 @@ class ProductItemFilter < ApplicationRecord
   has_many :values, class_name: "ProductItemFilterValue"
   has_many :billable_metric_filters, through: :values
 
+  delegate :attached_to_plan_or_subscription?, to: :product_item
+
   validates :name, presence: true
   validates :code,
     presence: true,

spec/models/product_item_filter_spec.rb

@@ -66,4 +66,17 @@
       expect(filter.reload.to_h).to eq("region" => %w[us eu], "scheme" => %w[visa])
     end
   end
+
+  describe "#attached_to_plan_or_subscription?" do
+    let(:product_item) { create(:product_item) }
+    let(:filter) { create(:product_item_filter, organization: product_item.organization, product_item:) }
+
+    it "delegates to the product item" do
+      expect(filter.attached_to_plan_or_subscription?).to be(false)
+
+      create(:subscription_product_item, organization: product_item.organization, product_item:)
+
+      expect(filter.attached_to_plan_or_subscription?).to be(true)
+    end
+  end
 end

spec/models/product_item_spec.rb

@@ -82,4 +82,24 @@
       end
     end
   end
+
+  describe "#attached_to_plan_or_subscription?" do
+    let(:product_item) { create(:product_item) }
+
+    it "is false when no plan or subscription references it" do
+      expect(product_item.attached_to_plan_or_subscription?).to be(false)
+    end
+
+    it "is true when a plan product item references it" do
+      create(:plan_product_item, organization: product_item.organization, product_item:)
+
+      expect(product_item.attached_to_plan_or_subscription?).to be(true)
+    end
+
+    it "is true when a subscription product item references it" do
+      create(:subscription_product_item, organization: product_item.organization, product_item:)
+
+      expect(product_item.attached_to_plan_or_subscription?).to be(true)
+    end
+  end
 end

spec/models/product_spec.rb

@@ -51,4 +51,27 @@
       expect(product.invoice_name).to eq("Name")
     end
   end
+
+  describe "#attached_to_plan_or_subscription?" do
+    let(:product) { create(:product) }
+
+    it "is false when the product is not in a plan and none of its items has a subscription" do
+      create(:product_item, organization: product.organization, product:)
+
+      expect(product.attached_to_plan_or_subscription?).to be(false)
+    end
+
+    it "is true when the product is attached to a plan" do
+      create(:plan_product, organization: product.organization, product:)
+
+      expect(product.attached_to_plan_or_subscription?).to be(true)
+    end
+
+    it "is true when one of its items has a subscription product item" do
+      item = create(:product_item, organization: product.organization, product:)
+      create(:subscription_product_item, organization: product.organization, product_item: item)
+
+      expect(product.attached_to_plan_or_subscription?).to be(true)
+    end
+  end
 end