Merge pull request #1682 from graygilmore/spree-money/comparable

Add Comparable to Spree::Money

CHANGELOG.md

@@ -1,15 +1,21 @@
 ## Solidus 2.2.0 (master, unreleased)
 
 *   Promotion and Shipping calculators can be created or have their type
-    changed without saving and reloading the page. [#1618](https://github.com/solidusio/solidus/pull/1618)
+    changed without saving and reloading the page.
+    [#1618](https://github.com/solidusio/solidus/pull/1618)
 
-*   Product slugs no longer have a minimum length validation to match the Product name validation.
+*   Product slugs no longer have a minimum length validation to match the
+    Product name validation.
     [#1616](https://github.com/solidusio/solidus/pull/1616)
 
 *   Changed the promotion field in the admin order search to only find orders
     which used the specified promotion code, instead of any code on an applied
     promotion. [#1662](https://github.com/solidusio/solidus/pull/1662)
 
+*   `Spree::Money` now includes `Comparable` and the `<=>` operator for
+    comparisons. A comparison will fail if the two objects do not use the same
+    currency. [#1682](https://github.com/solidusio/solidus/pull/1682)
+
 ## Solidus 2.1.0 (unreleased)
 
 *   The OrderUpdater (as used by `order.update!`) now fully updates taxes.
@@ -83,7 +89,7 @@
     For now `PromotionAction` provides a default remove_from method, with a
     deprecation warning that subclasses should define their own remove_from
     method.
-    
+
     [#1451](https://github.com/solidusio/solidus/pull/1451)
 
 *   Remove `is_default` boolean from `Spree::Price` model

core/lib/spree/money.rb

@@ -6,6 +6,8 @@ module Spree
   # Spree::Money is a relatively thin wrapper around Monetize which handles
   # formatting via Spree::Config.
   class Money
+    include Comparable
+    DifferentCurrencyError = Class.new(StandardError)
     RUBY_NUMERIC_STRING = /\A-?\d+(\.\d+)?\z/
 
     class <<self
@@ -92,6 +94,22 @@ def as_json(*)
       to_s
     end
 
+    def <=>(other)
+      if !other.respond_to?(:money)
+        raise TypeError, "Can't compare #{other.class} to Spree::Money"
+      end
+      if self.currency != other.currency
+        # By default, ::Money will try to run a conversion on `other.money` and
+        # try a comparison on that. We do not want any currency conversion to
+        # take place so we'll catch this here and raise an error.
+        raise(
+          DifferentCurrencyError,
+          "Can't compare #{self.currency} with #{other.currency}"
+        )
+      end
+      @money <=> other.money
+    end
+
     # Delegates comparison to the internal ruby money instance.
     #
     # @see http://www.rubydoc.info/gems/money/Money/Arithmetic#%3D%3D-instance_method

core/spec/lib/spree/money_spec.rb

@@ -268,4 +268,36 @@
       end
     end
   end
+
+  it "includes Comparable" do
+    expect(described_class).to include(Comparable)
+  end
+
+  describe "<=>" do
+    let(:usd_10) { Spree::Money.new(10, currency: "USD") }
+    let(:usd_20) { Spree::Money.new(20, currency: "USD") }
+    let(:usd_30) { Spree::Money.new(30, currency: "USD") }
+
+    it "compares the two amounts" do
+      expect(usd_20 <=> usd_20).to eq 0
+      expect(usd_20 <=> usd_10).to be > 0
+      expect(usd_20 <=> usd_30).to be < 0
+    end
+
+    context "with a non Spree::Money object" do
+      it "raises an error" do
+        expect { usd_10 <=> 20 }.to raise_error(TypeError)
+      end
+    end
+
+    context "with differing currencies" do
+      let(:cad) { Spree::Money.new(10, currency: "CAD") }
+
+      it "raises an error" do
+        expect { usd_10 <=> cad }.to raise_error(
+          Spree::Money::DifferentCurrencyError
+        )
+      end
+    end
+  end
 end