Fix #1902: ensure correct payment state when failed payments are present

Problem: order payments didn't seem to be loaded in any particular order,
and OrderUpdater#update_payment_state was relying on payment order to de-
termine payment state.

Strategy: Adapt a version of this method from a future version of Spree.
I tried to select a version where I would have to make the absolute mini-
mum number of changes to get it to work. See comments in code for justif-
ications of the changes that I did make.

app/models/spree/order_updater_decorator.rb

@@ -0,0 +1,41 @@
+module Spree
+  OrderUpdater.class_eval do
+    # TODO: This logic adapted from Spree 2.4, remove when we get there
+    # Handles state updating in a much more logical way than < 2.4
+    # Specifically, doesn't depend on payments.last to determine payment state
+    # Also swapped: == 0 for .zero?, .size == 0 for empty? and .size > 0 for !empty?
+    # See:
+    # https://github.com/spree/spree/commit/38b8456183d11fc1e00e395e7c9154c76ef65b85
+    # https://github.com/spree/spree/commit/7b264acff7824f5b3dc6651c106631d8f30b147a
+    def update_payment_state
+      last_state = order.payment_state
+      if payments.present? && payments.valid.empty?
+        order.payment_state = 'failed'
+      elsif order.state == 'canceled' && order.payment_total.zero?
+        order.payment_state = 'void'
+      else
+        # This part added so that we don't need to override order.outstanding_balance
+        balance = order.outstanding_balance
+        balance = -1 * order.payment_total if canceled_and_paid_for?
+        order.payment_state = 'balance_due' if balance > 0
+        order.payment_state = 'credit_owed' if balance < 0
+        order.payment_state = 'paid' if balance.zero?
+
+        # Original logic
+        # order.payment_state = 'balance_due' if order.outstanding_balance > 0
+        # order.payment_state = 'credit_owed' if order.outstanding_balance < 0
+        # order.payment_state = 'paid' if !order.outstanding_balance?
+      end
+      order.state_changed('payment') if last_state != order.payment_state
+      order.payment_state
+    end
+
+    private
+
+    # Taken from order.outstanding_balance in Spree 2.4
+    # See: https://github.com/spree/spree/commit/7b264acff7824f5b3dc6651c106631d8f30b147a
+    def canceled_and_paid_for?
+      order.canceled? && order.payments.present? && !order.payments.completed.empty?
+    end
+  end
+end

spec/models/spree/order_updater_spec.rb

@@ -0,0 +1,91 @@
+require 'spec_helper'
+
+describe Spree::OrderUpdater do
+  # Copied pretty much verbatim from Spree 2.4. Remove this file once we get there,
+  # assuming the unchanged 2.4 logic still works for us.
+  # Only changes are stubs of :empty? instead of :size
+  context "updating payment state" do
+    let(:order) { Spree::Order.new }
+    let(:updater) { order.updater }
+
+    it "is failed if no valid payments" do
+      order.stub_chain(:payments, :valid, :empty?).and_return(true)
+
+      updater.update_payment_state
+      order.payment_state.should == 'failed'
+    end
+
+    context "payment total is greater than order total" do
+      it "is credit_owed" do
+        order.payment_total = 2
+        order.total = 1
+
+        expect {
+          updater.update_payment_state
+        }.to change { order.payment_state }.to 'credit_owed'
+      end
+    end
+
+    context "order total is greater than payment total" do
+      it "is credit_owed" do
+        order.payment_total = 1
+        order.total = 2
+
+        expect {
+          updater.update_payment_state
+        }.to change { order.payment_state }.to 'balance_due'
+      end
+    end
+
+    context "order total equals payment total" do
+      it "is paid" do
+        order.payment_total = 30
+        order.total = 30
+
+        expect {
+          updater.update_payment_state
+        }.to change { order.payment_state }.to 'paid'
+      end
+    end
+
+    context "order is canceled" do
+      before do
+        order.state = 'canceled'
+      end
+
+      context "and is still unpaid" do
+        it "is void" do
+          order.payment_total = 0
+          order.total = 30
+          expect {
+            updater.update_payment_state
+          }.to change { order.payment_state }.to 'void'
+        end
+      end
+
+      context "and is paid" do
+        it "is credit_owed" do
+          order.payment_total = 30
+          order.total = 30
+          order.stub_chain(:payments, :valid, :empty?).and_return(false)
+          order.stub_chain(:payments, :completed, :empty?).and_return(false)
+          expect {
+            updater.update_payment_state
+          }.to change { order.payment_state }.to 'credit_owed'
+        end
+      end
+
+      context "and payment is refunded" do
+        it "is void" do
+          order.payment_total = 0
+          order.total = 30
+          order.stub_chain(:payments, :valid, :empty?).and_return(false)
+          order.stub_chain(:payments, :completed, :empty?).and_return(false)
+          expect {
+            updater.update_payment_state
+          }.to change { order.payment_state }.to 'void'
+        end
+      end
+    end
+  end
+end