From 5665b67288e5dba275dded5f1e28b1f17e20bbaa Mon Sep 17 00:00:00 2001
From: Christopher Rogers <chrissrogers@gmail.com>
Date: Wed, 29 Aug 2018 17:28:51 -0600
Subject: [PATCH] Fixes issue where tax exemption results in negative taxes

- Occurs if a merchant sets all items on a checkout to be tax exempt
- If a blanket amount discount is applied, then taxes will be subtracted according to the discount amount. Since discounts are not examptable, a negative tax amount would occur

Signed-off-by: Christopher Rogers <chrissrogers@gmail.com>
---
 lib/util/tax-ceil.js                          |  3 ++
 test/pricing/checkout/checkout.test.js        | 39 +++++++++++++++----
 .../fixtures/coupons/coop-fixed-all-5.json    | 21 ++++++++++
 3 files changed, 56 insertions(+), 7 deletions(-)
 create mode 100644 test/server/fixtures/coupons/coop-fixed-all-5.json

diff --git a/lib/util/tax-ceil.js b/lib/util/tax-ceil.js
index b04dc297f..4f7b1ec14 100644
--- a/lib/util/tax-ceil.js
+++ b/lib/util/tax-ceil.js
@@ -2,10 +2,13 @@
  * Ceilings the second decimal of a number without risk of
  * floating point math errors
  *
+ * - returns zero if the result is negative
+ *
  * @param {Number} number
  * @return {Number}
  */
 
 export default function taxCeil (number) {
+  number = Math.max(number, 0);
   return +(Math.ceil(number + 'e+2') + 'e-2');
 }
diff --git a/test/pricing/checkout/checkout.test.js b/test/pricing/checkout/checkout.test.js
index 43d6d17d5..71d76fa8b 100644
--- a/test/pricing/checkout/checkout.test.js
+++ b/test/pricing/checkout/checkout.test.js
@@ -14,6 +14,13 @@ describe('CheckoutPricing', function () {
     });
   });
 
+  beforeEach(function (done) {
+    subscriptionPricingFactory('tax_exempt', this.recurly, sub => {
+      this.subscriptionPricingExampleTaxExempt = sub;
+      done();
+    });
+  })
+
   /**
    * Subscriptions
    */
@@ -1413,13 +1420,6 @@ describe('CheckoutPricing', function () {
         });
 
         describe('given some tax exempt adjustments and subscriptions', () => {
-          beforeEach(function (done) {
-            subscriptionPricingFactory('tax_exempt', this.recurly, sub => {
-              this.subscriptionPricingExampleTaxExempt = sub;
-              done();
-            });
-          });
-
           beforeEach(function () {
             return this.pricing
               .subscription(this.subscriptionPricingExampleTaxExempt) // $2 setup fee
@@ -1504,6 +1504,31 @@ describe('CheckoutPricing', function () {
           });
         });
 
+        describe('given tax exempt items and a discount', () => {
+          beforeEach(function () {
+            // Reset to eliminate the pre-defined adjustments
+            this.pricing = this.recurly.Pricing.Checkout();
+            return this.pricing
+              .address({ country: 'US', postalCode: '94110' })
+              .subscription(this.subscriptionPricingExampleTaxExempt)
+              .adjustment({ amount: 10, taxExempt: true })
+              .adjustment({ amount: 27.25, taxExempt: true })
+              .coupon('coop-fixed-all-5')
+              .reprice();
+          });
+
+          it('does not discount negatively', function (done) {
+            this.pricing
+              .reprice()
+              .then(price => {
+                assert.equal(price.now.taxes, 0);
+                assert.equal(price.now.discount, 5);
+                done();
+              })
+              .done();
+          });
+        });
+
         describe('given VAT numbers on address and tax info', () => {
           it('takes the VAT number from the tax info', function (done) {
             sinon.spy(this.recurly, 'tax');
diff --git a/test/server/fixtures/coupons/coop-fixed-all-5.json b/test/server/fixtures/coupons/coop-fixed-all-5.json
new file mode 100644
index 000000000..1eb47a21c
--- /dev/null
+++ b/test/server/fixtures/coupons/coop-fixed-all-5.json
@@ -0,0 +1,21 @@
+{
+  "code": "coop-fixed-all-5",
+  "name": "Test coupon: $5 off all charges",
+  "discount": {
+    "type": "dollars",
+    "amount":
+      {
+        "USD": 5.0
+      }
+  },
+  "single_use": false,
+  "applies_for_months": null,
+  "duration": "forever",
+  "temporal_unit": null,
+  "temporal_amount": null,
+  "plans": [],
+  "applies_to_non_plan_charges": true,
+  "applies_to_plans": true,
+  "applies_to_all_plans": true,
+  "redemption_resource": "account"
+}