From b835e8475bcf4f0f4a186fb976fee69cfeb14cae Mon Sep 17 00:00:00 2001
From: Dmitry Semigradsky <semigradskyd@gmail.com>
Date: Tue, 10 Oct 2017 10:31:16 +0300
Subject: [PATCH] #28 Fix incorrect reducing

---
 src/__tests__/index.js | 9 ++++++++-
 src/lib/reducer.js     | 9 +++++++--
 2 files changed, 15 insertions(+), 3 deletions(-)

diff --git a/src/__tests__/index.js b/src/__tests__/index.js
index d6baba4..2437f69 100644
--- a/src/__tests__/index.js
+++ b/src/__tests__/index.js
@@ -49,6 +49,13 @@ test(
   '60px'
 )
 
+test(
+  'should reduce simple calc (6)',
+  testFixture,
+  'calc(100px - (100px - 100%))',
+  '100%'
+)
+
 test(
   'should reduce additions and subtractions (1)',
   testFixture,
@@ -144,7 +151,7 @@ test(
   'should ignore calc with css variables (5)',
   testFixture,
   'calc(10px - (100px - var(--mouseX)))',
-  'calc(-90px - var(--mouseX))'
+  'calc(-90px + var(--mouseX))'
 )
 
 test(
diff --git a/src/lib/reducer.js b/src/lib/reducer.js
index 860040e..2c69be5 100644
--- a/src/lib/reducer.js
+++ b/src/lib/reducer.js
@@ -95,8 +95,8 @@ function reduceAddSubExpression(node, precision) {
   ) {
     // value + (value + something) => (value + value) + something
     // value + (value - something) => (value + value) - something
-    // value - (value + something) => (value - value) + something
-    // value - (value - something) => (value - value) - something
+    // value - (value + something) => (value - value) - something
+    // value - (value - something) => (value - value) + something
     if (left.type === right.left.type) {
       node = Object.assign({ }, node)
       node.left = reduce({
@@ -106,6 +106,11 @@ function reduceAddSubExpression(node, precision) {
         right: right.left
       }, precision)
       node.right = right.right
+
+      if (node.operator === '-') {
+        node.operator = right.operator === '+' ? '-' : '+'
+      }
+
       return reduce(node, precision)
     }
     // value + (something + value) => (value + value) + something