Merge pull request MoOx#35 from Semigradsky/28-fix-incorrect-reducing

Fix incorrect reducing

Author: Semigradsky

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(

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