Fix consecutive substractions

Author: andyjansson

src/__tests__/index.js

@@ -168,6 +168,19 @@ test(
   'calc(1px + 1)'
 )
 
+test(
+  'should reduce consecutive substractions (#24) (1)',
+  testFixture,
+  'calc(100% - 120px - 60px)',
+  'calc(100% - 180px)'
+)
+
+test(
+  'should reduce consecutive substractions (#24) (2)',
+  testFixture,
+  'calc(100% - 10px - 20px)',
+  'calc(100% - 30px)'
+)
 
 test(
   'should produce simpler result (postcss-calc#25) (1)',

src/lib/reducer.js

@@ -115,12 +115,12 @@ function reduceAddSubExpression(node, precision) {
     // (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)
     else if (right.type === left.right.type) {
       node = Object.assign({ }, left)
       node.right = reduce({
         type: 'MathExpression',
-        operator: op,
+        operator: op === left.operator && op === '-' ? '+' : op,
         left: left.right,
         right: right
       }, precision)