fix 52: incorrect calculation when subtracting

Author: sylvainpolletvillard

src/__tests__/index.js

@@ -352,3 +352,10 @@ test(
   'calc(env(safe-area-inset-left))',
   'calc(env(safe-area-inset-left))'
 )
+
+test(
+  'should handle subtractions with different units',
+  testFixture,
+  'calc(100% - calc(666px + 1em + 2em + 100px))',
+  'calc(100% - 766px - 3em)'
+)

src/lib/reducer.js

@@ -62,7 +62,7 @@ function convertMathExpression(node, precision) {
   return node
 }
 
-function flip(operator) {
+export function flip(operator) {
   return operator === '+' ? '-' : '+'
 }
 

src/lib/stringifier.js

@@ -1,3 +1,5 @@
+import { flip } from "./reducer";
+
 const order = {
   "*": 0,
   "/": 0,
@@ -28,6 +30,11 @@ function stringify(node, prec) {
 
       if (right.type === 'MathExpression' && order[op] < order[right.operator])
         str += "(" + stringify(right, prec) + ")"
+      else if (right.type === 'MathExpression' && op === "-" && ["+", "-"].includes(right.operator)) {
+        // fix #52 : a-(b+c) = a-b-c
+        right.operator = flip(right.operator);
+        str += stringify(right, prec)
+      }
       else
         str += stringify(right, prec)