Merge pull request #39 from gyoshev/fix-subtraction-expressions

Fix subtraction expressions

src/__tests__/index.js

@@ -303,3 +303,24 @@ test(
  'calc(500px/2px)',
  'Cannot divide by "px", number expected'
 )
+
+test(
+ 'should reduce substraction from zero',
+ testFixture,
+ 'calc( 0 - 10px)',
+ '-10px'
+)
+
+test(
+ 'should reduce subtracted expression from zero',
+ testFixture,
+ 'calc( 0 - calc(1px + 1em) )',
+ 'calc(-1px + -1em)'
+)
+
+test(
+ 'should reduce nested expression',
+ testFixture,
+ 'calc( (1em - calc( 10px + 1em)) / 2)',
+ '-5px'
+)

src/lib/reducer.js

@@ -62,6 +62,20 @@ function convertMathExpression(node, precision) {
  return node
 }
 
+function flip(operator) {
+ return operator === '+' ? '-' : '+'
+}
+
+function flipValue(node) {
+ if (isValueType(node.type))
+ node.value = -node.value
+ else if (node.type == 'MathExpression') {
+ node.left = flipValue(node.left)
+ node.right = flipValue(node.right)
+ }
+ return node
+}
+
 function reduceAddSubExpression(node, precision) {
  const {left, right, operator: op} = node
 
@@ -77,6 +91,10 @@ function reduceAddSubExpression(node, precision) {
  if (left.value === 0 && op === "+")
  return right
 
+ // 0 - something => -something
+ if (left.value === 0 && op === "-")
+ return flipValue(right)
+
  // value + value
  // value - value
  if (left.type === right.type && isValueType(left.type)) {
@@ -115,13 +133,13 @@ function reduceAddSubExpression(node, precision) {
  }
  // value + (something + value) => (value + value) + something
  // value + (something - value) => (value - value) + something
- // value - (something + value) => (value + value) - something
- // value - (something - value) => (value - value) - something
+ // value - (something + value) => (value - value) - something
+ // value - (something - value) => (value + value) - something
  else if (left.type === right.right.type) {
  node = Object.assign({ }, node)
  node.left = reduce({
  type: 'MathExpression',
- operator: right.operator,
+ operator: op === '-' ? flip(right.operator) : right.operator,
  left: left,
  right: right.right
  }, precision)
@@ -183,7 +201,7 @@ function reduceAddSubExpression(node, precision) {
  return node
 }
 
-function reduceDivisionExpression(node) {
+function reduceDivisionExpression(node, precision) {
  if (!isValueType(node.right.type))
  return node
 
@@ -201,7 +219,7 @@ function reduceDivisionExpression(node) {
  ) {
  node.left.left.value /= node.right.value
  node.left.right.value /= node.right.value
- return node.left
+ return reduce(node.left, precision)
  }
  return node
  }
@@ -255,7 +273,7 @@ function reduceMathExpression(node, precision) {
  case "-":
  return reduceAddSubExpression(node, precision)
  case "/":
- return reduceDivisionExpression(node)
+ return reduceDivisionExpression(node, precision)
  case "*":
  return reduceMultiplicationExpression(node)
  }