Added spaces to the operators for CSS calc functions after CSS compression

src/main/groovy/com/eriwen/gradle/css/CssMinifier.groovy

@@ -2,6 +2,8 @@ package com.eriwen.gradle.css
 
 import com.yahoo.platform.yui.compressor.CssCompressor
 
+import java.util.regex.Matcher
+import java.util.regex.Pattern
 /**
  * Utility class that houses minification logic.
  *
@@ -38,5 +40,41 @@ class CssMinifier {
                 writer.close()
             }
         }
+
+        fixCalcFunc(outputFile)
+    }
+
+    /**
+     * Fix issues related to calc function that came after CSS compression
+     * @param file File where function calc shall be fixed
+     */
+    private void fixCalcFunc(File file) {
+        String text = file.text
+        file.withWriter(CHARSET) { writer ->
+            writer << addSpacesToOperatorsInCalcFunc(text)
+        }
+    }
+
+    /**
+     * Adds spaces to the operators for CSS calc functions
+     * @param string Input string
+     * @return Result
+     */
+    private String addSpacesToOperatorsInCalcFunc(String string) {
+        StringBuffer stringBuffer = new StringBuffer()
+        Pattern pattern = ~/calc\([^\)]*\)/
+        Matcher matcher = pattern.matcher(string)
+        while (matcher.find()) {
+            String calcStr = matcher.group()
+
+            calcStr = calcStr.replaceAll(~/(?<=[%|px|em|rem|vw|\d]+)\+/, " + ")
+            calcStr = calcStr.replaceAll(~/(?<=[%|px|em|rem|vw|\d]+)-/ , " - ")
+            calcStr = calcStr.replaceAll(~/(?<=[%|px|em|rem|vw|\d]+)\*/, " * ")
+            calcStr = calcStr.replaceAll(~/(?<=[%|px|em|rem|vw|\d]+)\//, " / ")
+
+            matcher.appendReplacement(stringBuffer, calcStr)
+        }
+        matcher.appendTail(stringBuffer)
+        stringBuffer.toString()
     }
 }

src/test/groovy/com/eriwen/gradle/css/CssPluginFunctionalTest.groovy

@@ -29,7 +29,7 @@ class CssPluginFunctionalTest extends FunctionalSpec {
         and:
         tempProjectDir.newFolder('src', 'custom', 'css')
         tempProjectDir.newFile("src/custom/css/file1.css") << "#id1 { color: green; }"
-        tempProjectDir.newFile("src/custom/css/file2.css") << ".class1 { color: red; }"
+        tempProjectDir.newFile("src/custom/css/file2.css") << ".class1 { color: red; width: calc(90% + 50px); }"
 
         when:
         BuildResult result = build('minifyCss')
@@ -38,7 +38,7 @@ class CssPluginFunctionalTest extends FunctionalSpec {
         File minifiedCss = new File(projectDir, 'build/all-min.css')
         minifiedCss.exists()
         minifiedCss.text.indexOf('#id1{color:green}') > -1
-        minifiedCss.text.indexOf('.class1{color:red}') > -1
+        minifiedCss.text.indexOf('.class1{color:red;width:calc(90% + 50px)}') > -1
 
         and:
         result.task(':combineCss').outcome == TaskOutcome.SUCCESS