Optimize regular expressions for identifying code types

By only matching one regex with a little bit more complexity and
differentiating the results by a capture group the performance of
checking for matches gets way better. Because this regex has to be
matched for each line it is compiled only once  to save this overhead
for most matches.

Author: ibbem

src/main/java/org/variantsync/diffdetective/diff/difftree/CodeType.java

@@ -1,5 +1,8 @@
 package org.variantsync.diffdetective.diff.difftree;
 
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+
 public enum CodeType {
     IF("if"),
     ENDIF("endif"),
@@ -20,23 +23,24 @@ public boolean isMacro() {
         return this != ROOT && this != CODE;
     }
 
-    final static String ifRegex = "^[+-]?\\s*#\\s*if.*$";
-    final static String endifRegex = "^[+-]?\\s*#\\s*endif.*$";
-    final static String elseRegex = "^[+-]?\\s*#\\s*else.*$";
-    final static String elifRegex = "^[+-]?\\s*#\\s*elif.*$";
+    final static Pattern regex = Pattern.compile("^[+-]?\\s*#\\s*(if|endif|else|elif)");
 
     public static CodeType ofDiffLine(String line) {
-        if (line.matches(ifRegex)) {
-            return IF;
-        } else if (line.matches(endifRegex)) {
-            return ENDIF;
-        } else if (line.matches(elseRegex)) {
-            return ELSE;
-        } else if (line.matches(elifRegex)) {
-            return ELIF;
-        } else {
-            return CODE;
+        Matcher matcher = regex.matcher(line);
+        if (matcher.find()) {
+            String id = matcher.group(1);
+            if (id.equals(IF.name)) {
+                return IF;
+            } else if (id.equals(ENDIF.name)) {
+                return ENDIF;
+            } else if (id.equals(ELSE.name)) {
+                return ELSE;
+            } else if (id.equals(ELIF.name)) {
+                return ELIF;
+            }
         }
+
+        return CODE;
     }
 
     public static CodeType fromName(final String name) {