[YouTube] Add parenthesis matching as way to parse decrypt function

From @Stypox

Author: XiangRongLin

extractor/src/main/java/org/schabi/newpipe/extractor/services/youtube/YoutubeThrottlingDecrypter.java

@@ -3,6 +3,7 @@
 import org.schabi.newpipe.extractor.exceptions.ParsingException;
 import org.schabi.newpipe.extractor.utils.JavaScript;
 import org.schabi.newpipe.extractor.utils.Parser;
+import org.schabi.newpipe.extractor.utils.StringUtil;
 
 import javax.annotation.Nonnull;
 import java.util.HashMap;
@@ -71,7 +72,20 @@ private String parseDecodeFunctionName(final String playerJsCode)
     @Nonnull
     private String parseDecodeFunction(final String playerJsCode, final String functionName)
             throws Parser.RegexException {
-        Pattern functionPattern = Pattern.compile(functionName + "=function(.*?};)\n",
+        try {
+            return parseWithParenthesisMatching(playerJsCode, functionName);
+        } catch (Exception e) {
+            return parseWithRegex(playerJsCode, functionName);
+        }
+    }
+
+    private String parseWithParenthesisMatching(final String playerJsCode, final String functionName) {
+        final String functionBase = functionName + "=function";
+        return functionBase + StringUtil.matchToClosingParenthesis(playerJsCode, functionBase) + ";";
+    }
+
+    private String parseWithRegex(final String playerJsCode, final String functionName) throws Parser.RegexException {
+        Pattern functionPattern = Pattern.compile(functionName + "=function(.*?}};)\n",
                 Pattern.DOTALL);
         return "function " + functionName + Parser.matchGroup1(functionPattern, playerJsCode);
     }

extractor/src/main/java/org/schabi/newpipe/extractor/utils/StringUtil.java

@@ -0,0 +1,47 @@
+package org.schabi.newpipe.extractor.utils;
+
+import edu.umd.cs.findbugs.annotations.NonNull;
+
+public class StringUtil {
+
+    private StringUtil() {
+    }
+
+    /**
+     * @param string The string to search in
+     * @param start A string from which to start searching.
+     * @return A substring where each '{' matches a '}'
+     * @throws IndexOutOfBoundsException If {@ string} does not contain {@code start}
+     */
+    @NonNull
+    public static String matchToClosingParenthesis(@NonNull final String string, @NonNull final String start) {
+        int startIndex = string.indexOf(start);
+        if (startIndex < 0) {
+            throw new IndexOutOfBoundsException();
+        }
+
+        startIndex += start.length();
+        int endIndex = startIndex;
+        while (string.charAt(endIndex) != '{') {
+            ++endIndex;
+        }
+        ++endIndex;
+
+        int openParenthesis = 1;
+        while (openParenthesis > 0) {
+            switch (string.charAt(endIndex)) {
+                case '{':
+                    ++openParenthesis;
+                    break;
+                case '}':
+                    --openParenthesis;
+                    break;
+                default:
+                    break;
+            }
+            ++endIndex;
+        }
+
+        return string.substring(startIndex, endIndex);
+    }
+}