import java.io.IOException;
import java.io.StringWriter;
import java.io.Writer;

public class TestCDATAScanner {

    public static boolean isLegalCharacter(char c) {
        return (c != '#');
    }

    public static void encodedata(Writer out, String value) throws IOException {
        final int len = value.length();
        int prevEnd = 0, cdataEndPos = value.indexOf("]]>");
        while (prevEnd < len) {
            final int end = (cdataEndPos < 0 ? len : cdataEndPos);
            // Write out stretches of legal characters in the range [prevEnd, end).
            for (int prevLegalCharPos = prevEnd; prevLegalCharPos < end; /*empty*/) {
                int illegalCharPos;
                for (illegalCharPos = prevLegalCharPos; true; ++illegalCharPos) {
                    if (illegalCharPos >= end || !isLegalCharacter(value.charAt(illegalCharPos))) {
                        break;
                    }
                }
                out.write(value, prevLegalCharPos, illegalCharPos - prevLegalCharPos);
                prevLegalCharPos = illegalCharPos + 1;
            }

            if (cdataEndPos >= 0) {
                out.write("]]]]><![CDATA[>");
                prevEnd = cdataEndPos + 3;
                cdataEndPos = value.indexOf("]]>", prevEnd);
            } else {
                prevEnd = end;
            }
        }
    }

    private static void writeEncodedData(Writer out, String value) throws IOException
    {
        final int len = value.length();
        char lastCopied = '\0';
        boolean encode = false;

        for (int i = 0; i < len; ++i) {
           final char c = value.charAt(i);
           if (lastCopied == ']' && c == ']')
           {
              encode = true;
           }

           if (isLegalCharacter(c)) {
                out.write(c);

                if (encode)
                {
                   out.write("]]><![CDATA["); // Fixed as per comment https://issues.apache.org/bugzilla/show_bug.cgi?id=54147#c1
                   encode = false;
                }
                else
                {
                   lastCopied = c;
                }
           }
        }
    }

    public static void main(String[] args) throws Throwable {
        final StringWriter out = new StringWriter();
        final String value = "#T#####his is a test ]]> test #]####### ]]## an##other tes######t #]]>##";
        writeEncodedData(out, value);
        out.write('\n');
        encodedata(out, value);
        System.out.println(out.toString());
    }
}