/*
    Licensed to the Apache Software Foundation (ASF) under one
    or more contributor license agreements.  See the NOTICE file
    distributed with this work for additional information
    regarding copyright ownership.  The ASF licenses this file
    to you under the Apache License, Version 2.0 (the
    "License"); you may not use this file except in compliance
    with the License.  You may obtain a copy of the License at

       http://www.apache.org/licenses/LICENSE-2.0

    Unless required by applicable law or agreed to in writing,
    software distributed under the License is distributed on an
    "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
    KIND, either express or implied.  See the License for the
    specific language governing permissions and limitations
    under the License.
 */
package org.apache.wiki.util;

import java.io.File;
import java.io.IOException;
import java.io.UnsupportedEncodingException;
import java.security.SecureRandom;
import java.util.Properties;
import java.util.Random;

import org.apache.commons.lang.StringUtils;
import org.apache.wiki.api.exceptions.NoRequiredPropertyException;


/**
 *  Contains a number of static utility methods.
 */
public final class TextUtil {

    static final String   HEX_DIGITS = "0123456789ABCDEF";

    /**
     *  Private constructor prevents instantiation.
     */
    private TextUtil() {}

    /**
     *  java.net.URLEncoder.encode() method in JDK < 1.4 is buggy.  This duplicates
     *  its functionality.
     *  @param rs the string to encode
     *  @return the URL-encoded string
     */
    protected static String urlEncode( byte[] rs ) {
        StringBuilder result = new StringBuilder(rs.length*2);

        // Does the URLEncoding.  We could use the java.net one, but
        // it does not eat byte[]s.

        for( int i = 0; i < rs.length; i++ ) {
            char c = ( char )rs[i];

            switch( c ) {
              case '_':
              case '.':
              case '*':
              case '-':
              case '/':
                result.append( c );
                break;

              case ' ':
                result.append( '+' );
                break;

              default:
                if( ( c >= 'a' && c <= 'z' ) ||
                    ( c >= 'A' && c <= 'Z' ) ||
                    ( c >= '0' && c <= '9' ) ) {
                    result.append( c );
                } else {
                    result.append( '%' );
                    result.append( HEX_DIGITS.charAt( ( c & 0xF0 ) >> 4 ) );
                    result.append( HEX_DIGITS.charAt( c & 0x0F ) );
                }
            }

        } // for

        return result.toString();
    }

    /**
     *  URL encoder does not handle all characters correctly.
     *  See <A HREF="http://developer.java.sun.com/developer/bugParade/bugs/4257115.html">
     *  Bug parade, bug #4257115</A> for more information.
     *  <P>
     *  Thanks to CJB for this fix.
     *
     *  @param bytes The byte array containing the bytes of the string
     *  @param encoding The encoding in which the string should be interpreted
     *  @return A decoded String
     *
     *  @throws UnsupportedEncodingException If the encoding is unknown.
     *  @throws IllegalArgumentException If the byte array is not a valid string.
     */
    protected static String urlDecode( byte[] bytes, String encoding )
              throws UnsupportedEncodingException, IllegalArgumentException {
        if( bytes == null ) {
            return null;
        }

        byte[] decodeBytes   = new byte[bytes.length];
        int decodedByteCount = 0;

        try {
            for( int count = 0; count < bytes.length; count++ ) {
                switch( bytes[count] ) {
                  case '+':
                    decodeBytes[decodedByteCount++] = ( byte ) ' ';
                    break ;

                  case '%':
                    decodeBytes[decodedByteCount++] = ( byte )( ( HEX_DIGITS.indexOf( bytes[++count] ) << 4 ) +
                                                                ( HEX_DIGITS.indexOf( bytes[++count] ) ) );
                    break ;

                  default:
                    decodeBytes[decodedByteCount++] = bytes[count] ;
                }
            }

        } catch( IndexOutOfBoundsException ae ) {
            throw new IllegalArgumentException( "Malformed UTF-8 string?" );
        }

        String processedPageName = null ;

        try {
            processedPageName = new String(decodeBytes, 0, decodedByteCount, encoding) ;
        } catch( UnsupportedEncodingException e ) {
            throw new UnsupportedEncodingException( "UTF-8 encoding not supported on this platform" );
        }

        return processedPageName;
    }

    /**
     *  As java.net.URLEncoder class, but this does it in UTF8 character set.
     *
     *  @param text The text to decode
     *  @return An URLEncoded string.
     */
    public static String urlEncodeUTF8( String text ) {
        // If text is null, just return an empty string
        if ( text == null ) {
            return "";
        }

        byte[] rs;

        try {
            rs = text.getBytes( "UTF-8" );
            return urlEncode( rs );
        } catch( UnsupportedEncodingException uee ) {
            throw new UnsupportedOperationException( "UTF-8 not supported!?!", uee );
        }
    }

    /**
     *  As java.net.URLDecoder class, but for UTF-8 strings.  null is a safe value and returns null.
     *
     *  @param utf8 The UTF-8 encoded string
     *  @return A plain, normal string.
     */
    public static String urlDecodeUTF8( String utf8 ) {
        String rs = null;

        if( utf8 == null ) return null;

        try {
            rs = urlDecode( utf8.getBytes( "ISO-8859-1" ), "UTF-8" );
        } catch( UnsupportedEncodingException uee ) {
            throw new UnsupportedOperationException( "UTF-8 or ISO-8859-1 not supported!?!", uee );
        }

        return rs;
    }

    /**
     * Provides encoded version of string depending on encoding. Encoding may be UTF-8 or ISO-8859-1 (default).
     *
     * <p>This implementation is the same as in FileSystemProvider.mangleName().
     *
     * @param data A string to encode
     * @param encoding The encoding in which to encode
     * @return An URL encoded string.
     */
    public static String urlEncode( String data, String encoding ) {
        // Presumably, the same caveats apply as in FileSystemProvider.
        // Don't see why it would be horribly kludgy, though.
        if( "UTF-8".equals( encoding ) ) {
            return TextUtil.urlEncodeUTF8( data );
        }

        try {
            return TextUtil.urlEncode( data.getBytes( encoding ) );
        } catch( UnsupportedEncodingException uee ) {
            throw new UnsupportedOperationException( "Could not encode String into" + encoding, uee );
        }
    }

    /**
     * Provides decoded version of string depending on encoding. Encoding may be UTF-8 or ISO-8859-1 (default).
     *
     * <p>This implementation is the same as in FileSystemProvider.unmangleName().
     *
     * @param data The URL-encoded string to decode
     * @param encoding The encoding to use
     * @return A decoded string.
     * @throws UnsupportedEncodingException If the encoding is unknown
     * @throws IllegalArgumentException If the data cannot be decoded.
     */
    public static String urlDecode( String data, String encoding )
        throws UnsupportedEncodingException, IllegalArgumentException {
        // Presumably, the same caveats apply as in FileSystemProvider.
        // Don't see why it would be horribly kludgy, though.
        if( "UTF-8".equals( encoding ) ) {
            return TextUtil.urlDecodeUTF8( data );
        }

        try {
            return TextUtil.urlDecode( data.getBytes(encoding), encoding );
        } catch( UnsupportedEncodingException uee ) {
            throw new UnsupportedOperationException("Could not decode String into" + encoding, uee );
        }

    }

    /**
     *  Replaces the relevant entities inside the String. All &amp; &gt;, &lt;, and &quot; are replaced by their
     *  respective names.
     *
     *  @since 1.6.1
     *  @param src The source string.
     *  @return The encoded string.
     */
    public static String replaceEntities( String src ) {
        src = replaceString( src, "&", "&amp;" );
        src = replaceString( src, "<", "&lt;" );
        src = replaceString( src, ">", "&gt;" );
        src = replaceString( src, "\"", "&quot;" );

        return src;
    }

    /**
     *  Replaces a string with an other string.
     *
     *  @param orig Original string.  Null is safe.
     *  @param src  The string to find.
     *  @param dest The string to replace <I>src</I> with.
     *  @return A string with the replacement done.
     */
    public static String replaceString( String orig, String src, String dest ) {
        if ( orig == null ) return null;
        if ( src == null || dest == null ) throw new NullPointerException();
        if ( src.length() == 0 ) return orig;

        StringBuilder res = new StringBuilder( orig.length() + 20 ); // Pure guesswork
        int start = 0;
        int end = 0;
        int last = 0;

        while ( ( start = orig.indexOf( src,end ) ) != -1 ) {
            res.append( orig.substring( last, start ) );
            res.append( dest );
            end  = start + src.length();
            last = start + src.length();
        }

        res.append( orig.substring( end ) );

        return res.toString();
    }

    /**
     *  Replaces a part of a string with a new String.
     *
     *  @param start Where in the original string the replacing should start.
     *  @param end Where the replacing should end.
     *  @param orig Original string.  Null is safe.
     *  @param text The new text to insert into the string.
     *  @return The string with the orig replaced with text.
     */
    public static String replaceString( String orig, int start, int end, String text ) {
        if( orig == null ) return null;

        StringBuilder buf = new StringBuilder(orig);
        buf.replace( start, end, text );
        return buf.toString();
    }

    /**
     *  Replaces a string with an other string. Case insensitive matching is used
     *
     *  @param orig Original string.  Null is safe.
     *  @param src  The string to find.
     *  @param dest The string to replace <I>src</I> with.
     *  @return A string with all instances of src replaced with dest.
     */
    public static String replaceStringCaseUnsensitive( String orig, String src, String dest ) {
        if( orig == null ) return null;

        StringBuilder res = new StringBuilder();
        int start        = 0;
        int end          = 0;
        int last         = 0;

        String origCaseUnsn = orig.toLowerCase();
        String srcCaseUnsn = src.toLowerCase();

        while( ( start = origCaseUnsn.indexOf( srcCaseUnsn, end ) ) != -1 ) {
            res.append( orig.substring( last, start ) );
            res.append( dest );
            end  = start + src.length();
            last = start + src.length();
        }

        res.append( orig.substring( end ) );

        return res.toString();
    }

    /**
     *  Parses an integer parameter, returning a default value if the value is null or a non-number.
     *
     *  @param value The value to parse
     *  @param defvalue A default value in case the value is not a number
     *  @return The parsed value (or defvalue).
     */
    public static int parseIntParameter( String value, int defvalue ) {
        int val = defvalue;

        try {
            val = Integer.parseInt( value.trim() );
        } catch( Exception e ) {}

        return val;
    }

    /**
     *  Gets an integer-valued property from a standard Properties list.
     *
     *  Before inspecting the props, we first check if there is a Java System Property with the same name, if it exists
     *  we use that value, if not we check an environment variable with that (almost) same name, almost meaning we replace
     *  dots with underscores.
     *
     *  If the value does not exist, or is a
     *  non-integer, returns defVal.
     *
     *  @since 2.1.48.
     *  @param props The property set to look through
     *  @param key   The key to look for
     *  @param defVal If the property is not found or is a non-integer, returns this value.
     *  @return The property value as an integer (or defVal).
     */
    public static int getIntegerProperty( Properties props,  String key, int defVal ) {
        String val = System.getProperties().getProperty(key, System.getenv(StringUtils.replace(key,".","_")));
        if (val == null) {
            val = props.getProperty(key);
        }
        return parseIntParameter( val, defVal );
    }

    /**
     *  Gets a boolean property from a standard Properties list. Returns the default value, in case the key has not
     *  been set.
     *  Before inspecting the props, we first check if there is a Java System Property with the same name, if it exists
     *  we use that value, if not we check an environment variable with that (almost) same name, almost meaning we replace
     *  dots with underscores.
     *  <P>
     *  The possible values for the property are "true"/"false", "yes"/"no", or "on"/"off".  Any value not
     *  recognized is always defined as "false".
     *
     *  @param props   A list of properties to search.
     *  @param key     The property key.
     *  @param defval  The default value to return.
     *
     *  @return True, if the property "key" was set to "true", "on", or "yes".
     *
     *  @since 2.0.11
     */
    public static boolean getBooleanProperty( Properties props, String key, boolean defval ) {
        String val = System.getProperties().getProperty(key, System.getenv(StringUtils.replace(key,".","_")));
        if (val == null) {
            val = props.getProperty(key);
        }
        if( val == null ) {
            return defval;
        }

        return isPositive( val );
    }

    /**
     *  Fetches a String property from the set of Properties.  This differs from Properties.getProperty() in a
     *  couple of key respects: First, property value is trim()med (so no extra whitespace back and front).
     *
     *  Before inspecting the props, we first check if there is a Java System Property with the same name, if it exists
     *  we use that value, if not we check an environment variable with that (almost) same name, almost meaning we replace
     *  dots with underscores.
     *
     *  @param props The Properties to search through
     *  @param key   The property key
     *  @param defval A default value to return, if the property does not exist.
     *  @return The property value.
     *  @since 2.1.151
     */
    public static String getStringProperty(Properties props, String key, String defval) {
        String val = System.getProperties().getProperty(key, System.getenv(StringUtils.replace(key,".","_")));
        if (val == null) {
            val = props.getProperty(key);
        }
        if (val == null) {
            return defval;
        }
        return val.trim();
    }

    /**
     *  Fetches a file path property from the set of Properties.
     *
     *  Before inspecting the props, we first check if there is a Java System Property with the same name, if it exists
     *  we use that value, if not we check an environment variable with that (almost) same name, almost meaning we replace
     *  dots with underscores.
     *
     *  If the implementation fails to create the canonical path it just returns
     *  the original value of the property which is a bit doggy.
     *
     *  @param props The Properties to search through
     *  @param key   The property key
     *  @param defval A default value to return, if the property does not exist.
     *  @return the canonical path of the file or directory being referenced
     *  @since 2.10.1
     */
    public static String getCanonicalFilePathProperty(Properties props, String key, String defval) {

        String result;
        String val = System.getProperties().getProperty(key, System.getenv(StringUtils.replace(key,".","_")));
        if (val == null) {
            val = props.getProperty(key);
        }

        if( val == null ) {
            val = defval;
        }

        try {
            result = new File(new File(val.trim()).getCanonicalPath()).getAbsolutePath();
        }
        catch(IOException e) {
            result = val.trim();
        }
        return result;
    }

    /**
     *  Throws an exception if a property is not found.
     *
     *  @param props A set of properties to search the key in.
     *  @param key   The key to look for.
     *  @return The required property
     *
     *  @throws NoRequiredPropertyException If the search key is not in the property set.
     */
    public static String getRequiredProperty( Properties props, String key ) throws NoRequiredPropertyException {
        String value = getStringProperty( props, key, null );
        if( value == null ) {
            throw new NoRequiredPropertyException( "Required property not found", key );
        }
        return value;
    }

    /**
     *  Returns true, if the string "val" denotes a positive string.  Allowed values are "yes", "on", and "true".
     *  Comparison is case-insignificant. Null values are safe.
     *
     *  @param val Value to check.
     *  @return True, if val is "true", "on", or "yes"; otherwise false.
     *
     *  @since 2.0.26
     */
    public static boolean isPositive( String val ) {
        if( val == null ) {
            return false;
        }
        val = val.trim();
        return val.equalsIgnoreCase( "true" ) || val.equalsIgnoreCase( "on" ) || val.equalsIgnoreCase( "yes" );
    }

    /**
     *  Makes sure that the POSTed data is conforms to certain rules.  These rules are:
     *  <UL>
     *  <LI>The data always ends with a newline (some browsers, such as NS4.x series, does not send a newline at
     *      the end, which makes the diffs a bit strange sometimes.
     *  <LI>The CR/LF/CRLF mess is normalized to plain CRLF.
     *  </UL>
     *
     *  The reason why we're using CRLF is that most browser already return CRLF since that is the closest thing to
     *  a HTTP standard.
     *
     *  @param postData The data to normalize
     *  @return Normalized data
     */
    public static String normalizePostData( String postData ) {
        StringBuilder sb = new StringBuilder();

        for( int i = 0; i < postData.length(); i++ ) {
            switch( postData.charAt(i) ) {
              case 0x0a: // LF, UNIX
                sb.append( "\r\n" );
                break;

              case 0x0d: // CR, either Mac or MSDOS
                sb.append( "\r\n" );
                // If it's MSDOS, skip the LF so that we don't add it again.
                if( i < postData.length() - 1 && postData.charAt( i + 1 ) == 0x0a ) {
                    i++;
                }
                break;

              default:
                sb.append( postData.charAt(i) );
                break;
            }
        }

        if( sb.length() < 2 || !sb.substring( sb.length()-2 ).equals( "\r\n" ) ) {
            sb.append( "\r\n" );
        }

        return sb.toString();
    }

    private static final int EOI   = 0;
    private static final int LOWER = 1;
    private static final int UPPER = 2;
    private static final int DIGIT = 3;
    private static final int OTHER = 4;
    private static final Random RANDOM = new SecureRandom();

    private static int getCharKind( int c ) {
        if( c == -1 ) {
            return EOI;
        }

        char ch = ( char )c;

        if( Character.isLowerCase( ch ) ) {
            return LOWER;
        } else if( Character.isUpperCase( ch ) ) {
            return UPPER;
        } else if( Character.isDigit( ch ) ) {
            return DIGIT;
        } else {
            return OTHER;
        }
    }

    /**
     *  Adds spaces in suitable locations of the input string.  This is used to transform a WikiName into a more
     *  readable format.
     *
     *  @param s String to be beautified.
     *  @return A beautified string.
     */
    public static String beautifyString( String s ) {
        return beautifyString( s, " " );
    }

    /**
     *  Adds spaces in suitable locations of the input string.  This is used to transform a WikiName into a more
     *  readable format.
     *
     *  @param s String to be beautified.
     *  @param space Use this string for the space character.
     *  @return A beautified string.
     *  @since 2.1.127
     */
    public static String beautifyString( String s, String space ) {
        if( s == null || s.length() == 0 ) {
            return "";
        }

        StringBuilder result = new StringBuilder();

        int cur     = s.charAt( 0 );
        int curKind = getCharKind( cur );

        int prevKind = LOWER;
        int nextKind = -1;

        int next = -1;
        int nextPos = 1;

        while( curKind != EOI ) {
            next = ( nextPos < s.length() ) ? s.charAt( nextPos++ ) : -1;
            nextKind = getCharKind( next );

            if( ( prevKind == UPPER ) && ( curKind == UPPER ) && ( nextKind == LOWER ) ) {
                result.append( space );
                result.append( ( char ) cur );
            } else {
                result.append((char) cur );
                if( ( ( curKind == UPPER ) && (nextKind == DIGIT) )
                    || ( ( curKind == LOWER ) && ( ( nextKind == DIGIT ) || ( nextKind == UPPER ) ) )
                    || ( ( curKind == DIGIT ) && ( ( nextKind == UPPER ) || ( nextKind == LOWER ) ) ) ) {
                    result.append( space );
                }
            }
            prevKind = curKind;
            cur      = next;
            curKind  = nextKind;
        }

        return result.toString();
    }

    /**
     *  Creates a Properties object based on an array which contains alternatively a key and a value.  It is useful
     *  for generating default mappings. For example:
     *  <pre>
     *     String[] properties = { "jspwiki.property1", "value1",
     *                             "jspwiki.property2", "value2 };
     *
     *     Properties props = TextUtil.createPropertes( values );
     *
     *     System.out.println( props.getProperty("jspwiki.property1") );
     *  </pre>
     *  would output "value1".
     *
     *  @param values Alternating key and value pairs.
     *  @return Property object
     *  @see java.util.Properties
     *  @throws IllegalArgumentException if the property array is missing a value for a key.
     *  @since 2.2.
     */
    public static Properties createProperties( String[] values ) throws IllegalArgumentException {
        if( values.length % 2 != 0 ) {
            throw new IllegalArgumentException( "One value is missing.");
        }

        Properties props = new Properties();
        for( int i = 0; i < values.length; i += 2 ) {
            props.setProperty( values[i], values[i + 1] );
        }

        return props;
    }

    /**
     *  Counts the number of sections (separated with "----") from the page.
     *
     *  @param pagedata The WikiText to parse.
     *  @return int Number of counted sections.
     *  @since 2.1.86.
     */
    public static int countSections( String pagedata ) {
        int tags  = 0;
        int start = 0;

        while( ( start = pagedata.indexOf( "----", start ) ) != -1 ) {
            tags++;
            start += 4; // Skip this "----"
        }

        //
        // The first section does not get the "----"
        //
        return pagedata.length() > 0 ? tags + 1 : 0;
    }

    /**
     *  Gets the given section (separated with "----") from the page text.
     *  Note that the first section is always #1.  If a page has no section markers,
     *  then there is only a single section, #1.
     *
     *  @param pagedata WikiText to parse.
     *  @param section  Which section to get.
     *  @return String  The section.
     *  @throws IllegalArgumentException If the page does not contain this many sections.
     *  @since 2.1.86.
     */
    public static String getSection( String pagedata, int section ) throws IllegalArgumentException {
        int tags  = 0;
        int start = 0;
        int previous = 0;

        while( ( start = pagedata.indexOf( "----", start ) ) != -1 ) {
            if( ++tags == section ) {
                return pagedata.substring( previous, start );
            }

            start += 4; // Skip this "----"
            // allow additional dashes, treat it as if it was a correct 4-dash
            while (start < pagedata.length() && pagedata.charAt( start ) == '-') {
                start++;
            }

            previous = start;
        }

        if( ++tags == section ) {
            return pagedata.substring( previous );
        }

        throw new IllegalArgumentException( "There is no section no. " + section + " on the page." );
    }

    /**
     *  A simple routine which just repeates the arguments.  This is useful for creating something like a line or
     *  something.
     *
     *  @param what String to repeat
     *  @param times How many times to repeat the string.
     *  @return Guess what?
     *  @since 2.1.98.
     */
    public static String repeatString( String what, int times ) {
        StringBuilder sb = new StringBuilder();
        for( int i = 0; i < times; i++ ) {
            sb.append( what );
        }

        return sb.toString();
    }

    /**
     *  Converts a string from the Unicode representation into something that can be embedded in a java
     *  properties file.  All references outside the ASCII range are replaced with \\uXXXX.
     *
     *  @param s The string to convert
     *  @return the ASCII string
     */
    public static String native2Ascii( String s ) {
        StringBuilder sb = new StringBuilder();
        for( int i = 0; i < s.length(); i++ ) {
            char aChar = s.charAt(i);
            if( ( aChar < 0x0020 ) || ( aChar > 0x007e ) ) {
                sb.append( '\\');
                sb.append( 'u');
                sb.append( toHex( ( aChar >> 12 ) & 0xF ) );
                sb.append( toHex( ( aChar >>  8 ) & 0xF ) );
                sb.append( toHex( ( aChar >>  4 ) & 0xF ) );
                sb.append( toHex( aChar        & 0xF ) );
            } else {
                sb.append( aChar );
            }
        }
        return sb.toString();
    }

    private static char toHex( int nibble ) {
        final char[] hexDigit = {
            '0','1','2','3','4','5','6','7','8','9','A','B','C','D','E','F'
        };
        return hexDigit[nibble & 0xF];
    }

    /**
     *  Generates a hexadecimal string from an array of bytes.  For example, if the array contains
     *  { 0x01, 0x02, 0x3E }, the resulting string will be "01023E".
     *
     * @param bytes A Byte array
     * @return A String representation
     * @since 2.3.87
     */
    public static String toHexString( byte[] bytes ) {
        StringBuilder sb = new StringBuilder( bytes.length * 2 );
        for( int i = 0; i < bytes.length; i++ ) {
            sb.append( toHex( bytes[i] >> 4 ) );
            sb.append( toHex( bytes[i] ) );
        }

        return sb.toString();
    }

    /**
     *  Returns true, if the argument contains a number, otherwise false. In a quick test this is roughly the same
     *  speed as Integer.parseInt() if the argument is a number, and roughly ten times the speed, if the argument
     *  is NOT a number.
     *
     *  @since 2.4
     *  @param s String to check
     *  @return True, if s represents a number.  False otherwise.
     */
    public static boolean isNumber( String s ) {
        if( s == null ) {
            return false;
        }

        if( s.length() > 1 && s.charAt(0) == '-' ) {
            s = s.substring(1);
        }

        for( int i = 0; i < s.length(); i++ ) {
            if( !Character.isDigit( s.charAt( i ) ) ) {
                return false;
            }
        }

        return true;
    }

    /** Length of password. @see #generateRandomPassword() */
    public static final int PASSWORD_LENGTH = 8;

    /**
     * Generate a random String suitable for use as a temporary password.
     *
     * @return String suitable for use as a temporary password
     * @since 2.4
     */
    public static String generateRandomPassword() {
        // Pick from some letters that won't be easily mistaken for each
        // other. So, for example, omit o O and 0, 1 l and L.
        String letters = "abcdefghjkmnpqrstuvwxyzABCDEFGHJKMNPQRSTUVWXYZ23456789+@";

        String pw = "";
        for( int i = 0; i < PASSWORD_LENGTH; i++ ) {
            int index = ( int )( RANDOM.nextDouble() * letters.length() );
            pw += letters.substring( index, index + 1 );
        }
        return pw;
    }

}