/*
 * Copyright (c) 2007, 2020 Oracle and/or its affiliates. All rights reserved.
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Distribution License v. 1.0, which is available at
 * http://www.eclipse.org/org/documents/edl-v10.php.
 *
 * SPDX-License-Identifier: BSD-3-Clause
 */

package jakarta.xml.bind;

import java.math.BigDecimal;
import java.math.BigInteger;
import java.util.Calendar;
import java.util.GregorianCalendar;
import java.util.TimeZone;

import javax.xml.namespace.QName;
import javax.xml.namespace.NamespaceContext;
import javax.xml.datatype.DatatypeFactory;
import javax.xml.datatype.DatatypeConfigurationException;

This class is the Jakarta XML Binding CI's default implementation of the DatatypeConverterInterface. 
 When client applications specify the use of the static print/parse methods in DatatypeConverter, it will delegate to this class. 

This class is responsible for whitespace normalization.
Author:
Ryan Shoemaker, Sun Microsystems, Inc.
Since:
JAXB 2.1/**
 * This class is the Jakarta XML Binding CI's default implementation of the
 * {@link DatatypeConverterInterface}.
 *
 * <p>
 * When client applications specify the use of the static print/parse
 * methods in {@link DatatypeConverter}, it will delegate
 * to this class.
 *
 * <p>
 * This class is responsible for whitespace normalization.
 *
 * @author <ul><li>Ryan Shoemaker, Sun Microsystems, Inc.</li></ul>
 * @since JAXB 2.1
 */
final class DatatypeConverterImpl implements DatatypeConverterInterface {

    
To avoid re-creating instances, we cache one instance.
/**
     * To avoid re-creating instances, we cache one instance.
     */
    public static final DatatypeConverterInterface theInstance = new DatatypeConverterImpl();

    protected DatatypeConverterImpl() {
    }

    public String parseString(String lexicalXSDString) {
        return lexicalXSDString;
    }

    public BigInteger parseInteger(String lexicalXSDInteger) {
        return _parseInteger(lexicalXSDInteger);
    }

    public static BigInteger _parseInteger(CharSequence s) {
        return new BigInteger(removeOptionalPlus(WhiteSpaceProcessor.trim(s)).toString());
    }

    public String printInteger(BigInteger val) {
        return _printInteger(val);
    }

    public static String _printInteger(BigInteger val) {
        return val.toString();
    }

    public int parseInt(String s) {
        return _parseInt(s);
    }

    
Faster but less robust String->int conversion.
Note that:

 
XML Schema allows '+', but Integer.valueOf(String) is not. 
XML Schema allows leading and trailing (but not in-between) whitespaces. Integer.valueOf(String) doesn't allow any. 
/**
     * Faster but less robust String->int conversion.
     *
     * Note that:
     * <ol>
     *  <li>XML Schema allows '+', but {@link Integer#valueOf(String)} is not.
     *  <li>XML Schema allows leading and trailing (but not in-between) whitespaces.
     *      {@link Integer#valueOf(String)} doesn't allow any.
     * </ol>
     */
    public static int _parseInt(CharSequence s) {
        int len = s.length();
        int sign = 1;

        int r = 0;

        for (int i = 0; i < len; i++) {
            char ch = s.charAt(i);
            if (WhiteSpaceProcessor.isWhiteSpace(ch)) {
                // skip whitespace
            } else if ('0' <= ch && ch <= '9') {
                r = r * 10 + (ch - '0');
            } else if (ch == '-') {
                sign = -1;
            } else if (ch == '+') {
                // noop
            } else {
                throw new NumberFormatException("Not a number: " + s);
            }
        }

        return r * sign;
    }

    public long parseLong(String lexicalXSLong) {
        return _parseLong(lexicalXSLong);
    }

    public static long _parseLong(CharSequence s) {
        return Long.parseLong(removeOptionalPlus(WhiteSpaceProcessor.trim(s)).toString());
    }

    public short parseShort(String lexicalXSDShort) {
        return _parseShort(lexicalXSDShort);
    }

    public static short _parseShort(CharSequence s) {
        return (short) _parseInt(s);
    }

    public String printShort(short val) {
        return _printShort(val);
    }

    public static String _printShort(short val) {
        return String.valueOf(val);
    }

    public BigDecimal parseDecimal(String content) {
        return _parseDecimal(content);
    }

    public static BigDecimal _parseDecimal(CharSequence content) {
        content = WhiteSpaceProcessor.trim(content);

        if (content.length() <= 0) {
            return null;
        }

        return new BigDecimal(content.toString());

        // from purely XML Schema perspective,
        // this implementation has a problem, since
        // in xs:decimal "1.0" and "1" is equal whereas the above
        // code will return different values for those two forms.
        //
        // the code was originally using com.sun.msv.datatype.xsd.NumberType.load,
        // but a profiling showed that the process of normalizing "1.0" into "1"
        // could take non-trivial time.
        //
        // also, from the user's point of view, one might be surprised if
        // 1 (not 1.0) is returned from "1.000"
    }

    public float parseFloat(String lexicalXSDFloat) {
        return _parseFloat(lexicalXSDFloat);
    }

    public static float _parseFloat(CharSequence _val) {
        String s = WhiteSpaceProcessor.trim(_val).toString();
        /* Incompatibilities of XML Schema's float "xfloat" and Java's float "jfloat"

         * jfloat.valueOf ignores leading and trailing whitespaces,
        whereas this is not allowed in xfloat.
         * jfloat.valueOf allows "float type suffix" (f, F) to be
        appended after float literal (e.g., 1.52e-2f), whereare
        this is not the case of xfloat.

        gray zone
        ---------
         * jfloat allows ".523". And there is no clear statement that mentions
        this case in xfloat. Although probably this is allowed.
         *
         */

        if (s.equals("NaN")) {
            return Float.NaN;
        }
        if (s.equals("INF")) {
            return Float.POSITIVE_INFINITY;
        }
        if (s.equals("-INF")) {
            return Float.NEGATIVE_INFINITY;
        }

        if (s.length() == 0
                || !isDigitOrPeriodOrSign(s.charAt(0))
                || !isDigitOrPeriodOrSign(s.charAt(s.length() - 1))) {
            throw new NumberFormatException();
        }

        // these screening process is necessary due to the wobble of Float.valueOf method
        return Float.parseFloat(s);
    }

    public String printFloat(float v) {
        return _printFloat(v);
    }

    public static String _printFloat(float v) {
        if (Float.isNaN(v)) {
            return "NaN";
        }
        if (v == Float.POSITIVE_INFINITY) {
            return "INF";
        }
        if (v == Float.NEGATIVE_INFINITY) {
            return "-INF";
        }
        return String.valueOf(v);
    }

    public double parseDouble(String lexicalXSDDouble) {
        return _parseDouble(lexicalXSDDouble);
    }

    public static double _parseDouble(CharSequence _val) {
        String val = WhiteSpaceProcessor.trim(_val).toString();

        if (val.equals("NaN")) {
            return Double.NaN;
        }
        if (val.equals("INF")) {
            return Double.POSITIVE_INFINITY;
        }
        if (val.equals("-INF")) {
            return Double.NEGATIVE_INFINITY;
        }

        if (val.length() == 0
                || !isDigitOrPeriodOrSign(val.charAt(0))
                || !isDigitOrPeriodOrSign(val.charAt(val.length() - 1))) {
            throw new NumberFormatException(val);
        }


        // these screening process is necessary due to the wobble of Float.valueOf method
        return Double.parseDouble(val);
    }

    public boolean parseBoolean(String lexicalXSDBoolean) {
        Boolean b = _parseBoolean(lexicalXSDBoolean);
        return (b == null) ? false : b.booleanValue();
    }

    public static Boolean _parseBoolean(CharSequence literal) {
        if (literal == null) {
            return null;
        }

        int i = 0;
        int len = literal.length();
        char ch;
        boolean value = false;

        if (literal.length() <= 0) {
            return null;
        }

        do {
            ch = literal.charAt(i++);
        } while (WhiteSpaceProcessor.isWhiteSpace(ch) && i < len);

        int strIndex = 0;

        switch (ch) {
            case '1':
                value = true;
                break;
            case '0':
                value = false;
                break;
            case 't':
                String strTrue = "rue";
                do {
                    ch = literal.charAt(i++);
                } while ((strTrue.charAt(strIndex++) == ch) && i < len && strIndex < 3);

                if (strIndex == 3) {
                    value = true;
                } else {
                    return false;
                }
//                    throw new IllegalArgumentException("String \"" + literal + "\" is not valid boolean value.");

                break;
            case 'f':
                String strFalse = "alse";
                do {
                    ch = literal.charAt(i++);
                } while ((strFalse.charAt(strIndex++) == ch) && i < len && strIndex < 4);


                if (strIndex == 4) {
                    value = false;
                } else {
                    return false;
                }
//                    throw new IllegalArgumentException("String \"" + literal + "\" is not valid boolean value.");

                break;
        }

        if (i < len) {
            do {
                ch = literal.charAt(i++);
            } while (WhiteSpaceProcessor.isWhiteSpace(ch) && i < len);
        }

        if (i == len) {
            return value;
        } else {
            return null;
        }
//            throw new IllegalArgumentException("String \"" + literal + "\" is not valid boolean value.");
    }

    public String printBoolean(boolean val) {
        return val ? "true" : "false";
    }

    public static String _printBoolean(boolean val) {
        return val ? "true" : "false";
    }

    public byte parseByte(String lexicalXSDByte) {
        return _parseByte(lexicalXSDByte);
    }

    public static byte _parseByte(CharSequence literal) {
        return (byte) _parseInt(literal);
    }

    public String printByte(byte val) {
        return _printByte(val);
    }

    public static String _printByte(byte val) {
        return String.valueOf(val);
    }

    public QName parseQName(String lexicalXSDQName, NamespaceContext nsc) {
        return _parseQName(lexicalXSDQName, nsc);
    }

    
Returns:
null if fails to convert./**
     * @return null if fails to convert.
     */
    public static QName _parseQName(CharSequence text, NamespaceContext nsc) {
        int length = text.length();

        // trim whitespace
        int start = 0;
        while (start < length && WhiteSpaceProcessor.isWhiteSpace(text.charAt(start))) {
            start++;
        }

        int end = length;
        while (end > start && WhiteSpaceProcessor.isWhiteSpace(text.charAt(end - 1))) {
            end--;
        }

        if (end == start) {
            throw new IllegalArgumentException("input is empty");
        }


        String uri;
        String localPart;
        String prefix;

        // search ':'
        int idx = start + 1;    // no point in searching the first char. that's not valid.
        while (idx < end && text.charAt(idx) != ':') {
            idx++;
        }

        if (idx == end) {
            uri = nsc.getNamespaceURI("");
            localPart = text.subSequence(start, end).toString();
            prefix = "";
        } else {
            // Prefix exists, check everything
            prefix = text.subSequence(start, idx).toString();
            localPart = text.subSequence(idx + 1, end).toString();
            uri = nsc.getNamespaceURI(prefix);
            // uri can never be null according to javadoc,
            // but some users reported that there are implementations that return null.
            if (uri == null || uri.length() == 0) // crap. the NamespaceContext interface is broken.
            // error: unbound prefix
            {
                throw new IllegalArgumentException("prefix " + prefix + " is not bound to a namespace");
            }
        }

        return new QName(uri, localPart, prefix);
    }

    public Calendar parseDateTime(String lexicalXSDDateTime) {
        return _parseDateTime(lexicalXSDDateTime);
    }

    public static GregorianCalendar _parseDateTime(CharSequence s) {
        String val = WhiteSpaceProcessor.trim(s).toString();
        return datatypeFactory.newXMLGregorianCalendar(val).toGregorianCalendar();
    }

    public String printDateTime(Calendar val) {
        return _printDateTime(val);
    }

    public static String _printDateTime(Calendar val) {
        return CalendarFormatter.doFormat("%Y-%M-%DT%h:%m:%s%z", val);
    }

    public byte[] parseBase64Binary(String lexicalXSDBase64Binary) {
        return _parseBase64Binary(lexicalXSDBase64Binary);
    }

    public byte[] parseHexBinary(String s) {
        final int len = s.length();

        // "111" is not a valid hex encoding.
        if (len % 2 != 0) {
            throw new IllegalArgumentException("hexBinary needs to be even-length: " + s);
        }

        byte[] out = new byte[len / 2];

        for (int i = 0; i < len; i += 2) {
            int h = hexToBin(s.charAt(i));
            int l = hexToBin(s.charAt(i + 1));
            if (h == -1 || l == -1) {
                throw new IllegalArgumentException("contains illegal character for hexBinary: " + s);
            }

            out[i / 2] = (byte) (h * 16 + l);
        }

        return out;
    }

    private static int hexToBin(char ch) {
        if ('0' <= ch && ch <= '9') {
            return ch - '0';
        }
        if ('A' <= ch && ch <= 'F') {
            return ch - 'A' + 10;
        }
        if ('a' <= ch && ch <= 'f') {
            return ch - 'a' + 10;
        }
        return -1;
    }
    private static final char[] hexCode = "0123456789ABCDEF".toCharArray();

    public String printHexBinary(byte[] data) {
        StringBuilder r = new StringBuilder(data.length * 2);
        for (byte b : data) {
            r.append(hexCode[(b >> 4) & 0xF]);
            r.append(hexCode[(b & 0xF)]);
        }
        return r.toString();
    }

    public long parseUnsignedInt(String lexicalXSDUnsignedInt) {
        return _parseLong(lexicalXSDUnsignedInt);
    }

    public String printUnsignedInt(long val) {
        return _printLong(val);
    }

    public int parseUnsignedShort(String lexicalXSDUnsignedShort) {
        return _parseInt(lexicalXSDUnsignedShort);
    }

    public Calendar parseTime(String lexicalXSDTime) {
        return datatypeFactory.newXMLGregorianCalendar(lexicalXSDTime).toGregorianCalendar();
    }

    public String printTime(Calendar val) {
        return CalendarFormatter.doFormat("%h:%m:%s%z", val);
    }

    public Calendar parseDate(String lexicalXSDDate) {
        return datatypeFactory.newXMLGregorianCalendar(lexicalXSDDate).toGregorianCalendar();
    }

    public String printDate(Calendar val) {
        return _printDate(val);
    }

    public static String _printDate(Calendar val) {
        return CalendarFormatter.doFormat((new StringBuilder("%Y-%M-%D").append("%z")).toString(),val);
    }

    public String parseAnySimpleType(String lexicalXSDAnySimpleType) {
        return lexicalXSDAnySimpleType;
//        return (String)SimpleURType.theInstance._createValue( lexicalXSDAnySimpleType, null );
    }

    public String printString(String val) {
//        return StringType.theInstance.convertToLexicalValue( val, null );
        return val;
    }

    public String printInt(int val) {
        return _printInt(val);
    }

    public static String _printInt(int val) {
        return String.valueOf(val);
    }

    public String printLong(long val) {
        return _printLong(val);
    }

    public static String _printLong(long val) {
        return String.valueOf(val);
    }

    public String printDecimal(BigDecimal val) {
        return _printDecimal(val);
    }

    public static String _printDecimal(BigDecimal val) {
        return val.toPlainString();
    }

    public String printDouble(double v) {
        return _printDouble(v);
    }

    public static String _printDouble(double v) {
        if (Double.isNaN(v)) {
            return "NaN";
        }
        if (v == Double.POSITIVE_INFINITY) {
            return "INF";
        }
        if (v == Double.NEGATIVE_INFINITY) {
            return "-INF";
        }
        return String.valueOf(v);
    }

    public String printQName(QName val, NamespaceContext nsc) {
        return _printQName(val, nsc);
    }

    public static String _printQName(QName val, NamespaceContext nsc) {
        // Double-check
        String qname;
        String prefix = nsc.getPrefix(val.getNamespaceURI());
        String localPart = val.getLocalPart();

        if (prefix == null || prefix.length() == 0) { // be defensive
            qname = localPart;
        } else {
            qname = prefix + ':' + localPart;
        }

        return qname;
    }

    public String printBase64Binary(byte[] val) {
        return _printBase64Binary(val);
    }

    public String printUnsignedShort(int val) {
        return String.valueOf(val);
    }

    public String printAnySimpleType(String val) {
        return val;
    }

    
Just return the string passed as a parameter but
installs an instance of this class as the DatatypeConverter
implementation. Used from static fixed value initializers.
/**
     * Just return the string passed as a parameter but
     * installs an instance of this class as the DatatypeConverter
     * implementation. Used from static fixed value initializers.
     */
    public static String installHook(String s) {
        DatatypeConverter.setDatatypeConverter(theInstance);
        return s;
    }
// base64 decoder
    private static final byte[] decodeMap = initDecodeMap();
    private static final byte PADDING = 127;

    private static byte[] initDecodeMap() {
        byte[] map = new byte[128];
        int i;
        for (i = 0; i < 128; i++) {
            map[i] = -1;
        }

        for (i = 'A'; i <= 'Z'; i++) {
            map[i] = (byte) (i - 'A');
        }
        for (i = 'a'; i <= 'z'; i++) {
            map[i] = (byte) (i - 'a' + 26);
        }
        for (i = '0'; i <= '9'; i++) {
            map[i] = (byte) (i - '0' + 52);
        }
        map['+'] = 62;
        map['/'] = 63;
        map['='] = PADDING;

        return map;
    }

    
computes the length of binary data speculatively.

Our requirement is to create byte[] of the exact length to store the binary data.
If we do this in a straight-forward way, it takes two passes over the data.
Experiments show that this is a non-trivial overhead (35% or so is spent on
the first pass in calculating the length.)

So the approach here is that we compute the length speculatively, without looking
at the whole contents. The obtained speculative value is never less than the
actual length of the binary data, but it may be bigger. So if the speculation
goes wrong, we'll pay the cost of reallocation and buffer copying.

If the base64 text is tightly packed with no indentation nor illegal char
(like what most web services produce), then the speculation of this method
will be correct, so we get the performance benefit.
/**
     * computes the length of binary data speculatively.
     *
     * <p>
     * Our requirement is to create byte[] of the exact length to store the binary data.
     * If we do this in a straight-forward way, it takes two passes over the data.
     * Experiments show that this is a non-trivial overhead (35% or so is spent on
     * the first pass in calculating the length.)
     *
     * <p>
     * So the approach here is that we compute the length speculatively, without looking
     * at the whole contents. The obtained speculative value is never less than the
     * actual length of the binary data, but it may be bigger. So if the speculation
     * goes wrong, we'll pay the cost of reallocation and buffer copying.
     *
     * <p>
     * If the base64 text is tightly packed with no indentation nor illegal char
     * (like what most web services produce), then the speculation of this method
     * will be correct, so we get the performance benefit.
     */
    private static int guessLength(String text) {
        final int len = text.length();

        // compute the tail '=' chars
        int j = len - 1;
        for (; j >= 0; j--) {
            byte code = decodeMap[text.charAt(j)];
            if (code == PADDING) {
                continue;
            }
            if (code == -1) // most likely this base64 text is indented. go with the upper bound
            {
                return text.length() / 4 * 3;
            }
            break;
        }

        j++;    // text.charAt(j) is now at some base64 char, so +1 to make it the size
        int padSize = len - j;
        if (padSize > 2) // something is wrong with base64. be safe and go with the upper bound
        {
            return text.length() / 4 * 3;
        }

        // so far this base64 looks like it's unindented tightly packed base64.
        // take a chance and create an array with the expected size
        return text.length() / 4 * 3 - padSize;
    }

    
Params:
text –  base64Binary data is likely to be long, and decoding requires each character to be accessed twice (once for counting length, another for decoding.) A benchmark showed that taking String is faster, presumably because JIT can inline a lot of string access (with data of 1K chars, it was twice as fast)/**
     * @param text
     *      base64Binary data is likely to be long, and decoding requires
     *      each character to be accessed twice (once for counting length, another
     *      for decoding.)
     *
     *      A benchmark showed that taking {@link String} is faster, presumably
     *      because JIT can inline a lot of string access (with data of 1K chars, it was twice as fast)
     */
    public static byte[] _parseBase64Binary(String text) {
        final int buflen = guessLength(text);
        final byte[] out = new byte[buflen];
        int o = 0;

        final int len = text.length();
        int i;

        final byte[] quadruplet = new byte[4];
        int q = 0;

        // convert each quadruplet to three bytes.
        for (i = 0; i < len; i++) {
            char ch = text.charAt(i);
            byte v = decodeMap[ch];

            if (v != -1) {
                quadruplet[q++] = v;
            }

            if (q == 4) {
                // quadruplet is now filled.
                out[o++] = (byte) ((quadruplet[0] << 2) | (quadruplet[1] >> 4));
                if (quadruplet[2] != PADDING) {
                    out[o++] = (byte) ((quadruplet[1] << 4) | (quadruplet[2] >> 2));
                }
                if (quadruplet[3] != PADDING) {
                    out[o++] = (byte) ((quadruplet[2] << 6) | (quadruplet[3]));
                }
                q = 0;
            }
        }

        if (buflen == o) // speculation worked out to be OK
        {
            return out;
        }

        // we overestimated, so need to create a new buffer
        byte[] nb = new byte[o];
        System.arraycopy(out, 0, nb, 0, o);
        return nb;
    }
    private static final char[] encodeMap = initEncodeMap();

    private static char[] initEncodeMap() {
        char[] map = new char[64];
        int i;
        for (i = 0; i < 26; i++) {
            map[i] = (char) ('A' + i);
        }
        for (i = 26; i < 52; i++) {
            map[i] = (char) ('a' + (i - 26));
        }
        for (i = 52; i < 62; i++) {
            map[i] = (char) ('0' + (i - 52));
        }
        map[62] = '+';
        map[63] = '/';

        return map;
    }

    public static char encode(int i) {
        return encodeMap[i & 0x3F];
    }

    public static byte encodeByte(int i) {
        return (byte) encodeMap[i & 0x3F];
    }

    public static String _printBase64Binary(byte[] input) {
        return _printBase64Binary(input, 0, input.length);
    }

    public static String _printBase64Binary(byte[] input, int offset, int len) {
        char[] buf = new char[((len + 2) / 3) * 4];
        int ptr = _printBase64Binary(input, offset, len, buf, 0);
        assert ptr == buf.length;
        return new String(buf);
    }

    
Encodes a byte array into a char array by doing base64 encoding.
The caller must supply a big enough buffer.
Returns:
 the value of ptr+((len+2)/3)*4, which is the new offset in the output buffer where the further bytes should be placed./**
     * Encodes a byte array into a char array by doing base64 encoding.
     *
     * The caller must supply a big enough buffer.
     *
     * @return
     *      the value of {@code ptr+((len+2)/3)*4}, which is the new offset
     *      in the output buffer where the further bytes should be placed.
     */
    public static int _printBase64Binary(byte[] input, int offset, int len, char[] buf, int ptr) {
        // encode elements until only 1 or 2 elements are left to encode
        int remaining = len;
        int i;
        for (i = offset;remaining >= 3; remaining -= 3, i += 3) {
            buf[ptr++] = encode(input[i] >> 2);
            buf[ptr++] = encode(
                    ((input[i] & 0x3) << 4)
                    | ((input[i + 1] >> 4) & 0xF));
            buf[ptr++] = encode(
                    ((input[i + 1] & 0xF) << 2)
                    | ((input[i + 2] >> 6) & 0x3));
            buf[ptr++] = encode(input[i + 2] & 0x3F);
        }
        // encode when exactly 1 element (left) to encode
        if (remaining == 1) {
            buf[ptr++] = encode(input[i] >> 2);
            buf[ptr++] = encode(((input[i]) & 0x3) << 4);
            buf[ptr++] = '=';
            buf[ptr++] = '=';
        }
        // encode when exactly 2 elements (left) to encode
        if (remaining == 2) {
            buf[ptr++] = encode(input[i] >> 2);
            buf[ptr++] = encode(((input[i] & 0x3) << 4)
                    | ((input[i + 1] >> 4) & 0xF));
            buf[ptr++] = encode((input[i + 1] & 0xF) << 2);
            buf[ptr++] = '=';
        }
        return ptr;
    }

    
Encodes a byte array into another byte array by first doing base64 encoding
then encoding the result in ASCII.
The caller must supply a big enough buffer.
Returns:
 the value of ptr+((len+2)/3)*4, which is the new offset in the output buffer where the further bytes should be placed./**
     * Encodes a byte array into another byte array by first doing base64 encoding
     * then encoding the result in ASCII.
     *
     * The caller must supply a big enough buffer.
     *
     * @return
     *      the value of {@code ptr+((len+2)/3)*4}, which is the new offset
     *      in the output buffer where the further bytes should be placed.
     */
    public static int _printBase64Binary(byte[] input, int offset, int len, byte[] out, int ptr) {
        byte[] buf = out;
        int remaining = len;
        int i;
        for (i=offset; remaining >= 3; remaining -= 3, i += 3 ) {
            buf[ptr++] = encodeByte(input[i]>>2);
            buf[ptr++] = encodeByte(
                        ((input[i]&0x3)<<4) |
                        ((input[i+1]>>4)&0xF));
            buf[ptr++] = encodeByte(
                        ((input[i+1]&0xF)<<2)|
                        ((input[i+2]>>6)&0x3));
            buf[ptr++] = encodeByte(input[i+2]&0x3F);
        }
        // encode when exactly 1 element (left) to encode
        if (remaining == 1) {
            buf[ptr++] = encodeByte(input[i]>>2);
            buf[ptr++] = encodeByte(((input[i])&0x3)<<4);
            buf[ptr++] = '=';
            buf[ptr++] = '=';
        }
        // encode when exactly 2 elements (left) to encode
        if (remaining == 2) {
            buf[ptr++] = encodeByte(input[i]>>2);
            buf[ptr++] = encodeByte(
                        ((input[i]&0x3)<<4) |
                        ((input[i+1]>>4)&0xF));
            buf[ptr++] = encodeByte((input[i+1]&0xF)<<2);
            buf[ptr++] = '=';
        }

        return ptr;
    }

    private static CharSequence removeOptionalPlus(CharSequence s) {
        int len = s.length();

        if (len <= 1 || s.charAt(0) != '+') {
            return s;
        }

        s = s.subSequence(1, len);
        char ch = s.charAt(0);
        if ('0' <= ch && ch <= '9') {
            return s;
        }
        if ('.' == ch) {
            return s;
        }

        throw new NumberFormatException();
    }

    private static boolean isDigitOrPeriodOrSign(char ch) {
        if ('0' <= ch && ch <= '9') {
            return true;
        }
        if (ch == '+' || ch == '-' || ch == '.') {
            return true;
        }
        return false;
    }
    private static final DatatypeFactory datatypeFactory;

    static {
        try {
            datatypeFactory = DatatypeFactory.newInstance();
        } catch (DatatypeConfigurationException e) {
            throw new Error(e);
        }
    }

    private static final class CalendarFormatter {

        public static String doFormat(String format, Calendar cal) throws IllegalArgumentException {
            int fidx = 0;
            int flen = format.length();
            StringBuilder buf = new StringBuilder();

            while (fidx < flen) {
                char fch = format.charAt(fidx++);

                if (fch != '%') {  // not a meta character
                    buf.append(fch);
                    continue;
                }

                // seen meta character. we don't do error check against the format
                switch (format.charAt(fidx++)) {
                    case 'Y': // year
                        formatYear(cal, buf);
                        break;

                    case 'M': // month
                        formatMonth(cal, buf);
                        break;

                    case 'D': // days
                        formatDays(cal, buf);
                        break;

                    case 'h': // hours
                        formatHours(cal, buf);
                        break;

                    case 'm': // minutes
                        formatMinutes(cal, buf);
                        break;

                    case 's': // parse seconds.
                        formatSeconds(cal, buf);
                        break;

                    case 'z': // time zone
                        formatTimeZone(cal, buf);
                        break;

                    default:
                        // illegal meta character. impossible.
                        throw new InternalError();
                }
            }

            return buf.toString();
        }

        private static void formatYear(Calendar cal, StringBuilder buf) {
            int year = cal.get(Calendar.YEAR);

            String s;
            if (year <= 0) // negative value
            {
                s = Integer.toString(1 - year);
            } else // positive value
            {
                s = Integer.toString(year);
            }

            while (s.length() < 4) {
                s = '0' + s;
            }
            if (year <= 0) {
                s = '-' + s;
            }

            buf.append(s);
        }

        private static void formatMonth(Calendar cal, StringBuilder buf) {
            formatTwoDigits(cal.get(Calendar.MONTH) + 1, buf);
        }

        private static void formatDays(Calendar cal, StringBuilder buf) {
            formatTwoDigits(cal.get(Calendar.DAY_OF_MONTH), buf);
        }

        private static void formatHours(Calendar cal, StringBuilder buf) {
            formatTwoDigits(cal.get(Calendar.HOUR_OF_DAY), buf);
        }

        private static void formatMinutes(Calendar cal, StringBuilder buf) {
            formatTwoDigits(cal.get(Calendar.MINUTE), buf);
        }

        private static void formatSeconds(Calendar cal, StringBuilder buf) {
            formatTwoDigits(cal.get(Calendar.SECOND), buf);
            if (cal.isSet(Calendar.MILLISECOND)) { // milliseconds
                int n = cal.get(Calendar.MILLISECOND);
                if (n != 0) {
                    String ms = Integer.toString(n);
                    while (ms.length() < 3) {
                        ms = '0' + ms; // left 0 paddings.
                    }
                    buf.append('.');
                    buf.append(ms);
                }
            }
        }

        
formats time zone specifier. /** formats time zone specifier. */
        private static void formatTimeZone(Calendar cal, StringBuilder buf) {
            TimeZone tz = cal.getTimeZone();

            if (tz == null) {
                return;
            }

            // otherwise print out normally.
            int offset = tz.getOffset(cal.getTime().getTime());

            if (offset == 0) {
                buf.append('Z');
                return;
            }

            if (offset >= 0) {
                buf.append('+');
            } else {
                buf.append('-');
                offset *= -1;
            }

            offset /= 60 * 1000; // offset is in milli-seconds

            formatTwoDigits(offset / 60, buf);
            buf.append(':');
            formatTwoDigits(offset % 60, buf);
        }

        
formats Integer into two-character-wide string. /** formats Integer into two-character-wide string. */
        private static void formatTwoDigits(int n, StringBuilder buf) {
            // n is always non-negative.
            if (n < 10) {
                buf.append('0');
            }
            buf.append(n);
        }
    }
}