/*

 * Copyright (c) 1995, 2013, Oracle and/or its affiliates. All rights reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

 * or visit www.oracle.com if you need additional information or have any

 * questions.

 */

package java.net;

import java.io.UnsupportedEncodingException;

import java.io.CharArrayWriter;

import java.nio.charset.Charset;

import java.nio.charset.IllegalCharsetNameException;

import java.nio.charset.UnsupportedCharsetException ;

import java.util.BitSet;

import sun.security.action.GetPropertyAction;

/**

 * Utility class for HTML form encoding. This class contains static methods

 * for converting a String to the <CODE>application/x-www-form-urlencoded</CODE> MIME

 * format. For more information about HTML form encoding, consult the HTML

 * <A HREF="http://www.w3.org/TR/html4/">specification</A>.

 *

 * <p>

 * When encoding a String, the following rules apply:

 *

 * <ul>

 * <li>The alphanumeric characters &quot;{@code a}&quot; through

 *     "{@code z}", "{@code A}" through

 *     "{@code Z}" and "{@code 0}"

 *     through "{@code 9}" remain the same.

 * <li>The special characters &quot;{@code .}&quot;,

 *     "{@code -}", "{@code *}", and

 *     "{@code _}" remain the same.

 * <li>The space character &quot; &nbsp; &quot; is

 *     converted into a plus sign "{@code +}".

 * <li>All other characters are unsafe and are first converted into

 *     one or more bytes using some encoding scheme. Then each byte is

 *     represented by the 3-character string

 *     &quot;<i>{@code %xy}</i>&quot;, where <i>xy</i> is the

 *     two-digit hexadecimal representation of the byte.

 *     The recommended encoding scheme to use is UTF-8. However,

 *     for compatibility reasons, if an encoding is not specified,

 *     then the default encoding of the platform is used.

 * </ul>

 *

 * <p>

 * For example using UTF-8 as the encoding scheme the string "The

 * string ü@foo-bar" would get converted to

 * "The+string+%C3%BC%40foo-bar" because in UTF-8 the character

 * ü is encoded as two bytes C3 (hex) and BC (hex), and the

 * character @ is encoded as one byte 40 (hex).

 *

 * @author  Herb Jellinek

 * @since   1.0

 */

public class URLEncoder {

    static BitSet dontNeedEncoding;

    static final int caseDiff = ('a' - 'A');

    static String dfltEncName = null;

    static {

        /* The list of characters that are not encoded has been

         * determined as follows:

         *

         * RFC 2396 states:

         * -----

         * Data characters that are allowed in a URI but do not have a

         * reserved purpose are called unreserved.  These include upper

         * and lower case letters, decimal digits, and a limited set of

         * punctuation marks and symbols.

         *

         * unreserved  = alphanum | mark

         *

         * mark        = "-" | "_" | "." | "!" | "~" | "*" | "'" | "(" | ")"

         *

         * Unreserved characters can be escaped without changing the

         * semantics of the URI, but this should not be done unless the

         * URI is being used in a context that does not allow the

         * unescaped character to appear.

         * -----

         *

         * It appears that both Netscape and Internet Explorer escape

         * all special characters from this list with the exception

         * of "-", "_", ".", "*". While it is not clear why they are

         * escaping the other characters, perhaps it is safest to

         * assume that there might be contexts in which the others

         * are unsafe if not escaped. Therefore, we will use the same

         * list. It is also noteworthy that this is consistent with

         * O'Reilly's "HTML: The Definitive Guide" (page 164).

         *

         * As a last note, Intenet Explorer does not encode the "@"

         * character which is clearly not unreserved according to the

         * RFC. We are being consistent with the RFC in this matter,

         * as is Netscape.

         *

         */

        dontNeedEncoding = new BitSet(256);

        int i;

        for (i = 'a'; i <= 'z'; i++) {

            dontNeedEncoding.set(i);

        }

        for (i = 'A'; i <= 'Z'; i++) {

            dontNeedEncoding.set(i);

        }

        for (i = '0'; i <= '9'; i++) {

            dontNeedEncoding.set(i);

        }

        dontNeedEncoding.set(' '); /* encoding a space to a + is done

                                    * in the encode() method */

        dontNeedEncoding.set('-');

        dontNeedEncoding.set('_');

        dontNeedEncoding.set('.');

        dontNeedEncoding.set('*');

    }

    /**

     * You can't call the constructor.

     */

    private URLEncoder() { }

    /**

     * Translates a string into {@code x-www-form-urlencoded}

     * format. This method uses the platform's default encoding

     * as the encoding scheme to obtain the bytes for unsafe characters.

     *

     * @param   s   {@code String} to be translated.

     * @deprecated The resulting string may vary depending on the platform's

     *             default encoding. Instead, use the encode(String,String)

     *             method to specify the encoding.

     * @return  the translated {@code String}.

     */

    @Deprecated

    public static String encode(String s) {

        String str = null;

        try {

            str = encode(s, dfltEncName);

        } catch (UnsupportedEncodingException e) {

            // The system should always have the platform default

        }

        return str;

    }

    /**

     * Translates a string into {@code application/x-www-form-urlencoded}

     * format using a specific encoding scheme. This method uses the

     * supplied encoding scheme to obtain the bytes for unsafe

     * characters.

     * <p>

     * <em><strong>Note:</strong> The <a href=

     * "http://www.w3.org/TR/html40/appendix/notes.html#non-ascii-chars">

     * World Wide Web Consortium Recommendation</a> states that

     * UTF-8 should be used. Not doing so may introduce

     * incompatibilities.</em>

     *

     * @param   s   {@code String} to be translated.

     * @param   enc   The name of a supported

     *    <a href="../lang/package-summary.html#charenc">character

     *    encoding</a>.

     * @return  the translated {@code String}.

     * @exception  UnsupportedEncodingException

     *             If the named encoding is not supported

     * @see URLDecoder#decode(java.lang.String, java.lang.String)

     * @since 1.4

     */

    public static String encode(String s, String enc)

        throws UnsupportedEncodingException {

        boolean needToChange = false;

        StringBuilder out = new StringBuilder(s.length());

        Charset charset;

        CharArrayWriter charArrayWriter = new CharArrayWriter();

        if (enc == null)

            throw new NullPointerException("charsetName");

        try {

            charset = Charset.forName(enc);

        } catch (IllegalCharsetNameException e) {

            throw new UnsupportedEncodingException(enc);

        } catch (UnsupportedCharsetException e) {

            throw new UnsupportedEncodingException(enc);

        }

        for (int i = 0; i < s.length();) {

            int c = (int) s.charAt(i);

            //System.out.println("Examining character: " + c);

            if (dontNeedEncoding.get(c)) {

                if (c == ' ') {

                    c = '+';

                    needToChange = true;

                }

                //System.out.println("Storing: " + c);

                out.append((char)c);

                i++;

            } else {

                // convert to external encoding before hex conversion

                do {

                    charArrayWriter.write(c);

                    /*

                     * If this character represents the start of a Unicode

                     * surrogate pair, then pass in two characters. It's not

                     * clear what should be done if a bytes reserved in the

                     * surrogate pairs range occurs outside of a legal

                     * surrogate pair. For now, just treat it as if it were

                     * any other character.

                     */

                    if (c >= 0xD800 && c <= 0xDBFF) {

                        /*

                          System.out.println(Integer.toHexString(c)

                          + " is high surrogate");

                        */

                        if ( (i+1) < s.length()) {

                            int d = (int) s.charAt(i+1);

                            /*

                              System.out.println("\tExamining "

                              + Integer.toHexString(d));

                            */

                            if (d >= 0xDC00 && d <= 0xDFFF) {

                                /*

                                  System.out.println("\t"

                                  + Integer.toHexString(d)

                                  + " is low surrogate");

                                */

                                charArrayWriter.write(d);

                                i++;

                            }

                        }

                    }

                    i++;

                } while (i < s.length() && !dontNeedEncoding.get((c = (int) s.charAt(i))));

                charArrayWriter.flush();

                String str = new String(charArrayWriter.toCharArray());

                byte[] ba = str.getBytes(charset);

                for (int j = 0; j < ba.length; j++) {

                    out.append('%');

                    char ch = Character.forDigit((ba[j] >> 4) & 0xF, 16);

                    // converting to use uppercase letter as part of

                    // the hex value if ch is a letter.

                    if (Character.isLetter(ch)) {

                        ch -= caseDiff;

                    }

                    out.append(ch);

                    ch = Character.forDigit(ba[j] & 0xF, 16);

                    if (Character.isLetter(ch)) {

                        ch -= caseDiff;

                    }

                    out.append(ch);

                }

                charArrayWriter.reset();

                needToChange = true;

            }

        }

        return (needToChange? out.toString() : s);

    }

}