/*
 *  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 java.net;

import java.io.UnsupportedEncodingException;

/**
 * This class is used to encode a string using the format required by
 * {@code application/x-www-form-urlencoded} MIME content type.
 */
public class URLEncoder {

    static final String digits = "0123456789ABCDEF";

    /**
     * Prevents this class from being instantiated.
     */
    private URLEncoder() {
    }

    /**
     * Encodes a given string {@code s} in a x-www-form-urlencoded string using
     * the specified encoding scheme {@code enc}.
     * <p>
     * All characters except letters ('a'..'z', 'A'..'Z') and numbers ('0'..'9')
     * and characters '.', '-', '*', '_' are converted into their hexadecimal
     * value prepended by '%'. For example: '#' -> %23. In addition, spaces are
     * substituted by '+'
     *
     * @param s
     *            the string to be encoded.
     * @return the encoded string.
     * @deprecated use {@link #encode(String, String)} instead.
     */
    @Deprecated
    public static String encode(String s) {
        // Guess a bit bigger for encoded form
        StringBuilder buf = new StringBuilder(s.length() + 16);
        for (int i = 0; i < s.length(); i++) {
            char ch = s.charAt(i);
            if ((ch >= 'a' && ch <= 'z') || (ch >= 'A' && ch <= 'Z')
                    || (ch >= '0' && ch <= '9') || ".-*_".indexOf(ch) > -1) {
                buf.append(ch);
            } else if (ch == ' ') {
                buf.append('+');
            } else {
                byte[] bytes = new String(new char[] { ch }).getBytes();
                for (int j = 0; j < bytes.length; j++) {
                    buf.append('%');
                    buf.append(digits.charAt((bytes[j] & 0xf0) >> 4));
                    buf.append(digits.charAt(bytes[j] & 0xf));
                }
            }
        }
        return buf.toString();
    }

    /**
     * Encodes the given string {@code s} in a x-www-form-urlencoded string
     * using the specified encoding scheme {@code enc}.
     * <p>
     * All characters except letters ('a'..'z', 'A'..'Z') and numbers ('0'..'9')
     * and characters '.', '-', '*', '_' are converted into their hexadecimal
     * value prepended by '%'. For example: '#' -> %23. In addition, spaces are
     * substituted by '+'
     *
     * @param s
     *            the string to be encoded.
     * @param enc
     *            the encoding scheme to be used.
     * @return the encoded string.
     * @throws UnsupportedEncodingException
     *             if the specified encoding scheme is invalid.
     */
    public static String encode(String s, String enc) throws UnsupportedEncodingException {
        if (s == null || enc == null) {
            throw new NullPointerException();
        }
        // check for UnsupportedEncodingException
        "".getBytes(enc);

        // Guess a bit bigger for encoded form
        StringBuilder buf = new StringBuilder(s.length() + 16);
        int start = -1;
        for (int i = 0; i < s.length(); i++) {
            char ch = s.charAt(i);
            if ((ch >= 'a' && ch <= 'z') || (ch >= 'A' && ch <= 'Z')
                    || (ch >= '0' && ch <= '9') || " .-*_".indexOf(ch) > -1) {
                if (start >= 0) {
                    convert(s.substring(start, i), buf, enc);
                    start = -1;
                }
                if (ch != ' ') {
                    buf.append(ch);
                } else {
                    buf.append('+');
                }
            } else {
                if (start < 0) {
                    start = i;
                }
            }
        }
        if (start >= 0) {
            convert(s.substring(start, s.length()), buf, enc);
        }
        return buf.toString();
    }

    private static void convert(String s, StringBuilder buf, String enc)
            throws UnsupportedEncodingException {
        byte[] bytes = s.getBytes(enc);
        for (int j = 0; j < bytes.length; j++) {
            buf.append('%');
            buf.append(digits.charAt((bytes[j] & 0xf0) >> 4));
            buf.append(digits.charAt(bytes[j] & 0xf));
        }
    }
}
