/**
 * Copyright 2010-2013 The Kuali Foundation
 *
 * Licensed under the Educational Community 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.opensource.org/licenses/ecl2.php
 *
 * 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.kuali.common.util;

import java.io.UnsupportedEncodingException;

import org.apache.commons.lang3.CharSet;
import org.apache.commons.lang3.StringUtils;

/**
 * A few (highly inefficient) methods for converting <code>String's</code> into the hex for a given encoding and back again.
 */
public class HexUtils {

        private static final String ZERO = "0";
        private static final int BYTE_MASK = 0x000000ff;
        private static final String[] HEX_RANGES = new String[] { "0-9", "A-F", "a-f" };
        private static final String HEX_RANGES_STRING = toString(HEX_RANGES);
        private static final CharSet HEX_CHARSET = CharSet.getInstance(HEX_RANGES);

        public static final CharSet getHexCharSet() {
                return HEX_CHARSET;
        }

        public static final String[] getHexRanges() {
                return HEX_RANGES;
        }

        protected static final String toString(String[] tokens) {
                StringBuilder sb = new StringBuilder();
                sb.append("[");
                for (int i = 0; i < HEX_RANGES.length; i++) {
                        if (i != 0) {
                                sb.append(",");
                        }
                        sb.append(HEX_RANGES[i]);
                }
                sb.append("]");
                return sb.toString();
        }

        /**
         * Convert <code>string</code> into a <code>byte[]</code> using the specified encoding, then convert each <code>byte</code> into its 2
         * digit hexadecimal form.
         */
        public static String toHexString(String string, String encoding) throws UnsupportedEncodingException {
                byte[] bytes = encoding == null ? string.getBytes() : string.getBytes(encoding);
                return toHexString(bytes);
        }

        /**
         * Convert each <code>byte</code> into its 2 digit hexadecimal form.
         */
        public static String toHexString(byte[] bytes) {
                StringBuilder sb = new StringBuilder();
                for (byte b : bytes) {
                        int masked = BYTE_MASK & b;
                        String hex = Integer.toHexString(masked).toUpperCase();
                        String padded = StringUtils.leftPad(hex, 2, ZERO);
                        sb.append(padded);
                }
                return sb.toString();
        }

        /**
         * Return true if every character is valid hex <code>0-9</code>, <code>a-f</code>, or <code>A-F</code>
         */
        public static final boolean isHex(char... chars) {
                for (char c : chars) {
                        if (!HEX_CHARSET.contains(c)) {
                                return false;
                        }
                }
                return true;
        }

        /**
         * Given a string in <code>strictly hex</code> format, return the corresponding <code>byte[]</code>. <code>strictly hex</code> in the
         * context of this method means that the string:<br>
         * 1 - Contains only the characters <code>a-f</code>, <code>A-F</code>, and <code>0-9</code><br>
         * 2 - Its length is an even number.
         */
        public static final byte[] getBytesFromHexString(String hex) {
                char[] chars = hex.toCharArray();
                int length = chars.length;
                if (length % 2 != 0) {
                        throw new IllegalArgumentException("Invalid hex string [" + hex + "].  String must contain an even number of characters.  " + length + " is not an even number!");
                }
                byte[] bytes = new byte[length / 2];
                int byteIndex = 0;
                for (int i = 0; i < length; i += 2) {
                        char c1 = chars[i];
                        char c2 = chars[i + 1];
                        String s = c1 + "" + c2;
                        if (!isHex(c1, c2)) {
                                int byteNumber = i / 2 + 1;
                                throw new IllegalArgumentException("Invalid hex string [" + hex + "].  Invalid hex detected at byte " + byteNumber + " [" + s
                                        + "].  Both characters must be in the range " + HEX_RANGES_STRING);
                        }
                        int integer = Integer.parseInt(s, 16);
                        int masked = integer & BYTE_MASK;
                        byte b = (byte) masked;
                        bytes[byteIndex++] = b;
                }
                return bytes;
        }

        /**
         * Given a string in <code>strictly hex</code> format and the <code>encoding</code> that was used to produce the hex, convert it back to
         * a Java <code>String</code>. <code>strictly hex</code> in the context of this method means that the string:<br>
         * 1 - Contains only the characters <code>a-f</code>, <code>A-F</code>, and <code>0-9</code><br>
         * 2 - Its length is an even number.
         */
        public static final String toStringFromHex(String hex, String encoding) throws UnsupportedEncodingException {
                byte[] bytes = getBytesFromHexString(hex);
                return StringUtils.toString(bytes, encoding);
        }

}