/**
 *
 * Copyright 2003-2007 Jive Software.
 *
 * Licensed 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.jivesoftware.smack.util;

import java.io.UnsupportedEncodingException;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.Collection;
import java.util.Random;
import java.util.logging.Level;
import java.util.logging.Logger;

/**
 * A collection of utility methods for String objects.
 */
public class StringUtils {
    private static final Logger LOGGER = Logger.getLogger(StringUtils.class.getName());

    public static final String QUOTE_ENCODE = """;
    public static final String APOS_ENCODE = "'";
    public static final String AMP_ENCODE = "&";
    public static final String LT_ENCODE = "<";
    public static final String GT_ENCODE = ">";

    /**
     * Escapes all necessary characters in the String so that it can be used
     * in an XML doc.
     *
     * @param string the string to escape.
     * @return the string with appropriate characters escaped.
     */
    public static CharSequence escapeForXML(final String string) {
        if (string == null) {
            return null;
        }
        final char[] input = string.toCharArray();
        final int len = input.length;
        final StringBuilder out = new StringBuilder((int)(len*1.3));
        CharSequence toAppend;
        char ch;
        int last = 0;
        int i = 0;
        while (i < len) {
            toAppend = null;
            ch = input[i];
            switch(ch) {
            case '<':
                toAppend = LT_ENCODE;
                break;
            case '>':
                toAppend = GT_ENCODE;
                break;
            case '&':
                toAppend = AMP_ENCODE;
                break;
            case '"':
                toAppend = QUOTE_ENCODE;
                break;
            case '\'':
                toAppend = APOS_ENCODE;
                break;
            default:
                break;
            }
            if (toAppend != null) {
                if (i > last) {
                    out.append(input, last, i - last);
                }
                out.append(toAppend);
                last = ++i;
            } else {
                i++;
            }
        }
        if (last == 0) {
            return string;
        }
        if (i > last) {
            out.append(input, last, i - last);
        }
        return out;
    }

    /**
     * Used by the hash method.
     */
    private static MessageDigest digest = null;

    /**
     * Hashes a String using the SHA-1 algorithm and returns the result as a
     * String of hexadecimal numbers. This method is synchronized to avoid
     * excessive MessageDigest object creation. If calling this method becomes
     * a bottleneck in your code, you may wish to maintain a pool of
     * MessageDigest objects instead of using this method.
     * <p>
     * A hash is a one-way function -- that is, given an
     * input, an output is easily computed. However, given the output, the
     * input is almost impossible to compute. This is useful for passwords
     * since we can store the hash and a hacker will then have a very hard time
     * determining the original password.
     *
     * @param data the String to compute the hash of.
     * @return a hashed version of the passed-in String
     */
    public synchronized static String hash(String data) {
        if (digest == null) {
            try {
                digest = MessageDigest.getInstance("SHA-1");
            }
            catch (NoSuchAlgorithmException nsae) {
                LOGGER.log(Level.SEVERE, "Failed to load the SHA-1 MessageDigest. Smack will be unable to function normally.", nsae);
            }
        }
        // Now, compute hash.
        try {
            digest.update(data.getBytes("UTF-8"));
        }
        catch (UnsupportedEncodingException e) {
            LOGGER.log(Level.SEVERE, "Error computing hash", e);
        }
        return encodeHex(digest.digest());
    }

    /**
     * Encodes an array of bytes as String representation of hexadecimal.
     *
     * @param bytes an array of bytes to convert to a hex string.
     * @return generated hex string.
     */
    public static String encodeHex(byte[] bytes) {
        StringBuilder hex = new StringBuilder(bytes.length * 2);

        for (byte aByte : bytes) {
            if (((int) aByte & 0xff) < 0x10) {
                hex.append("0");
            }
            hex.append(Integer.toString((int) aByte & 0xff, 16));
        }

        return hex.toString();
    }

    /**
     * Encodes a String as a base64 String.
     *
     * @param data a String to encode.
     * @return a base64 encoded String.
     */
    public static String encodeBase64(String data) {
        byte [] bytes = null;
        try {
            bytes = data.getBytes("ISO-8859-1");
        }
        catch (UnsupportedEncodingException uee) {
            throw new IllegalStateException(uee);
        }
        return encodeBase64(bytes);
    }

    /**
     * Encodes a byte array into a base64 String.
     *
     * @param data a byte array to encode.
     * @return a base64 encode String.
     */
    public static String encodeBase64(byte[] data) {
        return encodeBase64(data, false);
    }

    /**
     * Encodes a byte array into a bse64 String.
     *
     * @param data The byte arry to encode.
     * @param lineBreaks True if the encoding should contain line breaks and false if it should not.
     * @return A base64 encoded String.
     */
    public static String encodeBase64(byte[] data, boolean lineBreaks) {
        return encodeBase64(data, 0, data.length, lineBreaks);
    }

    /**
     * Encodes a byte array into a bse64 String.
     *
     * @param data The byte arry to encode.
     * @param offset the offset of the bytearray to begin encoding at.
     * @param len the length of bytes to encode.
     * @param lineBreaks True if the encoding should contain line breaks and false if it should not.
     * @return A base64 encoded String.
     */
    public static String encodeBase64(byte[] data, int offset, int len, boolean lineBreaks) {
        return Base64.encodeBytes(data, offset, len, (lineBreaks ?  Base64.NO_OPTIONS : Base64.DONT_BREAK_LINES));
    }

    /**
     * Decodes a base64 String.
     * Unlike Base64.decode() this method does not try to detect and decompress a gzip-compressed input.
     *
     * @param data a base64 encoded String to decode.
     * @return the decoded String.
     */
    public static byte[] decodeBase64(String data) {
        byte[] bytes;
        try {
            bytes = data.getBytes("UTF-8");
        } catch (java.io.UnsupportedEncodingException uee) {
            bytes = data.getBytes();
        }

        bytes = Base64.decode(bytes, 0, bytes.length, Base64.NO_OPTIONS);
        return bytes;
    }

    /**
     * Pseudo-random number generator object for use with randomString().
     * The Random class is not considered to be cryptographically secure, so
     * only use these random Strings for low to medium security applications.
     */
    private static Random randGen = new Random();

    /**
     * Array of numbers and letters of mixed case. Numbers appear in the list
     * twice so that there is a more equal chance that a number will be picked.
     * We can use the array to get a random number or letter by picking a random
     * array index.
     */
    private static char[] numbersAndLetters = ("0123456789abcdefghijklmnopqrstuvwxyz" +
                    "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ").toCharArray();

    /**
     * Returns a random String of numbers and letters (lower and upper case)
     * of the specified length. The method uses the Random class that is
     * built-in to Java which is suitable for low to medium grade security uses.
     * This means that the output is only pseudo random, i.e., each number is
     * mathematically generated so is not truly random.<p>
     *
     * The specified length must be at least one. If not, the method will return
     * null.
     *
     * @param length the desired length of the random String to return.
     * @return a random String of numbers and letters of the specified length.
     */
    public static String randomString(int length) {
        if (length < 1) {
            return null;
        }
        // Create a char buffer to put random letters and numbers in.
        char [] randBuffer = new char[length];
        for (int i=0; i<randBuffer.length; i++) {
            randBuffer[i] = numbersAndLetters[randGen.nextInt(71)];
        }
        return new String(randBuffer);
    }

    /**
     * Returns true if CharSequence is not null and is not empty, false otherwise
     * Examples:
     *    isNotEmpty(null) - false
     *    isNotEmpty("") - false
     *    isNotEmpty(" ") - true
     *    isNotEmpty("empty") - true
     *
     * @param cs checked CharSequence
     * @return true if string is not null and is not empty, false otherwise
     */
    public static boolean isNotEmpty(CharSequence cs) {
        return !isNullOrEmpty(cs);
    }

    /**
     * Returns true if the given CharSequence is not null or empty.
     *
     * @param cs
     * @return true if the given CharSequence is not null or empty
     */
    public static boolean isNullOrEmpty(CharSequence cs) {
        return cs == null || cs.length() == 0;
    }

    public static String collectionToString(Collection<String> collection) {
        StringBuilder sb = new StringBuilder();
        for (String s : collection) {
            sb.append(s);
            sb.append(" ");
        }
        String res = sb.toString();
        // Remove the trailing whitespace
        res = res.substring(0, res.length() - 1);
        return res;
    }
}