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/*
 * MIT License
 *
 * Copyright (c) 2017-2018 nuls.io
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in all
 * copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 *
 */
package io.nuls.core.crypto;

import java.math.BigInteger;
import java.util.Arrays;

/**
 * @author tag
 */
public class Base58 {
    public static final char[] ALPHABET = "123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz".toCharArray();
    private static final char ENCODED_ZERO = ALPHABET[0];
    private static final int[] INDEXES = new int[128];

    static {
        Arrays.fill(INDEXES, -1);
        for (int i = 0; i < ALPHABET.length; i++) {
            INDEXES[ALPHABET[i]] = i;
        }
    }

    /**
     * Encodes the given bytes as a base58 string (no checksum is appended)./将给定字节编码为Base58字符串（不追加校验和）
     *
     * @param input the bytes to encode
     * @return the base58-encoded string
     */
    public static String encode(byte[] input) {
        if (input.length == 0) {
            return "";
        }
        // Count leading zeros.
        int zeros = 0;
        while (zeros < input.length && input[zeros] == 0) {
            ++zeros;
        }
        // Convert base-256 digits to base-58 digits (plus conversion to ASCII characters)
        /**
         * since we modify it in-place
         * */
        input = Arrays.copyOf(input, input.length);
        /**
         * upper bound
         * */
        char[] encoded = new char[input.length * 2];
        int outputStart = encoded.length;
        for (int inputStart = zeros; inputStart < input.length; ) {
            encoded[--outputStart] = ALPHABET[divmod(input, inputStart, 256, 58)];
            if (input[inputStart] == 0) {
                ++inputStart; // optimization - skip leading zeros
            }
        }
        // Preserve exactly as many leading encoded zeros in output as there were leading zeros in input.
        while (outputStart < encoded.length && encoded[outputStart] == ENCODED_ZERO) {
            ++outputStart;
        }
        while (--zeros >= 0) {
            encoded[--outputStart] = ENCODED_ZERO;
        }
        // Return encoded string (including encoded leading zeros).
        return new String(encoded, outputStart, encoded.length - outputStart);
    }

    /**
     * Decodes the given base58 string into the original entity bytes./将给定的Base58字符串解码为原始数据字节
     *
     * @param input the base58-encoded string to decode
     * @return the decoded entity bytes
     * @throws Exception if the given string is not a valid base58 string
     */
    public static byte[] decode(String input) throws Exception {
        if (input.length() == 0) {
            return new byte[0];
        }
        // Convert the base58-encoded ASCII chars to a base58 byte sequence (base58 digits).
        byte[] input58 = new byte[input.length()];
        for (int i = 0; i < input.length(); ++i) {
            char c = input.charAt(i);
            int digit = c < 128 ? INDEXES[c] : -1;
            if (digit < 0) {
                throw new Exception("Illegal character " + c + " at position " + i);
            }
            input58[i] = (byte) digit;
        }
        // Count leading zeros.
        int zeros = 0;
        while (zeros < input58.length && input58[zeros] == 0) {
            ++zeros;
        }
        // Convert base-58 digits to base-256 digits.
        byte[] decoded = new byte[input.length()];
        int outputStart = decoded.length;
        for (int inputStart = zeros; inputStart < input58.length; ) {
            decoded[--outputStart] = divmod(input58, inputStart, 58, 256);
            if (input58[inputStart] == 0) {
                ++inputStart; // optimization - skip leading zeros
            }
        }
        // Ignore extra leading zeroes that were added during the calculation.
        while (outputStart < decoded.length && decoded[outputStart] == 0) {
            ++outputStart;
        }
        // Return decoded entity (including original number of leading zeros).
        return Arrays.copyOfRange(decoded, outputStart - zeros, decoded.length);
    }

    /***
     * 先将给定的Base58字符串解码为原始数据字节，然后再将字节数组转为对应的BigInteger
     * @param input   Base58字符串
     * */
    public static BigInteger decodeToBigInteger(String input) throws Exception {
        return new BigInteger(1, decode(input));
    }

    /**
     * Decodes the given base58 string into the original entity bytes, using the checksum in the
     * last 4 bytes of the decoded entity to verify that the rest are correct. The checksum is
     * removed from the returned entity.
     * 将给定的Base58字符串解码为原始数据字节，使用解码数据的最后4字节以验证其余数据是否正确校验和是从返回的数据中删除
     *
     * @param input the base58-encoded string to decode (which should include the checksum)
     * @return byte[]
     * @throws Exception if the input is not base 58 or the checksum does not validate.
     */
    public static byte[] decodeChecked(String input) throws Exception {
        byte[] decoded = decode(input);
        if (decoded.length < 4) {
            throw new Exception("Input too short");
        }
        byte[] data = Arrays.copyOfRange(decoded, 0, decoded.length - 4);
        byte[] checksum = Arrays.copyOfRange(decoded, decoded.length - 4, decoded.length);
        byte[] actualChecksum = Arrays.copyOfRange(Sha256Hash.hashTwice(data), 0, 4);
        if (!Arrays.equals(checksum, actualChecksum)) {
            throw new Exception("Checksum does not validate");
        }
        return data;
    }

    /**
     * Divides a number, represented as an array of bytes each containing a single digit
     * in the specified base, by the given divisor. The given number is modified in-place
     * to contain the quotient, and the return value is the remainder.
     * 将一个数字表示为一个字节数组，每个字节包含一个数字在指定的基数中，由给定的除数。给定的数字被修改到位包含商，返回值为余数。
     *
     * @param number     the number to divide
     * @param firstDigit the index within the array of the first non-zero digit
     *                   (this is used for optimization by skipping the leading zeros)
     * @param base       the base in which the number's digits are represented (up to 256)
     * @param divisor    the number to divide by (up to 256)
     * @return the remainder of the division operation
     */
    private static byte divmod(byte[] number, int firstDigit, int base, int divisor) {
        // this is just long division which accounts for the base of the input digits
        int remainder = 0;
        for (int i = firstDigit; i < number.length; i++) {
            int digit = (int) number[i] & 0xFF;
            int temp = remainder * base + digit;
            number[i] = (byte) (temp / divisor);
            remainder = temp % divisor;
        }
        return (byte) remainder;
    }

}