package tools;

import java.nio.charset.StandardCharsets;
import java.math.BigInteger;
import java.util.Arrays;

public class Base62 {

    private static final String BASE62 = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";

    public static String encode(byte[] input) {
        if (input.length == 0) {
            return "";
        }

        BigInteger value = new BigInteger(1, input);
        StringBuilder result = new StringBuilder();

        while (value.compareTo(BigInteger.ZERO) > 0) {
            BigInteger[] divmod = value.divideAndRemainder(BigInteger.valueOf(62));
            result.append(BASE62.charAt(divmod[1].intValue()));
            value = divmod[0];
        }

        for (byte b : input) {
            if (b == 0) {
                result.append(BASE62.charAt(0));
            } else {
                break;
            }
        }

        return result.reverse().toString();
    }

    public static byte[] decode(String input) {
        if (input.length() == 0) {
            return new byte[0];
        }

        BigInteger value = BigInteger.ZERO;
        for (char c : input.toCharArray()) {
            value = value.multiply(BigInteger.valueOf(62)).add(BigInteger.valueOf(BASE62.indexOf(c)));
        }

        byte[] bytes = value.toByteArray();
        if (bytes[0] == 0) {
            bytes = Arrays.copyOfRange(bytes, 1, bytes.length);
        }

        int leadingZeroes = 0;
        for (char c : input.toCharArray()) {
            if (c == BASE62.charAt(0)) {
                leadingZeroes++;
            } else {
                break;
            }
        }

        byte[] result = new byte[leadingZeroes + bytes.length];
        System.arraycopy(bytes, 0, result, leadingZeroes, bytes.length);
        return result;
    }

    public static void main(String[] args) {
        // Encoding example
        String input = "回□〓≡╝╚╔╗";
        String encoded = Base62.encode(input.getBytes(StandardCharsets.UTF_8));
        System.out.println("Encoded: " + encoded);

        // Decoding example
        String decoded = new String(Base62.decode(encoded), StandardCharsets.UTF_8);
        System.out.println("Decoded: " + decoded);
    }
}