import com.fasterxml.jackson.annotation.JsonIgnore;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;

import java.io.UnsupportedEncodingException;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;

/**
 * Compile the class with jackson-data bind dependency
 * <p>com.fasterxml.jackson.core<p/>
 */
class TRBlock {

    private static final String SHA1 = "SHA-1";
    private final static char[] hexArray = "0123456789abcdef".toCharArray();

    public int index;  // The index of the block
    public long timestamp; // Time stamp in epoch
    public Object data; // The data we want to store on the Block chain
    public String prevHash; // This is the chain/hash previous block
    public String nonce; // A Magical number that needs to be mined/found
    public int target; // Number of leading zeros in the current hash
    @JsonIgnore
    public String currHash; // Current hash

    /**
     *  Constructor for creating the block
     *
     * @param index the index of the block
     * @param timestamp the time stamp in epoch
     * @param data data to be stored in the block chain
     * @param prevHash hash of the previous block
     * @param nonce the nonce to be mined
     * @param target the number of leading zeros to mine the nonce
     */
    public TRBlock(int index, long timestamp, Object data, String prevHash,
                   String nonce, int target) {
        this.index = index;
        this.timestamp = timestamp;
        this.data = data;
        this.prevHash = prevHash;
        this.nonce = nonce;
        this.target = target;
    }

    /**
     * Convert a byte array into hexadecimal string
     * @param bytes data in bytes array
     * @return a string in hexadecimal
     */
    public static String bytesToHex(byte[] bytes) {
        char[] hexChars = new char[bytes.length * 2];
        for ( int j = 0; j < bytes.length; j++ ) {
            int v = bytes[j] & 0xFF;
            hexChars[j * 2] = hexArray[v >>> 4];
            hexChars[j * 2 + 1] = hexArray[v & 0x0F];
        }
        return new String(hexChars);
    }
    /**
     * Generate SHA1 hash from a text
     * @param data the text data to be hashed
     * @return a string in base64 encoded format
     * @throws java.security.NoSuchAlgorithmException
     */
    public static String generateSHA1Hash(String data) throws NoSuchAlgorithmException {
        MessageDigest messageDigest = MessageDigest.getInstance(SHA1);
        messageDigest.update(data.getBytes());
        byte [] hash = messageDigest.digest();
        messageDigest.reset();
        return bytesToHex(hash);
    }

    /**
     * Convert TRBlock into json string
     * @param obj object to be stringyfied
     * @return json string of the object
     * @throws JsonProcessingException
     */
    public static String stringify(Object obj) throws JsonProcessingException {
        ObjectMapper objectMapper = new ObjectMapper();
        return objectMapper.writeValueAsString(obj);
    }

    public static void main(String[] args) throws JsonProcessingException,
            UnsupportedEncodingException, NoSuchAlgorithmException {
        TRBlock block = new TRBlock(0, 1514528022, "Hello World",
                "000000000000000000000000000", "Random nonce", 8);
        System.out.println(generateSHA1Hash(stringify(block)));
    }

}