package mkri_blockchain_2;




import java.security.Key;
import java.security.MessageDigest;
import java.security.PrivateKey;
import java.security.PublicKey;
import java.security.Signature;
import java.util.*;


public class StringUtil {

	// Aplikuje Sha256 na string a vrátí výsledek .
	public static String applySha256(String input) {
		try {
			MessageDigest digest = MessageDigest.getInstance("SHA-256");

			// Aplikuje Sha256 na vstupní hodnotu
			byte[] hash = digest.digest(input.getBytes("UTF-8"));

			// Bude obsahovat hash jako hex číslo
			StringBuffer hexString = new StringBuffer();
			for (int i = 0; i < hash.length; i++) {
				String hex = Integer.toHexString(0xff & hash[i]);
				if (hex.length() == 1)
					hexString.append('0');
				hexString.append(hex);
			}
			return hexString.toString();
		} catch (Exception e) {
			throw new RuntimeException(e);
		}
	}

	public static byte[] applyECDSASig(PrivateKey privateKey, String input) {
		Signature dsa;
		byte[] output = new byte[0];
		try {
			dsa = Signature.getInstance("ECDSA", "BC");
			dsa.initSign(privateKey);
			byte[] strByte = input.getBytes();
			dsa.update(strByte);
			byte[] realSig = dsa.sign();
			output = realSig;
		} catch (Exception e) {
			throw new RuntimeException(e);
		}
		return output;
	}

	// Overeni podpisu
	public static boolean verifyECDSASig(PublicKey publicKey, String data, byte[] signature) {
		try {
			Signature ecdsaVerify = Signature.getInstance("ECDSA", "BC");
			ecdsaVerify.initVerify(publicKey);
			ecdsaVerify.update(data.getBytes());
			return ecdsaVerify.verify(signature);
		}catch(Exception e) {
			throw new RuntimeException(e);
		}
	}

	public static String getStringFromKey(Key key) {
		return Base64.getEncoder().encodeToString(key.getEncoded());
	}

	//Vraci obtiznost ciloveho stringu pro srovnani s hashem. napr difficulty = 5 vrati "00000"
	public static String getDificultyString(int difficulty){
		return new String(new char[difficulty]).replace('\0', '0');
	}

	//Vraci koren stromu
	public static String getMerkleRoot(ArrayList<Transaction> transactions) {
			int count = transactions.size();
			ArrayList<String> previousTreeLayer = new ArrayList<String>();
			for(Transaction transaction : transactions) {
				previousTreeLayer.add(transaction.transactionId);
			}
			ArrayList<String> treeLayer = previousTreeLayer;
			while(count > 1) {
				treeLayer = new ArrayList<String>();
				for(int i=1; i < previousTreeLayer.size(); i++) {
					treeLayer.add(applySha256(previousTreeLayer.get(i-1) + previousTreeLayer.get(i)));
				}
				count = treeLayer.size();
				previousTreeLayer = treeLayer;
			}
			String merkleRoot = (treeLayer.size() == 1) ? treeLayer.get(0) : "";
			return merkleRoot;
		}

}