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/*******************************************************************************
Copyright ArxanFintech Technology Ltd. 2018 All Rights Reserved.

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 com.arxanfintech.common.crypto;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

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

/**
 * An EC Private Key, technically a big positive integer capable of signing such that the signature can be verified
 * with the corresponding EC Public Key
 *
 * @see PublicKey
 */
public class PrivateKey implements Key {
    private static final Logger log = LoggerFactory.getLogger(PrivateKey.class);

    private final byte[] priv;
    private final Cryptography crypto;
    private PublicKey publicKey = null; // lazy initialization

    /**
     * Create from uncompressed binary representation
     */
    private PrivateKey(byte[] priv, Cryptography crypto) {
        this.priv = priv;
        this.crypto = crypto;
    }

    public static PrivateKey createNew(Cryptography crypto) {
        return new PrivateKey(crypto.createNewPrivateKey(), crypto);
    }

    @Override
    public byte[] toByteArray() {
        return priv.clone();
    }

    /**
     * @return the corresponding public key
     */
    public PublicKey getPublic() {
        if (publicKey == null) {
            publicKey = new PublicKey(crypto.getPublicFor(priv), crypto);
        }
        return publicKey;
    }

    /**
     * Sign a digest with this key.
     *
     * @param hash arbitrary data
     * @return signature
     */
    public byte[] sign(byte[] hash) {
        return crypto.sign(hash, toByteArray());
    }

    @Override
    public String toString() {
        return "private key of " + getPublic();
    }

    @Override
    public PrivateKey offsetKey(BigInteger offset) {
        return new PrivateKey(crypto.getPrivateKeyAtOffset(priv, offset.toByteArray()), crypto);
    }

    @Override
    public int hashCode() {
        return Arrays.hashCode(priv);
    }

    @Override
    public boolean equals(Object obj) {
        if (obj instanceof PrivateKey) {
            PrivateKey other = (PrivateKey) obj;
            return Arrays.equals(priv, other.priv);
        }
        return false;
    }
}