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 * Copyright (C) 2026, Leo Galambos
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 * 1. Redistributions of source code must retain the above copyright notice, this
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 * 3. All advertising materials mentioning features or use of this software must
 *    display the following acknowledgement:
 *    This product includes software developed by the Egothor project.
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package zeroecho.core.alg.bike;

import java.util.Arrays;
import java.util.Base64;
import java.util.Objects;
import java.util.concurrent.locks.ReentrantLock;

import javax.security.auth.Destroyable;

import zeroecho.core.marshal.PairSeq;
import zeroecho.core.marshal.PairSeq.Cursor;
import zeroecho.core.spec.AlgorithmKeySpec;

/**
 * <h2>Specification for a BIKE private key</h2>
 *
 * Wraps a BIKE private key encoded in standard PKCS#8 format. Provides
 * marshalling and unmarshalling support for interchange.
 *
 * <h3>Usage</h3> <pre>{@code
 * // Import a BIKE private key
 * BikePrivateKeySpec spec = new BikePrivateKeySpec(pkcs8Bytes);
 * PrivateKey key = bikeAlgorithm.privateKeyImporter(BikePrivateKeySpec.class).importPrivate(spec);
 *
 * // Marshal for storage or transport
 * PairSeq seq = BikePrivateKeySpec.marshal(spec);
 *
 * // Reconstruct from encoded representation
 * BikePrivateKeySpec restored = BikePrivateKeySpec.unmarshal(seq);
 * }</pre>
 *
 * @since 1.0
 */
public final class BikePrivateKeySpec implements AlgorithmKeySpec, Destroyable {

    private static final String PKCS8_B64 = "pkcs8.b64";
    private final byte[] pkcs8;
    private final ReentrantLock lifecycleLock = new ReentrantLock();
    private boolean destroyed;

    /**
     * Constructs a new spec from a PKCS#8 encoded private key.
     *
     * @param pkcs8Der PKCS#8 bytes (DER encoded)
     * @throws NullPointerException if {@code pkcs8Der} is null
     */
    public BikePrivateKeySpec(byte[] pkcs8Der) {
        this.pkcs8 = Objects.requireNonNull(pkcs8Der).clone();
    }

    /**
     * Returns a defensive copy of the PKCS#8 encoded key.
     *
     * @return cloned PKCS#8 bytes
     */
    public byte[] pkcs8() {
        lifecycleLock.lock();
        try {
            ensureActive();
            return pkcs8.clone();
        } finally {
            lifecycleLock.unlock();
        }
    }

    /**
     * Serializes the spec to a {@link PairSeq} with base64 encoding.
     *
     * <p>
     * Fields:
     * </p>
     * <ul>
     * <li>{@code type} = "BikePrivateKeySpec"</li>
     * <li>{@code pkcs8.b64} = base64 of encoded key (no padding)</li>
     * </ul>
     *
     * @param spec private key specification
     * @return serialized key representation
     */
    public static PairSeq marshal(BikePrivateKeySpec spec) {
        String b64 = spec.encodedKey();
        return PairSeq.of("type", "BikePrivateKeySpec", PKCS8_B64, b64);
    }

    /**
     * Deserializes a spec from a {@link PairSeq}.
     *
     * @param p serialized representation containing {@code pkcs8.b64}
     * @return reconstructed private key spec
     * @throws IllegalArgumentException if required field is missing
     */
    public static BikePrivateKeySpec unmarshal(PairSeq p) {
        String b64 = null;
        for (Cursor cur = p.cursor(); cur.next();) {
            if (PKCS8_B64.equals(cur.key())) {
                b64 = cur.value();
            }
        }
        if (b64 == null) {
            throw new IllegalArgumentException("BikePrivateKeySpec: missing pkcs8.b64");
        }
        byte[] decoded = Base64.getDecoder().decode(b64);
        try {
            return new BikePrivateKeySpec(decoded);
        } finally {
            Arrays.fill(decoded, (byte) 0);
        }
    }

    /**
     * Returns a diagnostic string including encoded length.
     *
     * @return human-readable description
     */
    @Override
    public String toString() {
        return "BikePrivateKeySpec[len=" + pkcs8.length + "]";
    }

    private String encodedKey() {
        lifecycleLock.lock();
        try {
            ensureActive();
            return Base64.getEncoder().withoutPadding().encodeToString(pkcs8);
        } finally {
            lifecycleLock.unlock();
        }
    }

    @Override
    public void destroy() {
        lifecycleLock.lock();
        try {
            if (!destroyed) {
                Arrays.fill(pkcs8, (byte) 0);
                destroyed = true;
            }
        } finally {
            lifecycleLock.unlock();
        }
    }

    @Override
    public boolean isDestroyed() {
        lifecycleLock.lock();
        try {
            return destroyed;
        } finally {
            lifecycleLock.unlock();
        }
    }

    private void ensureActive() {
        if (destroyed) {
            throw new IllegalStateException("BIKE private key specification has been destroyed");
        }
    }
}
