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package zeroecho.core.alg.chacha;

import zeroecho.core.SymmetricHeaderCodec;
import zeroecho.core.spec.ContextSpec;

/**
 * <h2>ChaCha base specification marker</h2>
 *
 * Common sealed interface for all ChaCha-family specifications. Implemented by
 * {@link ChaChaSpec} (raw stream cipher) and {@link ChaCha20Poly1305Spec}
 * (AEAD).
 *
 * <p>
 * Extends {@link zeroecho.core.spec.ContextSpec} to allow binding
 * algorithm-specific parameters into a context.
 * </p>
 *
 * <h3>Header support</h3>
 * <ul>
 * <li>{@link #header()} may return a {@link SymmetricHeaderCodec} that encodes
 * parameters (e.g., nonce, AAD hash) into the ciphertext stream.</li>
 * <li>If {@code null}, no header is used and parameters must be managed via
 * {@code CtxInterface} or other out-of-band means.</li>
 * </ul>
 *
 * <h3>Example</h3> <pre>{@code
 * ChaChaBaseSpec spec = ChaCha20Poly1305Spec.withHeader(
 *     new ChaCha20Poly1305HeaderCodec()
 * );
 * SymmetricHeaderCodec codec = spec.header(); // non-null
 * }</pre>
 *
 * @since 1.0
 */
public sealed interface ChaChaBaseSpec extends ContextSpec permits ChaChaSpec, ChaCha20Poly1305Spec {
    /**
     * Returns the optional header codec used to serialize/deserialize stream
     * headers for this ChaCha mode.
     *
     * @return {@link SymmetricHeaderCodec} instance, or {@code null} if no header
     */
    SymmetricHeaderCodec header(); // may be null
}
