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package zeroecho.core.context;

import zeroecho.core.tag.TagEngine;

/**
 * Context for computing unkeyed message digests and extendable-output functions
 * (XOFs) in streaming pipelines.
 *
 * <p>
 * A {@code DigestContext} combines digest/XOF state with the {@link TagEngine}
 * contract: the wrapped input stream passes bytes through while updating the
 * computation; at end-of-file, a fixed-length tag is appended (produce mode) or
 * compared with an expected tag (verify mode).
 * </p>
 *
 * <h2>Operation</h2>
 * <ul>
 * <li><b>Produce mode:</b> {@link TagEngine#wrap(java.io.InputStream)} emits
 * the original data, then appends the digest (or configured-length XOF output)
 * as a trailer.</li>
 * <li><b>Verify mode:</b> Provide the expected tag via
 * {@link TagEngine#setExpectedTag(byte[])}; the engine compares the computed
 * tag at EOF using the configured verification approach.</li>
 * </ul>
 *
 * <h2>Usage</h2>
 * <h3>Digest trailer</h3> <pre>
 * {@code
 * TagEngine<byte[]> eng = TagEngineBuilder.digest(DigestSpec.sha256()).get();
 * try (java.io.InputStream in = eng.wrap(upstream)) {
 *     in.transferTo(out);
 * }
 * }
 * </pre>
 *
 * <h3>Detached verification</h3> <pre>
 * {@code
 * TagEngine<byte[]> eng = TagEngineBuilder.digest(DigestSpec.sha256()).get();
 * eng.setExpectedTag(expectedDigest);
 * try (java.io.InputStream in = eng.wrap(bodyWithoutTrailer)) {
 *     in.transferTo(java.io.OutputStream.nullOutputStream());
 * }
 * }
 * </pre>
 *
 * <h2>Security considerations</h2>
 * <ul>
 * <li>Unkeyed digests do not provide authenticity; use {@link MacContext} or
 * {@link SignatureContext} for that.</li>
 * <li>For XOFs, choose an output length appropriate for your security
 * level.</li>
 * <li>Implementations are stateful and not guaranteed to be thread-safe.</li>
 * </ul>
 *
 * @since 1.0
 */
public non-sealed interface DigestContext extends TagEngine<byte[]>, CryptoContext {
}
