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 * Copyright (C) 2026, Leo Galambos
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 *    This product includes software developed by the Egothor project.
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package zeroecho.pki.spi.store;

import java.io.IOException;
import java.util.OptionalLong;

import zeroecho.pki.api.revocation.RevocationRecord;
import zeroecho.core.io.CancellationSignal;

/**
 * Stable, restartable ordered current-state view at one authoritative revision.
 *
 * <p>
 * A snapshot never exposes a complete collection. Each cursor yields one
 * immutable current state at a time and uses {@code long} ordinal accounting. ZeroEcho
 * core imposes no product-wide entry-count ceiling.
 * </p>
 *
 * <p>An exact checkpoint opens without population materialization. Building a
 * missing checkpoint uses a bounded-memory external sort; cursor traversal is
 * linear in the current-state count and uses constant auxiliary heap per entry.</p>
 */
public interface RevocationSnapshot extends AutoCloseable {

    /**
     * Returns stable non-secret snapshot provenance.
     *
     * @return non-blank snapshot identifier
     */
    String snapshotId();

    /** @return captured authoritative global revision */
    long revision();

    /** @return captured authoritative byte boundary */
    long boundary();

    /** @return captured authoritative global commitment in lowercase hexadecimal */
    String commitment();

    /**
     * Returns the current-state count when the store can provide it without
     * materialization.
     *
     * @return count or empty
     */
    OptionalLong count();

    /**
     * Opens a new pass over the same logical snapshot.
     *
     * @return closeable cursor
     * @throws IOException if the cursor cannot be opened
     */
    Cursor openCursor() throws IOException;

    /**
     * Releases snapshot resources.
     *
     * @throws IOException if cleanup fails
     */
    @Override
    void close() throws IOException;

    /**
     * One-pass current-state cursor.
     */
    interface Cursor extends AutoCloseable {

        /**
         * Advances to the next current state.
         *
         * @return {@code true} when {@link #current()} is available
         * @throws IOException if store reading fails
         */
        default boolean next() throws IOException {
            return next(CancellationSignal.NONE);
        }

        /**
         * Advances with cancellation.
         *
         * @param cancellation cancellation signal
         * @return {@code true} when a current state is available
         * @throws IOException if store reading fails
         */
        boolean next(CancellationSignal cancellation) throws IOException;

        /**
         * Returns the current state.
         *
         * @return immutable current state
         * @throws IllegalStateException if the cursor is not positioned on a value
         */
        RevocationRecord current();

        /**
         * Returns the zero-based current ordinal.
         *
         * @return non-negative ordinal
         * @throws IllegalStateException if the cursor is not positioned on a value
         */
        long ordinal();

        /**
         * Closes the cursor.
         *
         * @throws IOException if cleanup fails
         */
        @Override
        void close() throws IOException;
    }
}
