/*
 * Copyright Debezium Authors.
 *
 * Licensed under the Apache Software License version 2.0, available at http://www.apache.org/licenses/LICENSE-2.0
 */

package io.debezium.connector.postgresql.connection;

import java.sql.SQLException;
import java.util.concurrent.ExecutorService;

import org.postgresql.replication.PGReplicationStream;

/**
 * A stream from which messages sent by a logical decoding plugin can be consumed over a replication connection.
 *
 * @author Horia Chiorean (hchiorea@redhat.com)
 */
public interface ReplicationStream extends AutoCloseable {

    @FunctionalInterface
    interface ReplicationMessageProcessor {

        /**
         * Processes the given replication message.
         * @param message The replication message, never {@code null}.
         */
        void process(ReplicationMessage message) throws SQLException, InterruptedException;
    }

    /**
     * Blocks and waits for a replication message to be sent over a replication connection. Once a message has been received,
     * the value of the {@link #lastReceivedLsn() last received LSN} will also be updated accordingly.
     *
     * @param processor - a callback to which the arrived message is passed
     * @throws SQLException if anything unexpected fails
     * @see PGReplicationStream#read()
     */
    void read(ReplicationMessageProcessor processor) throws SQLException, InterruptedException;

    /**
     * Attempts to read a replication message from a replication connection, processing that message if it's available or returning
     * {@code false} if nothing is available. Once a message has been received, the value of the {@link #lastReceivedLsn() last received LSN}
     * will also be updated accordingly.
     *
     * @param processor - a callback to which the arrived message is passed
     * @return {@code true} if a message was received and processed
     * @throws SQLException if anything unexpected fails
     * @see PGReplicationStream#readPending()
     */
    boolean readPending(ReplicationMessageProcessor processor) throws SQLException, InterruptedException;

    /**
     * Sends a message to the server informing it about that latest position in the WAL that has successfully been
     * processed. Due to the internal buffering the messages sent to Kafka (and thus committed offsets) will usually
     * lag behind the latest received LSN, which is why this method must only be called after the accompanying event
     * has been sent to Kafka and the offset has been committed there.
     * <p>
     * This essentially tells the server that this stream has successfully processed messages up to the current read cursor
     * and so the server is free to discard older segments with earlier LSNs. It also affects the catch-up behavior once a slot
     * is restarted and the server attempt to bring it up-to-date.
     * </p>
     *
     * @throws SQLException if anything goes wrong
     */
    void flushLsn(Lsn lsn) throws SQLException;

    /**
     * Returns the value for the latest server received LSN during a read operation. The value is always updated once messages
     * are read via the {@link ReplicationConnection#startStreaming()} or {@link ReplicationConnection#startStreaming(Long)}
     * methods.
     *
     * @return a {@link Long} value, possibly null if this is called before anything has been read
     */
    Lsn lastReceivedLsn();

    /**
     * Returns the value for the LSN form which the streaming is executed.
     *
     * @return a {@link Long} value, possibly null if starting LSN is undefined
     */
    Lsn startLsn();

    /**
     * Starts a background thread to ensure the slot is kept alive, useful for when temporarily
     * stopping reads from the stream such as querying metadata, etc
     */
    void startKeepAlive(ExecutorService service);

    /**
     * Stops the background thread that is used to ensure the slot is kept alive.
     */
    void stopKeepAlive();

    /**
     * //TODO author=Horia Chiorean date=13/10/2016 description=Don't use this for now, because of the bug from the PG server
     * This is stream is closed atm. once the replication connection which created it is closed.
     * @see PGReplicationStream#close()
     */
    @Override
    void close() throws Exception;
}
