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/*
 License:

 blueprint-sdk is licensed under the terms of Eclipse Public License(EPL) v1.0
 (http://www.eclipse.org/legal/epl-v10.html)


 Distribution:

 Maven Central - https://search.maven.org/artifact/io.github.lempel/blueprint-sdk
 MVN Repository - https://mvnrepository.com/artifact/io.github.lempel/blueprint-sdk
 */

package blueprint.sdk.util.queue;

import javax.sql.DataSource;
import java.sql.SQLException;
import java.util.LinkedList;
import java.util.NoSuchElementException;
import java.util.UUID;

/**
 * Prototype for JDBC based Queue.

 * 

 * Must call {@link JdbcQueue#init()} before use.

 *
 * @author [email protected]
 * @since 2013. 8. 26.
 */
public abstract class JdbcQueue extends MessageQueue {
    /**
     * actual queue
     */
    final LinkedList queue = new LinkedList<>();

    /**
     * DataSource for persistence
     */
    final DataSource datasrc;

    /**
     * Constructor
     *
     * @param datasrc DataSource for persistence
     */
    @SuppressWarnings("WeakerAccess")
    public JdbcQueue(DataSource datasrc) {
        super();

        this.datasrc = datasrc;

        if (datasrc == null) {
            throw new NullPointerException("DataSource is null");
        }
    }

    /**
     * create table and load queue contents from DataSource
     *
     * @throws SQLException
     */
    public void init() throws SQLException {
        synchronized (queue) {
            createTable();
            load();
        }
    }

    @Override
    public void clear() throws JdbcQueueException {
        synchronized (queue) {
            try {
                emptyTable();
                queue.clear();
            } catch (SQLException e) {
                throw new JdbcQueueException(e);
            }
        }
    }

    @Override
    public void push(String element) {
        push(element, true);
    }

    /**
     * Push an element to queue.
     *
     * @param element    Element to push
     * @param persistent true: store to Database, false: don't store
     */
    @SuppressWarnings({"SameParameterValue", "WeakerAccess"})
    public void push(String element, boolean persistent) {
        if (element == null) {
            throw new NullPointerException("Can't push null");
        }

        JdbcElement item = new JdbcElement();
        item.uuid = UUID.randomUUID().toString();
        item.content = element;
        item.persistent = persistent;

        try {
            if (persistent) {
                insert(item);
            }
            synchronized (queue) {
                queue.push(item);
            }
            notifyWaiter();
        } catch (SQLException e) {
            throw new JdbcQueueException(e);
        }
    }

    @Override
    public String pop() throws JdbcQueueException {
        String result = null;

        try {
            JdbcElement element;
            synchronized (queue) {
                element = queue.pop();
            }

            if (element != null) {
                try {
                    if (element.persistent) {
                        delete(element);
                    }

                    result = element.content;
                } catch (SQLException e) {
                    synchronized (queue) {
                        queue.push(element);
                    }
                    notifyWaiter();
                    throw new JdbcQueueException(e);
                }
            }
        } catch (NoSuchElementException ignored) {
            // just return null
        }

        return result;
    }

    /**
     * Load queue contents from DBMS
     *
     * @throws SQLException Can't load
     */
    protected abstract void load() throws SQLException;

    /**
     * Create table for queue (if not exits)
     *
     * @throws SQLException Can't create
     */
    protected abstract void createTable() throws SQLException;

    /**
     * Empty table for queue
     *
     * @throws SQLException Can't delete
     */
    protected abstract void emptyTable() throws SQLException;

    /**
     * Insert queue element to table
     *
     * @param element element to insert
     * @throws SQLException Can't insert
     */
    protected abstract void insert(Element element) throws SQLException;

    /**
     * Delete queue element from table
     *
     * @param element element to delete
     * @throws SQLException Can't delete
     */
    protected abstract void delete(Element element) throws SQLException;
}

/**
 * Internal element of JdbcQueue
 *
 * @author [email protected]
 * @since 2013. 10. 25.
 */
class JdbcElement extends Element {
    /**
     * true: store to Database, false: don't store
     */
    // default true for load()
    public boolean persistent = true;
}