/*
 * ====================================================================
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 * ====================================================================
 *
 * This software consists of voluntary contributions made by many
 * individuals on behalf of the Apache Software Foundation.  For more
 * information on the Apache Software Foundation, please see
 * <http://www.apache.org/>.
 *
 */
package org.apache.hc.core5.pool;

import static java.lang.System.currentTimeMillis;

import java.io.Closeable;
import java.io.IOException;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicReference;

import org.apache.hc.core5.function.Callback;
import org.apache.hc.core5.util.Args;

/**
 * Pool entry containing a pool connection object along with its route.
 * <p>
 * The connection assigned to this pool entry may have an expiration time and also have an object
 * representing a connection state (usually a security principal or a unique token identifying
 * the user whose credentials have been used while establishing the connection).
 *
 * @param <T> the route type that represents the opposite endpoint of a pooled
 *   connection.
 * @param <C> the connection type.
 * @since 4.2
 */
public final class PoolEntry<T, C extends Closeable> {

    private final T route;
    private final long timeToLive;
    private final AtomicReference<C> connRef;

    private volatile Object state;
    private volatile long created;
    private volatile long updated;
    private volatile long expiry;
    private volatile long validityDeadline;

    /**
     * Creates new {@code PoolEntry} instance.
     *
     * @param route route to the opposite endpoint.
     * @param timeToLive maximum time to live. May be zero if the connection
     *   does not have an expiry deadline.
     * @param timeUnit time unit.
     */
    public PoolEntry(final T route, final long timeToLive, final TimeUnit timeUnit) {
        super();
        this.route = Args.notNull(route, "Route");
        this.connRef = new AtomicReference<>(null);
        this.timeToLive = timeToLive > 0 ? (timeUnit != null ? timeUnit : TimeUnit.MILLISECONDS).toMillis(timeToLive) : 0;
    }

    public PoolEntry(final T route) {
        this(route, 0, TimeUnit.MILLISECONDS);
    }

    public T getRoute() {
        return this.route;
    }

    public C getConnection() {
        return this.connRef.get();
    }

    /**
     * @since 4.4
     */
    public long getValidityDeadline() {
        return this.validityDeadline;
    }

    public Object getState() {
        return this.state;
    }

    public long getUpdated() {
        return this.updated;
    }

    public long getExpiry() {
        return this.expiry;
    }

    /**
     * @since 5.0
     */
    public boolean hasConnection() {
        return this.connRef.get() != null;
    }

    /**
     * @since 5.0
     */
    public void assignConnection(final C conn) {
        Args.notNull(conn, "connection");
        if (this.connRef.compareAndSet(null, conn)) {
            this.created = currentTimeMillis();
            this.updated = this.created;
            this.validityDeadline = this.timeToLive > 0 ? System.currentTimeMillis() + this.timeToLive : Long.MAX_VALUE;
            this.expiry = this.validityDeadline;
        } else {
            throw new IllegalStateException("Connection already assigned");
        }
    }

    /**
     * @since 5.0
     */
    public void discardConnection(final Callback<C> shutdownCallback) {
        final C connection = this.connRef.getAndSet(null);
        if (connection != null) {
            if (shutdownCallback != null) {
                shutdownCallback.execute(connection);
            } else {
                try {
                    connection.close();
                } catch (IOException ignore) {
                }
            }
            this.state = null;
            this.created = 0;
            this.updated = 0;
            this.expiry = 0;
            this.validityDeadline = 0;
        }
    }

    /**
     * @since 5.0
     */
    public void discardConnection() {
        discardConnection(null);
    }

    /**
     * @since 5.0
     */
    public void updateConnection(final long keepAlive, final TimeUnit timeUnit, final Object state) {
        Args.notNull(timeUnit, "Time unit");
        if (this.connRef.get() != null) {
            this.state = state;
            final long currentTime = System.currentTimeMillis();
            final long newExpiry = keepAlive > 0 ? currentTime + timeUnit.toMillis(keepAlive) : Long.MAX_VALUE;
            this.expiry = Math.min(newExpiry, getValidityDeadline());
            this.updated = currentTime;
        } else {
            throw new IllegalStateException("Connection not assigned");
        }
    }

    @Override
    public String toString() {
        final StringBuilder buffer = new StringBuilder();
        buffer.append("[route:");
        buffer.append(this.route);
        buffer.append("][state:");
        buffer.append(this.state);
        buffer.append("]");
        return buffer.toString();
    }

}