/*
 * Copyright 2018 NAVER Corp.
 *
 * Licensed 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.
 */

package com.navercorp.pinpoint.pluginit.utils;

        import java.net.DatagramSocket;
        import java.net.ServerSocket;
        import java.util.Random;
        import java.util.SortedSet;
        import java.util.TreeSet;
        import javax.net.ServerSocketFactory;

/**
 * copy spring framework
 * - https://github.com/spring-projects/spring-framework
 *
 * Simple utility methods for working with network sockets &mdash; for example,
 * for finding available ports on {@code localhost}.
 *
 * <p>Within this class, a TCP port refers to a port for a {@link ServerSocket};
 * whereas, a UDP port refers to a port for a {@link DatagramSocket}.
 *
 * @author Sam Brannen
 * @author Ben Hale
 * @author Arjen Poutsma
 * @author Gunnar Hillert
 * @since 4.0
 */
public class SocketUtils {

    /**
     * The default minimum value for port ranges used when finding an available
     * socket port.
     */
    public static final int PORT_RANGE_MIN = 1024;

    /**
     * The default maximum value for port ranges used when finding an available
     * socket port.
     */
    public static final int PORT_RANGE_MAX = 65535;


    private static final Random random = new Random(System.currentTimeMillis());


    /**
     * Although {@code SocketUtils} consists solely of static utility methods,
     * this constructor is intentionally {@code public}.
     * <h4>Rationale</h4>
     * <p>Static methods from this class may be invoked from within XML
     * configuration files using the Spring Expression Language (SpEL) and the
     * following syntax.
     * <pre><code>&lt;bean id="bean1" ... p:port="#{T(org.springframework.util.SocketUtils).findAvailableTcpPort(12000)}" /&gt;</code></pre>
     * If this constructor were {@code private}, you would be required to supply
     * the fully qualified class name to SpEL's {@code T()} function for each usage.
     * Thus, the fact that this constructor is {@code public} allows you to reduce
     * boilerplate configuration with SpEL as can be seen in the following example.
     * <pre><code>&lt;bean id="socketUtils" class="org.springframework.util.SocketUtils" /&gt;
     * &lt;bean id="bean1" ... p:port="#{socketUtils.findAvailableTcpPort(12000)}" /&gt;
     * &lt;bean id="bean2" ... p:port="#{socketUtils.findAvailableTcpPort(30000)}" /&gt;</code></pre>
     */
    public SocketUtils() {
        /* no-op */
    }


    /**
     * Find an available TCP port randomly selected from the range
     * [{@value #PORT_RANGE_MIN}, {@value #PORT_RANGE_MAX}].
     * @return an available TCP port number
     * @throws IllegalStateException if no available port could be found
     */
    public static int findAvailableTcpPort() {
        return findAvailableTcpPort(PORT_RANGE_MIN);
    }

    /**
     * Find an available TCP port randomly selected from the range
     * [{@code minPort}, {@value #PORT_RANGE_MAX}].
     * @param minPort the minimum port number
     * @return an available TCP port number
     * @throws IllegalStateException if no available port could be found
     */
    public static int findAvailableTcpPort(int minPort) {
        return findAvailableTcpPort(minPort, PORT_RANGE_MAX);
    }

    /**
     * Find an available TCP port randomly selected from the range
     * [{@code minPort}, {@code maxPort}].
     * @param minPort the minimum port number
     * @param maxPort the maximum port number
     * @return an available TCP port number
     * @throws IllegalStateException if no available port could be found
     */
    public static int findAvailableTcpPort(int minPort, int maxPort) {
        return SocketType.TCP.findAvailablePort(minPort, maxPort);
    }

    /**
     * Find the requested number of available TCP ports, each randomly selected
     * from the range [{@value #PORT_RANGE_MIN}, {@value #PORT_RANGE_MAX}].
     * @param numRequested the number of available ports to find
     * @return a sorted set of available TCP port numbers
     * @throws IllegalStateException if the requested number of available ports could not be found
     */
    public static SortedSet<Integer> findAvailableTcpPorts(int numRequested) {
        return findAvailableTcpPorts(numRequested, PORT_RANGE_MIN, PORT_RANGE_MAX);
    }

    /**
     * Find the requested number of available TCP ports, each randomly selected
     * from the range [{@code minPort}, {@code maxPort}].
     * @param numRequested the number of available ports to find
     * @param minPort the minimum port number
     * @param maxPort the maximum port number
     * @return a sorted set of available TCP port numbers
     * @throws IllegalStateException if the requested number of available ports could not be found
     */
    public static SortedSet<Integer> findAvailableTcpPorts(int numRequested, int minPort, int maxPort) {
        return SocketType.TCP.findAvailablePorts(numRequested, minPort, maxPort);
    }

    /**
     * Find an available UDP port randomly selected from the range
     * [{@value #PORT_RANGE_MIN}, {@value #PORT_RANGE_MAX}].
     * @return an available UDP port number
     * @throws IllegalStateException if no available port could be found
     */
    public static int findAvailableUdpPort() {
        return findAvailableUdpPort(PORT_RANGE_MIN);
    }

    /**
     * Find an available UDP port randomly selected from the range
     * [{@code minPort}, {@value #PORT_RANGE_MAX}].
     * @param minPort the minimum port number
     * @return an available UDP port number
     * @throws IllegalStateException if no available port could be found
     */
    public static int findAvailableUdpPort(int minPort) {
        return findAvailableUdpPort(minPort, PORT_RANGE_MAX);
    }

    /**
     * Find an available UDP port randomly selected from the range
     * [{@code minPort}, {@code maxPort}].
     * @param minPort the minimum port number
     * @param maxPort the maximum port number
     * @return an available UDP port number
     * @throws IllegalStateException if no available port could be found
     */
    public static int findAvailableUdpPort(int minPort, int maxPort) {
        return SocketType.UDP.findAvailablePort(minPort, maxPort);
    }

    /**
     * Find the requested number of available UDP ports, each randomly selected
     * from the range [{@value #PORT_RANGE_MIN}, {@value #PORT_RANGE_MAX}].
     * @param numRequested the number of available ports to find
     * @return a sorted set of available UDP port numbers
     * @throws IllegalStateException if the requested number of available ports could not be found
     */
    public static SortedSet<Integer> findAvailableUdpPorts(int numRequested) {
        return findAvailableUdpPorts(numRequested, PORT_RANGE_MIN, PORT_RANGE_MAX);
    }

    /**
     * Find the requested number of available UDP ports, each randomly selected
     * from the range [{@code minPort}, {@code maxPort}].
     * @param numRequested the number of available ports to find
     * @param minPort the minimum port number
     * @param maxPort the maximum port number
     * @return a sorted set of available UDP port numbers
     * @throws IllegalStateException if the requested number of available ports could not be found
     */
    public static SortedSet<Integer> findAvailableUdpPorts(int numRequested, int minPort, int maxPort) {
        return SocketType.UDP.findAvailablePorts(numRequested, minPort, maxPort);
    }


    private static enum SocketType {

        TCP {
            @Override
            protected boolean isPortAvailable(int port) {
                try {
                    ServerSocket serverSocket = ServerSocketFactory.getDefault().createServerSocket(port);
                    serverSocket.close();
                    return true;
                }
                catch (Exception ex) {
                    return false;
                }
            }
        },

        UDP {
            @Override
            protected boolean isPortAvailable(int port) {
                try {
                    DatagramSocket socket = new DatagramSocket(port);
                    socket.close();
                    return true;
                }
                catch (Exception ex) {
                    return false;
                }
            }
        };

        /**
         * Determine if the specified port for this {@code SocketType} is
         * currently available on {@code localhost}.
         */
        protected abstract boolean isPortAvailable(int port);

        /**
         * Find a pseudo-random port number within the range
         * [{@code minPort}, {@code maxPort}].
         * @param minPort the minimum port number
         * @param maxPort the maximum port number
         * @return a random port number within the specified range
         */
        private int findRandomPort(int minPort, int maxPort) {
            int portRange = maxPort - minPort;
            return minPort + random.nextInt(portRange);
        }

        /**
         * Find an available port for this {@code SocketType}, randomly selected
         * from the range [{@code minPort}, {@code maxPort}].
         * @param minPort the minimum port number
         * @param maxPort the maximum port number
         * @return an available port number for this socket type
         * @throws IllegalStateException if no available port could be found
         */
        int findAvailablePort(int minPort, int maxPort) {
            isTrue(minPort > 0, "'minPort' must be greater than 0");
            isTrue(maxPort > minPort, "'maxPort' must be greater than 'minPort'");
            isTrue(maxPort <= PORT_RANGE_MAX, "'maxPort' must be less than or equal to " + PORT_RANGE_MAX);

            int portRange = maxPort - minPort;
            int candidatePort;
            int searchCounter = 0;
            do {
                if (++searchCounter > portRange) {
                    throw new IllegalStateException(String.format(
                            "Could not find an available %s port in the range [%d, %d] after %d attempts", name(), minPort,
                            maxPort, searchCounter));
                }
                candidatePort = findRandomPort(minPort, maxPort);
            }
            while (!isPortAvailable(candidatePort));

            return candidatePort;
        }

        /**
         * Find the requested number of available ports for this {@code SocketType},
         * each randomly selected from the range [{@code minPort}, {@code maxPort}].
         * @param numRequested the number of available ports to find
         * @param minPort the minimum port number
         * @param maxPort the maximum port number
         * @return a sorted set of available port numbers for this socket type
         * @throws IllegalStateException if the requested number of available ports could not be found
         */
        SortedSet<Integer> findAvailablePorts(int numRequested, int minPort, int maxPort) {
            isTrue(minPort > 0, "'minPort' must be greater than 0");
            isTrue(maxPort > minPort, "'maxPort' must be greater than 'minPort'");
            isTrue(maxPort <= PORT_RANGE_MAX, "'maxPort' must be less than or equal to " + PORT_RANGE_MAX);
            isTrue(numRequested > 0, "'numRequested' must be greater than 0");
            isTrue((maxPort - minPort) >= numRequested,
                    "'numRequested' must not be greater than 'maxPort' - 'minPort'");

            final SortedSet<Integer> availablePorts = new TreeSet<Integer>();
            int attemptCount = 0;
            while ((++attemptCount <= numRequested + 100) && (availablePorts.size() < numRequested)) {
                availablePorts.add(findAvailablePort(minPort, maxPort));
            }

            if (availablePorts.size() != numRequested) {
                throw new IllegalStateException(String.format(
                        "Could not find %d available %s ports in the range [%d, %d]", numRequested, name(), minPort,
                        maxPort));
            }

            return availablePorts;
        }
    }

    private static void isTrue(boolean expression, String message) {
        if (!expression) {
            throw new IllegalArgumentException(message);
        }
    }
}
