/*

 * Copyright (c) 2016, 2018, Oracle and/or its affiliates. All rights reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

 * or visit www.oracle.com if you need additional information or have any

 * questions.

 */

import java.lang.System.Logger.Level;

import java.util.ArrayList;

import java.util.Map;

import java.util.HashMap;

import java.util.Iterator;

import java.util.LinkedHashMap;

import java.util.List;

import java.util.concurrent.locks.ReentrantLock;

/**

 * A Send Window Flow-Controller that is used to control outgoing Connection

 * and Stream flows, per HTTP/2 connection.

 *

 * A Http2Connection has its own unique single instance of a WindowController

 * that it shares with its Streams. Each stream must acquire the appropriate

 * amount of Send Window from the controller before sending data.

 *

 * WINDOW_UPDATE frames, both connection and stream specific, must notify the

 * controller of their increments. SETTINGS frame's INITIAL_WINDOW_SIZE must

 * notify the controller so that it can adjust the active stream's window size.

 */

final class WindowController {

    static final boolean DEBUG = Utils.DEBUG; // Revisit: temporary developer's flag

    static final System.Logger DEBUG_LOGGER =

            Utils.getDebugLogger("WindowController"::toString, DEBUG);

    /**

     * Default initial connection Flow-Control Send Window size, as per HTTP/2.

     */

    private static final int DEFAULT_INITIAL_WINDOW_SIZE = 64 * 1024 - 1;

    /** The connection Send Window size. */

    private int connectionWindowSize;

    /** A Map of the active streams, where the key is the stream id, and the

     *  value is the stream's Send Window size, which may be negative. */

    private final Map<Integer,Integer> streams = new HashMap<>();

    /** A Map of streams awaiting Send Window. The key is the stream id. The

     * value is a pair of the Stream ( representing the key's stream id ) and

     * the requested amount of send Window. */

    private final Map<Integer, Map.Entry<Stream<?>, Integer>> pending

            = new LinkedHashMap<>();

    private final ReentrantLock controllerLock = new ReentrantLock();

    /** A Controller with the default initial window size. */

    WindowController() {

        connectionWindowSize = DEFAULT_INITIAL_WINDOW_SIZE;

    }

//    /** A Controller with the given initial window size. */

//    WindowController(int initialConnectionWindowSize) {

//        connectionWindowSize = initialConnectionWindowSize;

//    }

    /** Registers the given stream with this controller. */

    void registerStream(int streamid, int initialStreamWindowSize) {

        controllerLock.lock();

        try {

            Integer old = streams.put(streamid, initialStreamWindowSize);

            if (old != null)

                throw new InternalError("Unexpected entry ["

                        + old + "] for streamid: " + streamid);

        } finally {

            controllerLock.unlock();

        }

    }

    /** Removes/De-registers the given stream with this controller. */

    void removeStream(int streamid) {

        controllerLock.lock();

        try {

            Integer old = streams.remove(streamid);

            // Odd stream numbers (client streams) should have been registered.

            // Even stream numbers (server streams - aka Push Streams) should

            // not be registered

            final boolean isClientStream = (streamid % 2) == 1;

            if (old == null && isClientStream) {

                throw new InternalError("Expected entry for streamid: " + streamid);

            } else if (old != null && !isClientStream) {

                throw new InternalError("Unexpected entry for streamid: " + streamid);

            }

        } finally {

            controllerLock.unlock();

        }

    }

    /**

     * Attempts to acquire the requested amount of Send Window for the given

     * stream.

     *

     * The actual amount of Send Window available may differ from the requested

     * amount. The actual amount, returned by this method, is the minimum of,

     * 1) the requested amount, 2) the stream's Send Window, and 3) the

     * connection's Send Window.

     *

     * A negative or zero value is returned if there's no window available.

     * When the result is negative or zero, this method arranges for the

     * given stream's {@link Stream#signalWindowUpdate()} method to be invoke at

     * a later time when the connection and/or stream window's have been

     * increased. The {@code tryAcquire} method should then be invoked again to

     * attempt to acquire the available window.

     */

    int tryAcquire(int requestAmount, int streamid, Stream<?> stream) {

        controllerLock.lock();

        try {

            Integer streamSize = streams.get(streamid);

            if (streamSize == null)

                throw new InternalError("Expected entry for streamid: "

                                        + streamid);

            int x = Math.min(requestAmount,

                             Math.min(streamSize, connectionWindowSize));

            if (x <= 0)  { // stream window size may be negative

                DEBUG_LOGGER.log(Level.DEBUG,

                        "Stream %d requesting %d but only %d available (stream: %d, connection: %d)",

                      streamid, requestAmount, Math.min(streamSize, connectionWindowSize),

                      streamSize, connectionWindowSize);

                // If there's not enough window size available, put the

                // caller in a pending list.

                pending.put(streamid, Map.entry(stream, requestAmount));

                return x;

            }

            // Remove the caller from the pending list ( if was waiting ).

            pending.remove(streamid);

            // Update window sizes and return the allocated amount to the caller.

            streamSize -= x;

            streams.put(streamid, streamSize);

            connectionWindowSize -= x;

            DEBUG_LOGGER.log(Level.DEBUG,

                  "Stream %d amount allocated %d, now %d available (stream: %d, connection: %d)",

                  streamid, x, Math.min(streamSize, connectionWindowSize),

                  streamSize, connectionWindowSize);

            return x;

        } finally {

            controllerLock.unlock();

        }

    }

    /**

     * Increases the Send Window size for the connection.

     *

     * A number of awaiting requesters, from unfulfilled tryAcquire requests,

     * may have their stream's {@link Stream#signalWindowUpdate()} method

     * scheduled to run ( i.e. awake awaiters ).

     *

     * @return false if, and only if, the addition of the given amount would

     *         cause the Send Window to exceed 2^31-1 (overflow), otherwise true

     */

    boolean increaseConnectionWindow(int amount) {

        List<Stream<?>> candidates = null;

        controllerLock.lock();

        try {

            int size = connectionWindowSize;

            size += amount;

            if (size < 0)

                return false;

            connectionWindowSize = size;

            DEBUG_LOGGER.log(Level.DEBUG, "Connection window size is now %d", size);

            // Notify waiting streams, until the new increased window size is

            // effectively exhausted.

            Iterator<Map.Entry<Integer,Map.Entry<Stream<?>,Integer>>> iter =

                    pending.entrySet().iterator();

            while (iter.hasNext() && size > 0) {

                Map.Entry<Integer,Map.Entry<Stream<?>,Integer>> item = iter.next();

                Integer streamSize = streams.get(item.getKey());

                if (streamSize == null) {

                    iter.remove();

                } else {

                    Map.Entry<Stream<?>,Integer> e = item.getValue();

                    int requestedAmount = e.getValue();

                    // only wakes up the pending streams for which there is

                    // at least 1 byte of space in both windows

                    int minAmount = 1;

                    if (size >= minAmount && streamSize >= minAmount) {

                        size -= Math.min(streamSize, requestedAmount);

                        iter.remove();

                        if (candidates == null)

                            candidates = new ArrayList<>();

                        candidates.add(e.getKey());

                    }

                }

            }

        } finally {

            controllerLock.unlock();

        }

        if (candidates != null) {

            candidates.forEach(Stream::signalWindowUpdate);

        }

        return true;

    }

    /**

     * Increases the Send Window size for the given stream.

     *

     * If the given stream is awaiting window size, from an unfulfilled

     * tryAcquire request, it will have its stream's {@link

     * Stream#signalWindowUpdate()} method scheduled to run ( i.e. awoken ).

     *

     * @return false if, and only if, the addition of the given amount would

     *         cause the Send Window to exceed 2^31-1 (overflow), otherwise true

     */

    boolean increaseStreamWindow(int amount, int streamid) {

        Stream<?> s = null;

        controllerLock.lock();

        try {

            Integer size = streams.get(streamid);

            if (size == null)

                throw new InternalError("Expected entry for streamid: " + streamid);

            size += amount;

            if (size < 0)

                return false;

            streams.put(streamid, size);

            DEBUG_LOGGER.log(Level.DEBUG,

                             "Stream %s window size is now %s", streamid, size);

            Map.Entry<Stream<?>,Integer> p = pending.get(streamid);

            if (p != null) {

                int minAmount = 1;

                // only wakes up the pending stream if there is at least

                // 1 byte of space in both windows

                if (size >= minAmount

                        && connectionWindowSize >= minAmount) {

                     pending.remove(streamid);

                     s = p.getKey();

                }

            }

        } finally {

            controllerLock.unlock();

        }

        if (s != null)

            s.signalWindowUpdate();

        return true;

    }

    /**

     * Adjusts, either increases or decreases, the active streams registered

     * with this controller.  May result in a stream's Send Window size becoming

     * negative.

     */

    void adjustActiveStreams(int adjustAmount) {

        assert adjustAmount != 0;

        controllerLock.lock();

        try {

            for (Map.Entry<Integer,Integer> entry : streams.entrySet()) {

                int streamid = entry.getKey();

                // the API only supports sending on Streams initialed by

                // the client, i.e. odd stream numbers

                if (streamid != 0 && (streamid % 2) != 0) {

                    Integer size = entry.getValue();

                    size += adjustAmount;

                    streams.put(streamid, size);

                    DEBUG_LOGGER.log(Level.DEBUG,

                        "Stream %s window size is now %s", streamid, size);

                }

            }

        } finally {

            controllerLock.unlock();

        }

    }

    /** Returns the Send Window size for the connection. */

    int connectionWindowSize() {

        controllerLock.lock();

        try {

            return connectionWindowSize;

        } finally {

            controllerLock.unlock();

        }

    }

//    /** Returns the Send Window size for the given stream. */

//    int streamWindowSize(int streamid) {

//        controllerLock.lock();

//        try {

//            Integer size = streams.get(streamid);

//            if (size == null)

//                throw new InternalError("Expected entry for streamid: " + streamid);

//            return size;

//        } finally {

//            controllerLock.unlock();

//        }

//    }

}