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package jdk.internal.net.http;

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;

import jdk.internal.net.http.common.Logger;
import jdk.internal.net.http.common.Utils;

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.
/**
 * 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 Logger debug =
            Utils.getDebugLogger("WindowController"::toString, Utils.DEBUG);

    
Default initial connection Flow-Control Send Window size, as per HTTP/2.
/**
     * 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. /** 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. /** 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. /** 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. /** 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. /** 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. /** 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 & 0x1) == 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 Stream.signalWindowUpdate() method to be invoke at a later time when the connection and/or stream window's have been increased. The tryAcquire method should then be invoked again to attempt to acquire the available window. /**
     * 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
                if (debug.on())
                    debug.log("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;
            if (debug.on())
                debug.log("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 Stream.signalWindowUpdate() method scheduled to run ( i.e. awake awaiters ). 
Returns:
false if, and only if, the addition of the given amount would
        cause the Send Window to exceed 2^31-1 (overflow), otherwise true/**
     * 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;
            if (debug.on())
                debug.log("Connection window size is now %d (amount added %d)",
                          size, amount);

            // 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 Stream.signalWindowUpdate() method scheduled to run ( i.e. awoken ). 
Returns:
false if, and only if, the addition of the given amount would
        cause the Send Window to exceed 2^31-1 (overflow), otherwise 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) {
                // The stream may have been cancelled.
                if (debug.on())
                    debug.log("WARNING: No entry found for streamid: %s. May be cancelled?",
                              streamid);
            } else {
                int prev = size;
                size = prev + amount;
                if (size < prev)
                    return false;
                streams.put(streamid, size);
                if (debug.on())
                    debug.log("Stream %s window size is now %s (amount added %d)",
                              streamid, size, amount);

                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.
/**
     * 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);
                    if (debug.on())
                        debug.log("Stream %s window size is now %s (adjusting amount %d)",
                                  streamid, size, adjustAmount);
                }
            }
        } finally {
            controllerLock.unlock();
        }
    }

    
Returns the Send Window size for the connection. /** 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. /** 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();
        }
    }

}