/*

 * 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

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 */

package java.net.http;

import java.io.IOException;

import java.io.UncheckedIOException;

import java.net.ProtocolException;

import java.net.http.WebSocket.Listener;

import java.nio.ByteBuffer;

import java.nio.CharBuffer;

import java.nio.channels.SelectionKey;

import java.util.Optional;

import java.util.concurrent.CompletionStage;

import java.util.concurrent.Executor;

import java.util.concurrent.atomic.AtomicBoolean;

import java.util.concurrent.atomic.AtomicLong;

import java.util.function.Supplier;

import static java.lang.System.Logger.Level.ERROR;

import static java.net.http.WSUtils.EMPTY_BYTE_BUFFER;

import static java.net.http.WSUtils.logger;

/*

 * Receives incoming data from the channel and converts it into a sequence of

 * messages, which are then passed to the listener.

 */

final class WSReceiver {

    private final Listener listener;

    private final WebSocket webSocket;

    private final Supplier<WSShared<ByteBuffer>> buffersSupplier =

            new WSSharedPool<>(() -> ByteBuffer.allocateDirect(32768), 2);

    private final RawChannel channel;

    private final RawChannel.RawEvent channelEvent;

    private final WSSignalHandler handler;

    private final AtomicLong demand = new AtomicLong();

    private final AtomicBoolean readable = new AtomicBoolean();

    private boolean started;

    private volatile boolean closed;

    private final WSFrame.Reader reader = new WSFrame.Reader();

    private final WSFrameConsumer frameConsumer;

    private WSShared<ByteBuffer> buf = WSShared.wrap(EMPTY_BYTE_BUFFER);

    private WSShared<ByteBuffer> data; // TODO: initialize with leftovers from the RawChannel

    WSReceiver(Listener listener, WebSocket webSocket, Executor executor,

               RawChannel channel) {

        this.listener = listener;

        this.webSocket = webSocket;

        this.channel = channel;

        handler = new WSSignalHandler(executor, this::react);

        channelEvent = createChannelEvent();

        this.frameConsumer = new WSFrameConsumer(new MessageConsumer());

    }

    private void react() {

        synchronized (this) {

            while (demand.get() > 0 && !closed) {

                try {

                    if (data == null) {

                        if (!getData()) {

                            break;

                        }

                    }

                    reader.readFrame(data, frameConsumer);

                    if (!data.hasRemaining()) {

                        data.dispose();

                        data = null;

                    }

                    // In case of exception we don't need to clean any state,

                    // since it's the terminal condition anyway. Nothing will be

                    // retried.

                } catch (WSProtocolException e) {

                    // Translate into ProtocolException

                    closeExceptionally(new ProtocolException().initCause(e));

                } catch (Exception e) {

                    closeExceptionally(e);

                }

            }

        }

    }

    void request(long n) {

        long newDemand = demand.accumulateAndGet(n, (p, i) -> p + i < 0 ? Long.MAX_VALUE : p + i);

        handler.signal();

        assert newDemand >= 0 : newDemand;

    }

    private boolean getData() throws IOException {

        if (!readable.get()) {

            return false;

        }

        if (!buf.hasRemaining()) {

            buf.dispose();

            buf = buffersSupplier.get();

            assert buf.hasRemaining() : buf;

        }

        int oldPosition = buf.position();

        int oldLimit = buf.limit();

        int numRead = channel.read(buf.buffer());

        if (numRead > 0) {

            data = buf.share(oldPosition, oldPosition + numRead);

            buf.select(buf.limit(), oldLimit); // Move window to the free region

            return true;

        } else if (numRead == 0) {

            readable.set(false);

            channel.registerEvent(channelEvent);

            return false;

        } else {

            assert numRead < 0 : numRead;

            throw new WSProtocolException

                    ("7.2.1.", "Stream ended before a Close frame has been received");

        }

    }

    void start() {

        synchronized (this) {

            if (started) {

                throw new IllegalStateException("Already started");

            }

            started = true;

            try {

                channel.registerEvent(channelEvent);

            } catch (IOException e) {

                throw new UncheckedIOException(e);

            }

            try {

                listener.onOpen(webSocket);

            } catch (Exception e) {

                closeExceptionally(new RuntimeException("onOpen threw an exception", e));

            }

        }

    }

    private void close() { // TODO: move to WS.java

        closed = true;

    }

    private void closeExceptionally(Throwable error) {  // TODO: move to WS.java

        close();

        try {

            listener.onError(webSocket, error);

        } catch (Exception e) {

            logger.log(ERROR, "onError threw an exception", e);

        }

    }

    private final class MessageConsumer implements WSMessageConsumer {

        @Override

        public void onText(WebSocket.MessagePart part, WSShared<CharBuffer> data) {

            decrementDemand();

            CompletionStage<?> cs;

            try {

                cs = listener.onText(webSocket, data.buffer(), part);

            } catch (Exception e) {

                closeExceptionally(new RuntimeException("onText threw an exception", e));

                return;

            }

            follow(cs, data, "onText");

        }

        @Override

        public void onBinary(WebSocket.MessagePart part, WSShared<ByteBuffer> data) {

            decrementDemand();

            CompletionStage<?> cs;

            try {

                cs = listener.onBinary(webSocket, data.buffer(), part);

            } catch (Exception e) {

                closeExceptionally(new RuntimeException("onBinary threw an exception", e));

                return;

            }

            follow(cs, data, "onBinary");

        }

        @Override

        public void onPing(WSShared<ByteBuffer> data) {

            decrementDemand();

            CompletionStage<?> cs;

            try {

                cs = listener.onPing(webSocket, data.buffer());

            } catch (Exception e) {

                closeExceptionally(new RuntimeException("onPing threw an exception", e));

                return;

            }

            follow(cs, data, "onPing");

        }

        @Override

        public void onPong(WSShared<ByteBuffer> data) {

            decrementDemand();

            CompletionStage<?> cs;

            try {

                cs = listener.onPong(webSocket, data.buffer());

            } catch (Exception e) {

                closeExceptionally(new RuntimeException("onPong threw an exception", e));

                return;

            }

            follow(cs, data, "onPong");

        }

        @Override

        public void onClose(WebSocket.CloseCode code, CharSequence reason) {

            decrementDemand();

            try {

                close();

                listener.onClose(webSocket, Optional.ofNullable(code), reason.toString());

            } catch (Exception e) {

                logger.log(ERROR, "onClose threw an exception", e);

            }

        }

    }

    private void follow(CompletionStage<?> cs, WSDisposable d, String source) {

        if (cs == null) {

            d.dispose();

        } else {

            cs.whenComplete((whatever, error) -> {

                if (error != null) {

                    String m = "CompletionStage returned by " + source + " completed exceptionally";

                    closeExceptionally(new RuntimeException(m, error));

                }

                d.dispose();

            });

        }

    }

    private void decrementDemand() {

        long newDemand = demand.decrementAndGet();

        assert newDemand >= 0 : newDemand;

    }

    private RawChannel.RawEvent createChannelEvent() {

        return new RawChannel.RawEvent() {

            @Override

            public int interestOps() {

                return SelectionKey.OP_READ;

            }

            @Override

            public void handle() {

                boolean wasNotReadable = readable.compareAndSet(false, true);

                assert wasNotReadable;

                handler.signal();

            }

            @Override

            public String toString() {

                return "Read readiness event [" + channel + "]";

            }

        };

    }

}