/*
    * Copyright 2014 The Netty Project
    *
    * The Netty Project 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:
    *
    * https://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 io.netty.handler.codec.http2;
  
  import io.netty.buffer.ByteBuf;
  import io.netty.util.concurrent.Future;
  import io.netty.util.concurrent.Promise;
  import io.netty.util.internal.UnstableApi;
  
  /**
   * Manager for the state of an HTTP/2 connection with the remote end-point.
   */
  @UnstableApi
  public interface Http2Connection {
      /**
       * Listener for life-cycle events for streams in this connection.
       */
      interface Listener {
          /**
           * Notifies the listener that the given stream was added to the connection. This stream may
           * not yet be active (i.e. {@code OPEN} or {@code HALF CLOSED}).
           * <p>
           * If a {@link RuntimeException} is thrown it will be logged and <strong>not propagated</strong>.
           * Throwing from this method is not supported and is considered a programming error.
           */
          void onStreamAdded(Http2Stream stream);
  
          /**
           * Notifies the listener that the given stream was made active (i.e. {@code OPEN} or {@code HALF CLOSED}).
           * <p>
           * If a {@link RuntimeException} is thrown it will be logged and <strong>not propagated</strong>.
           * Throwing from this method is not supported and is considered a programming error.
           */
          void onStreamActive(Http2Stream stream);
  
          /**
           * Notifies the listener that the given stream has transitioned from {@code OPEN} to {@code HALF CLOSED}.
           * This method will <strong>not</strong> be called until a state transition occurs from when
           * {@link #onStreamActive(Http2Stream)} was called.
           * The stream can be inspected to determine which side is {@code HALF CLOSED}.
           * <p>
           * If a {@link RuntimeException} is thrown it will be logged and <strong>not propagated</strong>.
           * Throwing from this method is not supported and is considered a programming error.
           */
          void onStreamHalfClosed(Http2Stream stream);
  
          /**
           * Notifies the listener that the given stream is now {@code CLOSED} in both directions and will no longer
           * be accessible via {@link #forEachActiveStream(Http2StreamVisitor)}.
           * <p>
           * If a {@link RuntimeException} is thrown it will be logged and <strong>not propagated</strong>.
           * Throwing from this method is not supported and is considered a programming error.
           */
          void onStreamClosed(Http2Stream stream);
  
          /**
           * Notifies the listener that the given stream has now been removed from the connection and
           * will no longer be returned via {@link Http2Connection#stream(int)}. The connection may
           * maintain inactive streams for some time before removing them.
           * <p>
           * If a {@link RuntimeException} is thrown it will be logged and <strong>not propagated</strong>.
           * Throwing from this method is not supported and is considered a programming error.
           */
          void onStreamRemoved(Http2Stream stream);
  
          /**
           * Called when a {@code GOAWAY} frame was sent for the connection.
           * <p>
           * If a {@link RuntimeException} is thrown it will be logged and <strong>not propagated</strong>.
           * Throwing from this method is not supported and is considered a programming error.
           * @param lastStreamId the last known stream of the remote endpoint.
           * @param errorCode    the error code, if abnormal closure.
           * @param debugData    application-defined debug data.
           */
          void onGoAwaySent(int lastStreamId, long errorCode, ByteBuf debugData);
  
          /**
           * Called when a {@code GOAWAY} was received from the remote endpoint. This event handler duplicates {@link
           * Http2FrameListener#onGoAwayRead(io.netty.channel.ChannelHandlerContext, int, long, ByteBuf)}
           * but is added here in order to simplify application logic for handling {@code GOAWAY} in a uniform way. An
           * application should generally not handle both events, but if it does this method is called second, after
           * notifying the {@link Http2FrameListener}.
           * <p>
           * If a {@link RuntimeException} is thrown it will be logged and <strong>not propagated</strong>.
           * Throwing from this method is not supported and is considered a programming error.
           * @param lastStreamId the last known stream of the remote endpoint.
          * @param errorCode    the error code, if abnormal closure.
          * @param debugData    application-defined debug data.
          */
         void onGoAwayReceived(int lastStreamId, long errorCode, ByteBuf debugData);
     }
 
     /**
      * A view of the connection from one endpoint (local or remote).
      */
     interface Endpoint<F extends Http2FlowController> {
         /**
          * Increment and get the next generated stream id this endpoint. If negative, the stream IDs are
          * exhausted for this endpoint an no further streams may be created.
          */
         int incrementAndGetNextStreamId();
 
         /**
          * Indicates whether the given streamId is from the set of IDs used by this endpoint to
          * create new streams.
          */
         boolean isValidStreamId(int streamId);
 
         /**
          * Indicates whether or not this endpoint may have created the given stream. This is {@code true} if
          * {@link #isValidStreamId(int)} and {@code streamId} <= {@link #lastStreamCreated()}.
          */
         boolean mayHaveCreatedStream(int streamId);
 
         /**
          * Indicates whether or not this endpoint created the given stream.
          */
         boolean created(Http2Stream stream);
 
         /**
          * Indicates whether or a stream created by this endpoint can be opened without violating
          * {@link #maxActiveStreams()}.
          */
         boolean canOpenStream();
 
         /**
          * Creates a stream initiated by this endpoint. This could fail for the following reasons:
          * <ul>
          * <li>The requested stream ID is not the next sequential ID for this endpoint.</li>
          * <li>The stream already exists.</li>
          * <li>{@link #canOpenStream()} is {@code false}.</li>
          * <li>The connection is marked as going away.</li>
          * </ul>
          * <p>
          * The initial state of the stream will be immediately set before notifying {@link Listener}s. The state
          * transition is sensitive to {@code halfClosed} and is defined by {@link Http2Stream#open(boolean)}.
          * @param streamId The ID of the stream
          * @param halfClosed see {@link Http2Stream#open(boolean)}.
          * @see Http2Stream#open(boolean)
          */
         Http2Stream createStream(int streamId, boolean halfClosed) throws Http2Exception;
 
         /**
          * Creates a push stream in the reserved state for this endpoint and notifies all listeners.
          * This could fail for the following reasons:
          * <ul>
          * <li>Server push is not allowed to the opposite endpoint.</li>
          * <li>The requested stream ID is not the next sequential stream ID for this endpoint.</li>
          * <li>The number of concurrent streams is above the allowed threshold for this endpoint.</li>
          * <li>The connection is marked as going away.</li>
          * <li>The parent stream ID does not exist or is not {@code OPEN} from the side sending the push
          * promise.</li>
          * <li>Could not set a valid priority for the new stream.</li>
          * </ul>
          *
          * @param streamId the ID of the push stream
          * @param parent the parent stream used to initiate the push stream.
          */
         Http2Stream reservePushStream(int streamId, Http2Stream parent) throws Http2Exception;
 
         /**
          * Indicates whether or not this endpoint is the server-side of the connection.
          */
         boolean isServer();
 
         /**
          * This is the <a href="https://tools.ietf.org/html/rfc7540#section-6.5.2">SETTINGS_ENABLE_PUSH</a> value sent
          * from the opposite endpoint. This method should only be called by Netty (not users) as a result of a
          * receiving a {@code SETTINGS} frame.
          */
         void allowPushTo(boolean allow);
 
         /**
          * This is the <a href="https://tools.ietf.org/html/rfc7540#section-6.5.2">SETTINGS_ENABLE_PUSH</a> value sent
          * from the opposite endpoint. The initial value must be {@code true} for the client endpoint and always false
          * for a server endpoint.
          */
         boolean allowPushTo();
 
         /**
          * Gets the number of active streams (i.e. {@code OPEN} or {@code HALF CLOSED}) that were created by this
          * endpoint.
          */
         int numActiveStreams();
 
         /**
          * Gets the maximum number of streams (created by this endpoint) that are allowed to be active at
          * the same time. This is the
          * <a href="https://tools.ietf.org/html/rfc7540#section-6.5.2">SETTINGS_MAX_CONCURRENT_STREAMS</a>
          * value sent from the opposite endpoint to restrict stream creation by this endpoint.
          * <p>
          * The default value returned by this method must be "unlimited".
          */
         int maxActiveStreams();
 
         /**
          * Sets the limit for {@code SETTINGS_MAX_CONCURRENT_STREAMS}.
          * @param maxActiveStreams The maximum number of streams (created by this endpoint) that are allowed to be
          * active at once. This is the
          * <a href="https://tools.ietf.org/html/rfc7540#section-6.5.2">SETTINGS_MAX_CONCURRENT_STREAMS</a> value sent
          * from the opposite endpoint to restrict stream creation by this endpoint.
          */
         void maxActiveStreams(int maxActiveStreams);
 
         /**
          * Gets the ID of the stream last successfully created by this endpoint.
          */
         int lastStreamCreated();
 
         /**
          * If a GOAWAY was received for this endpoint, this will be the last stream ID from the
          * GOAWAY frame. Otherwise, this will be {@code -1}.
          */
         int lastStreamKnownByPeer();
 
         /**
          * Gets the flow controller for this endpoint.
          */
         F flowController();
 
         /**
          * Sets the flow controller for this endpoint.
          */
         void flowController(F flowController);
 
         /**
          * Gets the {@link Endpoint} opposite this one.
          */
         Endpoint<? extends Http2FlowController> opposite();
     }
 
     /**
      * A key to be used for associating application-defined properties with streams within this connection.
      */
     interface PropertyKey {
     }
 
     /**
      * Close this connection. No more new streams can be created after this point and
      * all streams that exists (active or otherwise) will be closed and removed.
      * <p>Note if iterating active streams via {@link #forEachActiveStream(Http2StreamVisitor)} and an exception is
      * thrown it is necessary to call this method again to ensure the close completes.
      * @param promise Will be completed when all streams have been removed, and listeners have been notified.
      * @return A future that will be completed when all streams have been removed, and listeners have been notified.
      */
     Future<Void> close(Promise<Void> promise);
 
     /**
      * Creates a new key that is unique within this {@link Http2Connection}.
      */
     PropertyKey newKey();
 
     /**
      * Adds a listener of stream life-cycle events.
      */
     void addListener(Listener listener);
 
     /**
      * Removes a listener of stream life-cycle events. If the same listener was added multiple times
      * then only the first occurrence gets removed.
      */
     void removeListener(Listener listener);
 
     /**
      * Gets the stream if it exists. If not, returns {@code null}.
      */
     Http2Stream stream(int streamId);
 
     /**
      * Indicates whether or not the given stream may have existed within this connection. This is a short form
      * for calling {@link Endpoint#mayHaveCreatedStream(int)} on both endpoints.
      */
     boolean streamMayHaveExisted(int streamId);
 
     /**
      * Gets the stream object representing the connection, itself (i.e. stream zero). This object
      * always exists.
      */
     Http2Stream connectionStream();
 
     /**
      * Gets the number of streams that are actively in use (i.e. {@code OPEN} or {@code HALF CLOSED}).
      */
     int numActiveStreams();
 
     /**
      * Provide a means of iterating over the collection of active streams.
      *
      * @param visitor The visitor which will visit each active stream.
      * @return The stream before iteration stopped or {@code null} if iteration went past the end.
      */
     Http2Stream forEachActiveStream(Http2StreamVisitor visitor) throws Http2Exception;
 
     /**
      * Indicates whether or not the local endpoint for this connection is the server.
      */
     boolean isServer();
 
     /**
      * Gets a view of this connection from the local {@link Endpoint}.
      */
     Endpoint<Http2LocalFlowController> local();
 
     /**
      * Gets a view of this connection from the remote {@link Endpoint}.
      */
     Endpoint<Http2RemoteFlowController> remote();
 
     /**
      * Indicates whether or not a {@code GOAWAY} was received from the remote endpoint.
      */
     boolean goAwayReceived();
 
     /**
      * Indicates that a {@code GOAWAY} was received from the remote endpoint and sets the last known stream.
      * @param lastKnownStream The Last-Stream-ID in the
      * <a href="https://tools.ietf.org/html/rfc7540#section-6.8">GOAWAY</a> frame.
      * @param errorCode the Error Code in the
      * <a href="https://tools.ietf.org/html/rfc7540#section-6.8">GOAWAY</a> frame.
      * @param message The Additional Debug Data in the
      * <a href="https://tools.ietf.org/html/rfc7540#section-6.8">GOAWAY</a> frame. Note that reference count ownership
      * belongs to the caller (ownership is not transferred to this method).
      */
     void goAwayReceived(int lastKnownStream, long errorCode, ByteBuf message) throws Http2Exception;
 
     /**
      * Indicates whether or not a {@code GOAWAY} was sent to the remote endpoint.
      */
     boolean goAwaySent();
 
     /**
      * Updates the local state of this {@link Http2Connection} as a result of a {@code GOAWAY} to send to the remote
      * endpoint.
      * @param lastKnownStream The Last-Stream-ID in the
      * <a href="https://tools.ietf.org/html/rfc7540#section-6.8">GOAWAY</a> frame.
      * @param errorCode the Error Code in the
      * <a href="https://tools.ietf.org/html/rfc7540#section-6.8">GOAWAY</a> frame.
      * <a href="https://tools.ietf.org/html/rfc7540#section-6.8">GOAWAY</a> frame. Note that reference count ownership
      * belongs to the caller (ownership is not transferred to this method).
      * @return {@code true} if the corresponding {@code GOAWAY} frame should be sent to the remote endpoint.
      */
     boolean goAwaySent(int lastKnownStream, long errorCode, ByteBuf message) throws Http2Exception;
 }