/*
 * Copyright (C) 2011 The Android Open Source Project
 *
 * 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 okhttp3.internal.http2;

import java.io.Closeable;
import java.io.IOException;
import java.util.List;
import java.util.logging.Logger;
import okio.Buffer;
import okio.BufferedSource;
import okio.ByteString;
import okio.Source;
import okio.Timeout;

import static java.util.logging.Level.FINE;
import static okhttp3.internal.Util.format;
import static okhttp3.internal.http2.Http2.CONNECTION_PREFACE;
import static okhttp3.internal.http2.Http2.FLAG_ACK;
import static okhttp3.internal.http2.Http2.FLAG_COMPRESSED;
import static okhttp3.internal.http2.Http2.FLAG_END_HEADERS;
import static okhttp3.internal.http2.Http2.FLAG_END_STREAM;
import static okhttp3.internal.http2.Http2.FLAG_PADDED;
import static okhttp3.internal.http2.Http2.FLAG_PRIORITY;
import static okhttp3.internal.http2.Http2.INITIAL_MAX_FRAME_SIZE;
import static okhttp3.internal.http2.Http2.TYPE_CONTINUATION;
import static okhttp3.internal.http2.Http2.TYPE_DATA;
import static okhttp3.internal.http2.Http2.TYPE_GOAWAY;
import static okhttp3.internal.http2.Http2.TYPE_HEADERS;
import static okhttp3.internal.http2.Http2.TYPE_PING;
import static okhttp3.internal.http2.Http2.TYPE_PRIORITY;
import static okhttp3.internal.http2.Http2.TYPE_PUSH_PROMISE;
import static okhttp3.internal.http2.Http2.TYPE_RST_STREAM;
import static okhttp3.internal.http2.Http2.TYPE_SETTINGS;
import static okhttp3.internal.http2.Http2.TYPE_WINDOW_UPDATE;
import static okhttp3.internal.http2.Http2.frameLog;
import static okhttp3.internal.http2.Http2.ioException;
import static okio.ByteString.EMPTY;

/**
 * Reads HTTP/2 transport frames.
 *
 * <p>This implementation assumes we do not send an increased {@link Settings#getMaxFrameSize frame
 * size setting} to the peer. Hence, we expect all frames to have a max length of {@link
 * Http2#INITIAL_MAX_FRAME_SIZE}.
 */
final class Http2Reader implements Closeable {
  static final Logger logger = Logger.getLogger(Http2.class.getName());

  private final BufferedSource source;
  private final ContinuationSource continuation;
  private final boolean client;

  // Visible for testing.
  final Hpack.Reader hpackReader;

  /** Creates a frame reader with max header table size of 4096. */
  Http2Reader(BufferedSource source, boolean client) {
    this.source = source;
    this.client = client;
    this.continuation = new ContinuationSource(this.source);
    this.hpackReader = new Hpack.Reader(4096, continuation);
  }

  public void readConnectionPreface(Handler handler) throws IOException {
    if (client) {
      // The client reads the initial SETTINGS frame.
      if (!nextFrame(true, handler)) {
        throw ioException("Required SETTINGS preface not received");
      }
    } else {
      // The server reads the CONNECTION_PREFACE byte string.
      ByteString connectionPreface = source.readByteString(CONNECTION_PREFACE.size());
      if (logger.isLoggable(FINE)) logger.fine(format("<< CONNECTION %s", connectionPreface.hex()));
      if (!CONNECTION_PREFACE.equals(connectionPreface)) {
        throw ioException("Expected a connection header but was %s", connectionPreface.utf8());
      }
    }
  }

  public boolean nextFrame(boolean requireSettings, Handler handler) throws IOException {
    try {
      source.require(9); // Frame header size
    } catch (IOException e) {
      return false; // This might be a normal socket close.
    }

    //  0                   1                   2                   3
    //  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    // |                 Length (24)                   |
    // +---------------+---------------+---------------+
    // |   Type (8)    |   Flags (8)   |
    // +-+-+-----------+---------------+-------------------------------+
    // |R|                 Stream Identifier (31)                      |
    // +=+=============================================================+
    // |                   Frame Payload (0...)                      ...
    // +---------------------------------------------------------------+
    int length = readMedium(source);
    if (length < 0 || length > INITIAL_MAX_FRAME_SIZE) {
      throw ioException("FRAME_SIZE_ERROR: %s", length);
    }
    byte type = (byte) (source.readByte() & 0xff);
    if (requireSettings && type != TYPE_SETTINGS) {
      throw ioException("Expected a SETTINGS frame but was %s", type);
    }
    byte flags = (byte) (source.readByte() & 0xff);
    int streamId = (source.readInt() & 0x7fffffff); // Ignore reserved bit.
    if (logger.isLoggable(FINE)) logger.fine(frameLog(true, streamId, length, type, flags));

    switch (type) {
      case TYPE_DATA:
        readData(handler, length, flags, streamId);
        break;

      case TYPE_HEADERS:
        readHeaders(handler, length, flags, streamId);
        break;

      case TYPE_PRIORITY:
        readPriority(handler, length, flags, streamId);
        break;

      case TYPE_RST_STREAM:
        readRstStream(handler, length, flags, streamId);
        break;

      case TYPE_SETTINGS:
        readSettings(handler, length, flags, streamId);
        break;

      case TYPE_PUSH_PROMISE:
        readPushPromise(handler, length, flags, streamId);
        break;

      case TYPE_PING:
        readPing(handler, length, flags, streamId);
        break;

      case TYPE_GOAWAY:
        readGoAway(handler, length, flags, streamId);
        break;

      case TYPE_WINDOW_UPDATE:
        readWindowUpdate(handler, length, flags, streamId);
        break;

      default:
        // Implementations MUST discard frames that have unknown or unsupported types.
        source.skip(length);
    }
    return true;
  }

  private void readHeaders(Handler handler, int length, byte flags, int streamId)
      throws IOException {
    if (streamId == 0) throw ioException("PROTOCOL_ERROR: TYPE_HEADERS streamId == 0");

    boolean endStream = (flags & FLAG_END_STREAM) != 0;

    short padding = (flags & FLAG_PADDED) != 0 ? (short) (source.readByte() & 0xff) : 0;

    if ((flags & FLAG_PRIORITY) != 0) {
      readPriority(handler, streamId);
      length -= 5; // account for above read.
    }

    length = lengthWithoutPadding(length, flags, padding);

    List<Header> headerBlock = readHeaderBlock(length, padding, flags, streamId);

    handler.headers(endStream, streamId, -1, headerBlock);
  }

  private List<Header> readHeaderBlock(int length, short padding, byte flags, int streamId)
      throws IOException {
    continuation.length = continuation.left = length;
    continuation.padding = padding;
    continuation.flags = flags;
    continuation.streamId = streamId;

    // TODO: Concat multi-value headers with 0x0, except COOKIE, which uses 0x3B, 0x20.
    // http://tools.ietf.org/html/draft-ietf-httpbis-http2-17#section-8.1.2.5
    hpackReader.readHeaders();
    return hpackReader.getAndResetHeaderList();
  }

  private void readData(Handler handler, int length, byte flags, int streamId)
      throws IOException {
    if (streamId == 0) throw ioException("PROTOCOL_ERROR: TYPE_DATA streamId == 0");

    // TODO: checkState open or half-closed (local) or raise STREAM_CLOSED
    boolean inFinished = (flags & FLAG_END_STREAM) != 0;
    boolean gzipped = (flags & FLAG_COMPRESSED) != 0;
    if (gzipped) {
      throw ioException("PROTOCOL_ERROR: FLAG_COMPRESSED without SETTINGS_COMPRESS_DATA");
    }

    short padding = (flags & FLAG_PADDED) != 0 ? (short) (source.readByte() & 0xff) : 0;
    length = lengthWithoutPadding(length, flags, padding);

    handler.data(inFinished, streamId, source, length);
    source.skip(padding);
  }

  private void readPriority(Handler handler, int length, byte flags, int streamId)
      throws IOException {
    if (length != 5) throw ioException("TYPE_PRIORITY length: %d != 5", length);
    if (streamId == 0) throw ioException("TYPE_PRIORITY streamId == 0");
    readPriority(handler, streamId);
  }

  private void readPriority(Handler handler, int streamId) throws IOException {
    int w1 = source.readInt();
    boolean exclusive = (w1 & 0x80000000) != 0;
    int streamDependency = (w1 & 0x7fffffff);
    int weight = (source.readByte() & 0xff) + 1;
    handler.priority(streamId, streamDependency, weight, exclusive);
  }

  private void readRstStream(Handler handler, int length, byte flags, int streamId)
      throws IOException {
    if (length != 4) throw ioException("TYPE_RST_STREAM length: %d != 4", length);
    if (streamId == 0) throw ioException("TYPE_RST_STREAM streamId == 0");
    int errorCodeInt = source.readInt();
    ErrorCode errorCode = ErrorCode.fromHttp2(errorCodeInt);
    if (errorCode == null) {
      throw ioException("TYPE_RST_STREAM unexpected error code: %d", errorCodeInt);
    }
    handler.rstStream(streamId, errorCode);
  }

  private void readSettings(Handler handler, int length, byte flags, int streamId)
      throws IOException {
    if (streamId != 0) throw ioException("TYPE_SETTINGS streamId != 0");
    if ((flags & FLAG_ACK) != 0) {
      if (length != 0) throw ioException("FRAME_SIZE_ERROR ack frame should be empty!");
      handler.ackSettings();
      return;
    }

    if (length % 6 != 0) throw ioException("TYPE_SETTINGS length %% 6 != 0: %s", length);
    Settings settings = new Settings();
    for (int i = 0; i < length; i += 6) {
      short id = source.readShort();
      int value = source.readInt();

      switch (id) {
        case 1: // SETTINGS_HEADER_TABLE_SIZE
          break;
        case 2: // SETTINGS_ENABLE_PUSH
          if (value != 0 && value != 1) {
            throw ioException("PROTOCOL_ERROR SETTINGS_ENABLE_PUSH != 0 or 1");
          }
          break;
        case 3: // SETTINGS_MAX_CONCURRENT_STREAMS
          id = 4; // Renumbered in draft 10.
          break;
        case 4: // SETTINGS_INITIAL_WINDOW_SIZE
          id = 7; // Renumbered in draft 10.
          if (value < 0) {
            throw ioException("PROTOCOL_ERROR SETTINGS_INITIAL_WINDOW_SIZE > 2^31 - 1");
          }
          break;
        case 5: // SETTINGS_MAX_FRAME_SIZE
          if (value < INITIAL_MAX_FRAME_SIZE || value > 16777215) {
            throw ioException("PROTOCOL_ERROR SETTINGS_MAX_FRAME_SIZE: %s", value);
          }
          break;
        case 6: // SETTINGS_MAX_HEADER_LIST_SIZE
          break; // Advisory only, so ignored.
        default:
          break; // Must ignore setting with unknown id.
      }
      settings.set(id, value);
    }
    handler.settings(false, settings);
  }

  private void readPushPromise(Handler handler, int length, byte flags, int streamId)
      throws IOException {
    if (streamId == 0) {
      throw ioException("PROTOCOL_ERROR: TYPE_PUSH_PROMISE streamId == 0");
    }
    short padding = (flags & FLAG_PADDED) != 0 ? (short) (source.readByte() & 0xff) : 0;
    int promisedStreamId = source.readInt() & 0x7fffffff;
    length -= 4; // account for above read.
    length = lengthWithoutPadding(length, flags, padding);
    List<Header> headerBlock = readHeaderBlock(length, padding, flags, streamId);
    handler.pushPromise(streamId, promisedStreamId, headerBlock);
  }

  private void readPing(Handler handler, int length, byte flags, int streamId)
      throws IOException {
    if (length != 8) throw ioException("TYPE_PING length != 8: %s", length);
    if (streamId != 0) throw ioException("TYPE_PING streamId != 0");
    int payload1 = source.readInt();
    int payload2 = source.readInt();
    boolean ack = (flags & FLAG_ACK) != 0;
    handler.ping(ack, payload1, payload2);
  }

  private void readGoAway(Handler handler, int length, byte flags, int streamId)
      throws IOException {
    if (length < 8) throw ioException("TYPE_GOAWAY length < 8: %s", length);
    if (streamId != 0) throw ioException("TYPE_GOAWAY streamId != 0");
    int lastStreamId = source.readInt();
    int errorCodeInt = source.readInt();
    int opaqueDataLength = length - 8;
    ErrorCode errorCode = ErrorCode.fromHttp2(errorCodeInt);
    if (errorCode == null) {
      throw ioException("TYPE_GOAWAY unexpected error code: %d", errorCodeInt);
    }
    ByteString debugData = EMPTY;
    if (opaqueDataLength > 0) { // Must read debug data in order to not corrupt the connection.
      debugData = source.readByteString(opaqueDataLength);
    }
    handler.goAway(lastStreamId, errorCode, debugData);
  }

  private void readWindowUpdate(Handler handler, int length, byte flags, int streamId)
      throws IOException {
    if (length != 4) throw ioException("TYPE_WINDOW_UPDATE length !=4: %s", length);
    long increment = (source.readInt() & 0x7fffffffL);
    if (increment == 0) throw ioException("windowSizeIncrement was 0", increment);
    handler.windowUpdate(streamId, increment);
  }

  @Override public void close() throws IOException {
    source.close();
  }

  /**
   * Decompression of the header block occurs above the framing layer. This class lazily reads
   * continuation frames as they are needed by {@link Hpack.Reader#readHeaders()}.
   */
  static final class ContinuationSource implements Source {
    private final BufferedSource source;

    int length;
    byte flags;
    int streamId;

    int left;
    short padding;

    ContinuationSource(BufferedSource source) {
      this.source = source;
    }

    @Override public long read(Buffer sink, long byteCount) throws IOException {
      while (left == 0) {
        source.skip(padding);
        padding = 0;
        if ((flags & FLAG_END_HEADERS) != 0) return -1;
        readContinuationHeader();
        // TODO: test case for empty continuation header?
      }

      long read = source.read(sink, Math.min(byteCount, left));
      if (read == -1) return -1;
      left -= read;
      return read;
    }

    @Override public Timeout timeout() {
      return source.timeout();
    }

    @Override public void close() throws IOException {
    }

    private void readContinuationHeader() throws IOException {
      int previousStreamId = streamId;

      length = left = readMedium(source);
      byte type = (byte) (source.readByte() & 0xff);
      flags = (byte) (source.readByte() & 0xff);
      if (logger.isLoggable(FINE)) logger.fine(frameLog(true, streamId, length, type, flags));
      streamId = (source.readInt() & 0x7fffffff);
      if (type != TYPE_CONTINUATION) throw ioException("%s != TYPE_CONTINUATION", type);
      if (streamId != previousStreamId) throw ioException("TYPE_CONTINUATION streamId changed");
    }
  }

  static int readMedium(BufferedSource source) throws IOException {
    return (source.readByte() & 0xff) << 16
        | (source.readByte() & 0xff) << 8
        | (source.readByte() & 0xff);
  }

  static int lengthWithoutPadding(int length, byte flags, short padding)
      throws IOException {
    if ((flags & FLAG_PADDED) != 0) length--; // Account for reading the padding length.
    if (padding > length) {
      throw ioException("PROTOCOL_ERROR padding %s > remaining length %s", padding, length);
    }
    return (short) (length - padding);
  }

  interface Handler {
    void data(boolean inFinished, int streamId, BufferedSource source, int length)
        throws IOException;

    /**
     * Create or update incoming headers, creating the corresponding streams if necessary. Frames
     * that trigger this are HEADERS and PUSH_PROMISE.
     *
     * @param inFinished true if the sender will not send further frames.
     * @param streamId the stream owning these headers.
     * @param associatedStreamId the stream that triggered the sender to create this stream.
     */
    void headers(boolean inFinished, int streamId, int associatedStreamId,
        List<Header> headerBlock);

    void rstStream(int streamId, ErrorCode errorCode);

    void settings(boolean clearPrevious, Settings settings);

    /** HTTP/2 only. */
    void ackSettings();

    /**
     * Read a connection-level ping from the peer. {@code ack} indicates this is a reply. The data
     * in {@code payload1} and {@code payload2} opaque binary, and there are no rules on the
     * content.
     */
    void ping(boolean ack, int payload1, int payload2);

    /**
     * The peer tells us to stop creating streams.  It is safe to replay streams with {@code ID >
     * lastGoodStreamId} on a new connection.  In- flight streams with {@code ID <=
     * lastGoodStreamId} can only be replayed on a new connection if they are idempotent.
     *
     * @param lastGoodStreamId the last stream ID the peer processed before sending this message. If
     * {@code lastGoodStreamId} is zero, the peer processed no frames.
     * @param errorCode reason for closing the connection.
     * @param debugData only valid for HTTP/2; opaque debug data to send.
     */
    void goAway(int lastGoodStreamId, ErrorCode errorCode, ByteString debugData);

    /**
     * Notifies that an additional {@code windowSizeIncrement} bytes can be sent on {@code
     * streamId}, or the connection if {@code streamId} is zero.
     */
    void windowUpdate(int streamId, long windowSizeIncrement);

    /**
     * Called when reading a headers or priority frame. This may be used to change the stream's
     * weight from the default (16) to a new value.
     *
     * @param streamId stream which has a priority change.
     * @param streamDependency the stream ID this stream is dependent on.
     * @param weight relative proportion of priority in [1..256].
     * @param exclusive inserts this stream ID as the sole child of {@code streamDependency}.
     */
    void priority(int streamId, int streamDependency, int weight, boolean exclusive);

    /**
     * HTTP/2 only. Receive a push promise header block. <p> A push promise contains all the headers
     * that pertain to a server-initiated request, and a {@code promisedStreamId} to which response
     * frames will be delivered. Push promise frames are sent as a part of the response to {@code
     * streamId}.
     *
     * @param streamId client-initiated stream ID.  Must be an odd number.
     * @param promisedStreamId server-initiated stream ID.  Must be an even number.
     * @param requestHeaders minimally includes {@code :method}, {@code :scheme}, {@code
     * :authority}, and (@code :path}.
     */
    void pushPromise(int streamId, int promisedStreamId, List<Header> requestHeaders)
        throws IOException;

    /**
     * HTTP/2 only. Expresses that resources for the connection or a client- initiated stream are
     * available from a different network location or protocol configuration.
     *
     * <p>See <a href="http://tools.ietf.org/html/draft-ietf-httpbis-alt-svc-01">alt-svc</a>
     *
     * @param streamId when a client-initiated stream ID (odd number), the origin of this alternate
     * service is the origin of the stream. When zero, the origin is specified in the {@code origin}
     * parameter.
     * @param origin when present, the <a href="http://tools.ietf.org/html/rfc6454">origin</a> is
     * typically represented as a combination of scheme, host and port. When empty, the origin is
     * that of the {@code streamId}.
     * @param protocol an ALPN protocol, such as {@code h2}.
     * @param host an IP address or hostname.
     * @param port the IP port associated with the service.
     * @param maxAge time in seconds that this alternative is considered fresh.
     */
    void alternateService(int streamId, String origin, ByteString protocol, String host, int port,
        long maxAge);
  }
}
