/*
 * Copyright 2012 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.http.websocketx;

import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelHandler.Sharable;
import io.netty.channel.ChannelHandlerContext;
import io.netty.handler.codec.MessageToMessageEncoder;

import java.util.List;

/**
 * Encodes a {@link WebSocketFrame} into a {@link ByteBuf}.
 * <p>
 * For the detailed instruction on adding add Web Socket support to your HTTP server, take a look into the
 * <tt>WebSocketServer</tt> example located in the {@code io.netty.example.http.websocket} package.
 */
@Sharable
public class WebSocket00FrameEncoder extends MessageToMessageEncoder<WebSocketFrame> implements WebSocketFrameEncoder {
    private static final ByteBuf _0X00 = Unpooled.unreleasableBuffer(
            Unpooled.directBuffer(1, 1).writeByte(0x00)).asReadOnly();
    private static final ByteBuf _0XFF = Unpooled.unreleasableBuffer(
            Unpooled.directBuffer(1, 1).writeByte((byte) 0xFF)).asReadOnly();
    private static final ByteBuf _0XFF_0X00 = Unpooled.unreleasableBuffer(
            Unpooled.directBuffer(2, 2).writeByte((byte) 0xFF).writeByte(0x00)).asReadOnly();

    @Override
    protected void encode(ChannelHandlerContext ctx, WebSocketFrame msg, List<Object> out) throws Exception {
        if (msg instanceof TextWebSocketFrame) {
            // Text frame
            ByteBuf data = msg.content();

            out.add(_0X00.duplicate());
            out.add(data.retain());
            out.add(_0XFF.duplicate());
        } else if (msg instanceof CloseWebSocketFrame) {
            // Close frame, needs to call duplicate to allow multiple writes.
            // See https://github.com/netty/netty/issues/2768
            out.add(_0XFF_0X00.duplicate());
        } else {
            // Binary frame
            ByteBuf data = msg.content();
            int dataLen = data.readableBytes();

            ByteBuf buf = ctx.alloc().buffer(5);
            boolean release = true;
            try {
                // Encode type.
                buf.writeByte((byte) 0x80);

                // Encode length.
                int b1 = dataLen >>> 28 & 0x7F;
                int b2 = dataLen >>> 14 & 0x7F;
                int b3 = dataLen >>> 7 & 0x7F;
                int b4 = dataLen & 0x7F;
                if (b1 == 0) {
                    if (b2 == 0) {
                        if (b3 != 0) {
                            buf.writeByte(b3 | 0x80);
                        }
                        buf.writeByte(b4);
                    } else {
                        buf.writeByte(b2 | 0x80);
                        buf.writeByte(b3 | 0x80);
                        buf.writeByte(b4);
                    }
                } else {
                    buf.writeByte(b1 | 0x80);
                    buf.writeByte(b2 | 0x80);
                    buf.writeByte(b3 | 0x80);
                    buf.writeByte(b4);
                }

                // Encode binary data.
                out.add(buf);
                out.add(data.retain());
                release = false;
            } finally {
                if (release) {
                    buf.release();
                }
            }
        }
    }
}
