/*
 * Copyright 2012-2018 the original author or authors.
 *
 * 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 org.springframework.boot.devtools.tunnel.payload;

import java.io.IOException;
import java.io.InterruptedIOException;
import java.nio.ByteBuffer;
import java.nio.channels.Channels;
import java.nio.channels.ReadableByteChannel;
import java.nio.channels.WritableByteChannel;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import org.springframework.http.HttpHeaders;
import org.springframework.http.HttpInputMessage;
import org.springframework.http.HttpOutputMessage;
import org.springframework.http.MediaType;
import org.springframework.util.Assert;
import org.springframework.util.StringUtils;

/**
 * Encapsulates a payload data sent via a HTTP tunnel.
 *
 * @author Phillip Webb
 * @since 1.3.0
 */
public class HttpTunnelPayload {

        private static final String SEQ_HEADER = "x-seq";

        private static final int BUFFER_SIZE = 1024 * 100;

        protected static final char[] HEX_CHARS = "0123456789ABCDEF".toCharArray();

        private static final Log logger = LogFactory.getLog(HttpTunnelPayload.class);

        private final long sequence;

        private final ByteBuffer data;

        /**
         * Create a new {@link HttpTunnelPayload} instance.
         * @param sequence the sequence number of the payload
         * @param data the payload data
         */
        public HttpTunnelPayload(long sequence, ByteBuffer data) {
                Assert.isTrue(sequence > 0, "Sequence must be positive");
                Assert.notNull(data, "Data must not be null");
                this.sequence = sequence;
                this.data = data;
        }

        /**
         * Return the sequence number of the payload.
         * @return the sequence
         */
        public long getSequence() {
                return this.sequence;
        }

        /**
         * Assign this payload to the given {@link HttpOutputMessage}.
         * @param message the message to assign this payload to
         * @throws IOException in case of I/O errors
         */
        public void assignTo(HttpOutputMessage message) throws IOException {
                Assert.notNull(message, "Message must not be null");
                HttpHeaders headers = message.getHeaders();
                headers.setContentLength(this.data.remaining());
                headers.add(SEQ_HEADER, Long.toString(getSequence()));
                headers.setContentType(MediaType.APPLICATION_OCTET_STREAM);
                WritableByteChannel body = Channels.newChannel(message.getBody());
                while (this.data.hasRemaining()) {
                        body.write(this.data);
                }
                body.close();
        }

        /**
         * Write the content of this payload to the given target channel.
         * @param channel the channel to write to
         * @throws IOException in case of I/O errors
         */
        public void writeTo(WritableByteChannel channel) throws IOException {
                Assert.notNull(channel, "Channel must not be null");
                while (this.data.hasRemaining()) {
                        channel.write(this.data);
                }
        }

        /**
         * Return the {@link HttpTunnelPayload} for the given message or {@code null} if there
         * is no payload.
         * @param message the HTTP message
         * @return the payload or {@code null}
         * @throws IOException in case of I/O errors
         */
        public static HttpTunnelPayload get(HttpInputMessage message) throws IOException {
                long length = message.getHeaders().getContentLength();
                if (length <= 0) {
                        return null;
                }
                String seqHeader = message.getHeaders().getFirst(SEQ_HEADER);
                Assert.state(StringUtils.hasLength(seqHeader), "Missing sequence header");
                ReadableByteChannel body = Channels.newChannel(message.getBody());
                ByteBuffer payload = ByteBuffer.allocate((int) length);
                while (payload.hasRemaining()) {
                        body.read(payload);
                }
                body.close();
                payload.flip();
                return new HttpTunnelPayload(Long.valueOf(seqHeader), payload);
        }

        /**
         * Return the payload data for the given source {@link ReadableByteChannel} or null if
         * the channel timed out whilst reading.
         * @param channel the source channel
         * @return payload data or {@code null}
         * @throws IOException in case of I/O errors
         */
        public static ByteBuffer getPayloadData(ReadableByteChannel channel)
                        throws IOException {
                ByteBuffer buffer = ByteBuffer.allocate(BUFFER_SIZE);
                try {
                        int amountRead = channel.read(buffer);
                        Assert.state(amountRead != -1, "Target server connection closed");
                        buffer.flip();
                        return buffer;
                }
                catch (InterruptedIOException ex) {
                        return null;
                }
        }

        /**
         * Log incoming payload information at trace level to aid diagnostics.
         */
        public void logIncoming() {
                log("< ");
        }

        /**
         * Log incoming payload information at trace level to aid diagnostics.
         */
        public void logOutgoing() {
                log("> ");
        }

        private void log(String prefix) {
                if (logger.isTraceEnabled()) {
                        logger.trace(prefix + toHexString());
                }
        }

        /**
         * Return the payload as a hexadecimal string.
         * @return the payload as a hex string
         */
        public String toHexString() {
                byte[] bytes = this.data.array();
                char[] hex = new char[this.data.remaining() * 2];
                for (int i = this.data.position(); i < this.data.remaining(); i++) {
                        int b = bytes[i] & 0xFF;
                        hex[i * 2] = HEX_CHARS[b >>> 4];
                        hex[i * 2 + 1] = HEX_CHARS[b & 0x0F];
                }
                return new String(hex);
        }

}