/*
 * Copyright 2002-2018 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.http.codec.protobuf;

import java.io.IOException;
import java.io.OutputStream;
import java.util.Collections;
import java.util.List;
import java.util.Map;
import java.util.stream.Collectors;

import com.google.protobuf.Message;
import org.reactivestreams.Publisher;
import reactor.core.publisher.Flux;
import reactor.core.publisher.Mono;

import org.springframework.core.ResolvableType;
import org.springframework.core.io.buffer.DataBuffer;
import org.springframework.core.io.buffer.DataBufferFactory;
import org.springframework.http.MediaType;
import org.springframework.http.codec.HttpMessageEncoder;
import org.springframework.lang.Nullable;
import org.springframework.util.MimeType;

/**
 * An {@code Encoder} that writes {@link com.google.protobuf.Message}s
 * using <a href="https://developers.google.com/protocol-buffers/">Google Protocol Buffers</a>.
 *
 * <p>Flux are serialized using
 * <a href="https://developers.google.com/protocol-buffers/docs/techniques?hl=en#streaming">delimited Protobuf messages</a>
 * with the size of each message specified before the message itself. Single values are
 * serialized using regular Protobuf message format (without the size prepended before the message).
 *
 * <p>To generate {@code Message} Java classes, you need to install the {@code protoc} binary.
 *
 * <p>This encoder requires Protobuf 3 or higher, and supports
 * {@code "application/x-protobuf"} and {@code "application/octet-stream"} with the official
 * {@code "com.google.protobuf:protobuf-java"} library.
 *
 * @author Sébastien Deleuze
 * @since 5.1
 * @see ProtobufDecoder
 */
public class ProtobufEncoder extends ProtobufCodecSupport implements HttpMessageEncoder<Message> {

	private static final List<MediaType> streamingMediaTypes = MIME_TYPES
			.stream()
			.map(mimeType -> new MediaType(mimeType.getType(), mimeType.getSubtype(),
					Collections.singletonMap(DELIMITED_KEY, DELIMITED_VALUE)))
			.collect(Collectors.toList());


	@Override
	public boolean canEncode(ResolvableType elementType, @Nullable MimeType mimeType) {
		return Message.class.isAssignableFrom(elementType.toClass()) && supportsMimeType(mimeType);
	}

	@Override
	public Flux<DataBuffer> encode(Publisher<? extends Message> inputStream, DataBufferFactory bufferFactory,
			ResolvableType elementType, @Nullable MimeType mimeType, @Nullable Map<String, Object> hints) {

		return Flux
				.from(inputStream)
				.map(message -> encodeMessage(message, bufferFactory, !(inputStream instanceof Mono)));
	}

	private DataBuffer encodeMessage(Message message, DataBufferFactory bufferFactory, boolean streaming) {
		DataBuffer buffer = bufferFactory.allocateBuffer();
		OutputStream outputStream = buffer.asOutputStream();
		try {
			if (streaming) {
				message.writeDelimitedTo(outputStream);
			}
			else {
				message.writeTo(outputStream);
			}
			return buffer;
		}
		catch (IOException ex) {
			throw new IllegalStateException("Unexpected I/O error while writing to data buffer", ex);
		}
	}

	@Override
	public List<MediaType> getStreamingMediaTypes() {
		return streamingMediaTypes;
	}

	@Override
	public List<MimeType> getEncodableMimeTypes() {
		return getMimeTypes();
	}

}
