/*
 * Copyright 2002-2023 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
 *
 *      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 org.springframework.integration.stream;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.Reader;
import java.io.UnsupportedEncodingException;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

import org.springframework.context.ApplicationEventPublisher;
import org.springframework.context.ApplicationEventPublisherAware;
import org.springframework.integration.endpoint.AbstractMessageSource;
import org.springframework.messaging.MessagingException;
import org.springframework.util.Assert;

/**
 * A pollable source for {@link Reader Readers}.
 *
 * @author Mark Fisher
 * @author Gary Russell
 * @author Artem Bilan
 * @author Christian Tzolov
 */
public class CharacterStreamReadingMessageSource extends AbstractMessageSource<String>
		implements ApplicationEventPublisherAware {

	private final Lock lock = new ReentrantLock();

	private final BufferedReader reader;

	private final boolean blockToDetectEOF;

	private ApplicationEventPublisher applicationEventPublisher;

	/**
	 * Construct an instance with the provider reader.
	 * {@link #receive()} will return {@code null} when the reader is not ready.
	 * @param reader the reader.
	 */
	public CharacterStreamReadingMessageSource(Reader reader) {
		this(reader, -1, false);
	}

	/**
	 * Construct an instance with the provider reader and buffer size.
	 * {@link #receive()} will return {@code null} when the reader is not ready.
	 * @param reader the reader.
	 * @param bufferSize the buffer size.
	 */
	public CharacterStreamReadingMessageSource(Reader reader, int bufferSize) {
		this(reader, bufferSize, false);
	}

	/**
	 * Construct an instance with the provided reader and buffer size.
	 * When {@code blockToDetectEOF} is {@code false},
	 * {@link #receive()} will return {@code null} when the reader is not ready.
	 * When it is {@code true}, the thread will block until data is available; when the
	 * underlying stream is closed, a {@link StreamClosedEvent} is published to inform
	 * the application via an {@link org.springframework.context.ApplicationListener}.
	 * This can be useful, for example, when piping stdin
	 * <pre class="code">
	 *     cat foo.txt | java -jar my.jar
	 * </pre>
	 * or
	 * <pre class="code">
	 *     java -jar my.jar &lt; foo.txt
	 * </pre>
	 * @param reader the reader.
	 * @param bufferSize the buffer size; if negative use the default in
	 * {@link BufferedReader}.
	 * @param blockToDetectEOF true to block the thread until data is available and
	 * publish a {@link StreamClosedEvent} at EOF.
	 * @since 5.0
	 */
	public CharacterStreamReadingMessageSource(Reader reader, int bufferSize, boolean blockToDetectEOF) {
		Assert.notNull(reader, "reader must not be null");
		if (reader instanceof BufferedReader) {
			this.reader = (BufferedReader) reader;
		}
		else if (bufferSize > 0) {
			this.reader = new BufferedReader(reader, bufferSize);
		}
		else {
			this.reader = new BufferedReader(reader);
		}
		this.blockToDetectEOF = blockToDetectEOF;
	}

	@Override
	public void setApplicationEventPublisher(ApplicationEventPublisher applicationEventPublisher) {
		this.applicationEventPublisher = applicationEventPublisher;
	}

	@Override
	public String getComponentType() {
		return "stream:stdin-channel-adapter(character)";
	}

	@Override
	public String doReceive() {
		try {
			this.lock.lock();
			try {
				if (!this.blockToDetectEOF && !this.reader.ready()) {
					return null;
				}
				String line = this.reader.readLine();
				if (line == null && this.applicationEventPublisher != null) {
					this.applicationEventPublisher.publishEvent(new StreamClosedEvent(this));
				}
				return line;
			}
			finally {
				this.lock.unlock();
			}
		}
		catch (IOException e) {
			throw new MessagingException("IO failure occurred in adapter", e);
		}
	}


	/**
	 * Create a source that reads from {@link System#in}. EOF will not be detected.
	 * @return the stream.
	 */
	public static CharacterStreamReadingMessageSource stdin() {
		return new CharacterStreamReadingMessageSource(new InputStreamReader(System.in));
	}

	/**
	 * Create a source that reads from {@link System#in}. EOF will not be detected.
	 * @param charsetName the charset to use when converting bytes to String.
	 * @return the stream.
	 */
	public static CharacterStreamReadingMessageSource stdin(String charsetName) {
		try {
			return new CharacterStreamReadingMessageSource(new InputStreamReader(System.in, charsetName));
		}
		catch (UnsupportedEncodingException e) {
			throw new IllegalArgumentException("unsupported encoding: " + charsetName, e);
		}
	}

	/**
	 * Create a source that reads from {@link System#in}. EOF will be detected and the application
	 * context closed.
	 * @return the stream.
	 * @since 5.0
	 * @see CharacterStreamReadingMessageSource#CharacterStreamReadingMessageSource(Reader, int, boolean)
	 */
	public static CharacterStreamReadingMessageSource stdinPipe() {
		return new CharacterStreamReadingMessageSource(new InputStreamReader(System.in), -1, true);
	}

	/**
	 * Create a source that reads from {@link System#in}. EOF will be detected and the application
	 * context closed.
	 * @param charsetName the charset to use when converting bytes to String.
	 * @return the stream.
	 * @since 5.0
	 * @see CharacterStreamReadingMessageSource#CharacterStreamReadingMessageSource(Reader, int, boolean)
	 */
	public static CharacterStreamReadingMessageSource stdinPipe(String charsetName) {
		try {
			return new CharacterStreamReadingMessageSource(new InputStreamReader(System.in, charsetName), -1, true);
		}
		catch (UnsupportedEncodingException e) {
			throw new IllegalArgumentException("unsupported encoding: " + charsetName, e);
		}
	}

}
