/*
 * Copyright (C) 2012 The Guava 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 com.google.common.io;

import static com.google.common.base.Preconditions.checkNotNull;

import java.io.BufferedOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.io.Writer;
import java.nio.charset.Charset;

/**
 * A destination to which bytes can be written, such as a file. Unlike an
 * {@link OutputStream}, a {@code ByteSink} is not an open, stateful stream that
 * can be written to and closed. Instead, it is an immutable <i>supplier</i> of
 * {@code OutputStream} instances.
 *
 * <p>
 * {@code ByteSink} provides two kinds of methods:
 * <ul>
 * <li><b>Methods that return a stream:</b> These methods should return a
 * <i>new</i>, independent instance each time they are called. The caller is
 * responsible for ensuring that the returned stream is closed.
 * <li><b>Convenience methods:</b> These are implementations of common
 * operations that are typically implemented by opening a stream using one of
 * the methods in the first category, doing something and finally closing the
 * stream or channel that was opened.
 * </ul>
 *
 * @since 14.0
 * @author Colin Decker
 */
public abstract class ByteSink implements OutputSupplier<OutputStream> {

	/**
	 * Constructor for use by subclasses.
	 */
	protected ByteSink() {
	}

	/**
	 * Returns a {@link CharSink} view of this {@code ByteSink} that writes
	 * characters to this sink as bytes encoded with the given {@link Charset
	 * charset}.
	 */
	public CharSink asCharSink(Charset charset) {
		return new AsCharSink(charset);
	}

	/**
	 * Opens a new {@link OutputStream} for writing to this sink. This method should
	 * return a new, independent stream each time it is called.
	 *
	 * <p>
	 * The caller is responsible for ensuring that the returned stream is closed.
	 *
	 * @throws IOException if an I/O error occurs in the process of opening the
	 *                     stream
	 */
	public abstract OutputStream openStream() throws IOException;

	/**
	 * This method is a temporary method provided for easing migration from
	 * suppliers to sources and sinks.
	 *
	 * @since 15.0
	 * @deprecated This method is only provided for temporary compatibility with the
	 *             {@link OutputSupplier} interface and should not be called
	 *             directly. Use {@link #openStream} instead. This method is
	 *             scheduled for removal in Guava 18.0.
	 */
	@Override
	@Deprecated
	public final OutputStream getOutput() throws IOException {
		return openStream();
	}

	/**
	 * Opens a new buffered {@link OutputStream} for writing to this sink. The
	 * returned stream is not required to be a {@link BufferedOutputStream} in order
	 * to allow implementations to simply delegate to {@link #openStream()} when the
	 * stream returned by that method does not benefit from additional buffering
	 * (for example, a {@code ByteArrayOutputStream}). This method should return a
	 * new, independent stream each time it is called.
	 *
	 * <p>
	 * The caller is responsible for ensuring that the returned stream is closed.
	 *
	 * @throws IOException if an I/O error occurs in the process of opening the
	 *                     stream
	 * @since 15.0 (in 14.0 with return type {@link BufferedOutputStream})
	 */
	public OutputStream openBufferedStream() throws IOException {
		OutputStream out = openStream();
		return (out instanceof BufferedOutputStream) ? (BufferedOutputStream) out : new BufferedOutputStream(out);
	}

	/**
	 * Writes all the given bytes to this sink.
	 *
	 * @throws IOException if an I/O occurs in the process of writing to this sink
	 */
	public void write(byte[] bytes) throws IOException {
		checkNotNull(bytes);

		Closer closer = Closer.create();
		try {
			OutputStream out = closer.register(openStream());
			out.write(bytes);
			out.flush(); // https://code.google.com/p/guava-libraries/issues/detail?id=1330
		} catch (Throwable e) {
			throw closer.rethrow(e);
		} finally {
			closer.close();
		}
	}

	/**
	 * Writes all the bytes from the given {@code InputStream} to this sink. Does
	 * not close {@code input}.
	 *
	 * @throws IOException if an I/O occurs in the process of reading from
	 *                     {@code input} or writing to this sink
	 */
	public long writeFrom(InputStream input) throws IOException {
		checkNotNull(input);

		Closer closer = Closer.create();
		try {
			OutputStream out = closer.register(openStream());
			long written = ByteStreams.copy(input, out);
			out.flush(); // https://code.google.com/p/guava-libraries/issues/detail?id=1330
			return written;
		} catch (Throwable e) {
			throw closer.rethrow(e);
		} finally {
			closer.close();
		}
	}

	/**
	 * A char sink that encodes written characters with a charset and writes
	 * resulting bytes to this byte sink.
	 */
	private final class AsCharSink extends CharSink {

		private final Charset charset;

		private AsCharSink(Charset charset) {
			this.charset = checkNotNull(charset);
		}

		@Override
		public Writer openStream() throws IOException {
			return new OutputStreamWriter(ByteSink.this.openStream(), charset);
		}

		@Override
		public String toString() {
			return ByteSink.this.toString() + ".asCharSink(" + charset + ")";
		}
	}
}
