/*
 * 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.BufferedWriter;
import java.io.IOException;
import java.io.Reader;
import java.io.Writer;
import java.nio.charset.Charset;

/**
 * A destination to which characters can be written, such as a text file. Unlike
 * a {@link Writer}, a {@code CharSink} is not an open, stateful stream that can
 * be written to and closed. Instead, it is an immutable <i>supplier</i> of
 * {@code Writer} instances.
 *
 * <p>
 * {@code CharSink} provides two kinds of methods:
 * <ul>
 * <li><b>Methods that return a writer:</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 writer is closed.
 * <li><b>Convenience methods:</b> These are implementations of common
 * operations that are typically implemented by opening a writer using one of
 * the methods in the first category, doing something and finally closing the
 * writer that was opened.
 * </ul>
 *
 * <p>
 * Any {@link ByteSink} may be viewed as a {@code CharSink} with a specific
 * {@linkplain Charset character encoding} using
 * {@link ByteSink#asCharSink(Charset)}. Characters written to the resulting
 * {@code CharSink} will written to the {@code ByteSink} as encoded bytes.
 *
 * @since 14.0
 * @author Colin Decker
 */
public abstract class CharSink implements OutputSupplier<Writer> {

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

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

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

	/**
	 * Writes the given character sequence to this sink.
	 *
	 * @throws IOException if an I/O error in the process of writing to this sink
	 */
	public void write(CharSequence charSequence) throws IOException {
		checkNotNull(charSequence);

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

	/**
	 * Writes the given lines of text to this sink with each line (including the
	 * last) terminated with the operating system's default line separator. This
	 * method is equivalent to
	 * {@code writeLines(lines, System.getProperty("line.separator"))}.
	 *
	 * @throws IOException if an I/O error occurs in the process of writing to this
	 *                     sink
	 */
	public void writeLines(Iterable<? extends CharSequence> lines) throws IOException {
		writeLines(lines, System.getProperty("line.separator"));
	}

	/**
	 * Writes the given lines of text to this sink with each line (including the
	 * last) terminated with the given line separator.
	 *
	 * @throws IOException if an I/O error occurs in the process of writing to this
	 *                     sink
	 */
	public void writeLines(Iterable<? extends CharSequence> lines, String lineSeparator) throws IOException {
		checkNotNull(lines);
		checkNotNull(lineSeparator);

		Closer closer = Closer.create();
		try {
			Writer out = closer.register(openBufferedStream());
			for (CharSequence line : lines) {
				out.append(line).append(lineSeparator);
			}
			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 text from the given {@link Readable} (such as a
	 * {@link Reader}) to this sink. Does not close {@code readable} if it is
	 * {@code Closeable}.
	 *
	 * @throws IOException if an I/O error occurs in the process of reading from
	 *                     {@code readable} or writing to this sink
	 */
	public long writeFrom(Readable readable) throws IOException {
		checkNotNull(readable);

		Closer closer = Closer.create();
		try {
			Writer out = closer.register(openStream());
			long written = CharStreams.copy(readable, 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();
		}
	}
}
