/*
 * 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.BufferedReader;
import java.io.IOException;
import java.io.Reader;
import java.io.Writer;
import java.nio.charset.Charset;
import java.util.Iterator;
import java.util.List;
import java.util.regex.Pattern;

import javax.annotation.Nullable;

import com.google.common.annotations.Beta;
import com.google.common.base.Ascii;
import com.google.common.base.Splitter;
import com.google.common.collect.AbstractIterator;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.Lists;

/**
 * A readable source of characters, such as a text file. Unlike a
 * {@link Reader}, a {@code CharSource} is not an open, stateful stream of
 * characters that can be read and closed. Instead, it is an immutable
 * <i>supplier</i> of {@code Reader} instances.
 *
 * <p>
 * {@code CharSource} provides two kinds of methods:
 * <ul>
 * <li><b>Methods that return a reader:</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 reader is closed.
 * <li><b>Convenience methods:</b> These are implementations of common
 * operations that are typically implemented by opening a reader using one of
 * the methods in the first category, doing something and finally closing the
 * reader that was opened.
 * </ul>
 *
 * <p>
 * Several methods in this class, such as {@link #readLines()}, break the
 * contents of the source into lines. Like {@link BufferedReader}, these methods
 * break lines on any of {@code \n}, {@code \r} or {@code \r\n}, do not include
 * the line separator in each line and do not consider there to be an empty line
 * at the end if the contents are terminated with a line separator.
 *
 * <p>
 * Any {@link ByteSource} containing text encoded with a specific
 * {@linkplain Charset character encoding} may be viewed as a {@code CharSource}
 * using {@link ByteSource#asCharSource(Charset)}.
 *
 * @since 14.0
 * @author Colin Decker
 */
public abstract class CharSource implements InputSupplier<Reader> {

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

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

	/**
	 * Opens a new {@link BufferedReader} for reading from this source. This method
	 * should return a new, independent reader each time it is called.
	 *
	 * <p>
	 * The caller is responsible for ensuring that the returned reader is closed.
	 *
	 * @throws IOException if an I/O error occurs in the process of opening the
	 *                     reader
	 */
	public BufferedReader openBufferedStream() throws IOException {
		Reader reader = openStream();
		return (reader instanceof BufferedReader) ? (BufferedReader) reader : new BufferedReader(reader);
	}

	/**
	 * Appends the contents of this source to the given {@link Appendable} (such as
	 * a {@link Writer}). Does not close {@code appendable} if it is
	 * {@code Closeable}.
	 *
	 * @throws IOException if an I/O error occurs in the process of reading from
	 *                     this source or writing to {@code appendable}
	 */
	public long copyTo(Appendable appendable) throws IOException {
		checkNotNull(appendable);

		Closer closer = Closer.create();
		try {
			Reader reader = closer.register(openStream());
			return CharStreams.copy(reader, appendable);
		} catch (Throwable e) {
			throw closer.rethrow(e);
		} finally {
			closer.close();
		}
	}

	/**
	 * Copies the contents of this source to the given sink.
	 *
	 * @throws IOException if an I/O error occurs in the process of reading from
	 *                     this source or writing to {@code sink}
	 */
	public long copyTo(CharSink sink) throws IOException {
		checkNotNull(sink);

		Closer closer = Closer.create();
		try {
			Reader reader = closer.register(openStream());
			Writer writer = closer.register(sink.openStream());
			return CharStreams.copy(reader, writer);
		} catch (Throwable e) {
			throw closer.rethrow(e);
		} finally {
			closer.close();
		}
	}

	/**
	 * Reads the contents of this source as a string.
	 *
	 * @throws IOException if an I/O error occurs in the process of reading from
	 *                     this source
	 */
	public String read() throws IOException {
		Closer closer = Closer.create();
		try {
			Reader reader = closer.register(openStream());
			return CharStreams.toString(reader);
		} catch (Throwable e) {
			throw closer.rethrow(e);
		} finally {
			closer.close();
		}
	}

	/**
	 * Reads the first link of this source as a string. Returns {@code null} if this
	 * source is empty.
	 *
	 * <p>
	 * Like {@link BufferedReader}, this method breaks lines on any of {@code \n},
	 * {@code \r} or {@code \r\n}, does not include the line separator in the
	 * returned line and does not consider there to be an extra empty line at the
	 * end if the content is terminated with a line separator.
	 *
	 * @throws IOException if an I/O error occurs in the process of reading from
	 *                     this source
	 */
	public @Nullable String readFirstLine() throws IOException {
		Closer closer = Closer.create();
		try {
			BufferedReader reader = closer.register(openBufferedStream());
			return reader.readLine();
		} catch (Throwable e) {
			throw closer.rethrow(e);
		} finally {
			closer.close();
		}
	}

	/**
	 * Reads all the lines of this source as a list of strings. The returned list
	 * will be empty if this source is empty.
	 *
	 * <p>
	 * Like {@link BufferedReader}, this method breaks lines on any of {@code \n},
	 * {@code \r} or {@code \r\n}, does not include the line separator in the
	 * returned lines and does not consider there to be an extra empty line at the
	 * end if the content is terminated with a line separator.
	 *
	 * @throws IOException if an I/O error occurs in the process of reading from
	 *                     this source
	 */
	public ImmutableList<String> readLines() throws IOException {
		Closer closer = Closer.create();
		try {
			BufferedReader reader = closer.register(openBufferedStream());
			List<String> result = Lists.newArrayList();
			String line;
			while ((line = reader.readLine()) != null) {
				result.add(line);
			}
			return ImmutableList.copyOf(result);
		} catch (Throwable e) {
			throw closer.rethrow(e);
		} finally {
			closer.close();
		}
	}

	/**
	 * Reads lines of text from this source, processing each line as it is read
	 * using the given {@link LineProcessor processor}. Stops when all lines have
	 * been processed or the processor returns {@code false} and returns the result
	 * produced by the processor.
	 *
	 * <p>
	 * Like {@link BufferedReader}, this method breaks lines on any of {@code \n},
	 * {@code \r} or {@code \r\n}, does not include the line separator in the lines
	 * passed to the {@code processor} and does not consider there to be an extra
	 * empty line at the end if the content is terminated with a line separator.
	 *
	 * @throws IOException if an I/O error occurs in the process of reading from
	 *                     this source or if {@code processor} throws an
	 *                     {@code IOException}
	 * @since 16.0
	 */
	@Beta
	public <T> T readLines(LineProcessor<T> processor) throws IOException {
		checkNotNull(processor);

		Closer closer = Closer.create();
		try {
			Reader reader = closer.register(openStream());
			return CharStreams.readLines(reader, processor);
		} catch (Throwable e) {
			throw closer.rethrow(e);
		} finally {
			closer.close();
		}
	}

	/**
	 * Returns whether the source has zero chars. The default implementation is to
	 * open a stream and check for EOF.
	 *
	 * @throws IOException if an I/O error occurs
	 * @since 15.0
	 */
	public boolean isEmpty() throws IOException {
		Closer closer = Closer.create();
		try {
			Reader reader = closer.register(openStream());
			return reader.read() == -1;
		} catch (Throwable e) {
			throw closer.rethrow(e);
		} finally {
			closer.close();
		}
	}

	/**
	 * Concatenates multiple {@link CharSource} instances into a single source.
	 * Streams returned from the source will contain the concatenated data from the
	 * streams of the underlying sources.
	 *
	 * <p>
	 * Only one underlying stream will be open at a time. Closing the concatenated
	 * stream will close the open underlying stream.
	 *
	 * @param sources the sources to concatenate
	 * @return a {@code CharSource} containing the concatenated data
	 * @since 15.0
	 */
	public static CharSource concat(Iterable<? extends CharSource> sources) {
		return new ConcatenatedCharSource(sources);
	}

	/**
	 * Concatenates multiple {@link CharSource} instances into a single source.
	 * Streams returned from the source will contain the concatenated data from the
	 * streams of the underlying sources.
	 *
	 * <p>
	 * Only one underlying stream will be open at a time. Closing the concatenated
	 * stream will close the open underlying stream.
	 *
	 * <p>
	 * Note: The input {@code Iterator} will be copied to an {@code ImmutableList}
	 * when this method is called. This will fail if the iterator is infinite and
	 * may cause problems if the iterator eagerly fetches data for each source when
	 * iterated (rather than producing sources that only load data through their
	 * streams). Prefer using the {@link #concat(Iterable)} overload if possible.
	 *
	 * @param sources the sources to concatenate
	 * @return a {@code CharSource} containing the concatenated data
	 * @throws NullPointerException if any of {@code sources} is {@code null}
	 * @since 15.0
	 */
	public static CharSource concat(Iterator<? extends CharSource> sources) {
		return concat(ImmutableList.copyOf(sources));
	}

	/**
	 * Concatenates multiple {@link CharSource} instances into a single source.
	 * Streams returned from the source will contain the concatenated data from the
	 * streams of the underlying sources.
	 *
	 * <p>
	 * Only one underlying stream will be open at a time. Closing the concatenated
	 * stream will close the open underlying stream.
	 *
	 * @param sources the sources to concatenate
	 * @return a {@code CharSource} containing the concatenated data
	 * @throws NullPointerException if any of {@code sources} is {@code null}
	 * @since 15.0
	 */
	public static CharSource concat(CharSource... sources) {
		return concat(ImmutableList.copyOf(sources));
	}

	/**
	 * Returns a view of the given character sequence as a {@link CharSource}. The
	 * behavior of the returned {@code CharSource} and any {@code Reader} instances
	 * created by it is unspecified if the {@code charSequence} is mutated while it
	 * is being read, so don't do that.
	 *
	 * @since 15.0 (since 14.0 as {@code CharStreams.asCharSource(String)})
	 */
	public static CharSource wrap(CharSequence charSequence) {
		return new CharSequenceCharSource(charSequence);
	}

	/**
	 * Returns an immutable {@link CharSource} that contains no characters.
	 *
	 * @since 15.0
	 */
	public static CharSource empty() {
		return EmptyCharSource.INSTANCE;
	}

	private static class CharSequenceCharSource extends CharSource {

		private static final Splitter LINE_SPLITTER = Splitter.on(Pattern.compile("\r\n|\n|\r"));

		private final CharSequence seq;

		protected CharSequenceCharSource(CharSequence seq) {
			this.seq = checkNotNull(seq);
		}

		@Override
		public Reader openStream() {
			return new CharSequenceReader(seq);
		}

		@Override
		public String read() {
			return seq.toString();
		}

		@Override
		public boolean isEmpty() {
			return seq.length() == 0;
		}

		/**
		 * Returns an iterable over the lines in the string. If the string ends in a
		 * newline, a final empty string is not included to match the behavior of
		 * BufferedReader/LineReader.readLine().
		 */
		private Iterable<String> lines() {
			return new Iterable<String>() {
				@Override
				public Iterator<String> iterator() {
					return new AbstractIterator<String>() {
						Iterator<String> lines = LINE_SPLITTER.split(seq).iterator();

						@Override
						protected String computeNext() {
							if (lines.hasNext()) {
								String next = lines.next();
								// skip last line if it's empty
								if (lines.hasNext() || !next.isEmpty()) {
									return next;
								}
							}
							return endOfData();
						}
					};
				}
			};
		}

		@Override
		public String readFirstLine() {
			Iterator<String> lines = lines().iterator();
			return lines.hasNext() ? lines.next() : null;
		}

		@Override
		public ImmutableList<String> readLines() {
			return ImmutableList.copyOf(lines());
		}

		@Override
		public <T> T readLines(LineProcessor<T> processor) throws IOException {
			for (String line : lines()) {
				if (!processor.processLine(line)) {
					break;
				}
			}
			return processor.getResult();
		}

		@Override
		public String toString() {
			return "CharSource.wrap(" + Ascii.truncate(seq, 30, "...") + ")";
		}
	}

	private static final class EmptyCharSource extends CharSequenceCharSource {

		private static final EmptyCharSource INSTANCE = new EmptyCharSource();

		private EmptyCharSource() {
			super("");
		}

		@Override
		public String toString() {
			return "CharSource.empty()";
		}
	}

	private static final class ConcatenatedCharSource extends CharSource {

		private final Iterable<? extends CharSource> sources;

		ConcatenatedCharSource(Iterable<? extends CharSource> sources) {
			this.sources = checkNotNull(sources);
		}

		@Override
		public Reader openStream() throws IOException {
			return new MultiReader(sources.iterator());
		}

		@Override
		public boolean isEmpty() throws IOException {
			for (CharSource source : sources) {
				if (!source.isEmpty()) {
					return false;
				}
			}
			return true;
		}

		@Override
		public String toString() {
			return "CharSource.concat(" + sources + ")";
		}
	}
}
