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/*
 * Original Guava code is copyright (C) 2015 The Guava Authors.
 * Modifications from Guava are copyright (C) 2016 DiffPlug.
 *
 * 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.diffplug.common.io;

import java.io.IOException;
import java.io.Reader;
import java.util.Iterator;

import javax.annotation.Nullable;

import com.diffplug.common.base.Preconditions;

/**
 * A {@link Reader} that concatenates multiple readers.
 *
 * @author Bin Zhu
 * @since 1.0
 */
class MultiReader extends Reader {
	private final Iterator it;
	private Reader current;

	MultiReader(Iterator readers) throws IOException {
		this.it = readers;
		advance();
	}

	/**
	 * Closes the current reader and opens the next one, if any.
	 */
	private void advance() throws IOException {
		close();
		if (it.hasNext()) {
			current = it.next().openStream();
		}
	}

	@Override
	public int read(@Nullable char cbuf[], int off, int len) throws IOException {
		if (current == null) {
			return -1;
		}
		int result = current.read(cbuf, off, len);
		if (result == -1) {
			advance();
			return read(cbuf, off, len);
		}
		return result;
	}

	@Override
	public long skip(long n) throws IOException {
		Preconditions.checkArgument(n >= 0, "n is negative");
		if (n > 0) {
			while (current != null) {
				long result = current.skip(n);
				if (result > 0) {
					return result;
				}
				advance();
			}
		}
		return 0;
	}

	@Override
	public boolean ready() throws IOException {
		return (current != null) && current.ready();
	}

	@Override
	public void close() throws IOException {
		if (current != null) {
			try {
				current.close();
			} finally {
				current = null;
			}
		}
	}
}