/*
    * Copyright (C) 2008 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 com.google.common.base.Preconditions;
  
  import java.io.IOException;
  import java.io.Reader;
  import java.util.Iterator;
  
  import javax.annotation.Nullable;
  
  /**
   * A {@link Reader} that concatenates multiple readers.
   *
   * @author Bin Zhu
   * @since 1.0
   */
  class MultiReader extends Reader {
    private final Iterator<? extends CharSource> it;
    private Reader current;
  
    MultiReader(Iterator<? extends CharSource> 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;
        }
      }
    }
  }