/*
    * Copyright (C) 2007 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.IOException;
  import java.io.InputStream;
  import java.util.Iterator;
  
  import javax.annotation.Nullable;
  
  /**
   * An {@link InputStream} that concatenates multiple substreams. At most
   * one stream will be open at a time.
   *
   * @author Chris Nokleberg
   * @since 1.0
   */
  final class MultiInputStream extends InputStream {
  
    private Iterator<? extends ByteSource> it;
    private InputStream in;
  
    /**
     * Creates a new instance.
     *
     * @param it an iterator of I/O suppliers that will provide each substream
     */
    public MultiInputStream(
        Iterator<? extends ByteSource> it) throws IOException {
      this.it = checkNotNull(it);
      advance();
    }
  
    @Override public void close() throws IOException {
      if (in != null) {
        try {
          in.close();
        } finally {
          in = null;
        }
      }
    }
  
    /**
     * Closes the current input stream and opens the next one, if any.
     */
    private void advance() throws IOException {
      close();
      if (it.hasNext()) {
        in = it.next().openStream();
      }
    }
  
    @Override public int available() throws IOException {
      if (in == null) {
        return 0;
      }
      return in.available();
    }
  
    @Override public boolean markSupported() {
      return false;
    }
  
    @Override public int read() throws IOException {
      if (in == null) {
        return -1;
      }
      int result = in.read();
      if (result == -1) {
        advance();
        return read();
      }
      return result;
    }
  
    @Override public int read(@Nullable byte[] b, int off, int len) throws IOException {
      if (in == null) {
        return -1;
      }
      int result = in.read(b, off, len);
      if (result == -1) {
        advance();
       return read(b, off, len);
     }
     return result;
   }
 
   @Override public long skip(long n) throws IOException {
     if (in == null || n <= 0) {
       return 0;
     }
     long result = in.skip(n);
     if (result != 0) {
       return result;
     }
     if (read() == -1) {
       return 0;
     }
     return 1 + in.skip(n - 1);
   }
 }