/*
    * Licensed to the Apache Software Foundation (ASF) under one
    * or more contributor license agreements.  See the NOTICE file
    * distributed with this work for additional information
    * regarding copyright ownership.  The ASF licenses this file
    * to you 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 org.apache.giraph.utils.io;
  
  import org.apache.giraph.utils.ExtendedDataInput;
  import org.apache.giraph.utils.ExtendedDataOutput;
  import org.apache.giraph.utils.UnsafeByteArrayInputStream;
  
  import java.io.IOException;
  import java.util.ArrayList;
  import java.util.List;
  
  /**
   * Implementations of {@link ExtendedDataInput} are limited because they can
   * only handle up to 1GB of data. This {@link ExtendedDataInput} overcomes
   * that limitation, with almost no additional cost when data is not huge.
   *
   * Goes in pair with {@link BigDataOutput}
   */
  public class BigDataInput implements ExtendedDataInput {
    /** Empty data input */
    private static final ExtendedDataInput EMPTY_INPUT =
        new UnsafeByteArrayInputStream(new byte[0]);
  
    /** Input which we are currently reading from */
    private ExtendedDataInput currentInput;
    /** List of all data inputs which contain data */
    private final List<ExtendedDataInput> dataInputs;
    /** Which position within dataInputs are we currently reading from */
    private int currentPositionInInputs;
  
    /**
     * Constructor
     *
     * @param bigDataOutput {@link BigDataOutput} which we want to read data from
     */
    public BigDataInput(BigDataOutput bigDataOutput) {
      dataInputs = new ArrayList<ExtendedDataInput>(
          bigDataOutput.getNumberOfDataOutputs());
      for (ExtendedDataOutput dataOutput : bigDataOutput.getDataOutputs()) {
        dataInputs.add(bigDataOutput.getConf().createExtendedDataInput(
            dataOutput.getByteArray(), 0, dataOutput.getPos()));
      }
      currentPositionInInputs = -1;
      moveToNextDataInput();
    }
  
    /** Start reading the following data input */
    private void moveToNextDataInput() {
      currentPositionInInputs++;
      if (currentPositionInInputs < dataInputs.size()) {
        currentInput = dataInputs.get(currentPositionInInputs);
      } else {
        currentInput = EMPTY_INPUT;
      }
    }
  
    /**
     * Check if we read everything from the current data input, and move to the
     * next one if needed.
     */
    private void checkIfShouldMoveToNextDataInput() {
      if (currentInput.endOfInput()) {
        moveToNextDataInput();
      }
    }
  
    @Override
    public void readFully(byte[] b) throws IOException {
      readFully(b, 0, b.length);
    }
  
    @Override
    public void readFully(byte[] b, int off, int len) throws IOException {
      checkIfShouldMoveToNextDataInput();
      int available = currentInput.available();
      if (len <= available) {
        currentInput.readFully(b, off, len);
      } else {
        // When we are trying to read more bytes than there are in single chunk
        // we need to read part by part
        currentInput.readFully(b, off, available);
        readFully(b, off + available, len - available);
     }
   }
 
   @Override
   public boolean readBoolean() throws IOException {
     checkIfShouldMoveToNextDataInput();
     return currentInput.readBoolean();
   }
 
   @Override
   public byte readByte() throws IOException {
     checkIfShouldMoveToNextDataInput();
     return currentInput.readByte();
   }
 
   @Override
   public int readUnsignedByte() throws IOException {
     checkIfShouldMoveToNextDataInput();
     return currentInput.readUnsignedByte();
   }
 
   @Override
   public short readShort() throws IOException {
     checkIfShouldMoveToNextDataInput();
     return currentInput.readShort();
   }
 
   @Override
   public int readUnsignedShort() throws IOException {
     checkIfShouldMoveToNextDataInput();
     return currentInput.readUnsignedShort();
   }
 
   @Override
   public char readChar() throws IOException {
     checkIfShouldMoveToNextDataInput();
     return currentInput.readChar();
   }
 
   @Override
   public int readInt() throws IOException {
     checkIfShouldMoveToNextDataInput();
     return currentInput.readInt();
   }
 
   @Override
   public long readLong() throws IOException {
     checkIfShouldMoveToNextDataInput();
     return currentInput.readLong();
   }
 
   @Override
   public float readFloat() throws IOException {
     checkIfShouldMoveToNextDataInput();
     return currentInput.readFloat();
   }
 
   @Override
   public double readDouble() throws IOException {
     checkIfShouldMoveToNextDataInput();
     return currentInput.readDouble();
   }
 
   @Override
   public String readLine() throws IOException {
     checkIfShouldMoveToNextDataInput();
     return currentInput.readLine();
   }
 
   @Override
   public String readUTF() throws IOException {
     checkIfShouldMoveToNextDataInput();
     return currentInput.readUTF();
   }
 
   @Override
   public int skipBytes(int n) throws IOException {
     int bytesLeftToSkip = n;
     while (bytesLeftToSkip > 0) {
       int bytesSkipped = currentInput.skipBytes(bytesLeftToSkip);
       bytesLeftToSkip -= bytesSkipped;
       if (bytesLeftToSkip > 0) {
         moveToNextDataInput();
         if (endOfInput()) {
           break;
         }
       }
     }
     return n - bytesLeftToSkip;
   }
 
   @Override
   public int getPos() {
     int pos = 0;
     for (int i = 0; i <= currentPositionInInputs; i++) {
       pos += dataInputs.get(i).getPos();
     }
     return pos;
   }
 
   @Override
   public int available() {
     throw new UnsupportedOperationException("available: " +
         "Not supported with BigDataIO because overflow can happen");
   }
 
   @Override
   public boolean endOfInput() {
     return currentInput == EMPTY_INPUT ||
         (dataInputs.get(currentPositionInInputs).endOfInput() &&
             currentPositionInInputs == dataInputs.size() - 1);
   }
 }