/*
    * 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 com.google.common.annotations.Beta;
  import com.google.common.base.Preconditions;
  import com.google.common.primitives.Ints;
  import com.google.common.primitives.Longs;
  
  import java.io.DataInput;
  import java.io.DataInputStream;
  import java.io.EOFException;
  import java.io.FilterInputStream;
  import java.io.IOException;
  import java.io.InputStream;
  
  /**
   * An implementation of {@link DataInput} that uses little-endian byte ordering
   * for reading {@code short}, {@code int}, {@code float}, {@code double}, and
   * {@code long} values.
   * <p>
   * <b>Note:</b> This class intentionally violates the specification of its
   * supertype {@code DataInput}, which explicitly requires big-endian byte order.
   *
   * @author Chris Nokleberg
   * @author Keith Bottner
   * @since 8.0
   */
  @Beta
  public final class LittleEndianDataInputStream extends FilterInputStream
      implements DataInput {
  
    /**
     * Creates a {@code LittleEndianDataInputStream} that wraps the given stream.
     *
     * @param in the stream to delegate to
     */
    public LittleEndianDataInputStream(InputStream in) {
      super(Preconditions.checkNotNull(in));
    }
  
    /**
     * This method will throw an {@link UnsupportedOperationException}.
     */
    @Override
    public String readLine() {
      throw new UnsupportedOperationException("readLine is not supported");
    }
  
    @Override
    public void readFully(byte[] b) throws IOException {
      ByteStreams.readFully(this, b);
    }
  
    @Override
    public void readFully(byte[] b, int off, int len) throws IOException {
      ByteStreams.readFully(this, b, off, len);
    }
  
    @Override
    public int skipBytes(int n) throws IOException {
      return (int) in.skip(n);
    }
  
    @Override
    public int readUnsignedByte() throws IOException {
      int b1 = in.read();
      if (0 > b1) {
        throw new EOFException();
      }
      
      return b1;
    }
  
    /**
     * Reads an unsigned {@code short} as specified by
     * {@link DataInputStream#readUnsignedShort()}, except using little-endian
     * byte order.
     *
     * @return the next two bytes of the input stream, interpreted as an 
     *         unsigned 16-bit integer in little-endian byte order
     * @throws IOException if an I/O error occurs
     */
    @Override
    public int readUnsignedShort() throws IOException {
     byte b1 = readAndCheckByte();
     byte b2 = readAndCheckByte();
 
     return Ints.fromBytes((byte) 0, (byte) 0, b2, b1);
   }
 
   /**
    * Reads an integer as specified by {@link DataInputStream#readInt()}, except
    * using little-endian byte order.
    *
    * @return the next four bytes of the input stream, interpreted as an 
    *         {@code int} in little-endian byte order
    * @throws IOException if an I/O error occurs
    */
   @Override
   public int readInt() throws IOException {
     byte b1 = readAndCheckByte();
     byte b2 = readAndCheckByte();
     byte b3 = readAndCheckByte();
     byte b4 = readAndCheckByte();
 
     return Ints.fromBytes( b4, b3, b2, b1);
   }
 
   /**
    * Reads a {@code long} as specified by {@link DataInputStream#readLong()},
    * except using little-endian byte order.
    *
    * @return the next eight bytes of the input stream, interpreted as a 
    *         {@code long} in little-endian byte order
    * @throws IOException if an I/O error occurs
    */
   @Override
   public long readLong() throws IOException {
     byte b1 = readAndCheckByte();
     byte b2 = readAndCheckByte();
     byte b3 = readAndCheckByte();
     byte b4 = readAndCheckByte();
     byte b5 = readAndCheckByte();
     byte b6 = readAndCheckByte();
     byte b7 = readAndCheckByte();
     byte b8 = readAndCheckByte();
 
     return Longs.fromBytes(b8, b7, b6, b5, b4, b3, b2, b1);
   }
 
   /**
    * Reads a {@code float} as specified by {@link DataInputStream#readFloat()},
    * except using little-endian byte order.
    *
    * @return the next four bytes of the input stream, interpreted as a
    *         {@code float} in little-endian byte order
    * @throws IOException if an I/O error occurs
    */
   @Override
   public float readFloat() throws IOException {
     return Float.intBitsToFloat(readInt());
   }
 
   /**
    * Reads a {@code double} as specified by
    * {@link DataInputStream#readDouble()}, except using little-endian byte
    * order.
    *
    * @return the next eight bytes of the input stream, interpreted as a
    *         {@code double} in little-endian byte order
    * @throws IOException if an I/O error occurs
    */
   @Override
   public double readDouble() throws IOException {
     return Double.longBitsToDouble(readLong());
   }
 
   @Override
   public String readUTF() throws IOException {
     return new DataInputStream(in).readUTF();
   }
 
   /**
    * Reads a {@code short} as specified by {@link DataInputStream#readShort()},
    * except using little-endian byte order.
    *
    * @return the next two bytes of the input stream, interpreted as a
    *         {@code short} in little-endian byte order.
    * @throws IOException if an I/O error occurs.
    */
   @Override
   public short readShort() throws IOException {
     return (short) readUnsignedShort();
   }
 
   /**
    * Reads a char as specified by {@link DataInputStream#readChar()}, except
    * using little-endian byte order.
    *
    * @return the next two bytes of the input stream, interpreted as a 
    *         {@code char} in little-endian byte order
    * @throws IOException if an I/O error occurs
    */
   @Override
   public char readChar() throws IOException {
     return (char) readUnsignedShort();
   }
 
   @Override
   public byte readByte() throws IOException {
     return (byte) readUnsignedByte();
   }
 
   @Override
   public boolean readBoolean() throws IOException {
     return readUnsignedByte() != 0;
   }
 
   /**
    * Reads a byte from the input stream checking that the end of file (EOF)
    * has not been encountered.
    *  
    * @return byte read from input
    * @throws IOException if an error is encountered while reading
    * @throws EOFException if the end of file (EOF) is encountered.
    */
   private byte readAndCheckByte() throws IOException, EOFException {
     int b1 = in.read();
 
     if (-1 == b1) {
       throw new EOFException();
     }
 
     return (byte) b1;
   }
 
 }