/*
    * Copyright (C) 2008-2009, Google Inc.
    * Copyright (C) 2008, Jonas Fonseca <fonseca@diku.dk>
    * Copyright (C) 2008, Marek Zawirski <marek.zawirski@gmail.com>
    * Copyright (C) 2007, Robin Rosenberg <robin.rosenberg@dewire.com>
    * Copyright (C) 2006-2008, Shawn O. Pearce <spearce@spearce.org>
    * and other copyright owners as documented in the project's IP log.
    *
    * This program and the accompanying materials are made available
   * under the terms of the Eclipse Distribution License v1.0 which
   * accompanies this distribution, is reproduced below, and is
   * available at http://www.eclipse.org/org/documents/edl-v10.php
   *
   * All rights reserved.
   *
   * Redistribution and use in source and binary forms, with or
   * without modification, are permitted provided that the following
   * conditions are met:
   *
   * - Redistributions of source code must retain the above copyright
   *   notice, this list of conditions and the following disclaimer.
   *
   * - Redistributions in binary form must reproduce the above
   *   copyright notice, this list of conditions and the following
   *   disclaimer in the documentation and/or other materials provided
   *   with the distribution.
   *
   * - Neither the name of the Eclipse Foundation, Inc. nor the
   *   names of its contributors may be used to endorse or promote
   *   products derived from this software without specific prior
   *   written permission.
   *
   * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
   * CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
   * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
   * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
   * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
   * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
   * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
   * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
   * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
   * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
   * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
   * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
   */
  
  package org.eclipse.jgit.lib;
  
  import java.io.EOFException;
  import java.io.IOException;
  import java.io.OutputStream;
  
  import org.eclipse.jgit.errors.LargeObjectException;
  import org.eclipse.jgit.errors.MissingObjectException;
  import org.eclipse.jgit.util.IO;
  
  /**
   * Base class for a set of loaders for different representations of Git objects.
   * New loaders are constructed for every object.
   */
  public abstract class ObjectLoader {
  	/**
  	 * @return Git in pack object type, see {@link Constants}.
  	 */
  	public abstract int getType();
  
  	/**
  	 * @return size of object in bytes
  	 */
  	public abstract long getSize();
  
  	/**
  	 * @return true if this object is too large to obtain as a byte array.
  	 *         Objects over a certain threshold should be accessed only by their
  	 *         {@link #openStream()} to prevent overflowing the JVM heap.
  	 */
  	public boolean isLarge() {
  		try {
  			getCachedBytes();
  			return false;
  		} catch (LargeObjectException tooBig) {
  			return true;
  		}
  	}
  
  	/**
  	 * Obtain a copy of the bytes of this object.
  	 * <p>
  	 * Unlike {@link #getCachedBytes()} this method returns an array that might
  	 * be modified by the caller.
  	 *
  	 * @return the bytes of this object.
  	 * @throws LargeObjectException
  	 *             if the object won't fit into a byte array, because
  	 *             {@link #isLarge()} returns true. Callers should use
  	 *             {@link #openStream()} instead to access the contents.
  	 */
  	public final byte[] getBytes() throws LargeObjectException {
 		return cloneArray(getCachedBytes());
 	}
 
 	/**
 	 * Obtain a copy of the bytes of this object.
 	 *
 	 * If the object size is less than or equal to {@code sizeLimit} this method
 	 * will provide it as a byte array, even if {@link #isLarge()} is true. This
 	 * utility is useful for application code that absolutely must have the
 	 * object as a single contiguous byte array in memory.
 	 *
 	 * Unlike {@link #getCachedBytes(int)} this method returns an array that
 	 * might be modified by the caller.
 	 *
 	 * @param sizeLimit
 	 *            maximum number of bytes to return. If the object is larger
 	 *            than this limit, {@link LargeObjectException} will be thrown.
 	 * @return the bytes of this object.
 	 * @throws LargeObjectException
 	 *             if the object is bigger than {@code sizeLimit}, or if
 	 *             {@link OutOfMemoryError} occurs during allocation of the
 	 *             result array. Callers should use {@link #openStream()}
 	 *             instead to access the contents.
 	 * @throws MissingObjectException
 	 *             the object is large, and it no longer exists.
 	 * @throws IOException
 	 *             the object store cannot be accessed.
 	 */
 	public final byte[] getBytes(int sizeLimit) throws LargeObjectException,
 			MissingObjectException, IOException {
 		byte[] cached = getCachedBytes(sizeLimit);
 		try {
 			return cloneArray(cached);
 		} catch (OutOfMemoryError tooBig) {
 			throw new LargeObjectException.OutOfMemory(tooBig);
 		}
 	}
 
 	/**
 	 * Obtain a reference to the (possibly cached) bytes of this object.
 	 * <p>
 	 * This method offers direct access to the internal caches, potentially
 	 * saving on data copies between the internal cache and higher level code.
 	 * Callers who receive this reference <b>must not</b> modify its contents.
 	 * Changes (if made) will affect the cache but not the repository itself.
 	 *
 	 * @return the cached bytes of this object. Do not modify it.
 	 * @throws LargeObjectException
 	 *             if the object won't fit into a byte array, because
 	 *             {@link #isLarge()} returns true. Callers should use
 	 *             {@link #openStream()} instead to access the contents.
 	 */
 	public abstract byte[] getCachedBytes() throws LargeObjectException;
 
 	/**
 	 * Obtain a reference to the (possibly cached) bytes of this object.
 	 *
 	 * If the object size is less than or equal to {@code sizeLimit} this method
 	 * will provide it as a byte array, even if {@link #isLarge()} is true. This
 	 * utility is useful for application code that absolutely must have the
 	 * object as a single contiguous byte array in memory.
 	 *
 	 * This method offers direct access to the internal caches, potentially
 	 * saving on data copies between the internal cache and higher level code.
 	 * Callers who receive this reference <b>must not</b> modify its contents.
 	 * Changes (if made) will affect the cache but not the repository itself.
 	 *
 	 * @param sizeLimit
 	 *            maximum number of bytes to return. If the object size is
 	 *            larger than this limit and {@link #isLarge()} is true,
 	 *            {@link LargeObjectException} will be thrown.
 	 * @return the cached bytes of this object. Do not modify it.
 	 * @throws LargeObjectException
 	 *             if the object is bigger than {@code sizeLimit}, or if
 	 *             {@link OutOfMemoryError} occurs during allocation of the
 	 *             result array. Callers should use {@link #openStream()}
 	 *             instead to access the contents.
 	 * @throws MissingObjectException
 	 *             the object is large, and it no longer exists.
 	 * @throws IOException
 	 *             the object store cannot be accessed.
 	 */
 	public byte[] getCachedBytes(int sizeLimit) throws LargeObjectException,
 			MissingObjectException, IOException {
 		if (!isLarge())
 			return getCachedBytes();
 
 		ObjectStream in = openStream();
 		try {
 			long sz = in.getSize();
 			if (sizeLimit < sz)
 				throw new LargeObjectException.ExceedsLimit(sizeLimit, sz);
 
 			if (Integer.MAX_VALUE < sz)
 				throw new LargeObjectException.ExceedsByteArrayLimit();
 
 			byte[] buf;
 			try {
 				buf = new byte[(int) sz];
 			} catch (OutOfMemoryError notEnoughHeap) {
 				throw new LargeObjectException.OutOfMemory(notEnoughHeap);
 			}
 
 			IO.readFully(in, buf, 0, buf.length);
 			return buf;
 		} finally {
 			in.close();
 		}
 	}
 
 	/**
 	 * Obtain an input stream to read this object's data.
 	 *
 	 * @return a stream of this object's data. Caller must close the stream when
 	 *         through with it. The returned stream is buffered with a
 	 *         reasonable buffer size.
 	 * @throws MissingObjectException
 	 *             the object no longer exists.
 	 * @throws IOException
 	 *             the object store cannot be accessed.
 	 */
 	public abstract ObjectStream openStream() throws MissingObjectException,
 			IOException;
 
 	/**
 	 * Copy this object to the output stream.
 	 * <p>
 	 * For some object store implementations, this method may be more efficient
 	 * than reading from {@link #openStream()} into a temporary byte array, then
 	 * writing to the destination stream.
 	 * <p>
 	 * The default implementation of this method is to copy with a temporary
 	 * byte array for large objects, or to pass through the cached byte array
 	 * for small objects.
 	 *
 	 * @param out
 	 *            stream to receive the complete copy of this object's data.
 	 *            Caller is responsible for flushing or closing this stream
 	 *            after this method returns.
 	 * @throws MissingObjectException
 	 *             the object no longer exists.
 	 * @throws IOException
 	 *             the object store cannot be accessed, or the stream cannot be
 	 *             written to.
 	 */
 	public void copyTo(OutputStream out) throws MissingObjectException,
 			IOException {
 		if (isLarge()) {
 			ObjectStream in = openStream();
 			try {
 				final long sz = in.getSize();
 				byte[] tmp = new byte[8192];
 				long copied = 0;
 				while (copied < sz) {
 					int n = in.read(tmp);
 					if (n < 0)
 						throw new EOFException();
 					out.write(tmp, 0, n);
 					copied += n;
 				}
 				if (0 <= in.read())
 					throw new EOFException();
 			} finally {
 				in.close();
 			}
 		} else {
 			out.write(getCachedBytes());
 		}
 	}
 
 	private static byte[] cloneArray(final byte[] data) {
 		final byte[] copy = new byte[data.length];
 		System.arraycopy(data, 0, copy, 0, data.length);
 		return copy;
 	}
 
 	/**
 	 * Simple loader around the cached byte array.
 	 * <p>
 	 * ObjectReader implementations can use this stream type when the object's
 	 * content is small enough to be accessed as a single byte array.
 	 */
 	public static class SmallObject extends ObjectLoader {
 		private final int type;
 
 		private final byte[] data;
 
 		/**
 		 * Construct a small object loader.
 		 *
 		 * @param type
 		 *            type of the object.
 		 * @param data
 		 *            the object's data array. This array will be returned as-is
 		 *            for the {@link #getCachedBytes()} method.
 		 */
 		public SmallObject(int type, byte[] data) {
 			this.type = type;
 			this.data = data;
 		}
 
 		@Override
 		public int getType() {
 			return type;
 		}
 
 		@Override
 		public long getSize() {
 			return getCachedBytes().length;
 		}
 
 		@Override
 		public boolean isLarge() {
 			return false;
 		}
 
 		@Override
 		public byte[] getCachedBytes() {
 			return data;
 		}
 
 		@Override
 		public ObjectStream openStream() {
 			return new ObjectStream.SmallStream(this);
 		}
 	}
 }