/*
    * Copyright (C) 2010, 2020 Google Inc. and others
    *
    * This program and the accompanying materials are made available under the
    * terms of the Eclipse Distribution License v. 1.0 which is available at
    * https://www.eclipse.org/org/documents/edl-v10.php.
    *
    * SPDX-License-Identifier: BSD-3-Clause
    */
  
  package org.eclipse.jgit.diff;
  
  import java.io.BufferedInputStream;
  import java.io.FileNotFoundException;
  import java.io.IOException;
  import java.io.InputStream;
  
  import org.eclipse.jgit.errors.LargeObjectException;
  import org.eclipse.jgit.errors.MissingObjectException;
  import org.eclipse.jgit.lib.Constants;
  import org.eclipse.jgit.lib.ObjectId;
  import org.eclipse.jgit.lib.ObjectLoader;
  import org.eclipse.jgit.lib.ObjectReader;
  import org.eclipse.jgit.lib.ObjectStream;
  import org.eclipse.jgit.treewalk.TreeWalk;
  import org.eclipse.jgit.treewalk.WorkingTreeIterator;
  import org.eclipse.jgit.treewalk.filter.PathFilter;
  
  /**
   * Supplies the content of a file for
   * {@link org.eclipse.jgit.diff.DiffFormatter}.
   * <p>
   * A content source is not thread-safe. Sources may contain state, including
   * information about the last ObjectLoader they returned. Callers must be
   * careful to ensure there is no more than one ObjectLoader pending on any
   * source, at any time.
   */
  public abstract class ContentSource {
  	/**
  	 * Construct a content source for an ObjectReader.
  	 *
  	 * @param reader
  	 *            the reader to obtain blobs from.
  	 * @return a source wrapping the reader.
  	 */
  	public static ContentSource create(ObjectReader reader) {
  		return new ObjectReaderSource(reader);
  	}
  
  	/**
  	 * Construct a content source for a working directory.
  	 *
  	 * If the iterator is a {@link org.eclipse.jgit.treewalk.FileTreeIterator}
  	 * an optimized version is used that doesn't require seeking through a
  	 * TreeWalk.
  	 *
  	 * @param iterator
  	 *            the iterator to obtain source files through.
  	 * @return a content source wrapping the iterator.
  	 */
  	public static ContentSource create(WorkingTreeIterator iterator) {
  		return new WorkingTreeSource(iterator);
  	}
  
  	/**
  	 * Determine the size of the object.
  	 *
  	 * @param path
  	 *            the path of the file, relative to the root of the repository.
  	 * @param id
  	 *            blob id of the file, if known.
  	 * @return the size in bytes.
  	 * @throws java.io.IOException
  	 *             the file cannot be accessed.
  	 */
  	public abstract long size(String path, ObjectId id) throws IOException;
  
  	/**
  	 * Open the object.
  	 *
  	 * @param path
  	 *            the path of the file, relative to the root of the repository.
  	 * @param id
  	 *            blob id of the file, if known.
  	 * @return a loader that can supply the content of the file. The loader must
  	 *         be used before another loader can be obtained from this same
  	 *         source.
  	 * @throws java.io.IOException
  	 *             the file cannot be accessed.
  	 */
  	public abstract ObjectLoader open(String path, ObjectId id)
  			throws IOException;
  
  	private static class ObjectReaderSource extends ContentSource {
  		private final ObjectReader reader;
  
  		ObjectReaderSource(ObjectReader reader) {
  			this.reader = reader;
  		}
 
 		@Override
 		public long size(String path, ObjectId id) throws IOException {
 			try {
 				return reader.getObjectSize(id, Constants.OBJ_BLOB);
 			} catch (MissingObjectException ignore) {
 				return 0;
 			}
 		}
 
 		@Override
 		public ObjectLoader open(String path, ObjectId id) throws IOException {
 			return reader.open(id, Constants.OBJ_BLOB);
 		}
 	}
 
 	private static class WorkingTreeSource extends ContentSource {
 		private final TreeWalk tw;
 
 		private final WorkingTreeIterator iterator;
 
 		private String current;
 
 		WorkingTreeIterator ptr;
 
 		WorkingTreeSource(WorkingTreeIterator iterator) {
 			this.tw = new TreeWalk(iterator.getRepository(),
 					(ObjectReader) null);
 			this.tw.setRecursive(true);
 			this.iterator = iterator;
 		}
 
 		@Override
 		public long size(String path, ObjectId id) throws IOException {
 			seek(path);
 			return ptr.getEntryLength();
 		}
 
 		@Override
 		public ObjectLoader open(String path, ObjectId id) throws IOException {
 			seek(path);
 			long entrySize = ptr.getEntryContentLength();
 			return new ObjectLoader() {
 				@Override
 				public long getSize() {
 					return entrySize;
 				}
 
 				@Override
 				public int getType() {
 					return ptr.getEntryFileMode().getObjectType();
 				}
 
 				@Override
 				public ObjectStream openStream() throws MissingObjectException,
 						IOException {
 					long contentLength = entrySize;
 					InputStream in = ptr.openEntryStream();
 					in = new BufferedInputStream(in);
 					return new ObjectStream.Filter(getType(), contentLength, in);
 				}
 
 				@Override
 				public boolean isLarge() {
 					return true;
 				}
 
 				@Override
 				public byte[] getCachedBytes() throws LargeObjectException {
 					throw new LargeObjectException();
 				}
 			};
 		}
 
 		private void seek(String path) throws IOException {
 			if (!path.equals(current)) {
 				iterator.reset();
 				// Possibly this iterator had an associated DirCacheIterator,
 				// but we have no access to it and thus don't know about it.
 				// We have to reset this iterator here to work without
 				// DirCacheIterator and to descend always into ignored
 				// directories. Otherwise we might not find tracked files below
 				// ignored folders. Since we're looking only for a single
 				// specific path this is not a performance problem.
 				iterator.setWalkIgnoredDirectories(true);
 				iterator.setDirCacheIterator(null, -1);
 				tw.reset();
 				tw.addTree(iterator);
 				tw.setFilter(PathFilter.create(path));
 				current = path;
 				if (!tw.next())
 					throw new FileNotFoundException(path);
 				ptr = tw.getTree(0, WorkingTreeIterator.class);
 				if (ptr == null)
 					throw new FileNotFoundException(path);
 			}
 		}
 	}
 
 	/** A pair of sources to access the old and new sides of a DiffEntry. */
 	public static final class Pair {
 		private final ContentSource oldSource;
 
 		private final ContentSource newSource;
 
 		/**
 		 * Construct a pair of sources.
 		 *
 		 * @param oldSource
 		 *            source to read the old side of a DiffEntry.
 		 * @param newSource
 		 *            source to read the new side of a DiffEntry.
 		 */
 		public Pair(ContentSource oldSource, ContentSource newSource) {
 			this.oldSource = oldSource;
 			this.newSource = newSource;
 		}
 
 		/**
 		 * Determine the size of the object.
 		 *
 		 * @param side
 		 *            which side of the entry to read (OLD or NEW).
 		 * @param ent
 		 *            the entry to examine.
 		 * @return the size in bytes.
 		 * @throws IOException
 		 *             the file cannot be accessed.
 		 */
 		public long size(DiffEntry.Side side, DiffEntry ent) throws IOException {
 			switch (side) {
 			case OLD:
 				return oldSource.size(ent.oldPath, ent.oldId.toObjectId());
 			case NEW:
 				return newSource.size(ent.newPath, ent.newId.toObjectId());
 			default:
 				throw new IllegalArgumentException();
 			}
 		}
 
 		/**
 		 * Open the object.
 		 *
 		 * @param side
 		 *            which side of the entry to read (OLD or NEW).
 		 * @param ent
 		 *            the entry to examine.
 		 * @return a loader that can supply the content of the file. The loader
 		 *         must be used before another loader can be obtained from this
 		 *         same source.
 		 * @throws IOException
 		 *             the file cannot be accessed.
 		 */
 		public ObjectLoader open(DiffEntry.Side side, DiffEntry ent)
 				throws IOException {
 			switch (side) {
 			case OLD:
 				return oldSource.open(ent.oldPath, ent.oldId.toObjectId());
 			case NEW:
 				return newSource.open(ent.newPath, ent.newId.toObjectId());
 			default:
 				throw new IllegalArgumentException();
 			}
 		}
 	}
 }