/*
    * Copyright (C) 2010, Christian Halstrick <christian.halstrick@sap.com> 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.treewalk.filter;
  
  import java.io.IOException;
  import java.util.HashSet;
  import java.util.LinkedList;
  import java.util.List;
  import java.util.Set;
  
  import org.eclipse.jgit.dircache.DirCacheEntry;
  import org.eclipse.jgit.dircache.DirCacheIterator;
  import org.eclipse.jgit.errors.IncorrectObjectTypeException;
  import org.eclipse.jgit.errors.MissingObjectException;
  import org.eclipse.jgit.lib.FileMode;
  import org.eclipse.jgit.lib.ObjectReader;
  import org.eclipse.jgit.treewalk.TreeWalk;
  import org.eclipse.jgit.treewalk.WorkingTreeIterator;
  
  /**
   * A performance optimized variant of
   * {@link org.eclipse.jgit.treewalk.filter.TreeFilter#ANY_DIFF} which should be
   * used when among the walked trees there is a
   * {@link org.eclipse.jgit.dircache.DirCacheIterator} and a
   * {@link org.eclipse.jgit.treewalk.WorkingTreeIterator}. Please see the
   * documentation of {@link org.eclipse.jgit.treewalk.filter.TreeFilter#ANY_DIFF}
   * for a basic description of the semantics.
   * <p>
   * This filter tries to avoid computing content ids of the files in the
   * working-tree. In contrast to
   * {@link org.eclipse.jgit.treewalk.filter.TreeFilter#ANY_DIFF} this filter
   * takes care to first compare the entry from the
   * {@link org.eclipse.jgit.dircache.DirCacheIterator} with the entries from all
   * other iterators besides the
   * {@link org.eclipse.jgit.treewalk.WorkingTreeIterator}. Since all those
   * entries have fast access to content ids that is very fast. If a difference is
   * detected in this step this filter decides to include that path before even
   * looking at the working-tree entry.
   * <p>
   * If no difference is found then we have to compare index and working-tree as
   * the last step. By making use of
   * {@link org.eclipse.jgit.treewalk.WorkingTreeIterator#isModified(org.eclipse.jgit.dircache.DirCacheEntry, boolean, ObjectReader)}
   * we can avoid the computation of the content id if the file is not dirty.
   * <p>
   * Instances of this filter should not be used for multiple
   * {@link org.eclipse.jgit.treewalk.TreeWalk}s. Always construct a new instance
   * of this filter for each TreeWalk.
   */
  public class IndexDiffFilter extends TreeFilter {
  	private final int dirCache;
  
  	private final int workingTree;
  
  	private final boolean honorIgnores;
  
  	private final Set<String> ignoredPaths = new HashSet<>();
  
  	private final LinkedList<String> untrackedParentFolders = new LinkedList<>();
  
  	private final LinkedList<String> untrackedFolders = new LinkedList<>();
  
  	/**
  	 * Creates a new instance of this filter. Do not use an instance of this
  	 * filter in multiple treewalks.
  	 *
  	 * @param dirCacheIndex
  	 *            the index of the
  	 *            {@link org.eclipse.jgit.dircache.DirCacheIterator} in the
  	 *            associated treewalk
  	 * @param workingTreeIndex
  	 *            the index of the
  	 *            {@link org.eclipse.jgit.treewalk.WorkingTreeIterator} in the
  	 *            associated treewalk
  	 */
  	public IndexDiffFilter(int dirCacheIndex, int workingTreeIndex) {
  		this(dirCacheIndex, workingTreeIndex, true /* honor ignores */);
  	}
  
  	/**
  	 * Creates a new instance of this filter. Do not use an instance of this
  	 * filter in multiple treewalks.
  	 *
  	 * @param dirCacheIndex
  	 *            the index of the
  	 *            {@link org.eclipse.jgit.dircache.DirCacheIterator} in the
  	 *            associated treewalk
  	 * @param workingTreeIndex
  	 *            the index of the
  	 *            {@link org.eclipse.jgit.treewalk.WorkingTreeIterator} in the
  	 *            associated treewalk
  	 * @param honorIgnores
  	 *            true if the filter should skip working tree files that are
 	 *            declared as ignored by the standard exclude mechanisms.
 	 */
 	public IndexDiffFilter(int dirCacheIndex, int workingTreeIndex,
 			boolean honorIgnores) {
 		this.dirCache = dirCacheIndex;
 		this.workingTree = workingTreeIndex;
 		this.honorIgnores = honorIgnores;
 	}
 
 	/** {@inheritDoc} */
 	@Override
 	public boolean include(TreeWalk tw) throws MissingObjectException,
 			IncorrectObjectTypeException, IOException {
 		final int cnt = tw.getTreeCount();
 		final int wm = tw.getRawMode(workingTree);
 		WorkingTreeIterator wi = workingTree(tw);
 		String path = tw.getPathString();
 
 		DirCacheIterator di = tw.getTree(dirCache, DirCacheIterator.class);
 		if (di != null) {
 			DirCacheEntry dce = di.getDirCacheEntry();
 			if (dce != null) {
 				if (dce.isAssumeValid())
 					return false;
 				// Never filter index entries with a stage different from 0
 				if (dce.getStage() != 0)
 					return true;
 			}
 		}
 
 		if (!tw.isPostOrderTraversal()) {
 			// detect untracked Folders
 			// Whenever we enter a folder in the workingtree assume it will
 			// contain only untracked files and add it to
 			// untrackedParentFolders. If we later find tracked files we will
 			// remove it from this list
 			if (FileMode.TREE.equals(wm)
 					&& !(honorIgnores && wi.isEntryIgnored())) {
 				// Clean untrackedParentFolders. This potentially moves entries
 				// from untrackedParentFolders to untrackedFolders
 				copyUntrackedFolders(path);
 				// add the folder we just entered to untrackedParentFolders
 				untrackedParentFolders.addFirst(path);
 			}
 
 			// detect untracked Folders
 			// Whenever we see a tracked file we know that all of its parent
 			// folders do not belong into untrackedParentFolders anymore. Clean
 			// it.
 			for (int i = 0; i < cnt; i++) {
 				int rmode = tw.getRawMode(i);
 				if (i != workingTree && rmode != FileMode.TYPE_MISSING
 						&& FileMode.TREE.equals(rmode)) {
 					untrackedParentFolders.clear();
 					break;
 				}
 			}
 		}
 
 		// If the working tree file doesn't exist, it does exist for at least
 		// one other so include this difference.
 		if (wm == 0)
 			return true;
 
 		// If the path does not appear in the DirCache and its ignored
 		// we can avoid returning a result here, but only if its not in any
 		// other tree.
 		final int dm = tw.getRawMode(dirCache);
 		if (dm == FileMode.TYPE_MISSING) {
 			if (honorIgnores && wi.isEntryIgnored()) {
 				ignoredPaths.add(wi.getEntryPathString());
 				int i = 0;
 				for (; i < cnt; i++) {
 					if (i == dirCache || i == workingTree)
 						continue;
 					if (tw.getRawMode(i) != FileMode.TYPE_MISSING)
 						break;
 				}
 
 				// If i is cnt then the path does not appear in any other tree,
 				// and this working tree entry can be safely ignored.
 				return i != cnt;
 			}
 			// In working tree and not ignored, and not in DirCache.
 			return true;
 		}
 
 		// Always include subtrees as WorkingTreeIterator cannot provide
 		// efficient elimination of unmodified subtrees.
 		if (tw.isSubtree())
 			return true;
 
 		// Try the inexpensive comparisons between index and all real trees
 		// first. Only if we don't find a diff here we have to bother with
 		// the working tree
 		for (int i = 0; i < cnt; i++) {
 			if (i == dirCache || i == workingTree)
 				continue;
 			if (tw.getRawMode(i) != dm || !tw.idEqual(i, dirCache))
 				return true;
 		}
 
 		// Only one chance left to detect a diff: between index and working
 		// tree. Make use of the WorkingTreeIterator#isModified() method to
 		// avoid computing SHA1 on filesystem content if not really needed.
 		return wi.isModified(di == null ? null : di.getDirCacheEntry(), true,
 				tw.getObjectReader());
 	}
 
 	/**
 	 * Copy all entries which are still in untrackedParentFolders and which
 	 * belong to a path this treewalk has left into untrackedFolders. It is sure
 	 * that we will not find any tracked files underneath these paths. Therefore
 	 * these paths definitely belong to untracked folders.
 	 *
 	 * @param currentPath
 	 *            the current path of the treewalk
 	 */
 	private void copyUntrackedFolders(String currentPath) {
 		String pathToBeSaved = null;
 		while (!untrackedParentFolders.isEmpty() && !currentPath
 				.startsWith(untrackedParentFolders.getFirst() + '/')) {
 			pathToBeSaved = untrackedParentFolders.removeFirst();
 		}
 		if (pathToBeSaved != null) {
 			while (!untrackedFolders.isEmpty() && untrackedFolders.getLast()
 					.startsWith(pathToBeSaved + '/')) {
 				untrackedFolders.removeLast();
 			}
 			untrackedFolders.addLast(pathToBeSaved);
 		}
 	}
 
 	private WorkingTreeIterator workingTree(TreeWalk tw) {
 		return tw.getTree(workingTree, WorkingTreeIterator.class);
 	}
 
 	/** {@inheritDoc} */
 	@Override
 	public boolean shouldBeRecursive() {
 		// We cannot compare subtrees in the working tree, so encourage
 		// use of recursive walks where the subtrees are always dived into.
 		return true;
 	}
 
 	/** {@inheritDoc} */
 	@Override
 	public TreeFilter clone() {
 		return this;
 	}
 
 	/** {@inheritDoc} */
 	@Override
 	public String toString() {
 		return "INDEX_DIFF_FILTER"; //$NON-NLS-1$
 	}
 
 	/**
 	 * The method returns the list of ignored files and folders. Only the root
 	 * folder of an ignored folder hierarchy is reported. If a/b/c is listed in
 	 * the .gitignore then you should not expect a/b/c/d/e/f to be reported
 	 * here. Only a/b/c will be reported. Furthermore only ignored files /
 	 * folders are returned that are NOT in the index.
 	 *
 	 * @return ignored paths
 	 */
 	public Set<String> getIgnoredPaths() {
 		return ignoredPaths;
 	}
 
 	/**
 	 * <p>Getter for the field <code>untrackedFolders</code>.</p>
 	 *
 	 * @return all paths of folders which contain only untracked files/folders.
 	 *         If on the associated treewalk postorder traversal was turned on
 	 *         (see {@link org.eclipse.jgit.treewalk.TreeWalk#setPostOrderTraversal(boolean)}) then an
 	 *         empty list will be returned.
 	 */
 	public List<String> getUntrackedFolders() {
 		LinkedList<String> ret = new LinkedList<>(untrackedFolders);
 		if (!untrackedParentFolders.isEmpty()) {
 			String toBeAdded = untrackedParentFolders.getLast();
 			while (!ret.isEmpty() && ret.getLast().startsWith(toBeAdded))
 				ret.removeLast();
 			ret.addLast(toBeAdded);
 		}
 		return ret;
 	}
 }