/*
    * Copyright (C) 2016, 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.internal.storage.reftree;
  
  import static org.eclipse.jgit.lib.Constants.HEAD;
  import static org.eclipse.jgit.lib.Constants.OBJ_BLOB;
  import static org.eclipse.jgit.lib.Constants.R_REFS;
  import static org.eclipse.jgit.lib.Constants.encode;
  import static org.eclipse.jgit.lib.FileMode.GITLINK;
  import static org.eclipse.jgit.lib.FileMode.SYMLINK;
  import static org.eclipse.jgit.lib.FileMode.TYPE_GITLINK;
  import static org.eclipse.jgit.lib.FileMode.TYPE_SYMLINK;
  import static org.eclipse.jgit.lib.Ref.Storage.NEW;
  import static org.eclipse.jgit.lib.Ref.Storage.PACKED;
  import static org.eclipse.jgit.lib.RefDatabase.MAX_SYMBOLIC_REF_DEPTH;
  import static org.eclipse.jgit.transport.ReceiveCommand.Result.LOCK_FAILURE;
  import static org.eclipse.jgit.transport.ReceiveCommand.Result.REJECTED_OTHER_REASON;
  
  import java.io.IOException;
  import java.util.Collection;
  import java.util.HashMap;
  import java.util.Map;
  
  import org.eclipse.jgit.annotations.Nullable;
  import org.eclipse.jgit.dircache.DirCache;
  import org.eclipse.jgit.dircache.DirCacheBuilder;
  import org.eclipse.jgit.dircache.DirCacheEditor;
  import org.eclipse.jgit.dircache.DirCacheEditor.DeletePath;
  import org.eclipse.jgit.dircache.DirCacheEditor.PathEdit;
  import org.eclipse.jgit.dircache.DirCacheEntry;
  import org.eclipse.jgit.errors.CorruptObjectException;
  import org.eclipse.jgit.errors.DirCacheNameConflictException;
  import org.eclipse.jgit.errors.IncorrectObjectTypeException;
  import org.eclipse.jgit.errors.MissingObjectException;
  import org.eclipse.jgit.internal.JGitText;
  import org.eclipse.jgit.lib.ObjectId;
  import org.eclipse.jgit.lib.ObjectIdRef;
  import org.eclipse.jgit.lib.ObjectInserter;
  import org.eclipse.jgit.lib.ObjectReader;
  import org.eclipse.jgit.lib.Ref;
  import org.eclipse.jgit.lib.Repository;
  import org.eclipse.jgit.lib.SymbolicRef;
  import org.eclipse.jgit.revwalk.RevTree;
  import org.eclipse.jgit.util.RawParseUtils;
  
  /**
   * Tree of references in the reference graph.
   * <p>
   * The root corresponds to the {@code "refs/"} subdirectory, for example the
   * default reference {@code "refs/heads/master"} is stored at path
   * {@code "heads/master"} in a {@code RefTree}.
   * <p>
   * Normal references are stored as {@link org.eclipse.jgit.lib.FileMode#GITLINK}
   * tree entries. The ObjectId in the tree entry is the ObjectId the reference
   * refers to.
   * <p>
   * Symbolic references are stored as
   * {@link org.eclipse.jgit.lib.FileMode#SYMLINK} entries, with the blob storing
   * the name of the target reference.
   * <p>
   * Annotated tags also store the peeled object using a {@code GITLINK} entry
   * with the suffix <code>" ^"</code> (space carrot), for example
   * {@code "tags/v1.0"} stores the annotated tag object, while
   * <code>"tags/v1.0 ^"</code> stores the commit the tag annotates.
   * <p>
   * {@code HEAD} is a special case and stored as {@code "..HEAD"}.
   */
  public class RefTree {
  	/** Suffix applied to GITLINK to indicate its the peeled value of a tag. */
  	public static final String PEELED_SUFFIX = " ^"; //$NON-NLS-1$
  	static final String ROOT_DOTDOT = ".."; //$NON-NLS-1$
  
  	/**
  	 * Create an empty reference tree.
  	 *
  	 * @return a new empty reference tree.
  	 */
  	public static RefTree newEmptyTree() {
  		return new RefTree(DirCache.newInCore());
  	}
  
  	/**
  	 * Load a reference tree.
  	 *
  	 * @param reader
  	 *            reader to scan the reference tree with.
  	 * @param tree
  	 *            the tree to read.
  	 * @return the ref tree read from the commit.
  	 * @throws java.io.IOException
  	 *             the repository cannot be accessed through the reader.
 	 * @throws org.eclipse.jgit.errors.CorruptObjectException
 	 *             a tree object is corrupt and cannot be read.
 	 * @throws org.eclipse.jgit.errors.IncorrectObjectTypeException
 	 *             a tree object wasn't actually a tree.
 	 * @throws org.eclipse.jgit.errors.MissingObjectException
 	 *             a reference tree object doesn't exist.
 	 */
 	public static RefTree read(ObjectReader reader, RevTree tree)
 			throws MissingObjectException, IncorrectObjectTypeException,
 			CorruptObjectException, IOException {
 		return new RefTree(DirCache.read(reader, tree));
 	}
 
 	private DirCache contents;
 	private Map<ObjectId, String> pendingBlobs;
 
 	private RefTree(DirCache dc) {
 		this.contents = dc;
 	}
 
 	/**
 	 * Read one reference.
 	 * <p>
 	 * References are always returned peeled
 	 * ({@link org.eclipse.jgit.lib.Ref#isPeeled()} is true). If the reference
 	 * points to an annotated tag, the returned reference will be peeled and
 	 * contain {@link org.eclipse.jgit.lib.Ref#getPeeledObjectId()}.
 	 * <p>
 	 * If the reference is a symbolic reference and the chain depth is less than
 	 * {@link org.eclipse.jgit.lib.RefDatabase#MAX_SYMBOLIC_REF_DEPTH} the
 	 * returned reference is resolved. If the chain depth is longer, the
 	 * symbolic reference is returned without resolving.
 	 *
 	 * @param reader
 	 *            to access objects necessary to read the requested reference.
 	 * @param name
 	 *            name of the reference to read.
 	 * @return the reference; null if it does not exist.
 	 * @throws java.io.IOException
 	 *             cannot read a symbolic reference target.
 	 */
 	@Nullable
 	public Ref exactRef(ObjectReader reader, String name) throws IOException {
 		Ref r = readRef(reader, name);
 		if (r == null) {
 			return null;
 		} else if (r.isSymbolic()) {
 			return resolve(reader, r, 0);
 		}
 
 		DirCacheEntry p = contents.getEntry(peeledPath(name));
 		if (p != null && p.getRawMode() == TYPE_GITLINK) {
 			return new ObjectIdRef.PeeledTag(PACKED, r.getName(),
 					r.getObjectId(), p.getObjectId());
 		}
 		return r;
 	}
 
 	private Ref readRef(ObjectReader reader, String name) throws IOException {
 		DirCacheEntry e = contents.getEntry(refPath(name));
 		return e != null ? toRef(reader, e, name) : null;
 	}
 
 	private Ref toRef(ObjectReader reader, DirCacheEntry e, String name)
 			throws IOException {
 		int mode = e.getRawMode();
 		if (mode == TYPE_GITLINK) {
 			ObjectId id = e.getObjectId();
 			return new ObjectIdRef.PeeledNonTag(PACKED, name, id);
 		}
 
 		if (mode == TYPE_SYMLINK) {
 			ObjectId id = e.getObjectId();
 			String n = pendingBlobs != null ? pendingBlobs.get(id) : null;
 			if (n == null) {
 				byte[] bin = reader.open(id, OBJ_BLOB).getCachedBytes();
 				n = RawParseUtils.decode(bin);
 			}
 			Ref dst = new ObjectIdRef.Unpeeled(NEW, n, null);
 			return new SymbolicRef(name, dst);
 		}
 
 		return null; // garbage file or something; not a reference.
 	}
 
 	private Ref./org/eclipse/jgit/lib/Ref.html#Ref">Ref resolve(ObjectReader reader, Ref ref, int depth)
 			throws IOException {
 		if (ref.isSymbolic() && depth < MAX_SYMBOLIC_REF_DEPTH) {
 			Ref r = readRef(reader, ref.getTarget().getName());
 			if (r == null) {
 				return ref;
 			}
 			Ref dst = resolve(reader, r, depth + 1);
 			return new SymbolicRef(ref.getName(), dst);
 		}
 		return ref;
 	}
 
 	/**
 	 * Attempt a batch of commands against this RefTree.
 	 * <p>
 	 * The batch is applied atomically, either all commands apply at once, or
 	 * they all reject and the RefTree is left unmodified.
 	 * <p>
 	 * On success (when this method returns {@code true}) the command results
 	 * are left as-is (probably {@code NOT_ATTEMPTED}). Result fields are set
 	 * only when this method returns {@code false} to indicate failure.
 	 *
 	 * @param cmdList
 	 *            to apply. All commands should still have result NOT_ATTEMPTED.
 	 * @return true if the commands applied; false if they were rejected.
 	 */
 	public boolean apply(Collection<Command> cmdList) {
 		try {
 			DirCacheEditor ed = contents.editor();
 			for (Command cmd : cmdList) {
 				if (!isValidRef(cmd)) {
 					cmd.setResult(REJECTED_OTHER_REASON,
 							JGitText.get().funnyRefname);
 					Command.abort(cmdList, null);
 					return false;
 				}
 				apply(ed, cmd);
 			}
 			ed.finish();
 			return true;
 		} catch (DirCacheNameConflictException e) {
 			String r1 = refName(e.getPath1());
 			String r2 = refName(e.getPath2());
 			for (Command cmd : cmdList) {
 				if (r1.equals(cmd.getRefName())
 						|| r2.equals(cmd.getRefName())) {
 					cmd.setResult(LOCK_FAILURE);
 					break;
 				}
 			}
 			Command.abort(cmdList, null);
 			return false;
 		} catch (LockFailureException e) {
 			Command.abort(cmdList, null);
 			return false;
 		}
 	}
 
 	private static boolean isValidRef(Command cmd) {
 		String n = cmd.getRefName();
 		return HEAD.equals(n) || Repository.isValidRefName(n);
 	}
 
 	private void apply(DirCacheEditor ed, Command cmd) {
 		String path = refPath(cmd.getRefName());
 		Ref oldRef = cmd.getOldRef();
 		final Ref newRef = cmd.getNewRef();
 
 		if (newRef == null) {
 			checkRef(contents.getEntry(path), cmd);
 			ed.add(new DeletePath(path));
 			cleanupPeeledRef(ed, oldRef);
 			return;
 		}
 
 		if (newRef.isSymbolic()) {
 			final String dst = newRef.getTarget().getName();
 			ed.add(new PathEdit(path) {
 				@Override
 				public void apply(DirCacheEntry ent) {
 					checkRef(ent, cmd);
 					ObjectId id = Command.symref(dst);
 					ent.setFileMode(SYMLINK);
 					ent.setObjectId(id);
 					if (pendingBlobs == null) {
 						pendingBlobs = new HashMap<>(4);
 					}
 					pendingBlobs.put(id, dst);
 				}
 			}.setReplace(false));
 			cleanupPeeledRef(ed, oldRef);
 			return;
 		}
 
 		ed.add(new PathEdit(path) {
 			@Override
 			public void apply(DirCacheEntry ent) {
 				checkRef(ent, cmd);
 				ent.setFileMode(GITLINK);
 				ent.setObjectId(newRef.getObjectId());
 			}
 		}.setReplace(false));
 
 		if (newRef.getPeeledObjectId() != null) {
 			ed.add(new PathEdit(peeledPath(newRef.getName())) {
 				@Override
 				public void apply(DirCacheEntry ent) {
 					ent.setFileMode(GITLINK);
 					ent.setObjectId(newRef.getPeeledObjectId());
 				}
 			}.setReplace(false));
 		} else {
 			cleanupPeeledRef(ed, oldRef);
 		}
 	}
 
 	private static void checkRef(@Nullable DirCacheEntry ent, Command cmd) {
 		if (!cmd.checkRef(ent)) {
 			cmd.setResult(LOCK_FAILURE);
 			throw new LockFailureException();
 		}
 	}
 
 	private static void cleanupPeeledRef(DirCacheEditor ed, Ref ref) {
 		if (ref != null && !ref.isSymbolic()
 				&& (!ref.isPeeled() || ref.getPeeledObjectId() != null)) {
 			ed.add(new DeletePath(peeledPath(ref.getName())));
 		}
 	}
 
 	/**
 	 * Convert a path name in a RefTree to the reference name known by Git.
 	 *
 	 * @param path
 	 *            name read from the RefTree structure, for example
 	 *            {@code "heads/master"}.
 	 * @return reference name for the path, {@code "refs/heads/master"}.
 	 */
 	public static String refName(String path) {
 		if (path.startsWith(ROOT_DOTDOT)) {
 			return path.substring(2);
 		}
 		return R_REFS + path;
 	}
 
 	static String refPath(String name) {
 		if (name.startsWith(R_REFS)) {
 			return name.substring(R_REFS.length());
 		}
 		return ROOT_DOTDOT + name;
 	}
 
 	private static String peeledPath(String name) {
 		return refPath(name) + PEELED_SUFFIX;
 	}
 
 	/**
 	 * Write this reference tree.
 	 *
 	 * @param inserter
 	 *            inserter to use when writing trees to the object database.
 	 *            Caller is responsible for flushing the inserter before trying
 	 *            to read the objects, or exposing them through a reference.
 	 * @return the top level tree.
 	 * @throws java.io.IOException
 	 *             a tree could not be written.
 	 */
 	public ObjectId writeTree(ObjectInserter inserter) throws IOException {
 		if (pendingBlobs != null) {
 			for (String s : pendingBlobs.values()) {
 				inserter.insert(OBJ_BLOB, encode(s));
 			}
 			pendingBlobs = null;
 		}
 		return contents.writeTree(inserter);
 	}
 
 	/**
 	 * Create a deep copy of this RefTree.
 	 *
 	 * @return a deep copy of this RefTree.
 	 */
 	public RefTree copy() {
 		RefTree r = new RefTree(DirCache.newInCore());
 		DirCacheBuilder b = r.contents.builder();
 		for (int i = 0; i < contents.getEntryCount(); i++) {
 			b.add(new DirCacheEntry(contents.getEntry(i)));
 		}
 		b.finish();
 		if (pendingBlobs != null) {
 			r.pendingBlobs = new HashMap<>(pendingBlobs);
 		}
 		return r;
 	}
 
 	private static class LockFailureException extends RuntimeException {
 		private static final long serialVersionUID = 1L;
 	}
 }