/*
    * Copyright (C) 2016, Google Inc.
    * 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.
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   * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
   * CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
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  package org.eclipse.jgit.internal.storage.reftree;
  
  import static org.eclipse.jgit.lib.Constants.HEAD;
  import static org.eclipse.jgit.lib.Ref.Storage.LOOSE;
  import static org.eclipse.jgit.lib.Ref.Storage.PACKED;
  
  import java.io.IOException;
  import java.util.ArrayList;
  import java.util.Collection;
  import java.util.Collections;
  import java.util.HashMap;
  import java.util.List;
  import java.util.Map;
  
  import org.eclipse.jgit.annotations.Nullable;
  import org.eclipse.jgit.lib.BatchRefUpdate;
  import org.eclipse.jgit.lib.Config;
  import org.eclipse.jgit.lib.ObjectId;
  import org.eclipse.jgit.lib.ObjectIdRef;
  import org.eclipse.jgit.lib.Ref;
  import org.eclipse.jgit.lib.Ref.Storage;
  import org.eclipse.jgit.lib.RefDatabase;
  import org.eclipse.jgit.lib.RefRename;
  import org.eclipse.jgit.lib.RefUpdate;
  import org.eclipse.jgit.lib.Repository;
  import org.eclipse.jgit.lib.SymbolicRef;
  import org.eclipse.jgit.revwalk.RevObject;
  import org.eclipse.jgit.revwalk.RevTag;
  import org.eclipse.jgit.revwalk.RevWalk;
  import org.eclipse.jgit.util.RefList;
  import org.eclipse.jgit.util.RefMap;
  
  /**
   * Reference database backed by a
   * {@link org.eclipse.jgit.internal.storage.reftree.RefTree}.
   * <p>
   * The storage for RefTreeDatabase has two parts. The main part is a native Git
   * tree object stored under the {@code refs/txn} namespace. To avoid cycles,
   * references to {@code refs/txn} are not stored in that tree object, but
   * instead in a "bootstrap" layer, which is a separate
   * {@link org.eclipse.jgit.lib.RefDatabase} such as
   * {@link org.eclipse.jgit.internal.storage.file.RefDirectory} using local
   * reference files inside of {@code $GIT_DIR/refs}.
   */
  public class RefTreeDatabase extends RefDatabase {
  	private final Repository repo;
  	private final RefDatabase bootstrap;
  	private final String txnCommitted;
  
  	@Nullable
  	private final String txnNamespace;
  	private volatile Scanner.Result refs;
  
  	/**
  	 * Create a RefTreeDb for a repository.
  	 *
 	 * @param repo
 	 *            the repository using references in this database.
 	 * @param bootstrap
 	 *            bootstrap reference database storing the references that
 	 *            anchor the
 	 *            {@link org.eclipse.jgit.internal.storage.reftree.RefTree}.
 	 */
 	public RefTreeDatabase(Repository repo, RefDatabase bootstrap) {
 		Config cfg = repo.getConfig();
 		String committed = cfg.getString("reftree", null, "committedRef"); //$NON-NLS-1$ //$NON-NLS-2$
 		if (committed == null || committed.isEmpty()) {
 			committed = "refs/txn/committed"; //$NON-NLS-1$
 		}
 
 		this.repo = repo;
 		this.bootstrap = bootstrap;
 		this.txnNamespace = initNamespace(committed);
 		this.txnCommitted = committed;
 	}
 
 	/**
 	 * Create a RefTreeDb for a repository.
 	 *
 	 * @param repo
 	 *            the repository using references in this database.
 	 * @param bootstrap
 	 *            bootstrap reference database storing the references that
 	 *            anchor the
 	 *            {@link org.eclipse.jgit.internal.storage.reftree.RefTree}.
 	 * @param txnCommitted
 	 *            name of the bootstrap reference holding the committed RefTree.
 	 */
 	public RefTreeDatabase(Repository repo, RefDatabase bootstrap,
 			String txnCommitted) {
 		this.repo = repo;
 		this.bootstrap = bootstrap;
 		this.txnNamespace = initNamespace(txnCommitted);
 		this.txnCommitted = txnCommitted;
 	}
 
 	private static String initNamespace(String committed) {
 		int s = committed.lastIndexOf('/');
 		if (s < 0) {
 			return null;
 		}
 		return committed.substring(0, s + 1); // Keep trailing '/'.
 	}
 
 	Repository getRepository() {
 		return repo;
 	}
 
 	/**
 	 * Get the bootstrap reference database
 	 *
 	 * @return the bootstrap reference database, which must be used to access
 	 *         {@link #getTxnCommitted()}, {@link #getTxnNamespace()}.
 	 */
 	public RefDatabase getBootstrap() {
 		return bootstrap;
 	}
 
 	/**
 	 * Get name of bootstrap reference anchoring committed RefTree.
 	 *
 	 * @return name of bootstrap reference anchoring committed RefTree.
 	 */
 	public String getTxnCommitted() {
 		return txnCommitted;
 	}
 
 	/**
 	 * Get namespace used by bootstrap layer.
 	 *
 	 * @return namespace used by bootstrap layer, e.g. {@code refs/txn/}. Always
 	 *         ends in {@code '/'}.
 	 */
 	@Nullable
 	public String getTxnNamespace() {
 		return txnNamespace;
 	}
 
 	/** {@inheritDoc} */
 	@Override
 	public void create() throws IOException {
 		bootstrap.create();
 	}
 
 	/** {@inheritDoc} */
 	@Override
 	public boolean performsAtomicTransactions() {
 		return true;
 	}
 
 	/** {@inheritDoc} */
 	@Override
 	public void refresh() {
 		bootstrap.refresh();
 	}
 
 	/** {@inheritDoc} */
 	@Override
 	public void close() {
 		refs = null;
 		bootstrap.close();
 	}
 
 	/** {@inheritDoc} */
 	@Override
 	public Ref getRef(String name) throws IOException {
 		String[] needle = new String[SEARCH_PATH.length];
 		for (int i = 0; i < SEARCH_PATH.length; i++) {
 			needle[i] = SEARCH_PATH[i] + name;
 		}
 		return firstExactRef(needle);
 	}
 
 	/** {@inheritDoc} */
 	@Override
 	public Ref exactRef(String name) throws IOException {
 		if (!repo.isBare() && name.indexOf('/') < 0 && !HEAD.equals(name)) {
 			// Pass through names like MERGE_HEAD, ORIG_HEAD, FETCH_HEAD.
 			return bootstrap.exactRef(name);
 		} else if (conflictsWithBootstrap(name)) {
 			return null;
 		}
 
 		boolean partial = false;
 		Ref src = bootstrap.exactRef(txnCommitted);
 		Scanner.Result c = refs;
 		if (c == null || !c.refTreeId.equals(idOf(src))) {
 			c = Scanner.scanRefTree(repo, src, prefixOf(name), false);
 			partial = true;
 		}
 
 		Ref r = c.all.get(name);
 		if (r != null && r.isSymbolic()) {
 			r = c.sym.get(name);
 			if (partial && r.getObjectId() == null) {
 				// Attempting exactRef("HEAD") with partial scan will leave
 				// an unresolved symref as its target e.g. refs/heads/master
 				// was not read by the partial scan. Scan everything instead.
 				return getRefs(ALL).get(name);
 			}
 		}
 		return r;
 	}
 
 	private static String prefixOf(String name) {
 		int s = name.lastIndexOf('/');
 		if (s >= 0) {
 			return name.substring(0, s);
 		}
 		return ""; //$NON-NLS-1$
 	}
 
 	/** {@inheritDoc} */
 	@Override
 	public Map<String, Ref> getRefs(String prefix) throws IOException {
 		if (!prefix.isEmpty() && prefix.charAt(prefix.length() - 1) != '/') {
 			return new HashMap<>(0);
 		}
 
 		Ref src = bootstrap.exactRef(txnCommitted);
 		Scanner.Result c = refs;
 		if (c == null || !c.refTreeId.equals(idOf(src))) {
 			c = Scanner.scanRefTree(repo, src, prefix, true);
 			if (prefix.isEmpty()) {
 				refs = c;
 			}
 		}
 		return new RefMap(prefix, RefList.<Ref> emptyList(), c.all, c.sym);
 	}
 
 	private static ObjectId idOf(@Nullable Ref src) {
 		return src != null && src.getObjectId() != null
 				? src.getObjectId()
 				: ObjectId.zeroId();
 	}
 
 	/** {@inheritDoc} */
 	@Override
 	public List<Ref> getAdditionalRefs() throws IOException {
 		Collection<Ref> txnRefs;
 		if (txnNamespace != null) {
 			txnRefs = bootstrap.getRefsByPrefix(txnNamespace);
 		} else {
 			Ref r = bootstrap.exactRef(txnCommitted);
 			if (r != null && r.getObjectId() != null) {
 				txnRefs = Collections.singleton(r);
 			} else {
 				txnRefs = Collections.emptyList();
 			}
 		}
 
 		List<Ref> otherRefs = bootstrap.getAdditionalRefs();
 		List<Ref> all = new ArrayList<>(txnRefs.size() + otherRefs.size());
 		all.addAll(txnRefs);
 		all.addAll(otherRefs);
 		return all;
 	}
 
 	/** {@inheritDoc} */
 	@Override
 	public Ref peel(Ref ref) throws IOException {
 		Ref i = ref.getLeaf();
 		ObjectId id = i.getObjectId();
 		if (i.isPeeled() || id == null) {
 			return ref;
 		}
 		try (RevWalk rw = new RevWalk(repo)) {
 			RevObject obj = rw.parseAny(id);
 			if (obj instanceof RevTag) {
 				ObjectId p = rw.peel(obj).copy();
 				i = new ObjectIdRef.PeeledTag(PACKED, i.getName(), id, p);
 			} else {
 				i = new ObjectIdRef.PeeledNonTag(PACKED, i.getName(), id);
 			}
 		}
 		return recreate(ref, i);
 	}
 
 	private static Ref recreate(Ref old, Ref leaf) {
 		if (old.isSymbolic()) {
 			Ref dst = recreate(old.getTarget(), leaf);
 			return new SymbolicRef(old.getName(), dst);
 		}
 		return leaf;
 	}
 
 	/** {@inheritDoc} */
 	@Override
 	public boolean isNameConflicting(String name) throws IOException {
 		return conflictsWithBootstrap(name)
 				|| !getConflictingNames(name).isEmpty();
 	}
 
 	/** {@inheritDoc} */
 	@Override
 	public BatchRefUpdate newBatchUpdate() {
 		return new RefTreeBatch(this);
 	}
 
 	/** {@inheritDoc} */
 	@Override
 	public RefUpdate newUpdate(String name, boolean detach) throws IOException {
 		if (!repo.isBare() && name.indexOf('/') < 0 && !HEAD.equals(name)) {
 			return bootstrap.newUpdate(name, detach);
 		}
 		if (conflictsWithBootstrap(name)) {
 			return new AlwaysFailUpdate(this, name);
 		}
 
 		Ref r = exactRef(name);
 		if (r == null) {
 			r = new ObjectIdRef.Unpeeled(Storage.NEW, name, null);
 		}
 
 		boolean detaching = detach && r.isSymbolic();
 		if (detaching) {
 			r = new ObjectIdRef.Unpeeled(LOOSE, name, r.getObjectId());
 		}
 
 		RefTreeUpdate u = new RefTreeUpdate(this, r);
 		if (detaching) {
 			u.setDetachingSymbolicRef();
 		}
 		return u;
 	}
 
 	/** {@inheritDoc} */
 	@Override
 	public RefRename newRename(String fromName, String toName)
 			throws IOException {
 		RefUpdate from = newUpdate(fromName, true);
 		RefUpdate to = newUpdate(toName, true);
 		return new RefTreeRename(this, from, to);
 	}
 
 	boolean conflictsWithBootstrap(String name) {
 		if (txnNamespace != null && name.startsWith(txnNamespace)) {
 			return true;
 		} else if (txnCommitted.equals(name)) {
 			return true;
 		}
 
 		if (name.indexOf('/') < 0 && !HEAD.equals(name)) {
 			return true;
 		}
 
 		if (name.length() > txnCommitted.length()
 				&& name.charAt(txnCommitted.length()) == '/'
 				&& name.startsWith(txnCommitted)) {
 			return true;
 		}
 		return false;
 	}
 }