/*
 * Copyright (C) 2011, 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.
 *
 * 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,
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 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
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 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
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package org.eclipse.jgit.internal.storage.dfs;

import static org.eclipse.jgit.lib.Ref.UNDEFINED_UPDATE_INDEX;
import static org.eclipse.jgit.lib.Ref.Storage.NEW;

import java.io.IOException;
import java.util.Collections;
import java.util.List;
import java.util.Map;
import java.util.concurrent.atomic.AtomicReference;

import org.eclipse.jgit.errors.MissingObjectException;
import org.eclipse.jgit.lib.ObjectIdRef;
import org.eclipse.jgit.lib.Ref;
import org.eclipse.jgit.lib.RefDatabase;
import org.eclipse.jgit.lib.RefRename;
import org.eclipse.jgit.lib.RefUpdate;
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;

Abstract DfsRefDatabase class.
/**
 * Abstract DfsRefDatabase class.
 *
 */
public abstract class DfsRefDatabase extends RefDatabase {
	private final DfsRepository repository;

	private final AtomicReference<RefCache> cache;

	
Initialize the reference database for a repository.
Params:
repository – 
           the repository this database instance manages references for./**
	 * Initialize the reference database for a repository.
	 *
	 * @param repository
	 *            the repository this database instance manages references for.
	 */
	protected DfsRefDatabase(DfsRepository repository) {
		this.repository = repository;
		this.cache = new AtomicReference<>();
	}

	
Get the repository the database holds the references of.
Returns:
the repository the database holds the references of./**
	 * Get the repository the database holds the references of.
	 *
	 * @return the repository the database holds the references of.
	 */
	protected DfsRepository getRepository() {
		return repository;
	}

	boolean exists() throws IOException {
		return 0 < read().size();
	}

	
{@inheritDoc} /** {@inheritDoc} */
	@Override
	public Ref exactRef(String name) throws IOException {
		RefCache curr = read();
		Ref ref = curr.ids.get(name);
		return ref != null ? resolve(ref, 0, curr.ids) : null;
	}

	
{@inheritDoc} /** {@inheritDoc} */
	@Override
	public List<Ref> getAdditionalRefs() {
		return Collections.emptyList();
	}

	
{@inheritDoc} /** {@inheritDoc} */
	@Override
	public Map<String, Ref> getRefs(String prefix) throws IOException {
		RefCache curr = read();
		RefList<Ref> packed = RefList.emptyList();
		RefList<Ref> loose = curr.ids;
		RefList.Builder<Ref> sym = new RefList.Builder<>(curr.sym.size());

		for (int idx = 0; idx < curr.sym.size(); idx++) {
			Ref ref = curr.sym.get(idx);
			String name = ref.getName();
			ref = resolve(ref, 0, loose);
			if (ref != null && ref.getObjectId() != null) {
				sym.add(ref);
			} else {
				// A broken symbolic reference, we have to drop it from the
				// collections the client is about to receive. Should be a
				// rare occurrence so pay a copy penalty.
				int toRemove = loose.find(name);
				if (0 <= toRemove)
					loose = loose.remove(toRemove);
			}
		}

		return new RefMap(prefix, packed, loose, sym.toRefList());
	}

	private Ref resolve(Ref ref, int depth, RefList<Ref> loose)
			throws IOException {
		if (!ref.isSymbolic())
			return ref;

		Ref dst = ref.getTarget();

		if (MAX_SYMBOLIC_REF_DEPTH <= depth)
			return null; // claim it doesn't exist

		dst = loose.get(dst.getName());
		if (dst == null)
			return ref;

		dst = resolve(dst, depth + 1, loose);
		if (dst == null)
			return null;
		return new SymbolicRef(ref.getName(), dst);
	}

	
{@inheritDoc} /** {@inheritDoc} */
	@Override
	public Ref peel(Ref ref) throws IOException {
		final Ref oldLeaf = ref.getLeaf();
		if (oldLeaf.isPeeled() || oldLeaf.getObjectId() == null)
			return ref;

		Ref newLeaf = doPeel(oldLeaf);

		RefCache cur = read();
		int idx = cur.ids.find(oldLeaf.getName());
		if (0 <= idx && cur.ids.get(idx) == oldLeaf) {
			RefList<Ref> newList = cur.ids.set(idx, newLeaf);
			cache.compareAndSet(cur, new RefCache(newList, cur));
			cachePeeledState(oldLeaf, newLeaf);
		}

		return recreate(ref, newLeaf, hasVersioning());
	}

	Ref doPeel(Ref leaf) throws MissingObjectException,
			IOException {
		try (RevWalk rw = new RevWalk(repository)) {
			RevObject obj = rw.parseAny(leaf.getObjectId());
			if (obj instanceof RevTag) {
				return new ObjectIdRef.PeeledTag(
						leaf.getStorage(),
						leaf.getName(),
						leaf.getObjectId(),
						rw.peel(obj).copy(),
						hasVersioning() ? leaf.getUpdateIndex()
								: UNDEFINED_UPDATE_INDEX);
			} else {
				return new ObjectIdRef.PeeledNonTag(
						leaf.getStorage(),
						leaf.getName(),
						leaf.getObjectId(),
						hasVersioning() ? leaf.getUpdateIndex()
								: UNDEFINED_UPDATE_INDEX);
			}
		}
	}

	static Ref recreate(Ref old, Ref leaf, boolean hasVersioning) {
		if (old.isSymbolic()) {
			Ref dst = recreate(old.getTarget(), leaf, hasVersioning);
			return new SymbolicRef(old.getName(), dst,
					hasVersioning ? old.getUpdateIndex()
							: UNDEFINED_UPDATE_INDEX);
		}
		return leaf;
	}

	
{@inheritDoc} /** {@inheritDoc} */
	@Override
	public RefUpdate newUpdate(String refName, boolean detach)
			throws IOException {
		boolean detachingSymbolicRef = false;
		Ref ref = exactRef(refName);
		if (ref == null)
			ref = new ObjectIdRef.Unpeeled(NEW, refName, null);
		else
			detachingSymbolicRef = detach && ref.isSymbolic();

		DfsRefUpdate update = new DfsRefUpdate(this, ref);
		if (detachingSymbolicRef)
			update.setDetachingSymbolicRef();
		return update;
	}

	
{@inheritDoc} /** {@inheritDoc} */
	@Override
	public RefRename newRename(String fromName, String toName)
			throws IOException {
		RefUpdate src = newUpdate(fromName, true);
		RefUpdate dst = newUpdate(toName, true);
		return new DfsRefRename(src, dst);
	}

	
{@inheritDoc} /** {@inheritDoc} */
	@Override
	public boolean isNameConflicting(String refName) throws IOException {
		RefList<Ref> all = read().ids;

		// Cannot be nested within an existing reference.
		int lastSlash = refName.lastIndexOf('/');
		while (0 < lastSlash) {
			String needle = refName.substring(0, lastSlash);
			if (all.contains(needle))
				return true;
			lastSlash = refName.lastIndexOf('/', lastSlash - 1);
		}

		// Cannot be the container of an existing reference.
		String prefix = refName + '/';
		int idx = -(all.find(prefix) + 1);
		if (idx < all.size() && all.get(idx).getName().startsWith(prefix))
			return true;
		return false;
	}

	
{@inheritDoc} /** {@inheritDoc} */
	@Override
	public void create() {
		// Nothing to do.
	}

	
{@inheritDoc} /** {@inheritDoc} */
	@Override
	public void refresh() {
		clearCache();
	}

	
{@inheritDoc} /** {@inheritDoc} */
	@Override
	public void close() {
		clearCache();
	}

	void clearCache() {
		cache.set(null);
	}

	void stored(Ref ref) {
		RefCache oldCache, newCache;
		do {
			oldCache = cache.get();
			if (oldCache == null)
				return;
			newCache = oldCache.put(ref);
		} while (!cache.compareAndSet(oldCache, newCache));
	}

	void removed(String refName) {
		RefCache oldCache, newCache;
		do {
			oldCache = cache.get();
			if (oldCache == null)
				return;
			newCache = oldCache.remove(refName);
		} while (!cache.compareAndSet(oldCache, newCache));
	}

	private RefCache read() throws IOException {
		RefCache c = cache.get();
		if (c == null) {
			c = scanAllRefs();
			cache.set(c);
		}
		return c;
	}

	
Read all known references in the repository.
Throws:
IOException – 
            references cannot be accessed.
Returns:
all current references of the repository./**
	 * Read all known references in the repository.
	 *
	 * @return all current references of the repository.
	 * @throws java.io.IOException
	 *             references cannot be accessed.
	 */
	protected abstract RefCache scanAllRefs() throws IOException;

	
Compare a reference, and put if it matches.

Two reference match if and only if they satisfy the following:

If one reference is a symbolic ref, the other one should be a symbolic
ref.
If both are symbolic refs, the target names should be same.
If both are object ID refs, the object IDs should be same.

Params:
oldRef –  old value to compare to. If the reference is expected to not exist the old value has a storage of Storage.NEW and an ObjectId value of null.
newRef – 
           new reference to store.
Throws:
IOException – 
            the reference cannot be put due to a system error.
Returns:
true if the put was successful; false otherwise./**
	 * Compare a reference, and put if it matches.
	 * <p>
	 * Two reference match if and only if they satisfy the following:
	 *
	 * <ul>
	 * <li>If one reference is a symbolic ref, the other one should be a symbolic
	 * ref.
	 * <li>If both are symbolic refs, the target names should be same.
	 * <li>If both are object ID refs, the object IDs should be same.
	 * </ul>
	 *
	 * @param oldRef
	 *            old value to compare to. If the reference is expected to not
	 *            exist the old value has a storage of
	 *            {@link org.eclipse.jgit.lib.Ref.Storage#NEW} and an ObjectId
	 *            value of {@code null}.
	 * @param newRef
	 *            new reference to store.
	 * @return true if the put was successful; false otherwise.
	 * @throws java.io.IOException
	 *             the reference cannot be put due to a system error.
	 */
	protected abstract boolean compareAndPut(Ref oldRef, Ref newRef)
			throws IOException;

	
Compare a reference, and delete if it matches.
Params:
oldRef – 
           the old reference information that was previously read.
Throws:
IOException – 
            the reference could not be removed due to a system error.
Returns:
true if the remove was successful; false otherwise./**
	 * Compare a reference, and delete if it matches.
	 *
	 * @param oldRef
	 *            the old reference information that was previously read.
	 * @return true if the remove was successful; false otherwise.
	 * @throws java.io.IOException
	 *             the reference could not be removed due to a system error.
	 */
	protected abstract boolean compareAndRemove(Ref oldRef) throws IOException;

	
Update the cached peeled state of a reference

The ref database invokes this method after it peels a reference that had
not been peeled before. This allows the storage to cache the peel state
of the reference, and if it is actually peelable, the target that it
peels to, so that on-the-fly peeling doesn't have to happen on the next
reference read.
Params:
oldLeaf – 
           the old reference.
newLeaf – 
           the new reference, with peel information./**
	 * Update the cached peeled state of a reference
	 * <p>
	 * The ref database invokes this method after it peels a reference that had
	 * not been peeled before. This allows the storage to cache the peel state
	 * of the reference, and if it is actually peelable, the target that it
	 * peels to, so that on-the-fly peeling doesn't have to happen on the next
	 * reference read.
	 *
	 * @param oldLeaf
	 *            the old reference.
	 * @param newLeaf
	 *            the new reference, with peel information.
	 */
	protected void cachePeeledState(Ref oldLeaf, Ref newLeaf) {
		try {
			compareAndPut(oldLeaf, newLeaf);
		} catch (IOException e) {
			// Ignore an exception during caching.
		}
	}

	
Collection of references managed by this database. /** Collection of references managed by this database. */
	public static class RefCache {
		final RefList<Ref> ids;

		final RefList<Ref> sym;

		
Initialize a new reference cache.

The two reference lists supplied must be sorted in correct order
(string compare order) by name.
Params:
ids –  references that carry an ObjectId, and all of sym.
sym – 
           references that are symbolic references to others./**
		 * Initialize a new reference cache.
		 * <p>
		 * The two reference lists supplied must be sorted in correct order
		 * (string compare order) by name.
		 *
		 * @param ids
		 *            references that carry an ObjectId, and all of {@code sym}.
		 * @param sym
		 *            references that are symbolic references to others.
		 */
		public RefCache(RefList<Ref> ids, RefList<Ref> sym) {
			this.ids = ids;
			this.sym = sym;
		}

		RefCache(RefList<Ref> ids, RefCache old) {
			this(ids, old.sym);
		}

		
Returns:
number of references in this cache./** @return number of references in this cache. */
		public int size() {
			return ids.size();
		}

		
Find a reference by name.
Params:
name – 
           full name of the reference.
Returns:
the reference, if it exists, otherwise null./**
		 * Find a reference by name.
		 *
		 * @param name
		 *            full name of the reference.
		 * @return the reference, if it exists, otherwise null.
		 */
		public Ref get(String name) {
			return ids.get(name);
		}

		
Obtain a modified copy of the cache with a ref stored.

This cache instance is not modified by this method.
Params:
ref – 
           reference to add or replace.
Returns:
a copy of this cache, with the reference added or replaced./**
		 * Obtain a modified copy of the cache with a ref stored.
		 * <p>
		 * This cache instance is not modified by this method.
		 *
		 * @param ref
		 *            reference to add or replace.
		 * @return a copy of this cache, with the reference added or replaced.
		 */
		public RefCache put(Ref ref) {
			RefList<Ref> newIds = this.ids.put(ref);
			RefList<Ref> newSym = this.sym;
			if (ref.isSymbolic()) {
				newSym = newSym.put(ref);
			} else {
				int p = newSym.find(ref.getName());
				if (0 <= p)
					newSym = newSym.remove(p);
			}
			return new RefCache(newIds, newSym);
		}

		
Obtain a modified copy of the cache with the ref removed.

This cache instance is not modified by this method.
Params:
refName – 
           reference to remove, if it exists.
Returns:
a copy of this cache, with the reference removed./**
		 * Obtain a modified copy of the cache with the ref removed.
		 * <p>
		 * This cache instance is not modified by this method.
		 *
		 * @param refName
		 *            reference to remove, if it exists.
		 * @return a copy of this cache, with the reference removed.
		 */
		public RefCache remove(String refName) {
			RefList<Ref> newIds = this.ids;
			int p = newIds.find(refName);
			if (0 <= p)
				newIds = newIds.remove(p);

			RefList<Ref> newSym = this.sym;
			p = newSym.find(refName);
			if (0 <= p)
				newSym = newSym.remove(p);
			return new RefCache(newIds, newSym);
		}
	}
}