/*
    * Copyright (C) 2009, 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.file;
  
  import static java.nio.charset.StandardCharsets.UTF_8;
  import static org.eclipse.jgit.internal.storage.pack.PackExt.PACK;
  import static org.eclipse.jgit.internal.storage.pack.PackExt.BITMAP_INDEX;
  import static org.eclipse.jgit.internal.storage.pack.PackExt.INDEX;
  
  import java.io.BufferedReader;
  import java.io.File;
  import java.io.FileNotFoundException;
  import java.io.IOException;
  import java.nio.file.Files;
  import java.text.MessageFormat;
  import java.util.ArrayList;
  import java.util.Collection;
  import java.util.Collections;
  import java.util.HashSet;
  import java.util.List;
  import java.util.Objects;
  import java.util.Set;
  import java.util.concurrent.atomic.AtomicReference;
  
  import org.eclipse.jgit.internal.JGitText;
  import org.eclipse.jgit.internal.storage.pack.ObjectToPack;
  import org.eclipse.jgit.internal.storage.pack.PackExt;
  import org.eclipse.jgit.internal.storage.pack.PackWriter;
  import org.eclipse.jgit.lib.AbbreviatedObjectId;
  import org.eclipse.jgit.lib.AnyObjectId;
  import org.eclipse.jgit.lib.Config;
  import org.eclipse.jgit.lib.Constants;
  import org.eclipse.jgit.lib.ObjectDatabase;
  import org.eclipse.jgit.lib.ObjectId;
  import org.eclipse.jgit.lib.ObjectLoader;
  import org.eclipse.jgit.lib.RepositoryCache;
  import org.eclipse.jgit.lib.RepositoryCache.FileKey;
  import org.eclipse.jgit.util.FS;
  import org.eclipse.jgit.util.FileUtils;
  
  /**
   * Traditional file system based {@link org.eclipse.jgit.lib.ObjectDatabase}.
   * <p>
   * This is the classical object database representation for a Git repository,
   * where objects are stored loose by hashing them into directories by their
   * {@link org.eclipse.jgit.lib.ObjectId}, or are stored in compressed containers
   * known as {@link org.eclipse.jgit.internal.storage.file.Pack}s.
   * <p>
   * Optionally an object database can reference one or more alternates; other
   * ObjectDatabase instances that are searched in addition to the current
   * database.
   * <p>
   * Databases are divided into two halves: a half that is considered to be fast
   * to search (the {@code PackFile}s), and a half that is considered to be slow
   * to search (loose objects). When alternates are present the fast half is fully
   * searched (recursively through all alternates) before the slow half is
   * considered.
   */
  public class ObjectDirectory extends FileObjectDatabase {
  	/** Maximum number of candidates offered as resolutions of abbreviation. */
  	private static final int RESOLVE_ABBREV_LIMIT = 256;
  
  	private final AlternateHandle handle = new AlternateHandle(this);
  
  	private final Config config;
  
  	private final File objects;
  
  	private final File infoDirectory;
  
  	private final LooseObjects loose;
  
  	private final PackDirectory packed;
  
  	private final PackDirectory preserved;
  
  	private final File alternatesFile;
  
  	private final FS fs;
  
  	private final AtomicReference<AlternateHandle[]> alternates;
  
  	private final File shallowFile;
  
  	private FileSnapshot shallowFileSnapshot = FileSnapshot.DIRTY;
  
  	private Set<ObjectId> shallowCommitsIds;
  
  	/**
  	 * Initialize a reference to an on-disk object directory.
  	 *
 	 * @param cfg
 	 *            configuration this directory consults for write settings.
 	 * @param dir
 	 *            the location of the <code>objects</code> directory.
 	 * @param alternatePaths
 	 *            a list of alternate object directories
 	 * @param fs
 	 *            the file system abstraction which will be necessary to perform
 	 *            certain file system operations.
 	 * @param shallowFile
 	 *            file which contains IDs of shallow commits, null if shallow
 	 *            commits handling should be turned off
 	 * @throws java.io.IOException
 	 *             an alternate object cannot be opened.
 	 */
 	public ObjectDirectory(final Config cfg, final File dir,
 			File[] alternatePaths, FS fs, File shallowFile) throws IOException {
 		config = cfg;
 		objects = dir;
 		infoDirectory = new File(objects, "info"); //$NON-NLS-1$
 		File packDirectory = new File(objects, "pack"); //$NON-NLS-1$
 		File preservedDirectory = new File(packDirectory, "preserved"); //$NON-NLS-1$
 		alternatesFile = new File(objects, Constants.INFO_ALTERNATES);
 		loose = new LooseObjects(objects);
 		packed = new PackDirectory(config, packDirectory);
 		preserved = new PackDirectory(config, preservedDirectory);
 		this.fs = fs;
 		this.shallowFile = shallowFile;
 
 		alternates = new AtomicReference<>();
 		if (alternatePaths != null) {
 			AlternateHandle[] alt;
 
 			alt = new AlternateHandle[alternatePaths.length];
 			for (int i = 0; i < alternatePaths.length; i++)
 				alt[i] = openAlternate(alternatePaths[i]);
 			alternates.set(alt);
 		}
 	}
 
 	/** {@inheritDoc} */
 	@Override
 	public final File getDirectory() {
 		return loose.getDirectory();
 	}
 
 	/**
 	 * <p>Getter for the field <code>packDirectory</code>.</p>
 	 *
 	 * @return the location of the <code>pack</code> directory.
 	 */
 	public final File getPackDirectory() {
 		return packed.getDirectory();
 	}
 
 	/**
 	 * <p>Getter for the field <code>preservedDirectory</code>.</p>
 	 *
 	 * @return the location of the <code>preserved</code> directory.
 	 */
 	public final File getPreservedDirectory() {
 		return preserved.getDirectory();
 	}
 
 	/** {@inheritDoc} */
 	@Override
 	public boolean exists() {
 		return fs.exists(objects);
 	}
 
 	/** {@inheritDoc} */
 	@Override
 	public void create() throws IOException {
 		loose.create();
 		FileUtils.mkdir(infoDirectory);
 		packed.create();
 	}
 
 	/** {@inheritDoc} */
 	@Override
 	public ObjectDirectoryInserter newInserter() {
 		return new ObjectDirectoryInserter(this, config);
 	}
 
 	/**
 	 * Create a new inserter that inserts all objects as pack files, not loose
 	 * objects.
 	 *
 	 * @return new inserter.
 	 */
 	public PackInserter newPackInserter() {
 		return new PackInserter(this);
 	}
 
 	/** {@inheritDoc} */
 	@Override
 	public void close() {
 		loose.close();
 
 		packed.close();
 
 		// Fully close all loaded alternates and clear the alternate list.
 		AlternateHandle[] alt = alternates.get();
 		if (alt != null && alternates.compareAndSet(alt, null)) {
 			for(AlternateHandle od : alt)
 				od.close();
 		}
 	}
 
 	/** {@inheritDoc} */
 	@Override
 	public Collection<Pack> getPacks() {
 		return packed.getPacks();
 	}
 
 	/**
 	 * {@inheritDoc}
 	 * <p>
 	 * Add a single existing pack to the list of available pack files.
 	 */
 	@Override
 	public Pack openPack(File pack) throws IOException {
 		PackFile pf;
 		try {
 			pf = new PackFile(pack);
 		} catch (IllegalArgumentException e) {
 			throw new IOException(
 					MessageFormat.format(JGitText.get().notAValidPack, pack),
 					e);
 		}
 
 		String p = pf.getName();
 		// TODO(nasserg): See if PackFile can do these checks instead
 		if (p.length() != 50 || !p.startsWith("pack-") //$NON-NLS-1$
 				|| !pf.getPackExt().equals(PACK)) {
 			throw new IOException(
 					MessageFormat.format(JGitText.get().notAValidPack, pack));
 		}
 
 		PackFile bitmapIdx = pf.create(BITMAP_INDEX);
 		Pack res = new Pack(pack, bitmapIdx.exists() ? bitmapIdx : null);
 		packed.insert(res);
 		return res;
 	}
 
 	/** {@inheritDoc} */
 	@Override
 	public String toString() {
 		return "ObjectDirectory[" + getDirectory() + "]"; //$NON-NLS-1$ //$NON-NLS-2$
 	}
 
 	/** {@inheritDoc} */
 	@Override
 	public boolean has(AnyObjectId objectId) {
 		return loose.hasCached(objectId)
 				|| hasPackedOrLooseInSelfOrAlternate(objectId)
 				|| (restoreFromSelfOrAlternate(objectId, null)
 						&& hasPackedOrLooseInSelfOrAlternate(objectId));
 	}
 
 	private boolean hasPackedOrLooseInSelfOrAlternate(AnyObjectId objectId) {
 		return hasPackedInSelfOrAlternate(objectId, null)
 				|| hasLooseInSelfOrAlternate(objectId, null);
 	}
 
 	private boolean hasPackedInSelfOrAlternate(AnyObjectId objectId,
 			Set<AlternateHandle.Id> skips) {
 		if (hasPackedObject(objectId)) {
 			return true;
 		}
 		skips = addMe(skips);
 		for (AlternateHandle alt : myAlternates()) {
 			if (!skips.contains(alt.getId())) {
 				if (alt.db.hasPackedInSelfOrAlternate(objectId, skips)) {
 					return true;
 				}
 			}
 		}
 		return false;
 	}
 
 	private boolean hasLooseInSelfOrAlternate(AnyObjectId objectId,
 			Set<AlternateHandle.Id> skips) {
 		if (loose.has(objectId)) {
 			return true;
 		}
 		skips = addMe(skips);
 		for (AlternateHandle alt : myAlternates()) {
 			if (!skips.contains(alt.getId())) {
 				if (alt.db.hasLooseInSelfOrAlternate(objectId, skips)) {
 					return true;
 				}
 			}
 		}
 		return false;
 	}
 
 	boolean hasPackedObject(AnyObjectId objectId) {
 		return packed.has(objectId);
 	}
 
 	@Override
 	void resolve(Set<ObjectId> matches, AbbreviatedObjectId id)
 			throws IOException {
 		resolve(matches, id, null);
 	}
 
 	private void resolve(Set<ObjectId> matches, AbbreviatedObjectId id,
 			Set<AlternateHandle.Id> skips)
 			throws IOException {
 		if (!packed.resolve(matches, id, RESOLVE_ABBREV_LIMIT))
 			return;
 
 		if (!loose.resolve(matches, id, RESOLVE_ABBREV_LIMIT))
 			return;
 
 		skips = addMe(skips);
 		for (AlternateHandle alt : myAlternates()) {
 			if (!skips.contains(alt.getId())) {
 				alt.db.resolve(matches, id, skips);
 				if (matches.size() > RESOLVE_ABBREV_LIMIT) {
 					return;
 				}
 			}
 		}
 	}
 
 	@Override
 	ObjectLoader openObject(WindowCursor curs, AnyObjectId objectId)
 			throws IOException {
 		ObjectLoader ldr = openObjectWithoutRestoring(curs, objectId);
 		if (ldr == null && restoreFromSelfOrAlternate(objectId, null)) {
 			ldr = openObjectWithoutRestoring(curs, objectId);
 		}
 		return ldr;
 	}
 
 	private ObjectLoader openObjectWithoutRestoring(WindowCursor curs, AnyObjectId objectId)
 			throws IOException {
 		if (loose.hasCached(objectId)) {
 			ObjectLoader ldr = openLooseObject(curs, objectId);
 			if (ldr != null) {
 				return ldr;
 			}
 		}
 		ObjectLoader ldr = openPackedFromSelfOrAlternate(curs, objectId, null);
 		if (ldr != null) {
 			return ldr;
 		}
 		return openLooseFromSelfOrAlternate(curs, objectId, null);
 	}
 
 	private ObjectLoader openPackedFromSelfOrAlternate(WindowCursor curs,
 			AnyObjectId objectId, Set<AlternateHandle.Id> skips) {
 		ObjectLoader ldr = openPackedObject(curs, objectId);
 		if (ldr != null) {
 			return ldr;
 		}
 		skips = addMe(skips);
 		for (AlternateHandle alt : myAlternates()) {
 			if (!skips.contains(alt.getId())) {
 				ldr = alt.db.openPackedFromSelfOrAlternate(curs, objectId, skips);
 				if (ldr != null) {
 					return ldr;
 				}
 			}
 		}
 		return null;
 	}
 
 	private ObjectLoader openLooseFromSelfOrAlternate(WindowCursor curs,
 			AnyObjectId objectId, Set<AlternateHandle.Id> skips)
 					throws IOException {
 		ObjectLoader ldr = openLooseObject(curs, objectId);
 		if (ldr != null) {
 			return ldr;
 		}
 		skips = addMe(skips);
 		for (AlternateHandle alt : myAlternates()) {
 			if (!skips.contains(alt.getId())) {
 				ldr = alt.db.openLooseFromSelfOrAlternate(curs, objectId, skips);
 				if (ldr != null) {
 					return ldr;
 				}
 			}
 		}
 		return null;
 	}
 
 	ObjectLoader openPackedObject(WindowCursor curs, AnyObjectId objectId) {
 		return packed.open(curs, objectId);
 	}
 
 	@Override
 	ObjectLoader openLooseObject(WindowCursor curs, AnyObjectId id)
 			throws IOException {
 		return loose.open(curs, id);
 	}
 
 	@Override
 	long getObjectSize(WindowCursor curs, AnyObjectId id) throws IOException {
 		long sz = getObjectSizeWithoutRestoring(curs, id);
 		if (0 > sz && restoreFromSelfOrAlternate(id, null)) {
 			sz = getObjectSizeWithoutRestoring(curs, id);
 		}
 		return sz;
 	}
 
 	private long getObjectSizeWithoutRestoring(WindowCursor curs,
 			AnyObjectId id) throws IOException {
 		if (loose.hasCached(id)) {
 			long len = loose.getSize(curs, id);
 			if (0 <= len) {
 				return len;
 			}
 		}
 		long len = getPackedSizeFromSelfOrAlternate(curs, id, null);
 		if (0 <= len) {
 			return len;
 		}
 		return getLooseSizeFromSelfOrAlternate(curs, id, null);
 	}
 
 	private long getPackedSizeFromSelfOrAlternate(WindowCursor curs,
 			AnyObjectId id, Set<AlternateHandle.Id> skips) {
 		long len = packed.getSize(curs, id);
 		if (0 <= len) {
 			return len;
 		}
 		skips = addMe(skips);
 		for (AlternateHandle alt : myAlternates()) {
 			if (!skips.contains(alt.getId())) {
 				len = alt.db.getPackedSizeFromSelfOrAlternate(curs, id, skips);
 				if (0 <= len) {
 					return len;
 				}
 			}
 		}
 		return -1;
 	}
 
 	private long getLooseSizeFromSelfOrAlternate(WindowCursor curs,
 			AnyObjectId id, Set<AlternateHandle.Id> skips) throws IOException {
 		long len = loose.getSize(curs, id);
 		if (0 <= len) {
 			return len;
 		}
 		skips = addMe(skips);
 		for (AlternateHandle alt : myAlternates()) {
 			if (!skips.contains(alt.getId())) {
 				len = alt.db.getLooseSizeFromSelfOrAlternate(curs, id, skips);
 				if (0 <= len) {
 					return len;
 				}
 			}
 		}
 		return -1;
 	}
 
 	@Override
 	void selectObjectRepresentation(PackWriter packer, ObjectToPack otp,
 			WindowCursor curs) throws IOException {
 		selectObjectRepresentation(packer, otp, curs, null);
 	}
 
 	private void selectObjectRepresentation(PackWriter packer, ObjectToPack otp,
 			WindowCursor curs, Set<AlternateHandle.Id> skips) throws IOException {
 		packed.selectRepresentation(packer, otp, curs);
 
 		skips = addMe(skips);
 		for (AlternateHandle h : myAlternates()) {
 			if (!skips.contains(h.getId())) {
 				h.db.selectObjectRepresentation(packer, otp, curs, skips);
 			}
 		}
 	}
 
 	private boolean restoreFromSelfOrAlternate(AnyObjectId objectId,
 			Set<AlternateHandle.Id> skips) {
 		if (restoreFromSelf(objectId)) {
 			return true;
 		}
 
 		skips = addMe(skips);
 		for (AlternateHandle alt : myAlternates()) {
 			if (!skips.contains(alt.getId())) {
 				if (alt.db.restoreFromSelfOrAlternate(objectId, skips)) {
 					return true;
 				}
 			}
 		}
 		return false;
 	}
 
 	private boolean restoreFromSelf(AnyObjectId objectId) {
 		Pack preservedPack = preserved.getPack(objectId);
 		if (preservedPack == null) {
 			return false;
 		}
 		PackFile preservedFile = new PackFile(preservedPack.getPackFile());
 		// Restore the index last since the set will be considered for use once
 		// the index appears.
 		for (PackExt ext : PackExt.values()) {
 			if (!INDEX.equals(ext)) {
 				restore(preservedFile.create(ext));
 			}
 		}
 		restore(preservedFile.create(INDEX));
 		return true;
 	}
 
 	private boolean restore(PackFile preservedPack) {
 		PackFile restored = preservedPack
 				.createForDirectory(packed.getDirectory());
 		try {
 			Files.createLink(restored.toPath(), preservedPack.toPath());
 		} catch (IOException e) {
 			return false;
 		}
 		return true;
 	}
 
 	@Override
 	InsertLooseObjectResult insertUnpackedObject(File tmp, ObjectId id,
 			boolean createDuplicate) throws IOException {
 		// If the object is already in the repository, remove temporary file.
 		//
 		if (loose.hasCached(id)) {
 			FileUtils.delete(tmp, FileUtils.RETRY);
 			return InsertLooseObjectResult.EXISTS_LOOSE;
 		}
 		if (!createDuplicate && has(id)) {
 			FileUtils.delete(tmp, FileUtils.RETRY);
 			return InsertLooseObjectResult.EXISTS_PACKED;
 		}
 		return loose.insert(tmp, id);
 	}
 
 	@Override
 	Config getConfig() {
 		return config;
 	}
 
 	@Override
 	FS getFS() {
 		return fs;
 	}
 
 	@Override
 	Set<ObjectId> getShallowCommits() throws IOException {
 		if (shallowFile == null || !shallowFile.isFile())
 			return Collections.emptySet();
 
 		if (shallowFileSnapshot == null
 				|| shallowFileSnapshot.isModified(shallowFile)) {
 			shallowCommitsIds = new HashSet<>();
 
 			try (BufferedReader reader = open(shallowFile)) {
 				String line;
 				while ((line = reader.readLine()) != null) {
 					try {
 						shallowCommitsIds.add(ObjectId.fromString(line));
 					} catch (IllegalArgumentException ex) {
 						throw new IOException(MessageFormat
 								.format(JGitText.get().badShallowLine, line),
 								ex);
 					}
 				}
 			}
 
 			shallowFileSnapshot = FileSnapshot.save(shallowFile);
 		}
 
 		return shallowCommitsIds;
 	}
 
 	void closeAllPackHandles(File packFile) {
 		// if the packfile already exists (because we are rewriting a
 		// packfile for the same set of objects maybe with different
 		// PackConfig) then make sure we get rid of all handles on the file.
 		// Windows will not allow for rename otherwise.
 		if (packFile.exists()) {
 			for (Pack p : packed.getPacks()) {
 				if (packFile.getPath().equals(p.getPackFile().getPath())) {
 					p.close();
 					break;
 				}
 			}
 		}
 	}
 
 	AlternateHandle[] myAlternates() {
 		AlternateHandle[] alt = alternates.get();
 		if (alt == null) {
 			synchronized (alternates) {
 				alt = alternates.get();
 				if (alt == null) {
 					try {
 						alt = loadAlternates();
 					} catch (IOException e) {
 						alt = new AlternateHandle[0];
 					}
 					alternates.set(alt);
 				}
 			}
 		}
 		return alt;
 	}
 
 	Set<AlternateHandle.Id> addMe(Set<AlternateHandle.Id> skips) {
 		if (skips == null) {
 			skips = new HashSet<>();
 		}
 		skips.add(handle.getId());
 		return skips;
 	}
 
 	private AlternateHandle[] loadAlternates() throws IOException {
 		final List<AlternateHandle> l = new ArrayList<>(4);
 		try (BufferedReader br = open(alternatesFile)) {
 			String line;
 			while ((line = br.readLine()) != null) {
 				l.add(openAlternate(line));
 			}
 		}
 		return l.toArray(new AlternateHandle[0]);
 	}
 
 	private static BufferedReader open(File f)
 			throws IOException, FileNotFoundException {
 		return Files.newBufferedReader(f.toPath(), UTF_8);
 	}
 
 	private AlternateHandle openAlternate(String location)
 			throws IOException {
 		final File objdir = fs.resolve(objects, location);
 		return openAlternate(objdir);
 	}
 
 	private AlternateHandle openAlternate(File objdir) throws IOException {
 		final File parent = objdir.getParentFile();
 		if (FileKey.isGitRepository(parent, fs)) {
 			FileKey key = FileKey.exact(parent, fs);
 			FileRepository db = (FileRepository) RepositoryCache.open(key);
 			return new AlternateRepository(db);
 		}
 
 		ObjectDirectory db = new ObjectDirectory(config, objdir, null, fs, null);
 		return new AlternateHandle(db);
 	}
 
 	/**
 	 * Compute the location of a loose object file.
 	 */
 	@Override
 	public File fileFor(AnyObjectId objectId) {
 		return loose.fileFor(objectId);
 	}
 
 	static class AlternateHandle {
 		static class Id {
 			String alternateId;
 
 			public Id(File object) {
 				try {
 					this.alternateId = object.getCanonicalPath();
 				} catch (Exception e) {
 					alternateId = null;
 				}
 			}
 
 			@Override
 			public boolean equals(Object o) {
 				if (o == this) {
 					return true;
 				}
 				if (o == null || !(o instanceof Id)) {
 					return false;
 				}
 				Id aId = (Id) o;
 				return Objects.equals(alternateId, aId.alternateId);
 			}
 
 			@Override
 			public int hashCode() {
 				if (alternateId == null) {
 					return 1;
 				}
 				return alternateId.hashCode();
 			}
 		}
 
 		final ObjectDirectory db;
 
 		AlternateHandle(ObjectDirectory db) {
 			this.db = db;
 		}
 
 		void close() {
 			db.close();
 		}
 
 		public Id getId(){
 			return db.getAlternateId();
 		}
 	}
 
 	static class AlternateRepository extends AlternateHandle {
 		final FileRepository repository;
 
 		AlternateRepository(FileRepository r) {
 			super(r.getObjectDatabase());
 			repository = r;
 		}
 
 		@Override
 		void close() {
 			repository.close();
 		}
 	}
 
 	/** {@inheritDoc} */
 	@Override
 	public ObjectDatabase newCachedDatabase() {
 		return newCachedFileObjectDatabase();
 	}
 
 	CachedObjectDirectory newCachedFileObjectDatabase() {
 		return new CachedObjectDirectory(this);
 	}
 
 	AlternateHandle.Id getAlternateId() {
 		return new AlternateHandle.Id(objects);
 	}
 }