/*
 * 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.INDEX;
import static org.eclipse.jgit.internal.storage.pack.PackExt.PACK;

import java.io.BufferedReader;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.NoSuchFileException;
import java.nio.file.StandardCopyOption;
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;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * 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.PackFile}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 {
	private static final Logger LOG = LoggerFactory
			.getLogger(ObjectDirectory.class);

	/** 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 PackDirectory packed;

	private final File preservedDirectory;

	private final File alternatesFile;

	private final FS fs;

	private final AtomicReference<AlternateHandle[]> alternates;

	private final UnpackedObjectCache unpackedObjectCache;

	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"); //$NON-NLS-1$
		preservedDirectory = new File(packDirectory, "preserved"); //$NON-NLS-1$
		alternatesFile = new File(objects, Constants.INFO_ALTERNATES);
		packed = new PackDirectory(config, packDirectory);
		unpackedObjectCache = new UnpackedObjectCache();
		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 objects;
	}

	/**
	 * <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 preservedDirectory;
	}

	/** {@inheritDoc} */
	@Override
	public boolean exists() {
		return fs.exists(objects);
	}

	/** {@inheritDoc} */
	@Override
	public void create() throws IOException {
		FileUtils.mkdirs(objects);
		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() {
		unpackedObjectCache.clear();

		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<PackFile> getPacks() {
		return packed.getPacks();
	}

	/**
	 * {@inheritDoc}
	 * <p>
	 * Add a single existing pack to the list of available pack files.
	 */
	@Override
	public PackFile openPack(File pack)
			throws IOException {
		final String p = pack.getName();
		if (p.length() != 50 || !p.startsWith("pack-") || !p.endsWith(".pack")) //$NON-NLS-1$ //$NON-NLS-2$
			throw new IOException(MessageFormat.format(JGitText.get().notAValidPack, pack));

		// The pack and index are assumed to exist. The existence of other
		// extensions needs to be explicitly checked.
		//
		int extensions = PACK.getBit() | INDEX.getBit();
		final String base = p.substring(0, p.length() - 4);
		for (PackExt ext : PackExt.values()) {
			if ((extensions & ext.getBit()) == 0) {
				final String name = base + ext.getExtension();
				if (new File(pack.getParentFile(), name).exists())
					extensions |= ext.getBit();
			}
		}

		PackFile res = new PackFile(pack, extensions);
		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 unpackedObjectCache.isUnpacked(objectId)
				|| 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 (fileFor(objectId).exists()) {
			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;

		String fanOut = id.name().substring(0, 2);
		String[] entries = new File(getDirectory(), fanOut).list();
		if (entries != null) {
			for (String e : entries) {
				if (e.length() != Constants.OBJECT_ID_STRING_LENGTH - 2)
					continue;
				try {
					ObjectId entId = ObjectId.fromString(fanOut + e);
					if (id.prefixCompare(entId) == 0)
						matches.add(entId);
				} catch (IllegalArgumentException notId) {
					continue;
				}
				if (matches.size() > 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 {
		if (unpackedObjectCache.isUnpacked(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 {
		File path = fileFor(id);
		try (FileInputStream in = new FileInputStream(path)) {
			unpackedObjectCache.add(id);
			return UnpackedObject.open(in, path, id, curs);
		} catch (FileNotFoundException noFile) {
			if (path.exists()) {
				throw noFile;
			}
			unpackedObjectCache.remove(id);
			return null;
		}
	}

	@Override
	long getObjectSize(WindowCursor curs, AnyObjectId id)
			throws IOException {
		if (unpackedObjectCache.isUnpacked(id)) {
			long len = getLooseObjectSize(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 = getLooseObjectSize(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;
	}

	private long getLooseObjectSize(WindowCursor curs, AnyObjectId id)
			throws IOException {
		File f = fileFor(id);
		try (FileInputStream in = new FileInputStream(f)) {
			unpackedObjectCache.add(id);
			return UnpackedObject.getSize(in, id, curs);
		} catch (FileNotFoundException noFile) {
			if (f.exists()) {
				throw noFile;
			}
			unpackedObjectCache.remove(id);
			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);
			}
		}
	}

	@Override
	InsertLooseObjectResult insertUnpackedObject(File tmp, ObjectId id,
			boolean createDuplicate) throws IOException {
		// If the object is already in the repository, remove temporary file.
		//
		if (unpackedObjectCache.isUnpacked(id)) {
			FileUtils.delete(tmp, FileUtils.RETRY);
			return InsertLooseObjectResult.EXISTS_LOOSE;
		}
		if (!createDuplicate && has(id)) {
			FileUtils.delete(tmp, FileUtils.RETRY);
			return InsertLooseObjectResult.EXISTS_PACKED;
		}

		final File dst = fileFor(id);
		if (dst.exists()) {
			// We want to be extra careful and avoid replacing an object
			// that already exists. We can't be sure renameTo() would
			// fail on all platforms if dst exists, so we check first.
			//
			FileUtils.delete(tmp, FileUtils.RETRY);
			return InsertLooseObjectResult.EXISTS_LOOSE;
		}

		try {
			return tryMove(tmp, dst, id);
		} catch (NoSuchFileException e) {
			// It's possible the directory doesn't exist yet as the object
			// directories are always lazily created. Note that we try the
			// rename/move first as the directory likely does exist.
			//
			// Create the directory.
			//
			FileUtils.mkdir(dst.getParentFile(), true);
		} catch (IOException e) {
			// Any other IO error is considered a failure.
			//
			LOG.error(e.getMessage(), e);
			FileUtils.delete(tmp, FileUtils.RETRY);
			return InsertLooseObjectResult.FAILURE;
		}

		try {
			return tryMove(tmp, dst, id);
		} catch (IOException e) {
			// The object failed to be renamed into its proper location and
			// it doesn't exist in the repository either. We really don't
			// know what went wrong, so fail.
			//
			LOG.error(e.getMessage(), e);
			FileUtils.delete(tmp, FileUtils.RETRY);
			return InsertLooseObjectResult.FAILURE;
		}
	}

	private InsertLooseObjectResult tryMove(File tmp, File dst,
			ObjectId id)
			throws IOException {
		Files.move(FileUtils.toPath(tmp), FileUtils.toPath(dst),
				StandardCopyOption.ATOMIC_MOVE);
		dst.setReadOnly();
		unpackedObjectCache.add(id);
		return InsertLooseObjectResult.INSERTED;
	}

	@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 (PackFile 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);
	}

	/**
	 * {@inheritDoc}
	 * <p>
	 * Compute the location of a loose object file.
	 */
	@Override
	public File fileFor(AnyObjectId objectId) {
		String n = objectId.name();
		String d = n.substring(0, 2);
		String f = n.substring(2);
		return new File(new File(getDirectory(), d), f);
	}

	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);
	}
}