/*
    * 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 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.Set;
  
  import org.eclipse.jgit.internal.JGitText;
  import org.eclipse.jgit.internal.storage.file.FileObjectDatabase.InsertLooseObjectResult;
  import org.eclipse.jgit.lib.AbbreviatedObjectId;
  import org.eclipse.jgit.lib.AnyObjectId;
  import org.eclipse.jgit.lib.Constants;
  import org.eclipse.jgit.lib.ObjectId;
  import org.eclipse.jgit.lib.ObjectLoader;
  import org.eclipse.jgit.util.FileUtils;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  /**
   * Traditional file system based loose objects handler.
   * <p>
   * This is the loose object representation for a Git object database, where
   * objects are stored loose by hashing them into directories by their
   * {@link org.eclipse.jgit.lib.ObjectId}.
   */
  class LooseObjects {
  	private static final Logger LOG = LoggerFactory
  			.getLogger(LooseObjects.class);
  
  	/**
  	 * Maximum number of attempts to read a loose object for which a stale file
  	 * handle exception is thrown
  	 */
  	private final static int MAX_LOOSE_OBJECT_STALE_READ_ATTEMPTS = 5;
  
  	private final File directory;
  
  	private final UnpackedObjectCache unpackedObjectCache;
  
  	/**
  	 * Initialize a reference to an on-disk object directory.
  	 *
  	 * @param dir
  	 *            the location of the <code>objects</code> directory.
  	 */
  	LooseObjects(File dir) {
  		directory = dir;
  		unpackedObjectCache = new UnpackedObjectCache();
  	}
  
  	/**
  	 * Getter for the field <code>directory</code>.
  	 *
  	 * @return the location of the <code>objects</code> directory.
  	 */
  	File getDirectory() {
  		return directory;
  	}
  
  	void create() throws IOException {
  		FileUtils.mkdirs(directory);
  	}
  
  	void close() {
  		unpackedObjectCache().clear();
  	}
  
  	/** {@inheritDoc} */
  	@Override
  	public String toString() {
  		return "LooseObjects[" + directory + "]"; //$NON-NLS-1$ //$NON-NLS-2$
  	}
  
  	boolean hasCached(AnyObjectId id) {
  		return unpackedObjectCache().isUnpacked(id);
  	}
  
  	/**
  	 * Does the requested object exist as a loose object?
  	 *
  	 * @param objectId
  	 *            identity of the object to test for existence of.
  	 * @return {@code true} if the specified object is stored as a loose object.
  	 */
 	boolean has(AnyObjectId objectId) {
 		return fileFor(objectId).exists();
 	}
 
 	/**
 	 * Find objects matching the prefix abbreviation.
 	 *
 	 * @param matches
 	 *            set to add any located ObjectIds to. This is an output
 	 *            parameter.
 	 * @param id
 	 *            prefix to search for.
 	 * @param matchLimit
 	 *            maximum number of results to return. At most this many
 	 *            ObjectIds should be added to matches before returning.
 	 * @return {@code true} if the matches were exhausted before reaching
 	 *         {@code maxLimit}.
 	 */
 	boolean resolve(Set<ObjectId> matches, AbbreviatedObjectId id,
 			int matchLimit) {
 		String fanOut = id.name().substring(0, 2);
 		String[] entries = new File(directory, 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() > matchLimit) {
 					return false;
 				}
 			}
 		}
 		return true;
 	}
 
 	ObjectLoader open(WindowCursor curs, AnyObjectId id) throws IOException {
 		int readAttempts = 0;
 		while (readAttempts < MAX_LOOSE_OBJECT_STALE_READ_ATTEMPTS) {
 			readAttempts++;
 			File path = fileFor(id);
 			try {
 				return getObjectLoader(curs, path, id);
 			} catch (FileNotFoundException noFile) {
 				if (path.exists()) {
 					throw noFile;
 				}
 				break;
 			} catch (IOException e) {
 				if (!FileUtils.isStaleFileHandleInCausalChain(e)) {
 					throw e;
 				}
 				if (LOG.isDebugEnabled()) {
 					LOG.debug(MessageFormat.format(
 							JGitText.get().looseObjectHandleIsStale, id.name(),
 							Integer.valueOf(readAttempts), Integer.valueOf(
 									MAX_LOOSE_OBJECT_STALE_READ_ATTEMPTS)));
 				}
 			}
 		}
 		unpackedObjectCache().remove(id);
 		return null;
 	}
 
 	/**
 	 * Provides a loader for an objectId
 	 *
 	 * @param curs
 	 *            cursor on the database
 	 * @param path
 	 *            the path of the loose object
 	 * @param id
 	 *            the object id
 	 * @return a loader for the loose file object
 	 * @throws IOException
 	 *             when file does not exist or it could not be opened
 	 */
 	ObjectLoader getObjectLoader(WindowCursor curs, File path, AnyObjectId id)
 			throws IOException {
 		try (FileInputStream in = new FileInputStream(path)) {
 			unpackedObjectCache().add(id);
 			return UnpackedObject.open(in, path, id, curs);
 		}
 	}
 
 	/**
 	 * <p>
 	 * Getter for the field <code>unpackedObjectCache</code>.
 	 * </p>
 	 * This accessor is particularly useful to allow mocking of this class for
 	 * testing purposes.
 	 *
 	 * @return the cache of the objects currently unpacked.
 	 */
 	UnpackedObjectCache unpackedObjectCache() {
 		return unpackedObjectCache;
 	}
 
 	long getSize(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;
 		}
 	}
 
 	InsertLooseObjectResult insert(File tmp, ObjectId id) throws IOException {
 		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;
 	}
 
 	/**
 	 * Compute the location of a loose object file.
 	 *
 	 * @param objectId
 	 *            identity of the object to get the File location for.
 	 * @return {@link java.io.File} location of the specified loose object.
 	 */
 	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);
 	}
 }