/*
    * Copyright (C) 2009, Robin Rosenberg <robin.rosenberg@dewire.com> 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.FileNotFoundException;
  import java.io.IOException;
  import java.util.ArrayList;
  import java.util.Collections;
  import java.util.List;
  
  import org.eclipse.jgit.lib.Constants;
  import org.eclipse.jgit.lib.ReflogEntry;
  import org.eclipse.jgit.lib.ReflogReader;
  import org.eclipse.jgit.lib.Repository;
  import org.eclipse.jgit.util.IO;
  import org.eclipse.jgit.util.RawParseUtils;
  
  /**
   * Utility for reading reflog entries
   */
  class ReflogReaderImpl implements ReflogReader {
  	private File logName;
  
  	/**
  	 * @param db
  	 * @param refname
  	 */
  	ReflogReaderImpl(Repository db, String refname) {
  		logName = new File(db.getDirectory(), Constants.LOGS + '/' + refname);
  	}
  
  	/* (non-Javadoc)
  	 * @see org.eclipse.jgit.internal.storage.file.ReflogReaader#getLastEntry()
  	 */
  	/** {@inheritDoc} */
  	@Override
  	public ReflogEntry getLastEntry() throws IOException {
  		return getReverseEntry(0);
  	}
  
  	/* (non-Javadoc)
  	 * @see org.eclipse.jgit.internal.storage.file.ReflogReaader#getReverseEntries()
  	 */
  	/** {@inheritDoc} */
  	@Override
  	public List<ReflogEntry> getReverseEntries() throws IOException {
  		return getReverseEntries(Integer.MAX_VALUE);
  	}
  
  	/* (non-Javadoc)
  	 * @see org.eclipse.jgit.internal.storage.file.ReflogReaader#getReverseEntry(int)
  	 */
  	/** {@inheritDoc} */
  	@Override
  	public ReflogEntry getReverseEntry(int number) throws IOException {
  		if (number < 0)
  			throw new IllegalArgumentException();
  
  		final byte[] log;
  		try {
  			log = IO.readFully(logName);
  		} catch (FileNotFoundException e) {
  			if (logName.exists()) {
  				throw e;
  			}
  			return null;
  		}
  
  		int rs = RawParseUtils.prevLF(log, log.length);
  		int current = 0;
  		while (rs >= 0) {
  			rs = RawParseUtils.prevLF(log, rs);
  			if (number == current)
  				return new ReflogEntryImpl(log, rs < 0 ? 0 : rs + 2);
  			current++;
  		}
  		return null;
  	}
  
  	/* (non-Javadoc)
  	 * @see org.eclipse.jgit.internal.storage.file.ReflogReaader#getReverseEntries(int)
  	 */
  	/** {@inheritDoc} */
  	@Override
  	public List<ReflogEntry> getReverseEntries(int max) throws IOException {
  		final byte[] log;
  		try {
  			log = IO.readFully(logName);
  		} catch (FileNotFoundException e) {
  			if (logName.exists()) {
 				throw e;
 			}
 			return Collections.emptyList();
 		}
 
 		int rs = RawParseUtils.prevLF(log, log.length);
 		List<ReflogEntry> ret = new ArrayList<>();
 		while (rs >= 0 && max-- > 0) {
 			rs = RawParseUtils.prevLF(log, rs);
 			ReflogEntry entry = new ReflogEntryImpl(log, rs < 0 ? 0 : rs + 2);
 			ret.add(entry);
 		}
 		return ret;
 	}
 }