/*
    * Copyright (C) 2019, Google LLC 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.reftable;
  
  import org.eclipse.jgit.lib.ReflogEntry;
  import org.eclipse.jgit.lib.ReflogReader;
  
  import java.io.IOException;
  import java.util.ArrayList;
  import java.util.List;
  import java.util.concurrent.locks.Lock;
  
  /**
   * Implement the ReflogReader interface for a reflog stored in reftable.
   */
  public class ReftableReflogReader implements ReflogReader {
  	private final Lock lock;
  
  	private final Reftable reftable;
  
  	private final String refname;
  
  	ReftableReflogReader(Lock lock, Reftable merged, String refname) {
  		this.lock = lock;
  		this.reftable = merged;
  		this.refname = refname;
  	}
  
  	/** {@inheritDoc} */
  	@Override
  	public ReflogEntry getLastEntry() throws IOException {
  		lock.lock();
  		try {
  			LogCursor cursor = reftable.seekLog(refname);
  			return cursor.next() ? cursor.getReflogEntry() : null;
  		} finally {
  			lock.unlock();
  		}
  	}
  
  	/** {@inheritDoc} */
  	@Override
  	public List<ReflogEntry> getReverseEntries() throws IOException {
  		return getReverseEntries(Integer.MAX_VALUE);
  	}
  
  	/** {@inheritDoc} */
  	@Override
  	public ReflogEntry getReverseEntry(int number) throws IOException {
  		lock.lock();
  		try {
  			LogCursor cursor = reftable.seekLog(refname);
  			while (true) {
  				if (!cursor.next() || number < 0) {
  					return null;
  				}
  				if (number == 0) {
  					return cursor.getReflogEntry();
  				}
  				number--;
  			}
  		} finally {
  			lock.unlock();
  		}
  	}
  
  	/** {@inheritDoc} */
  	@Override
  	public List<ReflogEntry> getReverseEntries(int max) throws IOException {
  		lock.lock();
  		try {
  			LogCursor cursor = reftable.seekLog(refname);
  
  			List<ReflogEntry> result = new ArrayList<>();
  			while (cursor.next() && result.size() < max) {
  				result.add(cursor.getReflogEntry());
  			}
  
  			return result;
  		} finally {
  			lock.unlock();
  		}
  	}
  }