/*
 * Copyright (C) 2016, 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.ketch;

import org.eclipse.jgit.lib.AnyObjectId;
import org.eclipse.jgit.lib.ObjectId;

An ObjectId for a commit extended with incrementing log index.
 For any two LogIndex instances, A is an ancestor of C reachable through parent edges in the graph if A.index < C.index. LogIndex provides a performance optimization for Ketch, the same information can be obtained from RevWalk. 
 Index values are only valid within a single KetchLeader instance after it has won an election. By restricting scope to a single leader new leaders do not need to traverse the entire history to determine the next index for new proposals. This differs from Raft, where leader election uses the log index and the term number to determine which replica holds a sufficiently up-to-date log. Since Ketch uses Git objects for storage of its replicated log, it keeps the term number as Raft does but uses standard Git operations to imply the log index. 
 Round.runAsync(AnyObjectId) bumps the index as each new round is constructed. /**
 * An ObjectId for a commit extended with incrementing log index.
 * <p>
 * For any two LogIndex instances, {@code A} is an ancestor of {@code C}
 * reachable through parent edges in the graph if {@code A.index < C.index}.
 * LogIndex provides a performance optimization for Ketch, the same information
 * can be obtained from {@link org.eclipse.jgit.revwalk.RevWalk}.
 * <p>
 * Index values are only valid within a single
 * {@link org.eclipse.jgit.internal.ketch.KetchLeader} instance after it has won
 * an election. By restricting scope to a single leader new leaders do not need
 * to traverse the entire history to determine the next {@code index} for new
 * proposals. This differs from Raft, where leader election uses the log index
 * and the term number to determine which replica holds a sufficiently
 * up-to-date log. Since Ketch uses Git objects for storage of its replicated
 * log, it keeps the term number as Raft does but uses standard Git operations
 * to imply the log index.
 * <p>
 * {@link org.eclipse.jgit.internal.ketch.Round#runAsync(AnyObjectId)} bumps the
 * index as each new round is constructed.
 */
public class LogIndex extends ObjectId {
	static LogIndex unknown(AnyObjectId id) {
		return new LogIndex(id, 0);
	}

	private final long index;

	private LogIndex(AnyObjectId id, long index) {
		super(id);
		this.index = index;
	}

	LogIndex nextIndex(AnyObjectId id) {
		return new LogIndex(id, index + 1);
	}

	
Get index provided by the current leader instance.
Returns:
index provided by the current leader instance./**
	 * Get index provided by the current leader instance.
	 *
	 * @return index provided by the current leader instance.
	 */
	public long getIndex() {
		return index;
	}

	
Check if this log position committed before another log position.

Only valid for log positions in memory for the current leader.
Params:
c – 
           other (more recent) log position.
Returns:
true if this log position was before c or equal to c and therefore any agreement of c implies agreement on this log position./**
	 * Check if this log position committed before another log position.
	 * <p>
	 * Only valid for log positions in memory for the current leader.
	 *
	 * @param c
	 *            other (more recent) log position.
	 * @return true if this log position was before {@code c} or equal to c and
	 *         therefore any agreement of {@code c} implies agreement on this
	 *         log position.
	 */
	boolean isBefore(LogIndex c) {
		return index <= c.index;
	}

	
Create string suitable for debug logging containing the log index and
abbreviated ObjectId.
Returns:
string suitable for debug logging containing the log index and
        abbreviated ObjectId./**
	 * Create string suitable for debug logging containing the log index and
	 * abbreviated ObjectId.
	 *
	 * @return string suitable for debug logging containing the log index and
	 *         abbreviated ObjectId.
	 */
	@SuppressWarnings("boxing")
	public String describeForLog() {
		return String.format("%5d/%s", index, abbreviate(6).name()); //$NON-NLS-1$
	}

	
{@inheritDoc} /** {@inheritDoc} */
	@SuppressWarnings("boxing")
	@Override
	public String toString() {
		return String.format("LogId[%5d/%s]", index, name()); //$NON-NLS-1$
	}
}