/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.flink.runtime.checkpoint;

import java.io.Serializable;

import static org.apache.flink.util.Preconditions.checkArgument;

/**
 * Statistics for a single subtask that is part of a checkpoint.
 *
 * <p>Collects data that is spread over different close places:
 * {@link CheckpointMetaData},
 * {@link SubtaskState}, and
 * {@link PendingCheckpoint}.
 *
 * <p>This is the smallest immutable unit of the stats.
 */
public class SubtaskStateStats implements Serializable {

	private static final long serialVersionUID = 8928594531621862214L;

	/** Index of this sub task. */
	private final int subtaskIndex;

	/**
	 * Timestamp when the ack from this sub task was received at the
	 * coordinator.
	 */
	private final long ackTimestamp;

	/** Size of the checkpointed state at this subtask. */
	private final long stateSize;

	/** Checkpoint duration at the operator (sync part) in milliseconds. */
	private final long syncCheckpointDuration;

	/** Checkpoint duration at the operator (async part) in milliseconds. */
	private final long asyncCheckpointDuration;

	/** Number of buffered bytes during alignment. */
	private final long alignmentBuffered;

	/** Alignment duration in . */
	private final long alignmentDuration;

	/**
	 * Creates the stats for a single subtask.
	 *
	 * @param subtaskIndex Index of the subtask.
	 * @param ackTimestamp Timestamp when the acknowledgement of this subtask was received at the coordinator.
	 * @param stateSize Size of the checkpointed state at this subtask.
	 * @param syncCheckpointDuration Checkpoint duration at the task (synchronous part)
	 * @param asyncCheckpointDuration  Checkpoint duration at the task (asynchronous part)
	 * @param alignmentBuffered Bytes buffered during stream alignment (for exactly-once only).
	 * @param alignmentDuration Duration of the stream alignment (for exactly-once only).
	 */
	SubtaskStateStats(
			int subtaskIndex,
			long ackTimestamp,
			long stateSize,
			long syncCheckpointDuration,
			long asyncCheckpointDuration,
			long alignmentBuffered,
			long alignmentDuration) {

		checkArgument(subtaskIndex >= 0, "Negative subtask index");
		this.subtaskIndex = subtaskIndex;
		checkArgument(stateSize >= 0, "Negative state size");
		this.stateSize = stateSize;
		this.ackTimestamp = ackTimestamp;
		this.syncCheckpointDuration = syncCheckpointDuration;
		this.asyncCheckpointDuration = asyncCheckpointDuration;
		this.alignmentBuffered = alignmentBuffered;
		this.alignmentDuration = alignmentDuration;
	}

	/**
	 * Returns the subtask index.
	 *
	 * @return Subtask index.
	 */
	public int getSubtaskIndex() {
		return subtaskIndex;
	}

	/**
	 * Returns the size of the checkpointed state at this subtask.
	 *
	 * @return Checkpoint state size of the sub task.
	 */
	public long getStateSize() {
		return stateSize;
	}

	/**
	 * Returns the timestamp when the acknowledgement of this subtask was
	 * received at the coordinator.
	 *
	 * @return ACK timestamp at the coordinator.
	 */
	public long getAckTimestamp() {
		return ackTimestamp;
	}

	/**
	 * Computes the duration since the given trigger timestamp.
	 *
	 * <p>If the trigger timestamp is greater than the ACK timestamp, this
	 * returns <code>0</code>.
	 *
	 * @param triggerTimestamp Trigger timestamp of the checkpoint.
	 * @return Duration since the given trigger timestamp.
	 */
	public long getEndToEndDuration(long triggerTimestamp) {
		return Math.max(0, ackTimestamp - triggerTimestamp);
	}

	/**
	 * Returns the duration of the synchronous part of the checkpoint.
	 *
	 * <p>Can return <code>-1</code> if the runtime did not report this.
	 *
	 * @return Duration of the synchronous part of the checkpoint or <code>-1</code>.
	 */
	public long getSyncCheckpointDuration() {
		return syncCheckpointDuration;
	}

	/**
	 * Returns the duration of the asynchronous part of the checkpoint.
	 *
	 * <p>Can return <code>-1</code> if the runtime did not report this.
	 *
	 * @return Duration of the asynchronous part of the checkpoint or <code>-1</code>.
	 */
	public long getAsyncCheckpointDuration() {
		return asyncCheckpointDuration;
	}

	/**
	 * Returns the number of bytes buffered during stream alignment (for
	 * exactly-once only).
	 *
	 * <p>Can return <code>-1</code> if the runtime did not report this.
	 *
	 * @return Number of bytes buffered during stream alignment or <code>-1</code>.
	 */
	public long getAlignmentBuffered() {
		return alignmentBuffered;
	}

	/**
	 * Returns the duration of the stream alignment (for exactly-once only).
	 *
	 * <p>Can return <code>-1</code> if the runtime did not report this.
	 *
	 * @return Duration of the stream alignment or <code>-1</code>.
	 */
	public long getAlignmentDuration() {
		return alignmentDuration;
	}

}