/*
 * 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.cep.nfa;

import org.apache.flink.cep.nfa.sharedbuffer.EventId;
import org.apache.flink.cep.nfa.sharedbuffer.NodeId;

import javax.annotation.Nullable;

import java.util.Objects;

/**
 * Helper class which encapsulates the currentStateName of the NFA computation. It points to the current currentStateName,
 * the previous entry of the pattern, the current version and the starting timestamp
 * of the overall pattern.
 */
public class ComputationState {
	// pointer to the NFA currentStateName of the computation
	private final String currentStateName;

	// The current version of the currentStateName to discriminate the valid pattern paths in the SharedBuffer
	private final DeweyNumber version;

	// Timestamp of the first element in the pattern
	private final long startTimestamp;

	@Nullable
	private final NodeId previousBufferEntry;

	@Nullable
	private final EventId startEventID;

	private ComputationState(
			final String currentState,
			@Nullable final NodeId previousBufferEntry,
			final DeweyNumber version,
			@Nullable final EventId startEventID,
			final long startTimestamp) {
		this.currentStateName = currentState;
		this.version = version;
		this.startTimestamp = startTimestamp;
		this.previousBufferEntry = previousBufferEntry;
		this.startEventID = startEventID;
	}

	public EventId getStartEventID() {
		return startEventID;
	}

	public NodeId getPreviousBufferEntry() {
		return previousBufferEntry;
	}

	public long getStartTimestamp() {
		return startTimestamp;
	}

	public String getCurrentStateName() {
		return currentStateName;
	}

	public DeweyNumber getVersion() {
		return version;
	}

	@Override
	public boolean equals(Object obj) {
		if (obj instanceof ComputationState) {
			ComputationState other = (ComputationState) obj;
			return Objects.equals(currentStateName, other.currentStateName) &&
				Objects.equals(version, other.version) &&
				startTimestamp == other.startTimestamp &&
				Objects.equals(startEventID, other.startEventID) &&
				Objects.equals(previousBufferEntry, other.previousBufferEntry);
		} else {
			return false;
		}
	}

	@Override
	public String toString() {
		return "ComputationState{" +
			"currentStateName='" + currentStateName + '\'' +
			", version=" + version +
			", startTimestamp=" + startTimestamp +
			", previousBufferEntry=" + previousBufferEntry +
			", startEventID=" + startEventID +
			'}';
	}

	@Override
	public int hashCode() {
		return Objects.hash(currentStateName, version, startTimestamp, startEventID, previousBufferEntry);
	}

	public static ComputationState createStartState(final String state) {
		return createStartState(state, new DeweyNumber(1));
	}

	public static ComputationState createStartState(final String state, final DeweyNumber version) {
		return createState(state, null, version, -1L, null);
	}

	public static ComputationState createState(
			final String currentState,
			final NodeId previousEntry,
			final DeweyNumber version,
			final long startTimestamp,
			final EventId startEventID) {
		return new ComputationState(currentState, previousEntry, version, startEventID, startTimestamp);
	}
}