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Swirlds is a software platform designed to build fully-distributed applications that harness the power of the cloud without servers. Now you can develop applications with fairness in decision making, speed, trust and reliability, at a fraction of the cost of traditional server-based platforms.

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/*
 * Copyright (C) 2024 Hedera Hashgraph, LLC
 *
 * Licensed 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 com.swirlds.common.wiring.model;

import com.swirlds.common.context.PlatformContext;
import com.swirlds.common.wiring.model.internal.deterministic.DeterministicHeartbeatScheduler;
import com.swirlds.common.wiring.model.internal.deterministic.DeterministicTaskSchedulerBuilder;
import com.swirlds.common.wiring.schedulers.builders.TaskSchedulerBuilder;
import com.swirlds.common.wiring.wires.output.NoOpOutputWire;
import com.swirlds.common.wiring.wires.output.OutputWire;
import edu.umd.cs.findbugs.annotations.NonNull;
import java.time.Duration;
import java.time.Instant;
import java.util.ArrayList;
import java.util.List;
import java.util.Objects;

/**
 * A deterministic implementation of a wiring model. Suitable for testing, not intended for production use cases.
 */
public class DeterministicWiringModel extends TraceableWiringModel {

    private final PlatformContext platformContext;

    /**
     * Work that we will perform in the current cycle.
     */
    private List currentCycleWork = new ArrayList<>();

    /**
     * Work that we will perform in the next cycle.
     */
    private List nextCycleWork = new ArrayList<>();

    private final DeterministicHeartbeatScheduler heartbeatScheduler;

    /**
     * Constructor.
     *
     * @param platformContext the context for this node
     */
    DeterministicWiringModel(@NonNull final PlatformContext platformContext) {
        super(false);
        this.platformContext = Objects.requireNonNull(platformContext);
        this.heartbeatScheduler = new DeterministicHeartbeatScheduler(this, platformContext.getTime(), "heartbeat");
    }

    /**
     * Advance time. Amount of time that advances depends on how {@link com.swirlds.base.time.Time Time} has been
     * advanced.
     */
    public void tick() {
        for (final Runnable work : currentCycleWork) {
            work.run();
        }

        // Note: heartbeats are handled at their destinations during the next cycle.
        heartbeatScheduler.tick();

        currentCycleWork = nextCycleWork;
        nextCycleWork = new ArrayList<>();
    }

    /**
     * Submit a unit of work to be performed.
     *
     * @param work the work to be performed
     */
    private void submitWork(@NonNull final Runnable work) {
        // Work is never handled in the same cycle as when it is submitted.
        nextCycleWork.add(work);
    }

    /**
     * {@inheritDoc}
     */
    @NonNull
    @Override
    public  TaskSchedulerBuilder schedulerBuilder(@NonNull final String name) {
        return new DeterministicTaskSchedulerBuilder<>(platformContext, this, name, this::submitWork);
    }

    /**
     * {@inheritDoc}
     */
    @NonNull
    @Override
    public OutputWire buildHeartbeatWire(@NonNull final Duration period) {
        return heartbeatScheduler.buildHeartbeatWire(period);
    }

    /**
     * {@inheritDoc}
     */
    @NonNull
    @Override
    public OutputWire getHealthMonitorWire() {
        return new NoOpOutputWire<>(this, "HealthMonitor");
    }

    /**
     * {@inheritDoc}
     */
    @NonNull
    @Override
    public Duration getUnhealthyDuration() {
        return Duration.ZERO;
    }

    /**
     * {@inheritDoc}
     */
    @NonNull
    @Override
    public OutputWire buildHeartbeatWire(final double frequency) {
        return heartbeatScheduler.buildHeartbeatWire(frequency);
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public void start() {
        throwIfStarted();
        markAsStarted();
        heartbeatScheduler.start();
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public void stop() {
        throwIfNotStarted();
    }
}