/*
 * 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.maven.lifecycle.internal.concurrent;

import javax.inject.Inject;
import javax.inject.Named;
import javax.xml.stream.XMLStreamException;

import java.io.IOException;
import java.time.Duration;
import java.time.Instant;
import java.util.ArrayList;
import java.util.Collections;
import java.util.HashMap;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;
import java.util.Optional;
import java.util.Set;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.Executors;
import java.util.concurrent.locks.ReadWriteLock;
import java.util.concurrent.locks.ReentrantReadWriteLock;
import java.util.stream.Collectors;
import java.util.stream.Stream;

import org.apache.maven.api.Lifecycle;
import org.apache.maven.api.MonotonicClock;
import org.apache.maven.api.plugin.descriptor.AfterLink;
import org.apache.maven.api.services.LifecycleRegistry;
import org.apache.maven.api.services.MavenException;
import org.apache.maven.api.xml.XmlNode;
import org.apache.maven.api.xml.XmlService;
import org.apache.maven.execution.BuildFailure;
import org.apache.maven.execution.BuildSuccess;
import org.apache.maven.execution.ExecutionEvent;
import org.apache.maven.execution.MavenExecutionRequest;
import org.apache.maven.execution.MavenSession;
import org.apache.maven.execution.ProjectDependencyGraph;
import org.apache.maven.execution.ProjectExecutionEvent;
import org.apache.maven.execution.ProjectExecutionListener;
import org.apache.maven.impl.util.PhasingExecutor;
import org.apache.maven.internal.MultilineMessageHelper;
import org.apache.maven.internal.impl.DefaultLifecycleRegistry;
import org.apache.maven.internal.transformation.TransformerManager;
import org.apache.maven.lifecycle.LifecycleExecutionException;
import org.apache.maven.lifecycle.LifecycleNotFoundException;
import org.apache.maven.lifecycle.LifecyclePhaseNotFoundException;
import org.apache.maven.lifecycle.MojoExecutionConfigurator;
import org.apache.maven.lifecycle.internal.BuildThreadFactory;
import org.apache.maven.lifecycle.internal.CompoundProjectExecutionListener;
import org.apache.maven.lifecycle.internal.ExecutionEventCatapult;
import org.apache.maven.lifecycle.internal.GoalTask;
import org.apache.maven.lifecycle.internal.LifecycleTask;
import org.apache.maven.lifecycle.internal.MojoDescriptorCreator;
import org.apache.maven.lifecycle.internal.MojoExecutor;
import org.apache.maven.lifecycle.internal.ReactorBuildStatus;
import org.apache.maven.lifecycle.internal.ReactorContext;
import org.apache.maven.lifecycle.internal.Task;
import org.apache.maven.lifecycle.internal.TaskSegment;
import org.apache.maven.model.Plugin;
import org.apache.maven.model.PluginExecution;
import org.apache.maven.plugin.MavenPluginManager;
import org.apache.maven.plugin.MojoExecution;
import org.apache.maven.plugin.MojoNotFoundException;
import org.apache.maven.plugin.PluginDescriptorParsingException;
import org.apache.maven.plugin.descriptor.MojoDescriptor;
import org.apache.maven.plugin.descriptor.Parameter;
import org.apache.maven.plugin.descriptor.PluginDescriptor;
import org.apache.maven.project.MavenProject;
import org.codehaus.plexus.classworlds.realm.ClassRealm;
import org.eclipse.aether.repository.RemoteRepository;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import static org.apache.maven.api.Lifecycle.AFTER;
import static org.apache.maven.api.Lifecycle.AT;
import static org.apache.maven.api.Lifecycle.BEFORE;
import static org.apache.maven.api.Lifecycle.Phase.PACKAGE;
import static org.apache.maven.api.Lifecycle.Phase.READY;
import static org.apache.maven.lifecycle.internal.concurrent.BuildStep.CREATED;
import static org.apache.maven.lifecycle.internal.concurrent.BuildStep.EXECUTED;
import static org.apache.maven.lifecycle.internal.concurrent.BuildStep.FAILED;
import static org.apache.maven.lifecycle.internal.concurrent.BuildStep.PLAN;
import static org.apache.maven.lifecycle.internal.concurrent.BuildStep.PLANNING;
import static org.apache.maven.lifecycle.internal.concurrent.BuildStep.SCHEDULED;
import static org.apache.maven.lifecycle.internal.concurrent.BuildStep.SETUP;
import static org.apache.maven.lifecycle.internal.concurrent.BuildStep.SKIPPED;
import static org.apache.maven.lifecycle.internal.concurrent.BuildStep.TEARDOWN;

/**
 * Executes the Maven build plan in a concurrent manner, handling the lifecycle phases and plugin executions.
 * This executor implements a weave-mode build strategy, where builds are executed phase-by-phase rather than
 * project-by-project.
 *
 * <h2>Key Features:</h2>
 * <ul>
 *   <li>Concurrent execution of compatible build steps across projects</li>
 *   <li>Thread-safety validation for plugins</li>
 *   <li>Support for forked executions and lifecycle phases</li>
 *   <li>Dynamic build plan adjustment during execution</li>
 * </ul>
 *
 * <h2>Execution Strategy:</h2>
 * <p>The executor follows these main steps:</p>
 * <ol>
 *   <li>Initial plan creation based on project dependencies and task segments</li>
 *   <li>Concurrent execution of build steps while maintaining dependency order</li>
 *   <li>Dynamic replanning when necessary (e.g., for forked executions)</li>
 *   <li>Project setup, execution, and teardown phases management</li>
 * </ol>
 *
 * <h2>Thread Management:</h2>
 * <p>The number of threads used is determined by:</p>
 * <pre>
 * min(degreeOfConcurrency, numberOfProjects)
 * </pre>
 * where degreeOfConcurrency is set via the -T command-line option.
 *
 * <h2>Build Step States:</h2>
 * <ul>
 *   <li>CREATED: Initial state of a build step</li>
 *   <li>PLANNING: Step is being planned</li>
 *   <li>SCHEDULED: Step is queued for execution</li>
 *   <li>EXECUTED: Step has completed successfully</li>
 *   <li>FAILED: Step execution failed</li>
 * </ul>
 *
 * <p><strong>NOTE:</strong> This class is not part of any public API and can be changed or deleted without prior notice.</p>
 *
 * @since 3.0
 */
@Named
public class BuildPlanExecutor {

    private static final Object GLOBAL = new Object();

    private final Logger logger = LoggerFactory.getLogger(getClass());

    private final MojoExecutor mojoExecutor;
    private final ExecutionEventCatapult eventCatapult;
    private final ProjectExecutionListener projectExecutionListener;
    private final TransformerManager transformerManager;
    private final BuildPlanLogger buildPlanLogger;
    private final Map<String, MojoExecutionConfigurator> mojoExecutionConfigurators;
    private final MavenPluginManager mavenPluginManager;
    private final MojoDescriptorCreator mojoDescriptorCreator;
    private final LifecycleRegistry lifecycles;

    @Inject
    @SuppressWarnings("checkstyle:ParameterNumber")
    public BuildPlanExecutor(
            @Named("concurrent") MojoExecutor mojoExecutor,
            ExecutionEventCatapult eventCatapult,
            List<ProjectExecutionListener> listeners,
            TransformerManager transformerManager,
            BuildPlanLogger buildPlanLogger,
            Map<String, MojoExecutionConfigurator> mojoExecutionConfigurators,
            MavenPluginManager mavenPluginManager,
            MojoDescriptorCreator mojoDescriptorCreator,
            LifecycleRegistry lifecycles) {
        this.mojoExecutor = mojoExecutor;
        this.eventCatapult = eventCatapult;
        this.projectExecutionListener = new CompoundProjectExecutionListener(listeners);
        this.transformerManager = transformerManager;
        this.buildPlanLogger = buildPlanLogger;
        this.mojoExecutionConfigurators = mojoExecutionConfigurators;
        this.mavenPluginManager = mavenPluginManager;
        this.mojoDescriptorCreator = mojoDescriptorCreator;
        this.lifecycles = lifecycles;
    }

    public void execute(MavenSession session, ReactorContext reactorContext, List<TaskSegment> taskSegments)
            throws ExecutionException, InterruptedException {
        try (BuildContext ctx = new BuildContext(session, reactorContext, taskSegments)) {
            ctx.execute();
        }
    }

    class BuildContext implements AutoCloseable {
        final MavenSession session;
        final ReactorContext reactorContext;
        final PhasingExecutor executor;
        final Map<Object, Clock> clocks = new ConcurrentHashMap<>();
        final ReadWriteLock lock = new ReentrantReadWriteLock();
        final int threads;
        BuildPlan plan;

        BuildContext(MavenSession session, ReactorContext reactorContext, List<TaskSegment> taskSegments) {
            this.session = session;
            this.reactorContext = reactorContext;
            this.threads = Math.min(
                    session.getRequest().getDegreeOfConcurrency(),
                    session.getProjects().size());
            // Propagate the parallel flag to the root session
            session.setParallel(threads > 1);
            this.executor = new PhasingExecutor(Executors.newFixedThreadPool(threads, new BuildThreadFactory()));

            // build initial plan
            this.plan = buildInitialPlan(taskSegments);
        }

        BuildContext() {
            this.session = null;
            this.reactorContext = null;
            this.threads = 1;
            this.executor = null;
            this.plan = null;
        }

        public BuildPlan buildInitialPlan(List<TaskSegment> taskSegments) {
            int nThreads = Math.min(
                    session.getRequest().getDegreeOfConcurrency(),
                    session.getProjects().size());
            boolean parallel = nThreads > 1;
            // Propagate the parallel flag to the root session
            session.setParallel(parallel);

            ProjectDependencyGraph dependencyGraph = session.getProjectDependencyGraph();
            MavenProject rootProject = session.getTopLevelProject();

            Map<MavenProject, List<MavenProject>> allProjects = new LinkedHashMap<>();
            dependencyGraph
                    .getSortedProjects()
                    .forEach(p -> allProjects.put(p, dependencyGraph.getUpstreamProjects(p, false)));

            BuildPlan plan = new BuildPlan(allProjects);
            for (TaskSegment taskSegment : taskSegments) {
                Map<MavenProject, List<MavenProject>> projects = taskSegment.isAggregating()
                        ? Collections.singletonMap(rootProject, allProjects.get(rootProject))
                        : allProjects;

                BuildPlan segment = calculateMojoExecutions(projects, taskSegment.getTasks());
                plan.then(segment);
            }

            // Create plan, setup and teardown
            for (MavenProject project : plan.getAllProjects().keySet()) {
                BuildStep pplan = new BuildStep(PLAN, project, null);
                pplan.status.set(PLANNING); // the plan step always need planning
                BuildStep setup = new BuildStep(SETUP, project, null);
                BuildStep teardown = new BuildStep(TEARDOWN, project, null);
                teardown.executeAfter(setup);
                setup.executeAfter(pplan);
                plan.steps(project).forEach(step -> {
                    if (step.predecessors.stream().noneMatch(s -> s.project == project)) {
                        step.executeAfter(setup);
                    } else if (step.successors.stream().noneMatch(s -> s.project == project)) {
                        teardown.executeAfter(step);
                    }
                });
                Stream.of(pplan, setup, teardown).forEach(step -> plan.addStep(project, step.name, step));
            }

            return plan;
        }

        private void checkUnboundVersions(BuildPlan buildPlan) {
            String defaulModelId = DefaultLifecycleRegistry.DEFAULT_LIFECYCLE_MODELID;
            List<String> unversionedPlugins = buildPlan
                    .allSteps()
                    .flatMap(step -> step.mojos.values().stream().flatMap(map -> map.values().stream()))
                    .map(MojoExecution::getPlugin)
                    .filter(p -> p.getLocation("version") != null
                            && p.getLocation("version").getSource() != null
                            && defaulModelId.equals(
                                    p.getLocation("version").getSource().getModelId()))
                    .distinct()
                    .map(Plugin::getArtifactId) // managed by us, groupId is always o.a.m.plugins
                    .toList();
            if (!unversionedPlugins.isEmpty()) {
                logger.warn("Version not locked for default bindings plugins " + unversionedPlugins
                        + ", you should define versions in pluginManagement section of your " + "pom.xml or parent");
            }
        }

        private void checkThreadSafety(BuildPlan buildPlan) {
            if (threads > 1) {
                Set<MojoExecution> unsafeExecutions = buildPlan
                        .allSteps()
                        .flatMap(step -> step.mojos.values().stream().flatMap(map -> map.values().stream()))
                        .filter(execution -> !execution.getMojoDescriptor().isV4Api())
                        .collect(Collectors.toSet());
                if (!unsafeExecutions.isEmpty()) {
                    for (String s : MultilineMessageHelper.format("""
                                Your build is requesting concurrent execution, but this project contains the \
                                following plugin(s) that have goals not built with Maven 4 to support concurrent \
                                execution. While this /may/ work fine, please look for plugin updates and/or \
                                request plugins be made thread-safe. If reporting an issue, report it against the \
                                plugin in question, not against Apache Maven.""")) {
                        logger.warn(s);
                    }
                    if (logger.isDebugEnabled()) {
                        Set<MojoDescriptor> unsafeGoals = unsafeExecutions.stream()
                                .map(MojoExecution::getMojoDescriptor)
                                .collect(Collectors.toSet());
                        logger.warn("The following goals are not Maven 4 goals:");
                        for (MojoDescriptor unsafeGoal : unsafeGoals) {
                            logger.warn("  " + unsafeGoal.getId());
                        }
                    } else {
                        Set<Plugin> unsafePlugins = unsafeExecutions.stream()
                                .map(MojoExecution::getPlugin)
                                .collect(Collectors.toSet());
                        logger.warn("The following plugins are not Maven 4 plugins:");
                        for (Plugin unsafePlugin : unsafePlugins) {
                            logger.warn("  " + unsafePlugin.getId());
                        }
                        logger.warn("");
                        logger.warn("Enable verbose output (-X) to see precisely which goals are not marked as"
                                + " thread-safe.");
                    }
                    logger.warn(MultilineMessageHelper.separatorLine());
                }
            }
        }

        void execute() {
            try (var phase = executor.phase()) {
                plan();
                executePlan();
            } catch (Exception e) {
                session.getResult().addException(e);
            }
        }

        @Override
        public void close() {
            this.executor.close();
        }

        /**
         * Processes a single build step, deciding whether to schedule it for execution or skip it.
         *
         * @param step The build step to process
         */
        private void processStep(BuildStep step) {
            // 1. Apply reactor failure behavior to decide whether to schedule or skip
            ReactorBuildStatus status = reactorContext.getReactorBuildStatus();
            boolean isAfterStep = step.name.startsWith(AFTER);
            boolean shouldExecute;

            // Check if all predecessors are executed successfully
            boolean allPredecessorsExecuted = step.predecessors.stream().allMatch(s -> s.status.get() == EXECUTED);

            // Special case for after:* steps - they should run if their corresponding before:* step ran
            if (isAfterStep) {
                String phaseName = step.name.substring(AFTER.length());
                // Always process after:* steps for cleanup if their before:* step ran
                shouldExecute = plan.step(step.project, BEFORE + phaseName)
                        .map(s -> {
                            int stepStatus = s.status.get();
                            return stepStatus == EXECUTED;
                        })
                        .orElse(false);

                // Check if any predecessor failed - if so, we'll run the step but mark it as SKIPPED
                boolean anyPredecessorFailed = step.predecessors.stream().anyMatch(s -> s.status.get() == FAILED);

                // If any predecessor failed, we'll use a special status transition: CREATED -> SKIPPED
                // This ensures the step runs for cleanup but is marked as skipped in the end
                if (shouldExecute && anyPredecessorFailed) {
                    // We'll run the step but mark it as SKIPPED instead of SCHEDULED
                    if (step.status.compareAndSet(CREATED, SKIPPED)) {
                        logger.debug(
                                "Running after:* step {} for cleanup but marking it as SKIPPED because a predecessor failed",
                                step);
                        executor.execute(() -> {
                            try {
                                executeStep(step);
                                executePlan();
                            } catch (Exception e) {
                                step.status.compareAndSet(SKIPPED, FAILED);
                                // Store the exception in the step for handling in the TEARDOWN phase
                                step.exception = e;
                                logger.debug("Stored exception for step {} to be handled in TEARDOWN phase", step, e);
                                // Let the scheduler handle after:* phases and TEARDOWN in the next cycle
                                executePlan();
                            }
                        });
                        return; // Skip the rest of the method since we've handled this step
                    }
                }
            } else if (TEARDOWN.equals(step.name)) {
                // TEARDOWN should always run to ensure proper cleanup and error handling
                // We'll handle success/failure reporting inside the TEARDOWN phase
                shouldExecute = true;
            } else {
                // For regular steps:
                // Don't run for halted builds, blacklisted projects, or if predecessors failed
                shouldExecute = !status.isHalted() && !status.isBlackListed(step.project) && allPredecessorsExecuted;
            }

            // 2. Either schedule the step or mark it as skipped based on the decision
            if (shouldExecute && step.status.compareAndSet(CREATED, SCHEDULED)) {
                boolean nextIsPlanning = step.successors.stream().anyMatch(st -> PLAN.equals(st.name));
                executor.execute(() -> {
                    try {
                        executeStep(step);
                        if (nextIsPlanning) {
                            lock.writeLock().lock();
                            try {
                                plan();
                            } finally {
                                lock.writeLock().unlock();
                            }
                        }
                        executePlan();
                    } catch (Exception e) {
                        step.status.compareAndSet(SCHEDULED, FAILED);

                        // Store the exception in the step for handling in the TEARDOWN phase
                        step.exception = e;
                        logger.debug("Stored exception for step {} to be handled in TEARDOWN phase", step, e);

                        // Let the scheduler handle after:* phases and TEARDOWN in the next cycle
                        executePlan();
                    }
                });
            } else if (step.status.compareAndSet(CREATED, SKIPPED)) {
                // Skip the step and provide a specific reason
                if (!shouldExecute) {
                    if (status.isHalted()) {
                        logger.debug("Skipping step {} because the build is halted", step);
                    } else if (status.isBlackListed(step.project)) {
                        logger.debug("Skipping step {} because the project is blacklisted", step);
                    } else if (TEARDOWN.equals(step.name)) {
                        // This should never happen given we always process TEARDOWN steps
                        logger.warn("Unexpected skipping of TEARDOWN step {}", step);
                    } else {
                        logger.debug("Skipping step {} because a dependency has failed", step);
                    }
                } else {
                    // Skip because predecessors failed or were skipped
                    logger.debug(
                            "Skipping step {} because one or more predecessors did not execute successfully", step);
                }
                // Recursively call executePlan to process steps that depend on this one
                executePlan();
            }
        }

        private void executePlan() {
            // Even if the build is halted, we still want to execute TEARDOWN and after:* steps
            // for proper cleanup, so we don't return early here
            Clock global = getClock(GLOBAL);
            global.start();
            lock.readLock().lock();
            try {
                // Process build steps in a logical order:
                // 1. Find steps that are not yet started (CREATED status)
                // 2. Check if all their predecessors have completed (in a terminal state)
                // 3. Process each step (schedule or skip based on reactor failure behavior)
                plan.sortedNodes().stream()
                        // 1. Filter steps that are in CREATED state
                        .filter(BuildStep::isCreated)
                        // 2. Check if all predecessors are in a terminal state
                        .filter(step -> step.predecessors.stream().allMatch(BuildStep::isDone))
                        // 3. Process each step
                        .forEach(this::processStep);
            } finally {
                lock.readLock().unlock();
            }
        }

        /**
         * Executes a single build step, which can be one of:
         * - PLAN: Project build planning
         * - SETUP: Project initialization
         * - TEARDOWN: Project cleanup
         * - Default: Actual mojo/plugin executions
         *
         * @param step The build step to execute
         * @throws IOException If there's an IO error during execution
         * @throws LifecycleExecutionException If there's a lifecycle execution error
         */
        private void executeStep(BuildStep step) throws IOException, LifecycleExecutionException {
            Clock clock = getClock(step.project);
            switch (step.name) {
                case PLAN:
                    // Planning steps should be executed out of normal execution
                    throw new IllegalStateException();
                case SETUP:
                    attachToThread(step);
                    transformerManager.injectTransformedArtifacts(session.getRepositorySession(), step.project);
                    projectExecutionListener.beforeProjectExecution(new ProjectExecutionEvent(session, step.project));
                    eventCatapult.fire(ExecutionEvent.Type.ProjectStarted, session, null);
                    break;
                case TEARDOWN:
                    attachToThread(step);

                    // Check if there are any stored exceptions for this project
                    List<Throwable> failures = null;
                    boolean allStepsExecuted = true;
                    for (BuildStep projectStep : plan.steps(step.project).toList()) {
                        Exception exception = projectStep.exception;
                        if (exception != null) {
                            if (failures == null) {
                                failures = new ArrayList<>();
                            }
                            failures.add(exception);
                        }
                        allStepsExecuted &= step == projectStep || projectStep.status.get() == EXECUTED;
                    }

                    if (failures != null) {
                        // Handle the stored exception
                        Throwable failure;
                        if (failures.size() == 1) {
                            failure = failures.get(
                                    0); // Single exception, no need to wrap it in a LifecycleExecutionException
                        } else {
                            failure = new LifecycleExecutionException("Error building project");
                            failures.forEach(failure::addSuppressed);
                        }
                        handleBuildError(reactorContext, session, step.project, failure);
                    } else if (allStepsExecuted) {
                        // If there were no failures, report success
                        projectExecutionListener.afterProjectExecutionSuccess(
                                new ProjectExecutionEvent(session, step.project, Collections.emptyList()));
                        reactorContext
                                .getResult()
                                .addBuildSummary(new BuildSuccess(step.project, clock.wallTime(), clock.execTime()));
                        eventCatapult.fire(ExecutionEvent.Type.ProjectSucceeded, session, null);
                    } else {
                        eventCatapult.fire(ExecutionEvent.Type.ProjectSkipped, session, null);
                    }
                    break;
                default:
                    List<MojoExecution> executions = step.executions().toList();
                    if (!executions.isEmpty()) {
                        attachToThread(step);
                        clock.start();
                        try {
                            executions.forEach(mojoExecution -> {
                                mojoExecutionConfigurator(mojoExecution).configure(step.project, mojoExecution, true);
                                finalizeMojoConfiguration(mojoExecution);
                            });
                            mojoExecutor.execute(session, executions);
                        } finally {
                            clock.stop();
                        }
                    }
                    break;
            }
            step.status.compareAndSet(SCHEDULED, EXECUTED);
        }

        private void attachToThread(BuildStep step) {
            BuildPlanExecutor.attachToThread(step.project);
            session.setCurrentProject(step.project);
        }

        private Clock getClock(Object key) {
            return clocks.computeIfAbsent(key, p -> new Clock());
        }

        private void plan() {
            lock.writeLock().lock();
            try {
                Set<BuildStep> planSteps = plan.allSteps()
                        .filter(step -> PLAN.equals(step.name))
                        .filter(step -> step.predecessors.stream().allMatch(s -> s.status.get() == EXECUTED))
                        .filter(step -> step.status.compareAndSet(PLANNING, SCHEDULED))
                        .collect(Collectors.toSet());
                for (BuildStep step : planSteps) {
                    MavenProject project = step.project;
                    for (Plugin plugin : project.getBuild().getPlugins()) {
                        for (PluginExecution execution : plugin.getExecutions()) {
                            for (String goal : execution.getGoals()) {
                                MojoDescriptor mojoDescriptor = getMojoDescriptor(project, plugin, goal);
                                String phase =
                                        execution.getPhase() != null ? execution.getPhase() : mojoDescriptor.getPhase();
                                if (phase == null) {
                                    continue;
                                }
                                String tmpResolvedPhase = plan.aliases().getOrDefault(phase, phase);
                                String resolvedPhase = tmpResolvedPhase.startsWith(AT)
                                        ? tmpResolvedPhase.substring(AT.length())
                                        : tmpResolvedPhase;
                                plan.step(project, resolvedPhase).ifPresent(n -> {
                                    MojoExecution mojoExecution = new MojoExecution(mojoDescriptor, execution.getId());
                                    mojoExecution.setLifecyclePhase(phase);
                                    n.addMojo(mojoExecution, execution.getPriority());
                                    if (mojoDescriptor.getDependencyCollectionRequired() != null
                                            || mojoDescriptor.getDependencyResolutionRequired() != null) {
                                        for (MavenProject p :
                                                plan.getAllProjects().get(project)) {
                                            plan.step(p, AFTER + PACKAGE)
                                                    .ifPresent(a -> plan.requiredStep(project, resolvedPhase)
                                                            .executeAfter(a));
                                        }
                                    }
                                    // Apply @After annotation ordering constraints from the mojo descriptor
                                    applyAfterLinks(mojoDescriptor, project, resolvedPhase);
                                });
                            }
                        }
                    }
                }

                BuildPlan buildPlan = plan;
                for (BuildStep step :
                        planSteps.stream().flatMap(p -> plan.steps(p.project)).toList()) {
                    for (MojoExecution execution : step.executions().toList()) {
                        buildPlan = computeForkPlan(step, execution, buildPlan);
                    }
                }

                for (BuildStep step : planSteps) {
                    MavenProject project = step.project;
                    buildPlanLogger.writePlan(plan, project);
                    step.status.compareAndSet(SCHEDULED, EXECUTED);
                }

                checkThreadSafety(plan);
                checkUnboundVersions(plan);
            } finally {
                lock.writeLock().unlock();
            }
        }

        /**
         * Applies lifecycle ordering constraints from {@code @After} annotations on a mojo descriptor.
         * Each {@link AfterLink} is translated into build step ordering edges, matching the same
         * semantics as {@link Lifecycle.Link} processing in {@code calculateLifecycleMappings}.
         *
         * @param mojoDescriptor the mojo descriptor that may contain after links
         * @param project the project the mojo is bound to
         * @param resolvedPhase the resolved phase the mojo is bound to
         */
        private void applyAfterLinks(MojoDescriptor mojoDescriptor, MavenProject project, String resolvedPhase) {
            List<AfterLink> afterLinks = mojoDescriptor.getMojoDescriptorV4().getAfterLinks();
            if (afterLinks == null || afterLinks.isEmpty()) {
                return;
            }
            for (AfterLink afterLink : afterLinks) {
                String targetPhase = afterLink.getPhase();
                String type = afterLink.getType();
                if ("PROJECT".equals(type)) {
                    // Same-project ordering: this phase starts after target phase completes
                    plan.step(project, AFTER + targetPhase)
                            .ifPresent(targetAfter -> plan.requiredStep(project, BEFORE + resolvedPhase)
                                    .executeAfter(targetAfter));
                } else if ("DEPENDENCIES".equals(type)) {
                    // Cross-project ordering: this phase starts after each dependency's target phase completes
                    String scope = afterLink.getScope();
                    for (MavenProject dep :
                            filterByScope(project, plan.getAllProjects().get(project), scope)) {
                        plan.step(dep, AFTER + targetPhase)
                                .ifPresent(depAfter -> plan.requiredStep(project, BEFORE + resolvedPhase)
                                        .executeAfter(depAfter));
                    }
                } else if ("CHILDREN".equals(type)) {
                    // Parent-child ordering: bidirectional coordination with child modules
                    BuildStep before = plan.requiredStep(project, BEFORE + resolvedPhase);
                    BuildStep after = plan.requiredStep(project, AFTER + resolvedPhase);
                    if (project.getCollectedProjects() != null) {
                        project.getCollectedProjects().forEach(child -> {
                            plan.step(child, BEFORE + targetPhase).ifPresent(before::executeBefore);
                            plan.step(child, AFTER + targetPhase).ifPresent(after::executeAfter);
                        });
                    }
                }
            }
        }

        /**
         * Filters upstream projects by dependency scope. If the scope is null or empty,
         * all upstream projects are returned. Otherwise, only projects that the given
         * project depends on with a matching scope are included.
         * <p>
         * Matching is exact on the dependency's declared scope string (e.g. "compile",
         * "provided", "test"). Maven's default dependency scope is "compile" (when no
         * scope is declared), so a null scope in the model is treated as "compile" for
         * matching purposes. Note that this does <em>not</em> perform path-scope
         * resolution — for example, filtering by "compile" will not include
         * "provided"-scoped dependencies even though they contribute to
         * {@code PathScope.MAIN_COMPILE}. This keeps the filter simple and predictable;
         * broader scope-aware filtering can be added in a follow-up if needed.
         *
         * @param project the project whose dependencies to check
         * @param upstreamProjects the list of upstream reactor projects
         * @param scope the dependency scope to filter by, or null/empty for all
         * @return the filtered list of upstream projects
         */
        static List<MavenProject> filterByScope(
                MavenProject project, List<MavenProject> upstreamProjects, String scope) {
            if (scope == null || scope.isEmpty()) {
                return upstreamProjects;
            }
            return upstreamProjects.stream()
                    .filter(dep -> project.getDependencies().stream()
                            .anyMatch(d -> dep.getGroupId().equals(d.getGroupId())
                                    && dep.getArtifactId().equals(d.getArtifactId())
                                    && scope.equals(d.getScope() != null ? d.getScope() : "compile")))
                    .collect(Collectors.toList());
        }

        protected BuildPlan computeForkPlan(BuildStep step, MojoExecution execution, BuildPlan buildPlan) {
            MojoDescriptor mojoDescriptor = execution.getMojoDescriptor();
            PluginDescriptor pluginDescriptor = mojoDescriptor.getPluginDescriptor();
            String forkedGoal = mojoDescriptor.getExecuteGoal();
            String phase = mojoDescriptor.getExecutePhase();
            // We have a fork goal
            if (forkedGoal != null && !forkedGoal.isEmpty()) {
                MojoDescriptor forkedMojoDescriptor = pluginDescriptor.getMojo(forkedGoal);
                if (forkedMojoDescriptor == null) {
                    throw new MavenException(new MojoNotFoundException(forkedGoal, pluginDescriptor));
                }

                List<MavenProject> toFork = new ArrayList<>();
                toFork.add(step.project);
                if (mojoDescriptor.isAggregator() && step.project.getCollectedProjects() != null) {
                    toFork.addAll(step.project.getCollectedProjects());
                }

                BuildPlan plan = new BuildPlan();
                for (MavenProject project : toFork) {
                    BuildStep st = new BuildStep(forkedGoal, project, null);
                    MojoExecution mojoExecution = new MojoExecution(forkedMojoDescriptor, forkedGoal);
                    st.addMojo(mojoExecution, 0);
                    Map<String, BuildStep> n = new HashMap<>();
                    n.put(forkedGoal, st);
                    plan.addProject(project, n);
                }

                for (BuildStep astep : plan.allSteps().toList()) {
                    for (MojoExecution aexecution : astep.executions().toList()) {
                        plan = computeForkPlan(astep, aexecution, plan);
                    }
                }

                return plan;

            } else if (phase != null && !phase.isEmpty()) {
                String forkedLifecycle = mojoDescriptor.getExecuteLifecycle();
                Lifecycle lifecycle;
                if (forkedLifecycle != null && !forkedLifecycle.isEmpty()) {
                    org.apache.maven.api.plugin.descriptor.lifecycle.Lifecycle lifecycleOverlay;
                    try {
                        lifecycleOverlay = pluginDescriptor.getLifecycleMapping(forkedLifecycle);
                    } catch (IOException | XMLStreamException e) {
                        throw new MavenException(new PluginDescriptorParsingException(
                                pluginDescriptor.getPlugin(), pluginDescriptor.getSource(), e));
                    }
                    if (lifecycleOverlay == null) {
                        Optional<Lifecycle> lf = lifecycles.lookup(forkedLifecycle);
                        if (lf.isPresent()) {
                            lifecycle = lf.get();
                        } else {
                            throw new MavenException(new LifecycleNotFoundException(forkedLifecycle));
                        }
                    } else {
                        lifecycle = new PluginLifecycle(lifecycleOverlay, pluginDescriptor);
                    }
                } else {
                    if (execution.getLifecyclePhase() != null) {
                        String n = execution.getLifecyclePhase();
                        String phaseName = n.startsWith(BEFORE)
                                ? n.substring(BEFORE.length())
                                : n.startsWith(AFTER) ? n.substring(AFTER.length()) : n;
                        lifecycle = lifecycles.stream()
                                .filter(l -> l.allPhases().anyMatch(p -> phaseName.equals(p.name())))
                                .findFirst()
                                .orElse(null);
                        if (lifecycle == null) {
                            throw new IllegalStateException();
                        }
                    } else {
                        lifecycle = lifecycles.require(Lifecycle.DEFAULT);
                    }
                }

                String resolvedPhase = getResolvedPhase(lifecycle, phase);

                Map<MavenProject, List<MavenProject>> map = Collections.singletonMap(
                        step.project, plan.getAllProjects().get(step.project));
                BuildPlan forkedPlan = calculateLifecycleMappings(map, lifecycle, resolvedPhase);
                forkedPlan.then(buildPlan);
                return forkedPlan;
            } else {
                return buildPlan;
            }
        }

        private String getResolvedPhase(Lifecycle lifecycle, String phase) {
            return lifecycle.aliases().stream()
                    .filter(a -> phase.equals(a.v3Phase()))
                    .findFirst()
                    .map(Lifecycle.Alias::v4Phase)
                    .orElse(phase);
        }

        private String getResolvedPhase(String phase) {
            return lifecycles.stream()
                    .flatMap(l -> l.aliases().stream())
                    .filter(a -> phase.equals(a.v3Phase()))
                    .findFirst()
                    .map(Lifecycle.Alias::v4Phase)
                    .orElse(phase);
        }

        /**
         * Handles build errors by recording the error, notifying listeners, and updating the ReactorBuildStatus
         * based on the reactor failure behavior.
         * <p>
         * This method works in conjunction with the filtering in executePlan():
         * - For FAIL_FAST: Sets ReactorBuildStatus to halted, which causes executePlan to only process after:* steps
         * - For FAIL_AT_END: Blacklists the project and its dependents, which causes executePlan to skip them
         * - For FAIL_NEVER: Does nothing special, allowing all projects to continue building
         * <p>
         * Note: TEARDOWN steps are not executed for failed or blacklisted projects, as they're designed for
         * successful project completions.
         *
         * @param buildContext The reactor context
         * @param session The Maven session
         * @param mavenProject The project that failed
         * @param t The exception that caused the failure
         */
        protected void handleBuildError(
                final ReactorContext buildContext,
                final MavenSession session,
                final MavenProject mavenProject,
                Throwable t) {
            // record the error and mark the project as failed
            Clock clock = getClock(mavenProject);
            buildContext.getResult().addException(t);
            buildContext
                    .getResult()
                    .addBuildSummary(new BuildFailure(mavenProject, clock.execTime(), clock.wallTime(), t));

            // notify listeners about "soft" project build failures only
            if (t instanceof Exception exception && !(t instanceof RuntimeException)) {
                eventCatapult.fire(ExecutionEvent.Type.ProjectFailed, session, null, exception);
            }

            // reactor failure modes
            if (t instanceof RuntimeException || !(t instanceof Exception)) {
                // fail fast on RuntimeExceptions, Errors and "other" Throwables
                // assume these are system errors and further build is meaningless
                buildContext.getReactorBuildStatus().halt();
            } else if (MavenExecutionRequest.REACTOR_FAIL_NEVER.equals(session.getReactorFailureBehavior())) {
                // continue the build
            } else if (MavenExecutionRequest.REACTOR_FAIL_AT_END.equals(session.getReactorFailureBehavior())) {
                // continue the build but ban all projects that depend on the failed one
                buildContext.getReactorBuildStatus().blackList(mavenProject);
            } else if (MavenExecutionRequest.REACTOR_FAIL_FAST.equals(session.getReactorFailureBehavior())) {
                buildContext.getReactorBuildStatus().halt();
            } else {
                logger.error("invalid reactor failure behavior " + session.getReactorFailureBehavior());
                buildContext.getReactorBuildStatus().halt();
            }
        }

        public BuildPlan calculateMojoExecutions(Map<MavenProject, List<MavenProject>> projects, List<Task> tasks) {
            BuildPlan buildPlan = new BuildPlan(projects);

            for (Task task : tasks) {
                BuildPlan step;

                if (task instanceof GoalTask) {
                    String pluginGoal = task.getValue();

                    String executionId = "default-cli";
                    int executionIdx = pluginGoal.indexOf('@');
                    if (executionIdx > 0) {
                        executionId = pluginGoal.substring(executionIdx + 1);
                    }

                    step = new BuildPlan();
                    for (MavenProject project : projects.keySet()) {
                        BuildStep st = new BuildStep(pluginGoal, project, null);
                        MojoDescriptor mojoDescriptor = getMojoDescriptor(project, pluginGoal);
                        MojoExecution mojoExecution =
                                new MojoExecution(mojoDescriptor, executionId, MojoExecution.Source.CLI);
                        st.addMojo(mojoExecution, 0);
                        Map<String, BuildStep> n = new HashMap<>();
                        n.put(pluginGoal, st);
                        step.addProject(project, n);
                    }
                } else if (task instanceof LifecycleTask) {
                    String lifecyclePhase = task.getValue();

                    step = calculateLifecycleMappings(projects, lifecyclePhase);

                } else {
                    throw new IllegalStateException("unexpected task " + task);
                }

                buildPlan.then(step);
            }

            return buildPlan;
        }

        private MojoDescriptor getMojoDescriptor(MavenProject project, Plugin plugin, String goal) {
            try {
                return mavenPluginManager.getMojoDescriptor(
                        plugin, goal, project.getRemotePluginRepositories(), session.getRepositorySession());
            } catch (MavenException e) {
                throw e;
            } catch (Exception e) {
                throw new MavenException(e);
            }
        }

        private MojoDescriptor getMojoDescriptor(MavenProject project, String task) {
            try {
                return mojoDescriptorCreator.getMojoDescriptor(task, session, project);
            } catch (MavenException e) {
                throw e;
            } catch (Exception e) {
                throw new MavenException(e);
            }
        }

        public BuildPlan calculateLifecycleMappings(
                Map<MavenProject, List<MavenProject>> projects, String lifecyclePhase) {

            String resolvedPhase = getResolvedPhase(lifecyclePhase);
            String mainPhase = resolvedPhase.startsWith(BEFORE)
                    ? resolvedPhase.substring(BEFORE.length())
                    : resolvedPhase.startsWith(AFTER)
                            ? resolvedPhase.substring(AFTER.length())
                            : resolvedPhase.startsWith(AT) ? resolvedPhase.substring(AT.length()) : resolvedPhase;

            /*
             * Determine the lifecycle that corresponds to the given phase.
             */
            Lifecycle lifecycle = lifecycles.stream()
                    .filter(l -> l.allPhases().anyMatch(p -> mainPhase.equals(p.name())))
                    .findFirst()
                    .orElse(null);

            if (lifecycle == null) {
                throw new MavenException(new LifecyclePhaseNotFoundException(
                        "Unknown lifecycle phase \"" + lifecyclePhase
                                + "\". You must specify a valid lifecycle phase"
                                + " or a goal in the format <plugin-prefix>:<goal> or"
                                + " <plugin-group-id>:<plugin-artifact-id>[:<plugin-version>]:<goal>. Available lifecycle phases are: "
                                + lifecycles.stream()
                                        .flatMap(l -> l.allPhases().map(Lifecycle.Phase::name))
                                        .collect(Collectors.joining(", "))
                                + ".",
                        lifecyclePhase));
            }

            return calculateLifecycleMappings(projects, lifecycle, resolvedPhase);
        }

        public BuildPlan calculateLifecycleMappings(
                Map<MavenProject, List<MavenProject>> projects, Lifecycle lifecycle, String lifecyclePhase) {
            BuildPlan plan = new BuildPlan(projects);

            for (MavenProject project : projects.keySet()) {
                // For each phase, create and sequence the pre, run and post steps
                Map<String, BuildStep> steps = lifecycle
                        .allPhases()
                        .flatMap(phase -> {
                            BuildStep a = new BuildStep(BEFORE + phase.name(), project, phase);
                            BuildStep b = new BuildStep(phase.name(), project, phase);
                            BuildStep c = new BuildStep(AFTER + phase.name(), project, phase);
                            b.executeAfter(a);
                            c.executeAfter(b);
                            return Stream.of(a, b, c);
                        })
                        .collect(Collectors.toMap(n -> n.name, n -> n));
                // for each phase, make sure children phases are executed between before and after steps
                lifecycle.allPhases().forEach(phase -> phase.phases().forEach(child -> {
                    steps.get(BEFORE + child.name()).executeAfter(steps.get(BEFORE + phase.name()));
                    steps.get(AFTER + phase.name()).executeAfter(steps.get(AFTER + child.name()));
                }));
                // for each phase, create links between this project phases
                lifecycle.allPhases().forEach(phase -> {
                    phase.links().stream()
                            .filter(l -> l.pointer().type() == Lifecycle.Pointer.Type.PROJECT)
                            .forEach(link -> {
                                String n1 = phase.name();
                                String n2 = link.pointer().phase();
                                if (link.kind() == Lifecycle.Link.Kind.AFTER) {
                                    steps.get(BEFORE + n1).executeAfter(steps.get(AFTER + n2));
                                } else {
                                    steps.get(BEFORE + n2).executeAfter(steps.get(AFTER + n1));
                                }
                            });
                });

                // Only keep mojo executions before the end phase
                String endPhase = lifecyclePhase.startsWith(BEFORE) || lifecyclePhase.startsWith(AFTER)
                        ? lifecyclePhase
                        : lifecyclePhase.startsWith(AT)
                                ? lifecyclePhase.substring(AT.length())
                                : AFTER + lifecyclePhase;
                Set<BuildStep> toKeep = steps.get(endPhase).allPredecessors().collect(Collectors.toSet());
                toKeep.addAll(toKeep.stream()
                        .filter(s -> s.name.startsWith(BEFORE))
                        .map(s -> steps.get(AFTER + s.name.substring(BEFORE.length())))
                        .toList());
                steps.values().stream().filter(n -> !toKeep.contains(n)).forEach(BuildStep::skip);

                plan.addProject(project, steps);
            }

            // Create inter project dependencies
            plan.allSteps().filter(step -> step.phase != null).forEach(step -> {
                Lifecycle.Phase phase = step.phase;
                MavenProject project = step.project;
                phase.links().stream().forEach(link -> {
                    BuildStep before = plan.requiredStep(project, BEFORE + phase.name());
                    BuildStep after = plan.requiredStep(project, AFTER + phase.name());
                    Lifecycle.Pointer pointer = link.pointer();
                    String n2 = pointer.phase();
                    if (pointer instanceof Lifecycle.DependenciesPointer) {
                        // For dependencies: ensure current project's phase starts after dependency's phase completes
                        // Example: project's compile starts after dependency's package completes
                        String scope = ((Lifecycle.DependenciesPointer) pointer).scope();
                        filterByScope(project, projects.get(project), scope)
                                .forEach(p -> plan.step(p, AFTER + n2).ifPresent(before::executeAfter));
                    } else if (pointer instanceof Lifecycle.ChildrenPointer) {
                        // For children: ensure bidirectional phase coordination
                        project.getCollectedProjects().forEach(p -> {
                            // 1. Child's phase start waits for parent's phase start
                            plan.step(p, BEFORE + n2).ifPresent(before::executeBefore);
                            // 2. Parent's phase completion waits for child's phase completion
                            plan.step(p, AFTER + n2).ifPresent(after::executeAfter);
                        });
                    }
                });
            });

            // Keep projects in reactors by GAV
            Map<String, MavenProject> reactorGavs =
                    projects.keySet().stream().collect(Collectors.toMap(BuildPlanExecutor::gav, p -> p));

            // Go through all plugins
            List<Runnable> toResolve = new ArrayList<>();
            projects.keySet().forEach(project -> project.getBuild().getPlugins().forEach(plugin -> {
                MavenProject pluginProject = reactorGavs.get(gav(plugin));
                if (pluginProject != null) {
                    // In order to plan the project, we need all its plugins...
                    plan.requiredStep(project, PLAN).executeAfter(plan.requiredStep(pluginProject, READY));
                } else {
                    toResolve.add(() -> resolvePlugin(session, project.getRemotePluginRepositories(), plugin));
                }
            }));

            // Eagerly resolve all plugins in parallel
            toResolve.parallelStream().forEach(Runnable::run);

            // Keep track of phase aliases
            lifecycle.aliases().forEach(alias -> plan.aliases().put(alias.v3Phase(), alias.v4Phase()));

            return plan;
        }
    }

    private void resolvePlugin(MavenSession session, List<RemoteRepository> repositories, Plugin plugin) {
        try {
            mavenPluginManager.getPluginDescriptor(plugin, repositories, session.getRepositorySession());
        } catch (Exception e) {
            throw new MavenException(e);
        }
    }

    private static String gav(MavenProject p) {
        return p.getGroupId() + ":" + p.getArtifactId() + ":" + p.getVersion();
    }

    private static String gav(Plugin p) {
        return p.getGroupId() + ":" + p.getArtifactId() + ":" + p.getVersion();
    }

    /**
     * Post-processes the effective configuration for the specified mojo execution. This step discards all parameters
     * from the configuration that are not applicable to the mojo and injects the default values for any missing
     * parameters.
     *
     * @param mojoExecution The mojo execution whose configuration should be finalized, must not be {@code null}.
     */
    private void finalizeMojoConfiguration(MojoExecution mojoExecution) {
        MojoDescriptor mojoDescriptor = mojoExecution.getMojoDescriptor();

        XmlNode executionConfiguration = mojoExecution.getConfiguration() != null
                ? mojoExecution.getConfiguration().getDom()
                : null;
        if (executionConfiguration == null) {
            executionConfiguration = XmlNode.newInstance("configuration");
        }

        XmlNode defaultConfiguration = getMojoConfiguration(mojoDescriptor);

        List<XmlNode> children = new ArrayList<>();
        if (mojoDescriptor.getParameters() != null) {
            for (Parameter parameter : mojoDescriptor.getParameters()) {
                XmlNode parameterConfiguration = executionConfiguration.child(parameter.getName());

                if (parameterConfiguration == null) {
                    parameterConfiguration = executionConfiguration.child(parameter.getAlias());
                }

                XmlNode parameterDefaults = defaultConfiguration.child(parameter.getName());

                if (parameterConfiguration != null) {
                    parameterConfiguration = XmlService.merge(parameterConfiguration, parameterDefaults, Boolean.TRUE);
                } else {
                    parameterConfiguration = parameterDefaults;
                }

                if (parameterConfiguration != null) {
                    Map<String, String> attributes = new HashMap<>(parameterConfiguration.attributes());

                    String attributeForImplementation = parameterConfiguration.attribute("implementation");
                    String parameterForImplementation = parameter.getImplementation();
                    if ((attributeForImplementation == null || attributeForImplementation.isEmpty())
                            && ((parameterForImplementation != null) && !parameterForImplementation.isEmpty())) {
                        attributes.put("implementation", parameter.getImplementation());
                    }

                    parameterConfiguration = XmlNode.newInstance(
                            parameter.getName(),
                            parameterConfiguration.value(),
                            attributes,
                            parameterConfiguration.children(),
                            parameterConfiguration.inputLocation());

                    children.add(parameterConfiguration);
                }
            }
        }
        XmlNode finalConfiguration = XmlNode.newInstance("configuration", children);

        mojoExecution.setConfiguration(finalConfiguration);
    }

    private XmlNode getMojoConfiguration(MojoDescriptor mojoDescriptor) {
        if (mojoDescriptor.isV4Api()) {
            return MojoDescriptorCreator.convert(mojoDescriptor.getMojoDescriptorV4());
        } else {
            return MojoDescriptorCreator.convert(mojoDescriptor).getDom();
        }
    }

    private MojoExecutionConfigurator mojoExecutionConfigurator(MojoExecution mojoExecution) {
        String configuratorId = mojoExecution.getMojoDescriptor().getComponentConfigurator();
        if (configuratorId == null) {
            configuratorId = "default";
        }

        MojoExecutionConfigurator mojoExecutionConfigurator = mojoExecutionConfigurators.get(configuratorId);

        if (mojoExecutionConfigurator == null) {
            //
            // The plugin has a custom component configurator but does not have a custom mojo execution configurator
            // so fall back to the default mojo execution configurator.
            //
            mojoExecutionConfigurator = mojoExecutionConfigurators.get("default");
        }
        return mojoExecutionConfigurator;
    }

    public static void attachToThread(MavenProject currentProject) {
        ClassRealm projectRealm = currentProject.getClassRealm();
        if (projectRealm != null) {
            Thread.currentThread().setContextClassLoader(projectRealm);
        }
    }

    protected static class Clock {
        Instant start;
        Instant end;
        Instant resumed;
        Duration exec = Duration.ZERO;

        protected void start() {
            if (start == null) {
                start = MonotonicClock.now();
                resumed = start;
            } else {
                resumed = MonotonicClock.now();
            }
        }

        protected void stop() {
            end = MonotonicClock.now();
            exec = exec.plus(Duration.between(resumed, end));
        }

        protected Duration wallTime() {
            return start != null && end != null ? Duration.between(start, end) : Duration.ZERO;
        }

        protected Duration execTime() {
            return exec;
        }
    }
}
