hytale-gravity-flip/src/main/java/com/mythlane/gravityflip/physics/GravityApplier.java

package com.mythlane.gravityflip.physics;

import com.hypixel.hytale.component.ComponentType;
import com.hypixel.hytale.component.Ref;
import com.hypixel.hytale.component.Store;
import com.hypixel.hytale.server.core.entity.UUIDComponent;
import com.hypixel.hytale.server.core.modules.entity.component.TransformComponent;
import com.hypixel.hytale.server.core.modules.physics.component.PhysicsValues;
import com.hypixel.hytale.server.core.universe.world.World;
import com.hypixel.hytale.server.core.universe.world.storage.EntityStore;
import com.mythlane.gravityflip.region.GravityFlipRegion;
import com.mythlane.gravityflip.region.RegionSnapshot;

import java.util.Collection;
import java.util.Collections;
import java.util.HashSet;
import java.util.Set;
import java.util.UUID;
import java.util.concurrent.ConcurrentHashMap;
import java.util.function.Consumer;

/**
 * Tick-driven service that toggles the native {@code PhysicsValues.invertedGravity} flag on every
 * entity present in an enabled {@link GravityFlipRegion}. Mutations are queued via
 * {@code CommandBuffer.replaceComponent(...)} inside a {@code Store.forEachEntityParallel(...)}
 * lambda — the ECS engine commits them on the main thread after the parallel pass.
 *
 * <p>Dedup: a thread-safe {@link Set}{@code <UUID>} tracks entities flipped at the previous tick.
 * Entities that left an active region are restored to {@code invertedGravity=false} in a second
 * pass (trade-off documented in the plan — second O(N) scan accepted v1).
 */
public final class GravityApplier {
    // Lazy ComponentType holders — pattern identique à RegionRegistry.transform()
    // (évite static-init Hytale PluginBase pendant les tests).
    private static volatile ComponentType<EntityStore, PhysicsValues> physicsType;
    private static volatile ComponentType<EntityStore, UUIDComponent> uuidType;
    private static volatile ComponentType<EntityStore, TransformComponent> transformType;

    private static ComponentType<EntityStore, PhysicsValues> physicsType() {
        ComponentType<EntityStore, PhysicsValues> t = physicsType;
        if (t == null) {
            synchronized (GravityApplier.class) {
                t = physicsType;
                if (t == null) { t = PhysicsValues.getComponentType(); physicsType = t; }
            }
        }
        return t;
    }
    private static ComponentType<EntityStore, UUIDComponent> uuidType() {
        ComponentType<EntityStore, UUIDComponent> t = uuidType;
        if (t == null) {
            synchronized (GravityApplier.class) {
                t = uuidType;
                if (t == null) { t = UUIDComponent.getComponentType(); uuidType = t; }
            }
        }
        return t;
    }
    private static ComponentType<EntityStore, TransformComponent> transformType() {
        ComponentType<EntityStore, TransformComponent> t = transformType;
        if (t == null) {
            synchronized (GravityApplier.class) {
                t = transformType;
                if (t == null) { t = TransformComponent.getComponentType(); transformType = t; }
            }
        }
        return t;
    }

    // THREADING: écrit/lu depuis les workers ECS via forEachEntityParallel → ConcurrentHashMap.newKeySet obligatoire.
    private final Set<UUID> previouslyInverted = ConcurrentHashMap.newKeySet();
    private final Consumer<Throwable> errorHandler;

    public GravityApplier(Consumer<Throwable> errorHandler) {
        this.errorHandler = errorHandler == null ? t -> {} : errorHandler;
    }

    /** Tick entry point. NO-OP si world ou snapshot est null. */
    public void apply(World world, RegionSnapshot snapshot) {
        if (world == null || snapshot == null) return;
        Collection<GravityFlipRegion> enabledRegions = snapshot.byRegion().keySet();
        // Stratégie figée (cf. WARNING 1 résolu) : on accepte la duplication du containsPosition
        // (cf. must_haves trade-off) plutôt que de coupler à un nouveau contrat RegionSnapshot
        // qui exposerait des UUIDs préformés. Coût : 2 pass O(N) sur le store par tick.

        try {
            Store<EntityStore> store = world.getEntityStore().getStore();
            ComponentType<EntityStore, PhysicsValues> PHYST = physicsType();
            ComponentType<EntityStore, UUIDComponent>  UUIDT = uuidType();
            ComponentType<EntityStore, TransformComponent> TT = transformType();

            // PASS 1 — pour chaque entité avec PhysicsValues : si dans une région activée, queue le flip ON
            //          via cmdBuf.replaceComponent ET enregistre l'UUID dans currentlyInRegion (thread-safe).
            // THREADING: lambda sur worker ECS → currentlyInRegion = ConcurrentHashMap.newKeySet ; toutes les
            // mutations PhysicsValues passent par cmdBuf (jamais replaceValues direct).
            Set<UUID> currentlyInRegion = ConcurrentHashMap.newKeySet();
            store.forEachEntityParallel(PHYST, (index, chunk, cmdBuf) -> {
                TransformComponent t;
                UUIDComponent uc;
                PhysicsValues v;
                try {
                    t = chunk.getComponent(index, TT);
                    uc = chunk.getComponent(index, UUIDT);
                    v  = chunk.getComponent(index, PHYST);
                } catch (Throwable ignored) { return; }
                if (t == null || uc == null || v == null) return;

                com.hypixel.hytale.math.vector.Vector3d pos = t.getPosition();
                double x = pos.x, y = pos.y, z = pos.z;

                boolean inAnyRegion = false;
                for (GravityFlipRegion r : enabledRegions) {
                    if (r.asBox().containsPosition(x, y, z)) { inAnyRegion = true; break; }
                }
                if (!inAnyRegion) return;

                UUID u = uc.getUuid();
                currentlyInRegion.add(u);
                if (!v.isInvertedGravity()) {
                    Ref<EntityStore> ref = chunk.getReferenceTo(index);
                    cmdBuf.replaceComponent(ref, PHYST,
                            new PhysicsValues(v.getMass(), v.getDragCoefficient(), true));
                }
            });

            // PASS 2 — restore : pour chaque UUID dans previouslyInverted \ currentlyInRegion,
            //          re-localiser l'entité (second scan) et queue le flip OFF via cmdBuf.
            //          Trade-off perf accepté v1 — voir SUMMARY follow-up.
            Set<UUID> toRestore = ConcurrentHashMap.newKeySet();
            toRestore.addAll(previouslyInverted);
            toRestore.removeAll(currentlyInRegion);
            if (!toRestore.isEmpty()) {
                store.forEachEntityParallel(PHYST, (index, chunk, cmdBuf) -> {
                    UUIDComponent uc;
                    PhysicsValues v;
                    try {
                        uc = chunk.getComponent(index, UUIDT);
                        v  = chunk.getComponent(index, PHYST);
                    } catch (Throwable ignored) { return; }
                    if (uc == null || v == null) return;
                    if (toRestore.contains(uc.getUuid()) && v.isInvertedGravity()) {
                        Ref<EntityStore> ref = chunk.getReferenceTo(index);
                        cmdBuf.replaceComponent(ref, PHYST,
                                new PhysicsValues(v.getMass(), v.getDragCoefficient(), false));
                    }
                });
            }

            // Update tracker — ces ops sont sur le tick thread après la fin du pass parallel.
            // ConcurrentHashMap.newKeySet supporte clear()/addAll() concurrents safely.
            previouslyInverted.clear();
            previouslyInverted.addAll(currentlyInRegion);
        } catch (Throwable th) {
            errorHandler.accept(th);
        }
    }

    /** Pure data-diff utilitaire pour tests unitaires (pas de runtime Hytale). */
    public static DiffResult diff(Set<UUID> previous, Set<UUID> current) {
        Set<UUID> toFlip = new HashSet<>(current);
        toFlip.removeAll(previous);
        Set<UUID> toRestore = new HashSet<>(previous);
        toRestore.removeAll(current);
        return new DiffResult(toFlip, toRestore);
    }

    public static final class DiffResult {
        public final Set<UUID> toFlip;
        public final Set<UUID> toRestore;
        DiffResult(Set<UUID> f, Set<UUID> r) { this.toFlip = f; this.toRestore = r; }
    }

    // ---- Test hooks (package-private) ----

    /** Vue immuable du tracker — pour tests unitaires sémantiques (résolution WARNING 2). */
    Set<UUID> previouslyInvertedView() {
        return Collections.unmodifiableSet(previouslyInverted);
    }

    /**
     * Force une valeur du tracker hors runtime ECS — pour tester la sémantique sans dépendre de World/Store.
     * Package-private : NE PAS appeler depuis le code de production.
     */
    void __updateTrackerForTest(Set<UUID> newState) {
        previouslyInverted.clear();
        previouslyInverted.addAll(newState);
    }
}