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package coffee.liz.ecs;
import coffee.liz.ecs.model.Component;
import coffee.liz.ecs.model.Entity;
import coffee.liz.ecs.model.System;
import coffee.liz.ecs.model.World;
import lombok.RequiredArgsConstructor;
import lombok.extern.log4j.Log4j2;
import java.time.Duration;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.HashMap;
import java.util.HashSet;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;
import java.util.Queue;
import java.util.Set;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.stream.Collectors;
/** World that updates in {@link System#getDependencies()} topological order. */
@Log4j2
@RequiredArgsConstructor
public class DAGWorld<T> implements World<T> {
/** All entities in the world. */
protected final Set<Entity> entities = Collections.synchronizedSet(new HashSet<>());
/** Cache mapping component types to entities having that component. */
private final Map<Class<? extends Component>, Set<Entity>> componentCache = Collections
.synchronizedMap(new HashMap<>());
/** Deterministic ID's for spawned entities. */
private final AtomicInteger nextEntityId = new AtomicInteger(0);
/** All registered systems. */
protected final Map<Class<? extends System<T>>, System<T>> systems;
/** Ordered list of systems for execution. */
private final List<System<T>> systemExecutionOrder;
public DAGWorld(final Map<Class<? extends System<T>>, System<T>> systems) {
this.systems = systems;
this.systemExecutionOrder = buildExecutionOrder(systems.values().stream().toList());
log.debug("Executing in order: {}", systemExecutionOrder);
}
@Override
public Entity createEntity() {
final Entity entity = Entity.builder().id(nextEntityId.incrementAndGet()).build();
entities.add(entity);
return entity;
}
@Override
public void removeEntity(final Entity entity) {
entity.getComponentMap().keySet().forEach(componentType -> {
final Set<Entity> cachedEntities = componentCache.get(componentType);
if (cachedEntities != null) {
cachedEntities.remove(entity);
}
});
entities.remove(entity);
}
@Override
public Set<Entity> query(final Collection<Class<? extends Component>> components) {
if (components.isEmpty()) {
return Set.copyOf(entities);
}
final Class<? extends Component> firstType = components.iterator().next();
final Set<Entity> candidates = componentCache.get(firstType);
if (candidates == null) {
return Collections.emptySet();
}
return candidates.stream().filter(entity -> components.stream().allMatch(entity::has))
.collect(Collectors.toSet());
}
@Override
public void update(final T state, final Duration duration) {
systemExecutionOrder.forEach(system -> {
refreshComponentCache();
system.update(this, state, duration);
});
refreshComponentCache();
}
@SuppressWarnings("unchecked")
@Override
public <S extends System<T>> S getSystem(final Class<S> system) {
return (S) systems.get(system);
}
private void refreshComponentCache() {
componentCache.clear();
entities.forEach(entity -> entity.getComponentMap().keySet().forEach(
componentType -> componentCache.computeIfAbsent(componentType, _ -> new HashSet<>()).add(entity)));
}
private List<System<T>> buildExecutionOrder(final Collection<System<T>> systems) {
if (systems.isEmpty()) {
return Collections.emptyList();
}
final Map<Class<?>, System<T>> systemMap = systems.stream()
.collect(Collectors.toMap(System::getClass, system -> system));
final Map<Class<?>, Integer> inDegree = new HashMap<>();
final Map<Class<?>, Set<Class<?>>> adjacencyList = new HashMap<>();
systems.forEach(system -> {
final Class<?> systemClass = system.getClass();
inDegree.put(systemClass, 0);
adjacencyList.put(systemClass, new HashSet<>());
});
systems.forEach(system -> {
system.getDependencies().forEach(dependency -> {
if (systemMap.containsKey(dependency)) {
adjacencyList.get(dependency).add(system.getClass());
inDegree.merge(system.getClass(), 1, Integer::sum);
}
});
});
// Kahn's algorithm
final List<System<T>> result = new ArrayList<>();
final Queue<Class<?>> queue = new LinkedList<>(
inDegree.entrySet().stream().filter(entry -> entry.getValue() == 0).map(Map.Entry::getKey).toList());
while (!queue.isEmpty()) {
final Class<?> currentClass = queue.poll();
result.add(systemMap.get(currentClass));
adjacencyList.getOrDefault(currentClass, Collections.emptySet()).forEach(dependent -> {
final int newInDegree = inDegree.get(dependent) - 1;
inDegree.put(dependent, newInDegree);
if (newInDegree == 0) {
queue.add(dependent);
}
});
}
if (result.size() != systems.size()) {
throw new IllegalStateException("Circular dependency detected in systems");
}
return Collections.unmodifiableList(result);
}
@Override
public void close() throws Exception {
for (final System<T> system : systemExecutionOrder) {
system.close();
}
componentCache.clear();
entities.clear();
}
}
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