9 files changed, 625 insertions, 0 deletions
diff --git a/core/src/main/java/coffee/liz/ecs/DAGWorld.java b/core/src/main/java/coffee/liz/ecs/DAGWorld.java
new file mode 100644
index 0000000..716808a
--- /dev/null
+++ b/core/src/main/java/coffee/liz/ecs/DAGWorld.java
@@ -0,0 +1,158 @@
+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) {
+		refreshComponentCache();
+		systemExecutionOrder.forEach(system -> {
+			system.update(this, state, duration);
+		});
+	}
+
+	@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, k -> 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);
+	}
+}
diff --git a/core/src/main/java/coffee/liz/ecs/math/Mat2.java b/core/src/main/java/coffee/liz/ecs/math/Mat2.java
new file mode 100644
index 0000000..8be945c
--- /dev/null
+++ b/core/src/main/java/coffee/liz/ecs/math/Mat2.java
@@ -0,0 +1,91 @@
+package coffee.liz.ecs.math;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.function.BiFunction;
+import java.util.function.Function;
+import java.util.function.Supplier;
+
+public final class Mat2 {
+	private Mat2() {
+	}
+
+	/**
+	 * Initializes a mutable 2d matrix of given type.
+	 *
+	 * @param dimensions
+	 *            the dimensions
+	 * @param constructor
+	 *            the constructor
+	 * @return row-indexed 2d matrix of {@param dimensions}
+	 */
+	public static <T> List<List<T>> init(final Vec2<Integer> dimensions, final Function<Vec2<Integer>, T> constructor) {
+		final List<List<T>> rows = new ArrayList<>();
+		for (int y = 0; y < dimensions.getY(); y++) {
+			final List<T> row = new ArrayList<>(dimensions.getX());
+			for (int x = 0; x < dimensions.getX(); x++)
+				row.add(constructor.apply(Vec2i.builder().y(y).x(x).build()));
+			rows.add(row);
+		}
+		return rows;
+	}
+
+	/**
+	 * Convolves a {@link Convolver} across a matrix.
+	 *
+	 * @param mat
+	 *            is the row-indexed 2d matrix to convolve.
+	 * @param axes
+	 *            are the x/y major/minor axes.
+	 * @param init
+	 *            is the initial value of the convolution.
+	 * @param convolver
+	 *            is the {@link Convolver}.
+	 * @param finalReduction
+	 *            to apply after {@param convolver}.
+	 * @return result of {@param convolver} applied along axes at each cell.
+	 * @param <T>
+	 *            is the type of the matrix to convolve.
+	 * @param <R>
+	 *            is the type of the resulting type of each convolution.
+	 */
+	public static <T, R, U> List<List<U>> convolve(final List<List<T>> mat, final Vec2<Integer> axes,
+			final Supplier<R> init, final Convolver<T, R> convolver, final BiFunction<T, R, U> finalReduction) {
+		final List<List<R>> rows = new ArrayList<>();
+		for (int y = 0; y < mat.size(); y++) {
+			final List<R> row = new ArrayList<>(mat.get(y).size());
+			for (int x = 0; x < mat.get(y).size(); x++) {
+				final T center = mat.get(y).get(x);
+				R result = init.get();
+				for (int dy = -axes.getY(); dy <= axes.getY(); dy++) {
+					final int ry = y + dy;
+					if (ry < 0 || ry >= mat.size())
+						continue;
+					for (int dx = -axes.getX(); dx <= axes.getX(); dx++) {
+						final int rx = x + dx;
+						if (rx < 0 || rx >= mat.get(ry).size())
+							continue;
+						result = convolver.convolve(mat.get(ry).get(rx), Vec2i.builder().x(dx).y(dy).build(), result);
+					}
+				}
+				row.add(result);
+			}
+			rows.add(row);
+		}
+
+		final List<List<U>> reductions = new ArrayList<>();
+		for (int y = 0; y < mat.size(); y++) {
+			final List<U> reduction = new ArrayList<>(mat.get(y).size());
+			for (int x = 0; x < mat.get(y).size(); x++) {
+				reduction.add(finalReduction.apply(mat.get(y).get(x), rows.get(y).get(x)));
+			}
+			reductions.add(reduction);
+		}
+		return reductions;
+	}
+
+	@FunctionalInterface
+	public interface Convolver<T, R> {
+		R convolve(final T center, final Vec2<Integer> rel, final R reduction);
+	}
+}
diff --git a/core/src/main/java/coffee/liz/ecs/math/Vec2.java b/core/src/main/java/coffee/liz/ecs/math/Vec2.java
new file mode 100644
index 0000000..ec7e531
--- /dev/null
+++ b/core/src/main/java/coffee/liz/ecs/math/Vec2.java
@@ -0,0 +1,65 @@
+package coffee.liz.ecs.math;
+
+/**
+ * Cartesian vectors.
+ *
+ * @param <T>
+ *            the numeric type of vector components
+ */
+public interface Vec2<T> {
+	/**
+	 * @return the x coordinate
+	 */
+	T getX();
+
+	/**
+	 * @return the y coordinate
+	 */
+	T getY();
+
+	/**
+	 * Adds another vector to this vector.
+	 *
+	 * @param other
+	 *            the vector to add
+	 * @return a new vector with the result
+	 */
+	Vec2<T> plus(final Vec2<T> other);
+
+	/**
+	 * Subtracts another vector from this vector.
+	 *
+	 * @param other
+	 *            the vector to subtract
+	 * @return a new vector with the result
+	 */
+	Vec2<T> minus(final Vec2<T> other);
+
+	/**
+	 * Scales this vector by the given factors.
+	 *
+	 * @param scaleX
+	 *            the x scale factor
+	 * @param scaleY
+	 *            the y scale factor
+	 * @return a new scaled vector
+	 */
+	Vec2<T> scale(final T scaleX, final T scaleY);
+
+	/**
+	 * Length of the vector.
+	 *
+	 * @return length.
+	 */
+	float length();
+
+	/**
+	 * @return Vec2<Integer> components of {@link Vec2<T>}
+	 */
+	Vec2<Integer> intValue();
+
+	/**
+	 * @return Vec2<Float> components of {@link Vec2<T>}
+	 */
+	Vec2<Float> floatValue();
+}
diff --git a/core/src/main/java/coffee/liz/ecs/math/Vec2f.java b/core/src/main/java/coffee/liz/ecs/math/Vec2f.java
new file mode 100644
index 0000000..46f3fb8
--- /dev/null
+++ b/core/src/main/java/coffee/liz/ecs/math/Vec2f.java
@@ -0,0 +1,54 @@
+package coffee.liz.ecs.math;
+
+import static java.lang.Math.sqrt;
+
+import lombok.Builder;
+import lombok.Data;
+import lombok.Getter;
+import lombok.RequiredArgsConstructor;
+
+/** Float impl of {@link Vec2}. */
+@Getter
+@RequiredArgsConstructor
+@Data
+@Builder
+public final class Vec2f implements Vec2<Float> {
+	/** X coordinate. */
+	private final Float x;
+
+	/** Y coordinate. */
+	private final Float y;
+
+	@Override
+	public Vec2<Float> plus(final Vec2<Float> other) {
+		return new Vec2f(x + other.getX(), y + other.getY());
+	}
+
+	@Override
+	public Vec2<Float> minus(final Vec2<Float> other) {
+		return new Vec2f(x - other.getX(), y - other.getY());
+	}
+
+	@Override
+	public Vec2<Float> scale(final Float scaleX, final Float scaleY) {
+		return new Vec2f(x * scaleX, y * scaleY);
+	}
+
+	@Override
+	public float length() {
+		return (float) sqrt(x * x + y * y);
+	}
+
+	@Override
+	public Vec2<Float> floatValue() {
+		return this;
+	}
+
+	@Override
+	public Vec2<Integer> intValue() {
+		return Vec2i.builder().x(this.x.intValue()).y(this.y.intValue()).build();
+	}
+
+	/** Zero float vec */
+	public static Vec2<Float> ZERO = Vec2f.builder().x(0f).y(0f).build();
+}
diff --git a/core/src/main/java/coffee/liz/ecs/math/Vec2i.java b/core/src/main/java/coffee/liz/ecs/math/Vec2i.java
new file mode 100644
index 0000000..dbe246e
--- /dev/null
+++ b/core/src/main/java/coffee/liz/ecs/math/Vec2i.java
@@ -0,0 +1,57 @@
+package coffee.liz.ecs.math;
+
+import static java.lang.Math.sqrt;
+
+import lombok.Builder;
+import lombok.Data;
+import lombok.Getter;
+import lombok.RequiredArgsConstructor;
+
+/** Integer impl of {@link Vec2}. */
+@Getter
+@RequiredArgsConstructor
+@Builder
+@Data
+public final class Vec2i implements Vec2<Integer> {
+	/** X coordinate. */
+	private final Integer x;
+
+	/** Y coordinate. */
+	private final Integer y;
+
+	@Override
+	public Vec2<Integer> plus(final Vec2<Integer> other) {
+		return new Vec2i(x + other.getX(), y + other.getY());
+	}
+
+	@Override
+	public Vec2<Integer> minus(final Vec2<Integer> other) {
+		return new Vec2i(x - other.getX(), y - other.getY());
+	}
+
+	@Override
+	public Vec2<Integer> scale(final Integer scaleX, final Integer scaleY) {
+		return new Vec2i(x * scaleX, y * scaleY);
+	}
+
+	@Override
+	public Vec2<Float> floatValue() {
+		return Vec2f.builder().x(this.x.floatValue()).y(this.y.floatValue()).build();
+	}
+
+	@Override
+	public Vec2<Integer> intValue() {
+		return this;
+	}
+
+	@Override
+	public float length() {
+		return (float) sqrt(x * x + y * y);
+	}
+
+	public static final Vec2i NORTH = new Vec2i(0, -1);
+	public static final Vec2i SOUTH = new Vec2i(0, 1);
+	public static final Vec2i EAST = new Vec2i(1, 0);
+	public static final Vec2i WEST = new Vec2i(-1, 0);
+	public static final Vec2i ZERO = new Vec2i(0, 0);
+}
diff --git a/core/src/main/java/coffee/liz/ecs/model/Component.java b/core/src/main/java/coffee/liz/ecs/model/Component.java
new file mode 100644
index 0000000..f96ba95
--- /dev/null
+++ b/core/src/main/java/coffee/liz/ecs/model/Component.java
@@ -0,0 +1,8 @@
+package coffee.liz.ecs.model;
+
+/** Component of an {@link Entity}. */
+public interface Component {
+	default Class<? extends Component> getKey() {
+		return getClass();
+	}
+}
diff --git a/core/src/main/java/coffee/liz/ecs/model/Entity.java b/core/src/main/java/coffee/liz/ecs/model/Entity.java
new file mode 100644
index 0000000..e820e57
--- /dev/null
+++ b/core/src/main/java/coffee/liz/ecs/model/Entity.java
@@ -0,0 +1,105 @@
+package coffee.liz.ecs.model;
+
+import lombok.AllArgsConstructor;
+import lombok.Builder;
+import lombok.Data;
+import lombok.Getter;
+import lombok.RequiredArgsConstructor;
+
+import java.util.Collection;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.Map;
+import java.util.Set;
+
+@Getter
+@Builder
+@RequiredArgsConstructor
+@AllArgsConstructor
+@Data
+public class Entity {
+	/** Unique id. */
+	private final int id;
+
+	/** Instances of {@link Component}s. */
+	@Builder.Default
+	private Map<Class<? extends Component>, Component> componentMap = Collections.synchronizedMap(new HashMap<>());
+
+	/**
+	 * Check if entity has component type.
+	 *
+	 * @param componentType
+	 *            the {@link Component} class
+	 * @return true if component exists
+	 */
+	public boolean has(final Class<? extends Component> componentType) {
+		return componentMap.containsKey(componentType);
+	}
+
+	/**
+	 * Check if entity has all component types.
+	 *
+	 * @param components
+	 *            collection of {@link Component} classes
+	 * @return true if all components exist
+	 */
+	public boolean hasAll(final Collection<Class<? extends Component>> components) {
+		return components.stream().allMatch(this::has);
+	}
+
+	/**
+	 * Get component by type.
+	 *
+	 * @param componentType
+	 *            the {@link Component} class
+	 * @param <C>
+	 *            component type
+	 * @return the component or throw {@link IllegalArgumentException}
+	 */
+	@SuppressWarnings("unchecked")
+	public <C extends Component> C get(final Class<C> componentType) {
+		final C component = (C) componentMap.get(componentType);
+		if (component == null) {
+			throw new IllegalArgumentException(
+					"Entity with id " + getId() + " does not have required component " + componentType.getSimpleName());
+		}
+		return component;
+	}
+
+	/**
+	 * Add component to entity.
+	 *
+	 * @param component
+	 *            the {@link Component} to add
+	 * @param <C>
+	 *            component type
+	 * @return this {@link Entity} for chaining
+	 */
+	public <C extends Component> Entity add(final C component) {
+		componentMap.put(component.getKey(), component);
+		return this;
+	}
+
+	/**
+	 * Remove component from entity.
+	 *
+	 * @param componentType
+	 *            the {@link Component} class to remove
+	 * @param <C>
+	 *            component type
+	 * @return this {@link Entity} for chaining
+	 */
+	public <C extends Component> Entity remove(final Class<C> componentType) {
+		componentMap.remove(componentType);
+		return this;
+	}
+
+	/**
+	 * Get all component types.
+	 *
+	 * @return set of {@link Component} classes
+	 */
+	public Set<Class<? extends Component>> componentTypes() {
+		return componentMap.keySet();
+	}
+}
diff --git a/core/src/main/java/coffee/liz/ecs/model/System.java b/core/src/main/java/coffee/liz/ecs/model/System.java
new file mode 100644
index 0000000..220b917
--- /dev/null
+++ b/core/src/main/java/coffee/liz/ecs/model/System.java
@@ -0,0 +1,29 @@
+package coffee.liz.ecs.model;
+
+import java.time.Duration;
+import java.util.Collection;
+
+/**
+ * Updates the {@link World} state.
+ *
+ * @param <T>
+ *            is the state of the stuff outside the {@link World}.
+ */
+public interface System<T> {
+	/**
+	 * {@link System} clazzes that must run before this system.
+	 *
+	 * @return {@link Collection} of dependencies.
+	 */
+	Collection<Class<? extends System<T>>> getDependencies();
+
+	/**
+	 * @param world
+	 *            Is the {@link World}.
+	 * @param state
+	 *            Is the {@link T} state outside the {@param world}.
+	 * @param dt
+	 *            Is the timestep.
+	 */
+	void update(final World<T> world, final T state, final Duration dt);
+}
diff --git a/core/src/main/java/coffee/liz/ecs/model/World.java b/core/src/main/java/coffee/liz/ecs/model/World.java
new file mode 100644
index 0000000..96c7a74
--- /dev/null
+++ b/core/src/main/java/coffee/liz/ecs/model/World.java
@@ -0,0 +1,58 @@
+package coffee.liz.ecs.model;
+
+import java.time.Duration;
+import java.util.Collection;
+import java.util.Set;
+
+/**
+ * The state of the world.
+ *
+ * @param <T>
+ *            is the state of the stuff outside the world.
+ */
+public interface World<T> {
+	/**
+	 * Create unique {@link Entity} in the {@link World}.
+	 *
+	 * @return created {@link Entity}.
+	 */
+	Entity createEntity();
+
+	/**
+	 * Remove an entity from the {@link World}.
+	 *
+	 * @param entity
+	 *            to remove.
+	 */
+	void removeEntity(final Entity entity);
+
+	/**
+	 * Get entities with {@link Component}s.
+	 *
+	 * @param components
+	 *            to query for.
+	 * @return All entities with all {@param components}.
+	 */
+	Set<Entity> query(final Collection<Class<? extends Component>> components);
+
+	/**
+	 * Integrate the {@link World}.
+	 *
+	 * @param state
+	 *            Is the state outside the world.
+	 * @param duration
+	 *            Is the time step.
+	 */
+	void update(final T state, final Duration duration);
+
+	/**
+	 * Get world {@link System}.
+	 *
+	 * @param system
+	 *            is the Clazz.
+	 * @param <S>
+	 *            is the {@link System} type.
+	 * @return {@link System} instance of {@param system}.
+	 */
+	<S extends System<T>> S getSystem(final Class<S> system);
+}