Start planning out a Component system.

Huge thanks to all the great discussion on
http://forums.spongepowered.org/t/component-system-and-minecraft/76/39

Signed-off-by: Chris Sanders <zidane@outlook.com>

src/main/java/org/spongepowered/api/component/Component.java

@@ -0,0 +1,20 @@
+package org.spongepowered.api.component;
+
+import org.spongepowered.api.Game;
+
+/**
+ * Represents a data holder for a {@link org.spongepowered.api.component.ComponentHolder}.
+ */
+public interface Component<H> {
+    /**
+     * Returns the{@link org.spongepowered.api.component.ComponentHolder} holding this component.
+     * @return The holder
+     */
+    H getHolder();
+
+    /**
+     * Gets the {@link org.spongepowered.api.Game} object.
+     * @return The game
+     */
+    Game getGame();
+}

src/main/java/org/spongepowered/api/component/ComponentHolder.java

@@ -0,0 +1,7 @@
+package org.spongepowered.api.component;
+
+/**
+ * Marks an object as holding {@link org.spongepowered.api.component.Component}s.
+ */
+public interface ComponentHolder<C> {
+}

src/main/java/org/spongepowered/api/component/entity/EntityComponent.java

@@ -0,0 +1,10 @@
+package org.spongepowered.api.component.entity;
+
+import org.spongepowered.api.component.Component;
+import org.spongepowered.api.entity.Entity;
+
+/**
+ * Represents a {@link org.spongepowered.api.component.Component> attachable to {@link org.spongepowered.api.entity.Entity}s.
+ */
+public interface EntityComponent extends Component<Entity> {
+}

src/main/java/org/spongepowered/api/component/entity/attribute/Health.java

@@ -0,0 +1,20 @@
+package org.spongepowered.api.component.entity.attribute;
+
+import org.spongepowered.api.component.entity.EntityComponent;
+
+/**
+ * Gives the attribute "health" to an {@link org.spongepowered.api.entity.Entity}.
+ */
+public interface Health extends EntityComponent {
+    /**
+     * Gets the value of the current health
+     * @return The value
+     */
+    double getHealth();
+
+    /**
+     * Sets the value for the health
+     * @param value The value
+     */
+    void setHealth(double value);
+}

src/main/java/org/spongepowered/api/component/system/ComponentSystem.java

@@ -0,0 +1,39 @@
+package org.spongepowered.api.component.system;
+
+import org.spongepowered.api.component.Component;
+import org.spongepowered.api.component.ComponentHolder;
+
+import javax.annotation.Nullable;
+
+/**
+ * Represents a relationship system of {@link org.spongepowered.api.component.ComponentHolder}s and their {@link org.spongepowered.api.component.Component}s.
+ */
+public interface ComponentSystem {
+    /**
+     * Registers a {@link org.spongepowered.api.component.ComponentHolder} and {@link org.spongepowered.api.component.Component} relationship in the system
+     *
+     * @param holder The holder
+     * @param component The component
+     * @return The component, for chaining
+     */
+    public <T extends Component> T register(ComponentHolder<? super T> holder, T component);
+
+    /**
+     * Gets a {@link org.spongepowered.api.component.Component} for the {@link org.spongepowered.api.component.ComponentHolder} in the system.
+     *
+     * @param holder The holder
+     * @param clazz The component class
+     * @return The component
+     */
+    @Nullable
+    <T extends Component> T get(ComponentHolder<? super T> holder, Class<T> clazz);
+
+    /**
+     * Removes a {@link org.spongepowered.api.component.ComponentHolder} and {@link org.spongepowered.api.component.Component}'s relationship from the system.
+     *
+     * @param holder The holder
+     * @param clazz The component's class
+     * @return The component that was removed
+     */
+    public <T extends Component> T remove(ComponentHolder<? super T> holder, Class<T> clazz);
+}

src/main/java/org/spongepowered/api/component/system/TickableComponentSystem.java

@@ -0,0 +1,12 @@
+package org.spongepowered.api.component.system;
+
+/**
+ * Represents a system where {@link org.spongepowered.api.component.Component}s are processed each implementation's tick.
+ */
+public interface TickableComponentSystem extends ComponentSystem {
+    /**
+     * Called by the implementation to "process" the system
+     * @param dt Time since last tick
+     */
+    void tick(float dt);
+}

src/main/java/org/spongepowered/api/entity/Entity.java

@@ -23,9 +23,12 @@
  */
 package org.spongepowered.api.entity;
 
+import org.spongepowered.api.component.ComponentHolder;
+import org.spongepowered.api.component.entity.EntityComponent;
+
 import java.util.UUID;
 
-public interface Entity {
+public interface Entity extends ComponentHolder<EntityComponent> {
 
     /**
      * Gets the unique ID for this entity