Refactor into more modular architecture

entity.c

@@ -0,0 +1,88 @@
+#include "entity.h"
+
+#include <assert.h>
+#include <string.h>
+
+#define MAX_COMPONENTS_PER_ENTITY 4U
+
+typedef struct {
+	update_cb_t update;
+	remove_cb_t remove;
+	void *ref;
+} component_t;
+
+typedef struct {
+	bool marked;
+	unsigned count;
+	component_t components[MAX_COMPONENTS_PER_ENTITY];
+} entity_t;
+
+static unsigned count;
+static entity_t entities[MAX_ENTITIES];
+
+void entities_clear()
+{
+	count = 0;
+}
+
+void entities_purge()
+{
+	for (unsigned id = count - 1; id < count; --id) {
+		entity_t *e = entities + id;
+		if (!e->marked)
+			continue;
+
+		for (unsigned i = 0; i < e->count; ++i)
+			e->components[i].remove(e->components[i].ref);
+
+		const unsigned last = count - 1;
+		if (id != last) {
+			memcpy(e, entities + last, sizeof(entity_t));
+			for (unsigned i = 0; i < e->count; ++i)
+				e->components[i].update(id, e->components[i].ref);
+		}
+
+		--count;
+	}
+}
+
+unsigned entity_add()
+{
+	assert(count < MAX_ENTITIES);
+	const unsigned id = count++;
+	memset(entities + id, 0, sizeof(entity_t));
+	return id;
+}
+
+void entity_mark(unsigned id)
+{
+	assert(id < count);
+	entities[id].marked = true;
+}
+
+unsigned entity_add_component(
+    unsigned id, update_cb_t update, remove_cb_t remove, void *ref)
+{
+	assert(id < count);
+	entity_t *e = entities + id;
+
+	assert(e->count < MAX_COMPONENTS_PER_ENTITY);
+	const unsigned component_id = e->count++;
+	e->components[component_id] = (component_t) {
+		.update = update,
+		.remove = remove,
+		.ref = ref,
+	};
+
+	return component_id;
+}
+
+void entity_update_component(
+    unsigned entity_id, unsigned component_id, void *new_ref)
+{
+	assert(entity_id < count);
+	entity_t *e = entities + entity_id;
+
+	assert(component_id < e->count);
+	e->components[component_id].ref = new_ref;
+}