import (
	"github.com/wfranczyk/ento"
)
type Component1 struct{ value int }
type Component2 struct{ value int }
type Component3 struct{ value int }
type System struct {
	// Always use pointer to base component type (!)
	// Add `ento` tag to automatically bind components
	C1 *Component1 `ento:"required"`
	C2 *Component2 `ento:"required"`
	C3 *Component2 `ento:"optional"`
	// Systems can have non-component-bound fields
	calls int
}
// Update implements ento.System
// Based on `ento` tag, entities will be selected for update by the system.
// Entities that do not contain all the `required` components will be skipped.
func (s *System) Update(entity *ento.Entity) {
	// When Update is called, all the tagged components
	// will be already replaced with values from entity
	s.C1.value += s.C2.value
	// Optional field will be set to null if entity does not contain them
	if s.C3 != nil {
		s.C1.value += s.C3.value
	}
}
func main() {
	// Create the world and register components
	world := ento.NewWorldBuilder().
		// Use "zero-values" as values are ignored when registering
		WithSparseComponents(Component1{}, Component2{}, Component3{}).
		// Pre-allocate space for 256 entities (world can grow beyond that automatically)
		Build(256)
	// Add systems
	system := &System{}
	world.AddSystems(system)
	// Create entities (they are added to the world immediately)
	entity := world.NewEntity(Component1{1}, Component2{1})
	// Use Set to add or change their components
	entity.Set(Component3{1})
	// Update the world
	world.Update()
	// Use Get to receive component value (or nil if not present)
	var c1 *Component1
	entity.Get(&c1)
	println(c1.value == 3) // true
	// Use Rem to remove component from entity
	// As Component2 is `required` in the System
	// it will no longer be updated by it
	entity.Rem(Component2{})
	world.Update()
	entity.Get(&c1)
	println(c1.value == 3) // true - the entity is no longer updated by the system
}