entity

type CanChange interface {
	HasChanged(nextState State, now stime.Time) bool
}

type Entity interface {
	// Unique ID
	Id() Id

	// Location in the world
	Cell() coord.Cell

	// Returns a bounding object incorporating
	// the entities potential interaction with
	// the other entities in the world.
	Bounds() coord.Bounds

	// Returns the set of entity flags that can
	// set whether something collides or whether
	// an entity has been changed or not.
	Flags() Flag

	// Returns a state value that represents
	// the entity in its current state.
	ToState() State
}

type Flag uint64

type Id int64

type Removed struct {
	Entity
	RemovedAt stime.Time
}

type RemovedState struct {
	Id           Id
	EntityBounds coord.Bounds
}

type State interface {
	// Unique ID
	EntityId() Id

	// Bounds of the entity
	Bounds() coord.Bounds

	// Compare to another entity
	IsDifferentFrom(State) bool
}

type StateById map[Id]State

type StateSlice []State