ecs.nim

# ECS

type
  EntityID = distinct int
  ComponentID = distinct int

  ComponentManger = object
    create: proc (id: EntityID) # note: does not really work
    destroy: proc (id: EntityID)

var
  components: BTree[ComponentID, ComponentManager]
  consistsOf: BTree[EntityID, seq[ComponentID]]
  eid: EntityID # for unique ID generation

template declareComponent(id: ComponentID; t: typeDesc; update) =
  var data: BTree[EntityID, t]

  proc updateAll() =
    for x in data: update(x)

  proc create(e: EntityID; value: t) = data.insert(e, value)
  proc destroy(e: EntityID) = data.remove(e)

  components.insert(id, ComponentManger(create: create, destroy: destroy))


proc createEntity(parts: seq[ComponentID]): EntityID =
  inc eid.int
  result = eid
  consistsOf.insert(result, parts)

proc destroyEntity(e: EntityID) =
  let parts = consistsOf.get(e)
  for p in parts:
    components.get(p).destroy()

# Position component:

type
  Position = object
    x, y, z: float32

proc update(p: var Position) = discard

declareComponent(ComponentID 1, Position, update)


# Physics component:

type
  Physics = object
    acc, vel: float32

proc update(p: var Physics) = discard

declareComponent(ComponentID 2, Physics, update)


# declare a Person with 2 legs (positions) and a physics component:
let araq = createEntity(@[ComponentID 1, 1, 2])
create(araq, Position(1, 2, 3))
create(araq, Position(2, 3, 4))
create(araq, Physics(1, 2))