# pack.ludic - 0.R: what happened is an action; what it means for a state is that state's reducer.
# The entry dispatches; drain_actions() runs every reducer of each action, in order, each given its
# own state - and an action a reducer dispatches goes behind the queue.
program PackActions {
  state Pack {
    items: []int = new []int
    weight: int = 0
  }
  state Log {
    lines: []string = new []string
  }
  action PickUp { item: int, kg: int = 1 }
  action Drop { item: int }
  action Overload {}

  reducer Pack on PickUp(p: mut Pack, a: PickUp) {
    push(p.items, a.item)
    p.weight += a.kg
    if p.weight > 10 { dispatch Overload {} }
  }
  reducer Log on PickUp(l: mut Log, a: PickUp) { push(l.lines, `picked {a.item}`) }
  reducer Pack on Drop(p: mut Pack, a: Drop) {
    var kept = new []int
    for i in 0 .. len(p.items) { if p.items[i] != a.item { push(kept, p.items[i]) } }
    p.items = kept
  }
  reducer Log on Overload(l: mut Log, a: Overload) { push(l.lines, "too heavy") }

  entry (p: Pack, l: Log) {
    dispatch PickUp { item: 7 }
    dispatch PickUp { item: 9, kg: 12 }
    dispatch Drop { item: 7 }
    print(len(p.items))                    # 0: nothing is reduced until the queue is drained
    drain_actions()
    print(`{len(p.items)} {p.items[0]} {p.weight}`)
    for i in 0 .. len(l.lines) { print(l.lines[i]) }
  }
}