# verbs.ludic - the only way a count changes, and each change is said once
function iv_change(inventory_st: mut InventoryState, it: int, after: int) -> void {
  let before = inventory_st.iv_counts[it]
  if before == after { return }
  inventory_st.iv_counts[it] = after
  let c = new ItemChanged
  c.item = it
  c.before = before
  c.after = after
  q_push(inv_changes(inventory_st), c)
}

# as many of n as there is room for; returns how many went in
export function inv_add(inventory_st: mut InventoryState, it: int, n: int) -> int {
  if not iv_valid(inventory_st, it) or n <= 0 { return 0 }
  let k = Math.min(n, inv_room(inventory_st, it))
  if k > 0 { iv_change(inventory_st, it, inventory_st.iv_counts[it] + k) }
  return k
}

# all n or none
export function inv_take(inventory_st: mut InventoryState, it: int, n: int) -> bool {
  if not iv_valid(inventory_st, it) or inventory_st.iv_counts[it] < n { return false }
  if n > 0 { iv_change(inventory_st, it, inventory_st.iv_counts[it] - n) }
  return true
}

# a count outright, room or not (a starting kit, a correction, the network's word); never below 0
export function inv_set(inventory_st: mut InventoryState, it: int, n: int) -> void {
  if not iv_valid(inventory_st, it) { return }
  iv_change(inventory_st, it, Math.max(n, 0))
}

# everything gone, silently: a new trip, or before a load
export function inv_clear(inventory_st: mut InventoryState) -> void {
  inventory_st.iv_counts = new []int
  for i in 0 .. inv_kinds(inventory_st) { push(inventory_st.iv_counts, 0) }
}