# wallet.ludic - the purse, its verbs, its facts and its save section
export property MoneyChanged {
  before: int = 0
  after: int = 0
}

export state WalletState {
  wl_money: int = 0
  wl_changes: Queue<MoneyChanged> = wl_changes__new()
}

export function wallet_changes(wallet_st: WalletState) -> Queue<MoneyChanged> {
  return wallet_st.wl_changes
}

export function wallet_money(wallet_st: WalletState) -> int { return wallet_st.wl_money }
export function wallet_can(wallet_st: WalletState, n: int) -> bool { return wallet_st.wl_money >= n }

# the purse holds exactly n (a starting purse, a correction, the network's word)
export function wallet_set(wallet_st: mut WalletState, n: int) -> void {
  if n == wallet_st.wl_money { return }
  var c = q_rec(wallet_changes(wallet_st))
  if c == null {
    @alloc_ok("past the ring: more of these in a frame than its records, then kept in it")
    c = new MoneyChanged
    q_ring_add(wallet_changes(wallet_st), c)
  }
  c.before = wallet_st.wl_money
  c.after = n
  wallet_st.wl_money = n
  q_push(wallet_changes(wallet_st), c)
}

export function wallet_earn(wallet_st: mut WalletState, n: int) -> void { wallet_set(wallet_st, wallet_st.wl_money + n) }

# only what is there: false, and nothing spent, when it is not
export function wallet_spend(wallet_st: mut WalletState, n: int) -> bool {
  if n > wallet_st.wl_money { return false }
  wallet_set(wallet_st, wallet_st.wl_money - n)
  return true
}

# a cost that happens whether or not it can be paid (a rescue, a fine); never below zero
export function wallet_lose(wallet_st: mut WalletState, n: int) -> void { wallet_set(wallet_st, Math.max(wallet_st.wl_money - n, 0)) }

export function wallet_reset(wallet_st: mut WalletState) -> void {
  wallet_st.wl_money = 0
  q_clear(wallet_changes(wallet_st))
}

export function wallet_save(wallet_st: WalletState) -> Val {
  let v = Value.object()
  sv_put_int(v, "money", wallet_st.wl_money)
  return v
}

export function wallet_load(wallet_st: mut WalletState, v: Val, version: int) -> void {
  wallet_st.wl_money = sv_int(v, "money", 0)
  q_clear(wallet_changes(wallet_st))
}

export function wallet_system() -> System {
  let s = system_new("wallet", PH_COMMIT)
  s.reset = fn wallet_reset
  s.save = fn wallet_save
  s.load = fn wallet_load
  return s
}
function wl_changes__new() -> Queue<MoneyChanged> { return queue_new("wallet.changes") }