shootout.gno

  1package penalty
  2
  3// Side is who takes a kick.
  4type Side uint8
  5
  6const (
  7	SidePlayer Side = iota + 1
  8	SideChain
  9)
 10
 11func (s Side) String() string {
 12	switch s {
 13	case SidePlayer:
 14		return "player"
 15	case SideChain:
 16		return "chain"
 17	}
 18	return "none"
 19}
 20
 21// Other returns the opposing side.
 22func (s Side) Other() Side {
 23	if s == SidePlayer {
 24		return SideChain
 25	}
 26	return SidePlayer
 27}
 28
 29// RegulationKicks is how many kicks each side takes before sudden death.
 30const RegulationKicks = 5
 31
 32// Shootout is the score of a penalty shootout in which the player always
 33// kicks first in each round:
 34//
 35//   - each side takes RegulationKicks kicks, alternating;
 36//   - it ends early as soon as one side cannot be caught with the kicks the
 37//     other has left;
 38//   - level after regulation, it goes to sudden death: rounds of one kick
 39//     each, decided when one side scores and the other does not.
 40type Shootout struct {
 41	PlayerKicks int
 42	PlayerGoals int
 43	ChainKicks  int
 44	ChainGoals  int
 45}
 46
 47// Next returns who kicks next (SidePlayer at the start of every round).
 48func (s Shootout) Next() Side {
 49	if s.PlayerKicks == s.ChainKicks {
 50		return SidePlayer
 51	}
 52	return SideChain
 53}
 54
 55// Round is the 1-based number of the round in progress.
 56func (s Shootout) Round() int { return s.ChainKicks + 1 }
 57
 58// SuddenDeath reports whether regulation is over.
 59func (s Shootout) SuddenDeath() bool { return s.ChainKicks >= RegulationKicks }
 60
 61// Record adds a kick for side. It panics if side is out of turn or the
 62// shootout is already decided.
 63func (s *Shootout) Record(side Side, scored bool) {
 64	if s.Winner() != 0 {
 65		panic("penalty: the shootout is already decided")
 66	}
 67	if side != s.Next() {
 68		panic("penalty: " + side.String() + " is kicking out of turn")
 69	}
 70	g := 0
 71	if scored {
 72		g = 1
 73	}
 74	if side == SidePlayer {
 75		s.PlayerKicks++
 76		s.PlayerGoals += g
 77	} else {
 78		s.ChainKicks++
 79		s.ChainGoals += g
 80	}
 81}
 82
 83// Winner returns the side that has won, or 0 while undecided.
 84func (s Shootout) Winner() Side {
 85	if s.PlayerKicks <= RegulationKicks && s.ChainKicks <= RegulationKicks {
 86		playerLeft := RegulationKicks - s.PlayerKicks
 87		chainLeft := RegulationKicks - s.ChainKicks
 88		if s.PlayerGoals > s.ChainGoals+chainLeft {
 89			return SidePlayer
 90		}
 91		if s.ChainGoals > s.PlayerGoals+playerLeft {
 92			return SideChain
 93		}
 94		return 0
 95	}
 96	// Sudden death: decided only once both have kicked in the round.
 97	if s.PlayerKicks == s.ChainKicks && s.PlayerGoals != s.ChainGoals {
 98		if s.PlayerGoals > s.ChainGoals {
 99			return SidePlayer
100		}
101		return SideChain
102	}
103	return 0
104}