gamestate.go

package tictactoe

type GameState uint32

const (
	Empty GameState = iota
	O
	X
)

func (gs GameState) String() string {
	s := make([]byte, 12)
	for i := range s {
		if i&0x3 == 3 {
			s[i] = '\n'
		} else {
			switch gs & 3 {
			case O:
				s[i] = 'O'
			case X:
				s[i] = 'X'
			default:
				s[i] = '-'
			}
			gs = gs >> 2
		}
	}

	return string(s)
}

func GameStateFromString(s string) GameState {
	var gs GameState
	for _, c := range s {
		switch c {
		case 'O':
			gs |= O << 18
		case 'X':
			gs |= X << 18
		case '-':
		default:
			gs = gs << 2
		}
		gs = gs >> 2
	}
	return gs
}

const (
	Pos1 GameState = 0x3 << (iota * 2)
	Pos2
	Pos3
	Pos4
	Pos5
	Pos6
	Pos7
	Pos8
	Pos9
	TopMask       = Pos1 | Pos2 | Pos3 // 0x3C
	MiddleMask    = Pos4 | Pos5 | Pos6 // 0xFC0
	BottomMask    = Pos7 | Pos8 | Pos9 // 0x3F000
	LeftMask      = Pos1 | Pos4 | Pos7 // 0x30C3
	CenterMask    = Pos2 | Pos5 | Pos8 // 0xC30C
	RightMask     = Pos3 | Pos6 | Pos9 // 0x30C30
	AngleDownMask = Pos1 | Pos5 | Pos9 // 0x30303
	AngleUpMask   = Pos3 | Pos5 | Pos7 // 0x3330
	AllO          = 0x15555
	AllX          = 0x2AAAA
)

func (gs GameState) Winner() GameState {
	switch {
	case gs&TopMask == AllO&TopMask:
		return O
	case gs&TopMask == AllX&TopMask:
		return X
	case gs&MiddleMask == AllO&MiddleMask:
		return O
	case gs&MiddleMask == AllX&MiddleMask:
		return X
	case gs&BottomMask == AllO&BottomMask:
		return O
	case gs&BottomMask == AllX&BottomMask:
		return X
	case gs&LeftMask == AllO&LeftMask:
		return O
	case gs&LeftMask == AllX&LeftMask:
		return X
	case gs&CenterMask == AllO&CenterMask:
		return O
	case gs&CenterMask == AllX&CenterMask:
		return X
	case gs&RightMask == AllO&RightMask:
		return O
	case gs&RightMask == AllX&RightMask:
		return X
	case gs&AngleDownMask == AllO&AngleDownMask:
		return O
	case gs&AngleDownMask == AllX&AngleDownMask:
		return X
	case gs&AngleUpMask == AllO&AngleUpMask:
		return O
	case gs&AngleUpMask == AllX&AngleUpMask:
		return X
	default:
		return Empty
	}
}

func (gs GameState) AvailableMoves() []GameState {
	moves := make([]GameState, 0, 9)
	for i := Pos1; i <= Pos9; i = i << 2 {
		if Empty == i&gs {
			moves = append(moves, i)
		}
	}
	return moves
}