game.go

package oxo3d

/*
Shouldn't really need state in the players

Should initialise from the board from flat each time

Which makes them functions probably with subfunctions

Note that the evaluation isn't being updated properly because of that - when the human plays it goes wrong

*/

// FIXME make it so can serialize and unserialize the game for save/load

// FIXME could declare draw when no more lines are available?

import (
	"bytes"
	"fmt"
)

const (
	// We keep count of how many X and O there are on each line by encoding them like this
	// numberOfXs * 5 + numberOfOs
	// Since Xs and Os are both 0..4 the max value here is 24
	XS                = 5
	OS                = 1
	maxEncodedOxCount = XS * XS

	// players
	NOONE = 0
	ME    = 1
	YOU   = -1
	DRAW  = 2

	// A score larger than any possible score
	INF = 0x7FFFFFFF
)

// Global variables
var (
	// movet holds the positions of the 76 possible lines
	movet [76][4]int

	// for each space on the board, moveb records the number of all the
	// lines which go through that square (indexed into movet)
	moveb [64][]int
)

// Initialise the global variables
func init() {
	// movet holds the positions of the 76 possible lines
	for a := 0; a < 16; a++ {
		for b := 0; b < 4; b++ {
			movet[a][b] = a*4 + b
			movet[a+16][b] = a + 4*b + 3*(a&0xC)
			movet[a+32][b] = a + 16*b
		}
	}
	for a := 0; a < 4; a++ {
		for b := 0; b < 4; b++ {
			movet[a+48][b] = 16*a + 5*b
			movet[a+52][b] = 16*a + 3*b + 3
			movet[a+56][b] = a + 20*b
			movet[a+60][b] = a + 12*b + 12
			movet[a+64][b] = 4*a + 17*b
			movet[a+68][b] = 4*a + 15*b + 3
		}
	}
	for a := 0; a < 4; a++ {
		movet[72][a] = 21 * a
		movet[73][a] = 19*a + 3
		movet[74][a] = 13*a + 12
		movet[75][a] = 11*a + 15
	}

	// for each space on the board, moveb records the index of all the
	// lines which go through that square (indexed into movet)
	for line := range movet {
		for b := 0; b < 4; b++ {
			pos := movet[line][b]
			moveb[pos] = append(moveb[pos], line)
		}
	}
}

type Oxo3d struct {
	plays   []int
	board   [64]int
	lines   [76]int
	lastGo  int
	winline int
	moves   int
	first   bool // who went first
	isMyGo  bool
	winner  int
}

// Setup all the things which need to be done for every game.
//  Note that the state of first is flipped for the next game
func (o *Oxo3d) newGame(first bool) {
	o.plays = make([]int, 0, 64)
	for i := range o.board {
		o.board[i] = 0
	}
	for i := range o.lines {
		o.lines[i] = 0
	}
	o.lastGo = -1
	o.winline = -1
	o.moves = 0
	o.isMyGo = first
	o.first = !first
	o.winner = NOONE
}

// Create a new Oxo3d instance
func NewOxo3d(first bool) *Oxo3d {
	o := &Oxo3d{}
	o.newGame(first)
	return o
}

// Returns NOONE, ME, YOU or DRAW for who won
func (o *Oxo3d) WhoWon() int {
	if o.winner != NOONE {
		return o.winner
	}
	if o.moves == 64 {
		return DRAW
	}
	return NOONE
}

// Returns true if it is my go
func (o *Oxo3d) IsMyGo() bool {
	return o.isMyGo
}

// Returns true if the move is to an empty square
// Returns false if occupied or invalid
func (o *Oxo3d) ValidMove(Go int) bool {
	if Go < 0 || Go >= 64 {
		return false
	}
	if o.board[Go] != NOONE {
		return false
	}
	return true
}

// Board returns the state of the board at that position, either ME,
// YOU or NOONE
func (o *Oxo3d) Board(Go int) int {
	return o.board[Go]
}

// Marked returns a flag as to whether the position should be
// higlighted.  This will highlight the last move and any winning
// lines.
func (o *Oxo3d) Marked(Go int) bool {
	if Go == o.lastGo {
		return true
	}
	if o.winline >= 0 {
		for _, a := range movet[o.winline] {
			if Go == a {
				return true
			}
		}
	}
	return false
}

// Turn the board into a string
func (o *Oxo3d) String() string {
	var buf bytes.Buffer
	win := o.WhoWon()
	if win == ME {
		buf.WriteString("I win\n")
	} else if win == YOU {
		buf.WriteString("You win\n")
	} else if win == DRAW {
		buf.WriteString("A draw\n")
	}
	symbols := [3]string{"O", ".", "X"}
	for a := 0; a < 64; a += 4 {
		if (a & 0xC) == 0 {
			buf.WriteString("+-------------+-------------+\n")
		}
		buf.WriteString("|")
		for b := a; b < a+4; b++ {
			buf.WriteString(" ")
			buf.WriteString(symbols[o.Board(b)+1])
			if o.Marked(b) {
				buf.WriteString("*")
			} else {
				buf.WriteString(" ")
			}
		}
		buf.WriteString(" |")
		for b := a; b < a+4; b++ {
			fmt.Fprintf(&buf, " %2d", b)
		}
		buf.WriteString(" |\n")
	}
	return buf.String()
}

// Test to see if someone won or it was a draw
func (o *Oxo3d) GameOver() bool {
	return o.WhoWon() != NOONE
}

// Keep internal state up to date when a piece is played
func (o *Oxo3d) Play(Go int, myGo bool) {
	if !o.ValidMove(Go) {
		panic("Illegal move")
	}
	who := ME
	encodedWho := XS
	if !myGo {
		who = YOU
		encodedWho = OS
	}
	fourInARow := 4 * encodedWho
	o.lastGo = Go
	o.plays = append(o.plays, Go)
	o.moves += 1
	o.board[Go] = who
	o.winner = NOONE
	o.winline = -1
	for _, a := range moveb[Go] {
		ox := o.lines[a] + encodedWho
		o.lines[a] = ox
		if ox == fourInARow {
			o.winner = who
			o.winline = a
		}
	}
	if myGo != o.isMyGo {
		panic("Not my go!")
	}
	o.isMyGo = !o.isMyGo
	//isMyGo = false; // FIXME
}

// Unplay the last move keeping internal state up to date
func (o *Oxo3d) UnPlay() {
	// FIXME some assertions?
	if len(o.plays) <= 0 {
		panic("No moves to unplay")
	}
	Go := o.plays[len(o.plays)-1]
	o.plays = o.plays[:len(o.plays)-1]
	who := o.board[Go]
	if who == NOONE {
		panic("Unplaying no one")
	}
	encodedWho := XS
	if who != ME {
		encodedWho = OS
	}
	if len(o.plays) <= 0 {
		o.lastGo = -1
	} else {
		o.lastGo = o.plays[len(o.plays)-1]
	}
	o.moves -= 1
	o.board[Go] = NOONE
	o.winner = NOONE
	o.winline = -1
	for _, a := range moveb[Go] {
		o.lines[a] -= encodedWho
	}
	o.isMyGo = !o.isMyGo
}

// Do the computer move
func (o *Oxo3d) MyGo(Go int) {
	o.Play(Go, true)
}

// Do the opponents move
func (o *Oxo3d) YourGo(Go int) {
	o.Play(Go, false)
}