package main

import (
	"bufio"
	"bytes"
	"encoding/base64"
	"fmt"
	"log"
	"os/exec"
	"strconv"
	"strings"
	"time"

	"code.rocket9labs.com/tslocum/bgammon"
)

func reverseString(s string) string {
	runes := []rune(s)
	for i, j := 0, len(runes)-1; i < j; i, j = i+1, j-1 {
		runes[i], runes[j] = runes[j], runes[i]
	}
	return string(runes)
}

func gnubgPosition(g *bgammon.Game) string {
	var opponent int8 = 2
	start := 0
	end := 25
	boardStart := 1
	boardEnd := 24
	delta := 1
	playerBarSpace := bgammon.SpaceBarPlayer
	opponentBarSpace := bgammon.SpaceBarOpponent
	switch g.Turn {
	case 1:
	case 2:
		opponent = 1
		start = 25
		end = 0
		boardStart = 24
		boardEnd = 1
		delta = -1
		playerBarSpace = bgammon.SpaceBarOpponent
		opponentBarSpace = bgammon.SpaceBarPlayer
	default:
		log.Fatalf("failed to analyze game: zero turn")
	}

	var buf []byte
	for space := boardStart; space != end; space += delta {
		playerCheckers := bgammon.PlayerCheckers(g.Board[space], g.Turn)
		for i := int8(0); i < playerCheckers; i++ {
			buf = append(buf, '1')
		}
		buf = append(buf, '0')
	}
	playerCheckers := bgammon.PlayerCheckers(g.Board[playerBarSpace], g.Turn)
	for i := int8(0); i < playerCheckers; i++ {
		buf = append(buf, '1')
	}
	buf = append(buf, '0')

	for space := boardEnd; space != start; space -= delta {
		opponentCheckers := bgammon.PlayerCheckers(g.Board[space], opponent)
		for i := int8(0); i < opponentCheckers; i++ {
			buf = append(buf, '1')
		}
		buf = append(buf, '0')
	}
	opponentCheckers := bgammon.PlayerCheckers(g.Board[opponentBarSpace], opponent)
	for i := int8(0); i < opponentCheckers; i++ {
		buf = append(buf, '1')
	}
	buf = append(buf, '0')

	for i := len(buf); i < 80; i++ {
		buf = append(buf, '0')
	}

	var out []byte
	for i := 0; i < len(buf); i += 8 {
		s := reverseString(string(buf[i : i+8]))
		v, err := strconv.ParseUint(s, 2, 8)
		if err != nil {
			panic(err)
		}
		out = append(out, byte(v))
	}

	position := base64.StdEncoding.EncodeToString(out)
	if len(position) == 0 {
		return ""
	}
	for position[len(position)-1] == '=' {
		position = position[:len(position)-1]
	}
	return position
}

func parseMoves(moves []byte) ([4][2]int8, error) {
	var c int        // Input cursor.
	var m [4][2]int8 // Parsed moves.
	var mc int       // Parsed moves cursor.

	// Parse moves separated by spaces.
	l := len(moves)
	for c < l {
		var moveLength int
		for i := c; i < l; i++ {
			if moves[i] == ' ' {
				break
			}
			moveLength++
		}
		if moveLength == 0 {
			return [4][2]int8{}, fmt.Errorf("failed to parse gnubg moves: no moves: %s", moves)
		}

		move := moves[c : c+moveLength]
		move = bytes.ReplaceAll(move, []byte("*"), nil)

		count := 1
		paren := bytes.IndexRune(move, '(')
		if paren != -1 {
			var err error
			count, err = strconv.Atoi(string(move[paren+1]))
			if err != nil {
				return [4][2]int8{}, fmt.Errorf("failed to parse gnubg moves: invalid count: %s", moves)
			}
			mv := append(move[:paren], move[paren+3:]...)
			move = mv
		}

		slash := bytes.IndexRune(move, '/')
		if slash == -1 {
			return [4][2]int8{}, fmt.Errorf("failed to parse gnubg moves: invalid count: %s", moves)
		}
		nextSlash := bytes.IndexRune(move[slash+1:], '/')
		var remaining []byte
		if nextSlash != -1 {
			remaining = move[slash+nextSlash+2:]
			move = move[:slash+nextSlash+1]
		}
		from := bgammon.ParseSpace(string(move[:slash]))
		if from < 0 || from > 27 {
			return [4][2]int8{}, fmt.Errorf("failed to parse gnubg moves: invalid from (%s): %s", move[:slash], moves)
		}
		to := bgammon.ParseSpace(string(move[slash+1:]))
		if to < 0 || to > 27 {
			return [4][2]int8{}, fmt.Errorf("failed to parse gnubg moves: invalid to (%s): %s", move[:slash], moves)
		}

		for i := 0; i < count; i++ {
			m[mc][0], m[mc][1] = int8(from), int8(to)
			ok := Game.AddLocalMove([]int8{int8(from), int8(to)})
			if !ok {
				return [4][2]int8{}, fmt.Errorf("failed to add local moves (%d/%d): %s", from, to, moves)
			}
			mc++

			if len(remaining) > 0 {
				rm, err := parseMoves(append([]byte(strconv.Itoa(int(to))+"/"), remaining...))
				if err != nil {
					return [4][2]int8{}, fmt.Errorf("failed to parse gnubg moves: invalid remaining moves (%s): %s", append([]byte(strconv.Itoa(int(to))+"/"), remaining...), moves)
				}
				for j := 0; j < 4; j++ {
					if rm[j][0] == 0 && rm[j][1] == 0 {
						break
					}
					m[mc][0], m[mc][1] = int8(rm[j][0]), int8(rm[j][1])
					mc++
				}
			}
		}

		// Advance to the next move.
		c += moveLength + 1
	}

	// Relocate bear-off moves after moves within the board.
	var mb, mo [][2]int8
	for j := 0; j < 4; j++ {
		if m[j][0] == 0 && m[j][1] == 0 {
			break
		} else if m[j][1] == bgammon.SpaceHomePlayer {
			mo = append(mo, m[j])
			continue
		}
		mb = append(mb, m[j])
	}
	m = [4][2]int8{}
	mc = 0
	for _, mv := range mb {
		m[mc] = mv
		mc++
	}
	for _, mv := range mo {
		m[mc] = mv
		mc++
	}
	return m, nil
}

// analyze returns the best moves provided by the gnubg engine.
func analyze(g *bgammon.Game) ([4][2]int8, error) {
	cmd := exec.Command("gnubg", "--tty", "--quiet", "--no-rc")
	stdin, err := cmd.StdinPipe()
	if err != nil {
		log.Fatal(err)
	}
	stdout, err := cmd.StdoutPipe()
	if err != nil {
		log.Fatal(err)
	}
	stderr, err := cmd.StderrPipe()
	if err != nil {
		log.Fatal(err)
	}
	err = cmd.Start()
	if err != nil {
		log.Fatal(err)
	}

	var moves []byte
	var ready bool
	go func() {
		scanner := bufio.NewScanner(stdout)
		for scanner.Scan() {
			buf := scanner.Bytes()
			if bytes.Contains(buf, []byte("The dice have been set")) || bytes.Contains(buf, []byte("The cube has been set")) {
				ready = true
			} else if ready && moves == nil && (bytes.Contains(buf, []byte("Rolled")) || bytes.Contains(buf, []byte("gnubg moves")) || bytes.Contains(buf, []byte("gnubg doubles")) || bytes.Contains(buf, []byte("gnubg accepts")) || bytes.Contains(buf, []byte("gnubg refuses the cube")) || bytes.Contains(buf, []byte("gnubg offers to resign"))) {
				moves = make([]byte, len(buf))
				copy(moves, buf)
			}
			log.Println(string(buf))
		}
	}()

	go func() {
		scanner := bufio.NewScanner(stderr)
		for scanner.Scan() {
			log.Println("!!!", string(scanner.Bytes()))
		}
	}()

	var extra []string
	if g.DoublePlayer != 0 {
		extra = append(extra, fmt.Sprintf("set cube owner %d", g.DoublePlayer-1))
	}
	if g.DoubleValue != 0 {
		extra = append(extra, fmt.Sprintf("set cube value %d", g.DoubleValue))
	}
	if g.DoubleOffered {
		extra = append(extra, "double")
	} else if g.Roll1 != 0 && g.Roll2 != 0 {
		extra = append(extra, fmt.Sprintf("set dice %d %d", g.Roll1, g.Roll2))
		extra = append(extra, "play")
	} else {
		extra = append(extra, "play")
	}

	stdin.Write([]byte(fmt.Sprintf("set automatic roll off\nset automatic move off\nnew game\nset beavers 0\nset score %d %d %d\nset board %s\nset turn %d\n%s\n", g.Player1.Points, g.Player2.Points, g.Points, gnubgPosition(g), g.Turn-1, strings.Join(extra, "\n"))))
	t := time.NewTicker(50 * time.Millisecond)
	for {
		<-t.C
		if moves != nil {
			stdin.Write([]byte("quit\ny\n"))
			t.Stop()
			break
		}
	}

	err = cmd.Wait()
	if err != nil {
		return [4][2]int8{}, err
	}

	acceptCube := bytes.Contains(moves, []byte("gnubg accepts"))
	if acceptCube {
		return [4][2]int8{{-1, -1}}, nil
	}

	double := bytes.Contains(moves, []byte("gnubg doubles"))
	if double {
		return [4][2]int8{{-2, -2}}, nil
	}

	rollDice := bytes.Contains(moves, []byte("Rolled"))
	if rollDice {
		return [4][2]int8{{-3, -3}}, nil
	}

	resign := bytes.Contains(moves, []byte("gnubg offers to resign")) || bytes.Contains(moves, []byte("gnubg refuses the cube"))
	if resign {
		return [4][2]int8{{-4, -4}}, nil
	}

	movesWord := bytes.Index(moves, []byte("moves"))
	if movesWord == -1 {
		return [4][2]int8{}, fmt.Errorf("failed to parse gnubg moves: %s", moves)
	}
	moves = bytes.TrimSpace(moves[movesWord+6:])
	if !bytes.HasSuffix(moves, []byte(".")) {
		return [4][2]int8{}, fmt.Errorf("failed to parse gnubg moves: %s", moves)
	}
	moves = moves[:len(moves)-1]

	return parseMoves(moves)
}

func FlipSpace(space int8, player int8, variant int8) int8 {
	if player == 1 {
		return space
	}
	if space < 1 || space > 24 {
		switch space {
		case bgammon.SpaceHomePlayer:
			return bgammon.SpaceHomeOpponent
		case bgammon.SpaceHomeOpponent:
			return bgammon.SpaceHomePlayer
		case bgammon.SpaceBarPlayer:
			return bgammon.SpaceBarOpponent
		case bgammon.SpaceBarOpponent:
			return bgammon.SpaceBarPlayer
		default:
			return -1
		}
	}
	if variant == bgammon.VariantTabula {
		return space
	}
	return 24 - space + 1
}

func FlipMoves(moves [4][2]int8, player int8, variant int8) [4][2]int8 {
	var m [4][2]int8
	for i := 0; i < 4; i++ {
		if moves[i][0] == 0 && moves[i][1] == 0 {
			break
		}
		m[i][0], m[i][1] = FlipSpace(moves[i][0], player, variant), FlipSpace(moves[i][1], player, variant)
	}
	return m
}