square.go

//
// FrankyGo - UCI chess engine in GO for learning purposes
//
// MIT License
//
// Copyright (c) 2018-2020 Frank Kopp
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in all
// copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
// SOFTWARE.
//

package types

import (
	"fmt"

	"github.com/frankkopp/FrankyGo/internal/assert"
)

// Square represent exactly on square on a chess board.
type Square uint8

//noinspection GoUnusedConst
const (
	SqA1   Square = iota // 0
	SqB1   Square = iota // 1
	SqC1   Square = iota
	SqD1   Square = iota
	SqE1   Square = iota
	SqF1   Square = iota
	SqG1   Square = iota
	SqH1   Square = iota
	SqA2   Square = iota
	SqB2   Square = iota
	SqC2   Square = iota
	SqD2   Square = iota
	SqE2   Square = iota
	SqF2   Square = iota
	SqG2   Square = iota
	SqH2   Square = iota
	SqA3   Square = iota
	SqB3   Square = iota
	SqC3   Square = iota
	SqD3   Square = iota
	SqE3   Square = iota
	SqF3   Square = iota
	SqG3   Square = iota
	SqH3   Square = iota
	SqA4   Square = iota
	SqB4   Square = iota
	SqC4   Square = iota
	SqD4   Square = iota
	SqE4   Square = iota
	SqF4   Square = iota
	SqG4   Square = iota
	SqH4   Square = iota
	SqA5   Square = iota
	SqB5   Square = iota
	SqC5   Square = iota
	SqD5   Square = iota
	SqE5   Square = iota
	SqF5   Square = iota
	SqG5   Square = iota
	SqH5   Square = iota
	SqA6   Square = iota
	SqB6   Square = iota
	SqC6   Square = iota
	SqD6   Square = iota
	SqE6   Square = iota
	SqF6   Square = iota
	SqG6   Square = iota
	SqH6   Square = iota
	SqA7   Square = iota
	SqB7   Square = iota
	SqC7   Square = iota
	SqD7   Square = iota
	SqE7   Square = iota
	SqF7   Square = iota
	SqG7   Square = iota
	SqH7   Square = iota
	SqA8   Square = iota
	SqB8   Square = iota
	SqC8   Square = iota
	SqD8   Square = iota
	SqE8   Square = iota
	SqF8   Square = iota
	SqG8   Square = iota
	SqH8   Square = iota // 63
	SqNone Square = iota // 64
)

// IsValid checks a value of type square if it represents a valid
// square on a chess board (e.q. sq < 64).
func (sq Square) IsValid() bool {
	return sq < SqNone
}

// FileOf returns the file of the square
func (sq Square) FileOf() File {
	return File(sq & 7)
}

// RankOf returns the rank of the square
func (sq Square) RankOf() Rank {
	return Rank(sq >> 3)
}

// MakeSquare returns a square based on the string given or SqNone if
// no valid square could be read from the string
func MakeSquare(s string) Square {
	if assert.DEBUG {
		assert.Assert(len(s) == 2, "square string is not 2 characters long")
	}
	file := File(s[0] - 'a')
	rank := Rank(s[1] - '1')
	if !file.IsValid() || !rank.IsValid() {
		return SqNone
	}
	return SquareOf(file, rank)
}

// String returns a string of the file letter and rank number (e.g. e5)
// if the sq is not a valid square returns "-"
func (sq Square) String() string {
	if !sq.IsValid() {
		return "-"
	}
	return sq.FileOf().String() + sq.RankOf().String()
}

// SquareOf returns a square from file and rank
// Returns SqNone for invalid files or ranks
func SquareOf(f File, r Rank) Square {
	if !f.IsValid() || !r.IsValid() {
		return SqNone
	}
	return Square((int(r) << 3) + int(f))
}

// To returns the square on the chess board in the given direction
func (sq Square) To(d Direction) Square {
	// Precomputed
	// order:  North, East, South, West, Northeast, Southeast, Southwest, Northwest
	switch d {
	case North:
		return sqTo[sq][0]
	case East:
		return sqTo[sq][1]
	case South:
		return sqTo[sq][2]
	case West:
		return sqTo[sq][3]
	case Northeast:
		return sqTo[sq][4]
	case Southeast:
		return sqTo[sq][5]
	case Southwest:
		return sqTo[sq][6]
	case Northwest:
		return sqTo[sq][7]
	default:
		panic(fmt.Sprintf("Invalid direction %d", d))
	}
}

var sqTo [SqLength][8]Square

func init() {
	for sq := SqA1; sq < SqNone; sq++ {
		for i, dir := range Directions {
			sqTo[sq][i] = sq.toPreCompute(dir)
		}
	}
}

func (sq Square) toPreCompute(d Direction) Square {
	// overflow To south or north are easily detected <0 ot >63
	// east and west need check
	switch d {
	case North:
		sq += Square(d)
	case East:
		if sq.FileOf() < FileH {
			sq += Square(d)
		} else {
			return SqNone
		}
	case South:
		sq += Square(d)
	case West:
		if sq.FileOf() > FileA {
			sq += Square(d)
		} else {
			return SqNone
		}
	case Northeast:
		if sq.FileOf() < FileH {
			sq += Square(d)
		} else {
			return SqNone
		}
	case Southeast:
		if sq.FileOf() < FileH {
			sq += Square(d)
		} else {
			return SqNone
		}
	case Southwest:
		if sq.FileOf() > FileA {
			sq += Square(d)
		} else {
			return SqNone
		}
	case Northwest:
		if sq.FileOf() > FileA {
			sq += Square(d)
		} else {
			return SqNone
		}
	default:
		panic(fmt.Sprintf("Invalid direction %d", d))
	}
	if sq.IsValid() {
		return sq
	} else {
		return SqNone
	}
}