package main

const FEN_STARTING_POSITION = "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1"
const FEN_STARTING_POSITION_BLACK = "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR b KQkq - 0 1"
const FEN_STARTING_POSITION_ONLY_PAWNS = "4k3/pppppppp/8/8/8/8/PPPPPPPP/4K3 w KQkq - 0 1"
const FEN_STARTING_POSITION_EP_E4 = "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq e4 0 1"
const FEN_STARTING_POSITION_ONLY_KNIGHTS = "1n2k1n1/8/8/8/8/8/8/1N2K1N1 w - - 0 1"
const FEN_STARTING_POSITION_ONLY_KNIGHTS_BLACK = "1n2k1n1/8/8/8/8/8/8/1N2K1N1 b - - 0 1"
const FEN_TEST_KNIGHT_CAPTURES = "4k1n1/8/8/8/8/2n5/8/1N2K1N1 b - - 0 1"
const FEN_TEST_ONLY_KINGS = "8/8/3k4/8/3K4/8/8/8 w - - 0 1"
const FEN_TEST_ONLY_KNIGHTS = "8/8/3k4/8/3K4/8/8/8 w - - 0 1"
const FEN_TRICKY_WHITE = "r3k2r/p1ppqpb1/bn2pnp1/3PN3/1p2P3/2N2Q1p/PPPBBPPP/R3K2R w KQkq - "
const FEN_TRICKY_BLACK = "r3k2r/p1ppqpb1/bn2pnp1/3PN3/1p2P3/2N2Q1p/PPPBBPPP/R3K2R b KQkq - "
const FEN_TEST_EP = "8/2p5/3p4/KP5r/1R3p1k/8/4P1P1/8 w - - "
const FEN_SCHOLARS_MATE = "r1bqkb1r/pppp1ppp/2n2n2/4p2Q/2B1P3/8/PPPP1PPP/RNB1K1NR w KQkq - 4 4"
const FEN_FRIED_LIVER_BLACK = "r1bqkb1r/pppp1ppp/2n2n2/4p1N1/2B1P3/8/PPPP1PPP/RNBQK2R b KQkq - 5 4"
const FEN_FRIED_LIVER_WHITE = "r1bqkb1r/ppp2ppp/2np1n2/4p1N1/2B1P3/8/PPPP1PPP/RNBQK2R w KQkq - 0 5"
const FEN_KNIGHT_FORK = "rn1qk2r/pp3ppp/2p1pn2/6N1/8/1PP3P1/P4PBP/R2Q1RK1 w - - 0 1"
const FEN_MATE_0_TEST = "r1bqkb1r/pppp1Qpp/2n2n2/4p3/2B1P3/8/PPPP1PPP/RNB1K1NR b KQkq - 0 1"
const FEN_MATE_4_TEST = "r7/q6p/2k1p3/2N1Q3/1ppP4/P2b4/1P4PP/K2R4 b - - 0 1"
const FEN_BONGCLOUD = "rnbqkbnr/pppp1ppp/8/4p3/4P3/8/PPPPKPPP/RNBQ1BNR b kq - 1 2"
const FEN_PERPETUAL = "6k1/5pp1/6p1/8/8/3Q3P/5PP1/6K1 w - - 0 1"
const FEN_MATE_3 = "r4rk1/ppp1q1p1/2n2pP1/8/8/2N5/PPP1BQ2/2KR3R w - - 0 1"
const FEN_BLACK_DOUBLE_CHECK = "4k3/8/8/8/4N3/8/8/4R1K1 w - - 0 1"

const (
	Pieces   = iota // 0
	Side            // 1
	Castling        // 2
	EP
	FiftyMove
	PlyCount
)

func LoadFen(fen string) {
	ResetBoard()

	var bracketCount int = 0
	var squareCount int = 0

	var setting int = Pieces

	var ep_file_index = -1
	var ep_rank_index = -1

	for character_index := 0; character_index < len(fen); character_index++ {
		switch setting {
		case Pieces:
			Load_Fen_Sort_Pieces(&bracketCount, fen[character_index], &setting, &squareCount)
		case Side:
			Load_Fen_Sort_Side(&setting, fen[character_index])
		case Castling:
			Load_Fen_Sort_Castling(&setting, fen[character_index])
		case EP:
			Load_Fen_Sort_EP(&setting, fen[character_index], &ep_file_index, &ep_rank_index)
		case FiftyMove:
			Load_Fen_Sort_Fifty_Move(&setting, fen[character_index])
		case PlyCount:
			return
		}
	}
}
func Load_Fen_Sort_Pieces(bracketCount *int, character_in_fen byte, setting *int, squareCount *int) {
	if *bracketCount == 7 && character_in_fen == ' ' {
		*setting++
		return
	}
	if *bracketCount > 7 {
		*bracketCount = 0
	}
	if *squareCount > 7 {
		*squareCount = 0
	}
	var square = (*bracketCount * 8) + *squareCount

	switch character_in_fen {

	case 'B':
		PieceArray[WB] = SetBit(PieceArray[WB], square)
		*squareCount++
	case 'R':
		PieceArray[WR] = SetBit(PieceArray[WR], square)
		*squareCount++
	case 'P':
		PieceArray[WP] = SetBit(PieceArray[WP], square)
		*squareCount++
	case 'Q':
		PieceArray[WQ] = SetBit(PieceArray[WQ], square)
		*squareCount++
	case 'K':
		PieceArray[WK] = SetBit(PieceArray[WK], square)
		*squareCount++
	case 'N':
		PieceArray[WN] = SetBit(PieceArray[WN], square)
		*squareCount++
	case 'b':
		PieceArray[BB] = SetBit(PieceArray[BB], square)
		*squareCount++
	case 'p':
		PieceArray[BP] = SetBit(PieceArray[BP], square)
		*squareCount++
	case 'q':
		PieceArray[BQ] = SetBit(PieceArray[BQ], square)
		*squareCount++
	case 'r':
		PieceArray[BR] = SetBit(PieceArray[BR], square)
		*squareCount++
	case 'n':
		PieceArray[BN] = SetBit(PieceArray[BN], square)
		*squareCount++
	case 'k':
		PieceArray[BK] = SetBit(PieceArray[BK], square)
		*squareCount++
	case '/':
		*squareCount = 0
		*bracketCount++
	case '1':
		*squareCount += 1
	case '2':
		*squareCount += 2
	case '3':
		*squareCount += 3
	case '4':
		*squareCount += 4
	case '5':
		*squareCount += 5
	case '6':
		*squareCount += 6
	case '7':
		*squareCount += 7
	case '8':
		*squareCount += 8
	}
}
func Load_Fen_Sort_Side(setting *int, character_in_fen byte) {
	switch character_in_fen {
	case 'w':
		whiteToPlay = true
	case 'b':
		whiteToPlay = false
	case ' ':
		*setting++
	}
}
func Load_Fen_Sort_Castling(setting *int, character_in_fen byte) {
	switch character_in_fen {
	case 'K':
		CastleRights[0] = true
	case 'Q':
		CastleRights[1] = true
	case 'k':
		CastleRights[2] = true
	case 'q':
		CastleRights[3] = true
	case '-':
		CastleRights[0] = false
		CastleRights[1] = false
		CastleRights[2] = false
		CastleRights[3] = false
	case ' ':
		*setting++
	}
}
func Load_Fen_Sort_EP(setting *int, character_in_fen byte, file_index *int, rank_index *int) {

	if character_in_fen == '-' {
		ep = NO_SQUARE
	}
	if character_in_fen == ' ' {

		if *file_index != -1 && *rank_index != -1 {
			ep = uint8(Convert_to_64(*file_index, *rank_index))
		}
		*setting++
	}

	switch character_in_fen {

	case 'a':
		*file_index = 0
		return
	case 'b':
		*file_index = 1
		return
	case 'c':
		*file_index = 2
		return
	case 'd':
		*file_index = 3
		return
	case 'e':
		*file_index = 4
		return
	case 'f':
		*file_index = 5
		return
	case 'g':
		*file_index = 6
		return
	case 'h':
		*file_index = 7
		return
	}

	switch character_in_fen {

	case '1':
		*rank_index = 7
		return
	case '2':
		*rank_index = 6
		return
	case '3':
		*rank_index = 5
		return
	case '4':
		*rank_index = 4
		return
	case '5':
		*rank_index = 3
		return
	case '6':
		*rank_index = 2
		return
	case '7':
		*rank_index = 1
		return
	case '8':
		*rank_index = 0
		return
	}
}
func Convert_to_64(file int, rank int) int {
	return (rank * 8) + file
}
func Load_Fen_Sort_Fifty_Move(setting *int, character_in_fen byte) {
	if character_in_fen == ' ' {
		*setting++
		return
	}
}