gchess

-module(position).
-compile([no_auto_import, nowarn_unused_vars]).

-export([are_the_same/2, file_to_string/1, rank_to_string/1, to_string/1, file_to_int/1, rank_to_int/1, to_int/1, distance_between/2, to_bitboard/1, int_to_rank/1, int_to_file/1, from_int/1, get_file/2, get_file_relative/3, get_rank/2, get_position/3, get_rank_relative/3, get_position_relative/4, get_rear_white_rank/1, get_rear_black_rank/1, get_rear_rank/2, get_rear_position/2]).
-export_type([position/0, file/0, rank/0]).

-type position() :: {position, file(), rank()}.

-type file() :: a | b | c | d | e | f | g | h.

-type rank() :: one | two | three | four | five | six | seven | eight.

-spec are_the_same(position(), position()) -> boolean().
are_the_same(Position1, Position2) ->
    (erlang:element(2, Position1) =:= erlang:element(2, Position2)) andalso (erlang:element(
        3,
        Position1
    )
    =:= erlang:element(3, Position2)).

-spec file_to_string(file()) -> binary().
file_to_string(File) ->
    case File of
        a ->
            <<"a"/utf8>>;

        b ->
            <<"b"/utf8>>;

        c ->
            <<"c"/utf8>>;

        d ->
            <<"d"/utf8>>;

        e ->
            <<"e"/utf8>>;

        f ->
            <<"f"/utf8>>;

        g ->
            <<"g"/utf8>>;

        h ->
            <<"h"/utf8>>
    end.

-spec rank_to_string(rank()) -> binary().
rank_to_string(Rank) ->
    case Rank of
        one ->
            <<"1"/utf8>>;

        two ->
            <<"2"/utf8>>;

        three ->
            <<"3"/utf8>>;

        four ->
            <<"4"/utf8>>;

        five ->
            <<"5"/utf8>>;

        six ->
            <<"6"/utf8>>;

        seven ->
            <<"7"/utf8>>;

        eight ->
            <<"8"/utf8>>
    end.

-spec to_string(position()) -> binary().
to_string(Position) ->
    File = file_to_string(erlang:element(2, Position)),
    Rank = rank_to_string(erlang:element(3, Position)),
    Pos_as_string = <<File/binary, Rank/binary>>,
    Pos_as_string.

-spec file_to_int(file()) -> integer().
file_to_int(File) ->
    case File of
        a ->
            0;

        b ->
            1;

        c ->
            2;

        d ->
            3;

        e ->
            4;

        f ->
            5;

        g ->
            6;

        h ->
            7
    end.

-spec rank_to_int(rank()) -> integer().
rank_to_int(Rank) ->
    case Rank of
        one ->
            0;

        two ->
            1;

        three ->
            2;

        four ->
            3;

        five ->
            4;

        six ->
            5;

        seven ->
            6;

        eight ->
            7
    end.

-spec to_int(position()) -> integer().
to_int(Position) ->
    File = file_to_int(erlang:element(2, Position)),
    Rank = rank_to_int(erlang:element(3, Position)),
    Pos_as_int = File + (Rank * 8),
    Pos_as_int.

-spec distance_between(position(), position()) -> integer().
distance_between(Position1, Position2) ->
    Pos1_as_int = to_int(Position1),
    Pos2_as_int = to_int(Position2),
    Distance = Pos1_as_int - Pos2_as_int,
    Distance.

-spec to_bitboard(position()) -> bitboard:bitboard().
to_bitboard(Position) ->
    Pos_as_int = to_int(Position),
    Bitboard = bitboard:shift_left({bitboard, 1}, Pos_as_int),
    Bitboard.

-spec int_to_rank(integer()) -> rank().
int_to_rank(I) ->
    case I of
        0 ->
            one;

        1 ->
            two;

        2 ->
            three;

        3 ->
            four;

        4 ->
            five;

        5 ->
            six;

        6 ->
            seven;

        7 ->
            eight
    end.

-spec int_to_file(integer()) -> file().
int_to_file(I) ->
    case I of
        0 ->
            a;

        1 ->
            b;

        2 ->
            c;

        3 ->
            d;

        4 ->
            e;

        5 ->
            f;

        6 ->
            g;

        7 ->
            h
    end.

-spec from_int(integer()) -> gleam@option:option(position()).
from_int(I) ->
    case I of
        I@1 when (I@1 >= 0) andalso (I@1 < 64) ->
            File = int_to_file(I@1 rem 8),
            Rank = int_to_rank(I@1 div 8),
            {some, {position, File, Rank}};

        _ ->
            none
    end.

-spec get_file(file(), integer()) -> file().
get_file(File, Y) ->
    File_as_int = file_to_int(File),
    New_file_as_int = File_as_int + Y,
    New_file = int_to_file(New_file_as_int),
    New_file.

-spec get_file_relative(file(), integer(), color:color()) -> file().
get_file_relative(File, Y, Relative_to) ->
    case Relative_to of
        white ->
            get_file(File, Y);

        black ->
            get_file(File, - Y)
    end.

-spec get_rank(rank(), integer()) -> rank().
get_rank(Rank, X) ->
    Rank_as_int = rank_to_int(Rank),
    New_rank_as_int = Rank_as_int + X,
    New_rank = int_to_rank(New_rank_as_int),
    New_rank.

-spec get_position(position(), integer(), integer()) -> position().
get_position(Position, X, Y) ->
    File = get_file(erlang:element(2, Position), Y),
    Rank = get_rank(erlang:element(3, Position), X),
    {position, File, Rank}.

-spec get_rank_relative(rank(), integer(), color:color()) -> rank().
get_rank_relative(Rank, X, Relative_to) ->
    case Relative_to of
        white ->
            get_rank(Rank, X);

        black ->
            get_rank(Rank, - X)
    end.

-spec get_position_relative(position(), integer(), integer(), color:color()) -> position().
get_position_relative(Position, X, Y, Relative_to) ->
    File = get_file_relative(erlang:element(2, Position), Y, Relative_to),
    Rank = get_rank_relative(erlang:element(3, Position), X, Relative_to),
    {position, File, Rank}.

-spec get_rear_white_rank(rank()) -> rank().
get_rear_white_rank(Rank) ->
    case Rank of
        one ->
            one;

        two ->
            one;

        three ->
            two;

        four ->
            three;

        five ->
            four;

        six ->
            five;

        seven ->
            six;

        eight ->
            seven
    end.

-spec get_rear_black_rank(rank()) -> rank().
get_rear_black_rank(Rank) ->
    case Rank of
        one ->
            two;

        two ->
            three;

        three ->
            four;

        four ->
            five;

        five ->
            six;

        six ->
            seven;

        seven ->
            eight;

        eight ->
            eight
    end.

-spec get_rear_rank(rank(), color:color()) -> rank().
get_rear_rank(Rank, Color) ->
    case Color of
        white ->
            get_rear_white_rank(Rank);

        black ->
            get_rear_black_rank(Rank)
    end.

-spec get_rear_position(position(), color:color()) -> position().
get_rear_position(Position, Color) ->
    Rank = get_rear_rank(erlang:element(3, Position), Color),
    {position, erlang:element(2, Position), Rank}.