boyer_moore

-module(boyer_moore_ffi).
-export([build_pattern/1, search/3]).

build_pattern(Pattern) ->
    case bit_size(Pattern) of
        NonAligned when (NonAligned rem 8) /= 0 -> {error, nil};
        Aligned ->
            case Aligned of
                0 ->
                    {error, nil};
                _ ->
                    CompiledPattern = binary:compile_pattern(Pattern),
                    {ok, {searcher, fun(Data, Bounds) -> search(Data, CompiledPattern, Bounds) end}}
            end
    end.

search(Data, CompiledPattern, {bounds, Start, End}) ->
    DataSize = byte_size(Data),

    RealStart =
        case Start of
            {some, N} when N < 0 -> 0;
            {some, N} when N >= DataSize -> DataSize;
            {some, N} -> N;
            none -> 0
        end,

    RealEnd =
        case End of
            {some, N2} when N2 < RealStart -> RealStart;
            {some, N2} when N2 >= DataSize -> DataSize;
            {some, N2} -> N2;
            none -> DataSize
        end,

    Length = RealEnd - RealStart,

    case binary:match(Data, CompiledPattern, [{scope, {RealStart, Length}}]) of
        nomatch -> {error, nil};
        {Pos, _Length} -> {ok, Pos}
    end.