-module(png).
-compile(export_all).
-record(png_info, {width, height, bitDepth, colourType, compression, filter, interlace}).

getSize(TempSize) ->
  io:format("getSize(~p)~n",[binary_to_list(TempSize)]),
  getSize(binary_to_list(TempSize),0, 65536*256).
getSize([], Acc, Mult) -> erlang:trunc(Acc);
getSize([Temp|Size], Acc, Mult) ->
  getSize(Size,Acc+(Temp*Mult), Mult/256).

sizeOfPNG(Filename) ->
  A=getPngGeometry(Filename),
  {element(2,A), element(3,A)}.

getPngGeometry(Filename) ->
    {ok, FileRef}=file:open(Filename, [read, raw, binary]),
    Status = file:read(FileRef,8),
    {ok,Sign} = Status,
    case Sign of
      <<137,80,78,71,13,10,26,10>> ->
        {ok,TempSize} = file:read(FileRef,4),
        {ok,IHeader} = file:read(FileRef,4),
        case IHeader of
          <<"IHDR">> ->
            io:format("IHDR matches~n",[]),
            Size = getSize(TempSize),
            io:format("Size = ~p~n",[Size]),
            {ok,Chunk} = file:read(FileRef,Size),
            <<Width:32, Height:32, BitDepth:8, ColourType:8, Compression:8, Filter:8, Interlace:8>> = Chunk,
            file:close(FileRef),
            #png_info{width=Width, height=Height, bitDepth=BitDepth,
            colourType=ColourType, compression=Compression, 
            filter=Filter, interlace=Interlace};
          _ ->
            file:close(FileRef),
            no_IHDR_block
        end;        
      _ ->
        file:close(FileRef),
        not_a_PNG_file
    end.