%%% Utility functions for zlib.
-module(yaws_zlib).
-author('carsten@codimi.de').

-export([gzipInit/1, gzipEnd/1, gzipDeflate/4, gzip/1]).


gzipInit(Z) ->
    ok = zlib:deflateInit(Z, default, deflated, -15, 8, default),
    undefined.


gzipEnd(Z) ->
    zlib:deflateEnd(Z).


gzipDeflate(Z, undefined, Bin, Flush) ->
    Crc32 = zlib:crc32(Z),
    Head = <<
						% ID
	    16#1f, 16#8b,
						% deflate
	    8:8,
						% flags
	    0:8, 
						% mtime
	    0:32, 
						% xflags
	    0:8, 
						% OS_UNKNOWN
						% Set to Unix instead?
	    255:8>>,
    {ok, Priv, Bs} = gzipDeflate(Z, {Crc32,0}, Bin, Flush),
    {ok, Priv, [Head | Bs]};
    
gzipDeflate(Z, {Crc32,Size}, Bin, Flush) ->
    Bs = case zlib:deflate(Z, Bin, Flush) of
	{ok, Bs1} -> Bs1;
	Bs1 when is_list(Bs1) -> Bs1
    end,
    {ok, Crc1} = crc32(Z, Crc32, Bin),
    Size1 = Size+size(Bin),
    Data = 
	if
	    Flush == finish ->
						% Appending should not
						% hurt, so let's be a
						% bit more consistent
						% here.
		Bs ++ [<<Crc1:32/little, Size1:32/little>>];
	    true ->
		Bs
	end,
    {ok, {Crc1, Size1}, Data}.


%% like zlib:gzip/1, but returns an io list

gzip(Data) when binary(Data) ->
    Z = zlib:open(),
    {ok, _, D} = gzipDeflate(Z, gzipInit(Z), Data, finish),
    gzipEnd(Z),
    zlib:close(Z),
    {ok, D};

gzip(Data) ->
    Z = zlib:open(),
    gzip_loop(Z, gzipInit(Z), Data, [], []).

gzip_loop(Z, P, [], [], A) ->
    {ok, _, D} = gzipDeflate(Z, P, <<>>, finish),
    gzipEnd(Z),
    zlib:close(Z),
    {ok, [A|D]};
gzip_loop(Z, P, B, C, A) when binary(B) ->
    {ok, P1, D} = gzipDeflate(Z, P, B, none),
    gzip_loop(Z, P1, C, [],
	      case D of
		 [] -> A;
		 _ -> 
		      case A of
			  [] -> D;
			  _ -> [A|D]
		      end
	      end);
gzip_loop(Z, P, [I|T], C, A) when integer(I) ->
    gzip_loop(Z, P, list_to_binary([I|T]), C, A);
gzip_loop(Z, P, [H], C, A) ->
    gzip_loop(Z, P, H, C, A);
gzip_loop(Z, P, [H|T], C, A) ->
    gzip_loop(Z, P, H, [T|C], A);
gzip_loop(Z, P, [], C, A) ->
    gzip_loop(Z, P, C, [], A);
gzip_loop(Z, P, I, C, A) when integer(I) ->
    gzip_loop(Z, P, <<I>>, C, A).


%% To work around a bug in zlib.

crc32(Z, CRC, Binary) ->
    case port_control(Z, 17, <<CRC:32, Binary/binary>>) of
	[2,A,B,C,D] -> {ok, (A bsl 24)+(B bsl 16)+(C bsl 8)+D}
    end.