%% @author Bob Ippolito <bob@mochimedia.com>
%% @copyright 2007 Mochi Media, Inc.

%% @doc Case preserving (but case insensitive) HTTP Header dictionary.

-module(mochiweb_headers).
-author('bob@mochimedia.com').
-export([empty/0, from_list/1, insert/3, enter/3, get_value/2, lookup/2]).
-export([delete_any/2, get_primary_value/2, get_combined_value/2]).
-export([default/3, enter_from_list/2, default_from_list/2]).
-export([to_list/1, make/1]).
-export([from_binary/1]).

%% @type headers().
%% @type key() = atom() | binary() | string().
%% @type value() = atom() | binary() | string() | integer().

%% @spec empty() -> headers()
%% @doc Create an empty headers structure.
empty() ->
    gb_trees:empty().

%% @spec make(headers() | [{key(), value()}]) -> headers()
%% @doc Construct a headers() from the given list.
make(L) when is_list(L) ->
    from_list(L);
%% assume a non-list is already mochiweb_headers.
make(T) ->
    T.

%% @spec from_binary(iolist()) -> headers()
%% @doc Transforms a raw HTTP header into a mochiweb headers structure.
%%
%%      The given raw HTTP header can be one of the following:
%%
%%      1) A string or a binary representing a full HTTP header ending with
%%         double CRLF.
%%         Examples:
%%         ```
%%         "Content-Length: 47\r\nContent-Type: text/plain\r\n\r\n"
%%         <<"Content-Length: 47\r\nContent-Type: text/plain\r\n\r\n">>'''
%%
%%      2) A list of binaries or strings where each element represents a raw
%%         HTTP header line ending with a single CRLF.
%%         Examples:
%%         ```
%%         [<<"Content-Length: 47\r\n">>, <<"Content-Type: text/plain\r\n">>]
%%         ["Content-Length: 47\r\n", "Content-Type: text/plain\r\n"]
%%         ["Content-Length: 47\r\n", <<"Content-Type: text/plain\r\n">>]'''
%%
from_binary(RawHttpHeader) when is_binary(RawHttpHeader) ->
    from_binary(RawHttpHeader, []);
from_binary(RawHttpHeaderList) ->
    from_binary(list_to_binary([RawHttpHeaderList, "\r\n"])).

from_binary(RawHttpHeader, Acc) ->
    case erlang:decode_packet(httph, RawHttpHeader, []) of
        {ok, {http_header, _, H, _, V}, Rest} ->
            from_binary(Rest, [{H, V} | Acc]);
        _ ->
            make(Acc)
    end.

%% @spec from_list([{key(), value()}]) -> headers()
%% @doc Construct a headers() from the given list.
from_list(List) ->
    lists:foldl(fun ({K, V}, T) -> insert(K, V, T) end, empty(), List).

%% @spec enter_from_list([{key(), value()}], headers()) -> headers()
%% @doc Insert pairs into the headers, replace any values for existing keys.
enter_from_list(List, T) ->
    lists:foldl(fun ({K, V}, T1) -> enter(K, V, T1) end, T, List).

%% @spec default_from_list([{key(), value()}], headers()) -> headers()
%% @doc Insert pairs into the headers for keys that do not already exist.
default_from_list(List, T) ->
    lists:foldl(fun ({K, V}, T1) -> default(K, V, T1) end, T, List).

%% @spec to_list(headers()) -> [{key(), string()}]
%% @doc Return the contents of the headers. The keys will be the exact key
%%      that was first inserted (e.g. may be an atom or binary, case is
%%      preserved).
to_list(T) ->
    F = fun ({K, {array, L}}, Acc) ->
                L1 = lists:reverse(L),
                lists:foldl(fun (V, Acc1) -> [{K, V} | Acc1] end, Acc, L1);
            (Pair, Acc) ->
                [Pair | Acc]
        end,
    lists:reverse(lists:foldl(F, [], gb_trees:values(T))).

%% @spec get_value(key(), headers()) -> string() | undefined
%% @doc Return the value of the given header using a case insensitive search.
%%      undefined will be returned for keys that are not present.
get_value(K, T) ->
    case lookup(K, T) of
        {value, {_, V}} ->
            expand(V);
        none ->
            undefined
    end.

%% @spec get_primary_value(key(), headers()) -> string() | undefined
%% @doc Return the value of the given header up to the first semicolon using
%%      a case insensitive search. undefined will be returned for keys
%%      that are not present.
get_primary_value(K, T) ->
    case get_value(K, T) of
        undefined ->
            undefined;
        V ->
            lists:takewhile(fun (C) -> C =/= $; end, V)
    end.

%% @spec get_combined_value(key(), headers()) -> string() | undefined
%% @doc Return the value from the given header using a case insensitive search.
%%      If the value of the header is a comma-separated list where holds values
%%      are all identical, the identical value will be returned.
%%      undefined will be returned for keys that are not present or the
%%      values in the list are not the same.
%%
%%      NOTE: The process isn't designed for a general purpose. If you need
%%            to access all values in the combined header, please refer to
%%            '''tokenize_header_value/1'''.
%%
%%      Section 4.2 of the RFC 2616 (HTTP 1.1) describes multiple message-header
%%      fields with the same field-name may be present in a message if and only
%%      if the entire field-value for that header field is defined as a
%%      comma-separated list [i.e., #(values)].
get_combined_value(K, T) ->
    case get_value(K, T) of
        undefined ->
            undefined;
        V ->
            case sets:to_list(sets:from_list(tokenize_header_value(V))) of
                [Val] ->
                    Val;
                _ ->
                    undefined
            end
    end.

%% @spec lookup(key(), headers()) -> {value, {key(), string()}} | none
%% @doc Return the case preserved key and value for the given header using
%%      a case insensitive search. none will be returned for keys that are
%%      not present.
lookup(K, T) ->
    case gb_trees:lookup(normalize(K), T) of
        {value, {K0, V}} ->
            {value, {K0, expand(V)}};
        none ->
            none
    end.

%% @spec default(key(), value(), headers()) -> headers()
%% @doc Insert the pair into the headers if it does not already exist.
default(K, V, T) ->
    K1 = normalize(K),
    V1 = any_to_list(V),
    try gb_trees:insert(K1, {K, V1}, T)
    catch
        error:{key_exists, _} ->
            T
    end.

%% @spec enter(key(), value(), headers()) -> headers()
%% @doc Insert the pair into the headers, replacing any pre-existing key.
enter(K, V, T) ->
    K1 = normalize(K),
    V1 = any_to_list(V),
    gb_trees:enter(K1, {K, V1}, T).

%% @spec insert(key(), value(), headers()) -> headers()
%% @doc Insert the pair into the headers, merging with any pre-existing key.
%%      A merge is done with Value = V0 ++ ", " ++ V1.
insert(K, V, T) ->
    K1 = normalize(K),
    V1 = any_to_list(V),
    try gb_trees:insert(K1, {K, V1}, T)
    catch
        error:{key_exists, _} ->
            {K0, V0} = gb_trees:get(K1, T),
            V2 = merge(K1, V1, V0),
            gb_trees:update(K1, {K0, V2}, T)
    end.

%% @spec delete_any(key(), headers()) -> headers()
%% @doc Delete the header corresponding to key if it is present.
delete_any(K, T) ->
    K1 = normalize(K),
    gb_trees:delete_any(K1, T).

%% Internal API

tokenize_header_value(undefined) ->
    undefined;
tokenize_header_value(V) ->
    reversed_tokens(trim_and_reverse(V, false), [], []).

trim_and_reverse([S | Rest], Reversed) when S=:=$ ; S=:=$\n; S=:=$\t ->
    trim_and_reverse(Rest, Reversed);
trim_and_reverse(V, false) ->
    trim_and_reverse(lists:reverse(V), true);
trim_and_reverse(V, true) ->
    V.

reversed_tokens([], [], Acc) ->
    Acc;
reversed_tokens([], Token, Acc) ->
    [Token | Acc];
reversed_tokens("\"" ++ Rest, [], Acc) ->
    case extract_quoted_string(Rest, []) of
        {String, NewRest} ->
            reversed_tokens(NewRest, [], [String | Acc]);
        undefined ->
            undefined
    end;
reversed_tokens("\"" ++ _Rest, _Token, _Acc) ->
    undefined;
reversed_tokens([C | Rest], [], Acc) when C=:=$ ;C=:=$\n;C=:=$\t;C=:=$, ->
    reversed_tokens(Rest, [], Acc);
reversed_tokens([C | Rest], Token, Acc) when C=:=$ ;C=:=$\n;C=:=$\t;C=:=$, ->
    reversed_tokens(Rest, [], [Token | Acc]);
reversed_tokens([C | Rest], Token, Acc) ->
    reversed_tokens(Rest, [C | Token], Acc);
reversed_tokens(_, _, _) ->
    undefeined.

extract_quoted_string([], _Acc) ->
    undefined;
extract_quoted_string("\"\\" ++ Rest, Acc) ->
    extract_quoted_string(Rest, "\"" ++ Acc);
extract_quoted_string("\"" ++ Rest, Acc) ->
    {Acc, Rest};
extract_quoted_string([C | Rest], Acc) ->
    extract_quoted_string(Rest, [C | Acc]).

expand({array, L}) ->
    mochiweb_util:join(lists:reverse(L), ", ");
expand(V) ->
    V.

merge("set-cookie", V1, {array, L}) ->
    {array, [V1 | L]};
merge("set-cookie", V1, V0) ->
    {array, [V1, V0]};
merge(_, V1, V0) ->
    V0 ++ ", " ++ V1.

normalize(K) when is_list(K) ->
    string:to_lower(K);
normalize(K) when is_atom(K) ->
    normalize(atom_to_list(K));
normalize(K) when is_binary(K) ->
    normalize(binary_to_list(K)).

any_to_list(V) when is_list(V) ->
    V;
any_to_list(V) when is_atom(V) ->
    atom_to_list(V);
any_to_list(V) when is_binary(V) ->
    binary_to_list(V);
any_to_list(V) when is_integer(V) ->
    integer_to_list(V).

%%
%% Tests.
%%
-ifdef(TEST).
-include_lib("eunit/include/eunit.hrl").

make_test() ->
    Identity = make([{hdr, foo}]),
    ?assertEqual(
       Identity,
       make(Identity)).

enter_from_list_test() ->
    H = make([{hdr, foo}]),
    ?assertEqual(
       [{baz, "wibble"}, {hdr, "foo"}],
       to_list(enter_from_list([{baz, wibble}], H))),
    ?assertEqual(
       [{hdr, "bar"}],
       to_list(enter_from_list([{hdr, bar}], H))),
    ok.

default_from_list_test() ->
    H = make([{hdr, foo}]),
    ?assertEqual(
       [{baz, "wibble"}, {hdr, "foo"}],
       to_list(default_from_list([{baz, wibble}], H))),
    ?assertEqual(
       [{hdr, "foo"}],
       to_list(default_from_list([{hdr, bar}], H))),
    ok.

get_primary_value_test() ->
    H = make([{hdr, foo}, {baz, <<"wibble;taco">>}]),
    ?assertEqual(
       "foo",
       get_primary_value(hdr, H)),
    ?assertEqual(
       undefined,
       get_primary_value(bar, H)),
    ?assertEqual(
       "wibble",
       get_primary_value(<<"baz">>, H)),
    ok.

get_combined_value_test() ->
    H = make([{hdr, foo}, {baz, <<"wibble,taco">>}, {content_length, "123, 123"},
              {test, " 123,  123,     123  , 123,123 "},
              {test2, "456,  123,     123  , 123"},
              {test3, "123"}, {test4, " 123, "}]),
    ?assertEqual(
       "foo",
       get_combined_value(hdr, H)),
    ?assertEqual(
       undefined,
       get_combined_value(bar, H)),
    ?assertEqual(
       undefined,
       get_combined_value(<<"baz">>, H)),
    ?assertEqual(
       "123",
       get_combined_value(<<"content_length">>, H)),
    ?assertEqual(
       "123",
       get_combined_value(<<"test">>, H)),
    ?assertEqual(
       undefined,
       get_combined_value(<<"test2">>, H)),
    ?assertEqual(
       "123",
       get_combined_value(<<"test3">>, H)),
    ?assertEqual(
       "123",
       get_combined_value(<<"test4">>, H)),
    ok.

set_cookie_test() ->
    H = make([{"set-cookie", foo}, {"set-cookie", bar}, {"set-cookie", baz}]),
    ?assertEqual(
       [{"set-cookie", "foo"}, {"set-cookie", "bar"}, {"set-cookie", "baz"}],
       to_list(H)),
    ok.

headers_test() ->
    H = ?MODULE:make([{hdr, foo}, {"Hdr", "bar"}, {'Hdr', 2}]),
    [{hdr, "foo, bar, 2"}] = ?MODULE:to_list(H),
    H1 = ?MODULE:insert(taco, grande, H),
    [{hdr, "foo, bar, 2"}, {taco, "grande"}] = ?MODULE:to_list(H1),
    H2 = ?MODULE:make([{"Set-Cookie", "foo"}]),
    [{"Set-Cookie", "foo"}] = ?MODULE:to_list(H2),
    H3 = ?MODULE:insert("Set-Cookie", "bar", H2),
    [{"Set-Cookie", "foo"}, {"Set-Cookie", "bar"}] = ?MODULE:to_list(H3),
    "foo, bar" = ?MODULE:get_value("set-cookie", H3),
    {value, {"Set-Cookie", "foo, bar"}} = ?MODULE:lookup("set-cookie", H3),
    undefined = ?MODULE:get_value("shibby", H3),
    none = ?MODULE:lookup("shibby", H3),
    H4 = ?MODULE:insert("content-type",
                        "application/x-www-form-urlencoded; charset=utf8",
                        H3),
    "application/x-www-form-urlencoded" = ?MODULE:get_primary_value(
                                             "content-type", H4),
    H4 = ?MODULE:delete_any("nonexistent-header", H4),
    H3 = ?MODULE:delete_any("content-type", H4),
    HB = <<"Content-Length: 47\r\nContent-Type: text/plain\r\n\r\n">>,
    H_HB = ?MODULE:from_binary(HB),
    H_HB = ?MODULE:from_binary(binary_to_list(HB)),
    "47" = ?MODULE:get_value("Content-Length", H_HB),
    "text/plain" = ?MODULE:get_value("Content-Type", H_HB),
    L_H_HB = ?MODULE:to_list(H_HB),
    2 = length(L_H_HB),
    true = lists:member({'Content-Length', "47"}, L_H_HB),
    true = lists:member({'Content-Type', "text/plain"}, L_H_HB),
    HL = [ <<"Content-Length: 47\r\n">>, <<"Content-Type: text/plain\r\n">> ],
    HL2 = [ "Content-Length: 47\r\n", <<"Content-Type: text/plain\r\n">> ],
    HL3 = [ <<"Content-Length: 47\r\n">>, "Content-Type: text/plain\r\n" ],
    H_HL = ?MODULE:from_binary(HL),
    H_HL = ?MODULE:from_binary(HL2),
    H_HL = ?MODULE:from_binary(HL3),
    "47" = ?MODULE:get_value("Content-Length", H_HL),
    "text/plain" = ?MODULE:get_value("Content-Type", H_HL),
    L_H_HL = ?MODULE:to_list(H_HL),
    2 = length(L_H_HL),
    true = lists:member({'Content-Length', "47"}, L_H_HL),
    true = lists:member({'Content-Type', "text/plain"}, L_H_HL),
    [] = ?MODULE:to_list(?MODULE:from_binary(<<>>)),
    [] = ?MODULE:to_list(?MODULE:from_binary(<<"">>)),
    [] = ?MODULE:to_list(?MODULE:from_binary(<<"\r\n">>)),
    [] = ?MODULE:to_list(?MODULE:from_binary(<<"\r\n\r\n">>)),
    [] = ?MODULE:to_list(?MODULE:from_binary("")),
    [] = ?MODULE:to_list(?MODULE:from_binary([<<>>])),
    [] = ?MODULE:to_list(?MODULE:from_binary([<<"">>])),
    [] = ?MODULE:to_list(?MODULE:from_binary([<<"\r\n">>])),
    [] = ?MODULE:to_list(?MODULE:from_binary([<<"\r\n\r\n">>])),
    ok.

tokenize_header_value_test() ->
    ?assertEqual(["a quote in a \"quote\"."],
                 tokenize_header_value("\"a quote in a \\\"quote\\\".\"")),
    ?assertEqual(["abc"], tokenize_header_value("abc")),
    ?assertEqual(["abc", "def"], tokenize_header_value("abc def")),
    ?assertEqual(["abc", "def"], tokenize_header_value("abc , def")),
    ?assertEqual(["abc", "def"], tokenize_header_value(",abc ,, def,,")),
    ?assertEqual(["abc def"], tokenize_header_value("\"abc def\"      ")),
    ?assertEqual(["abc, def"], tokenize_header_value("\"abc, def\"")),
    ?assertEqual(["\\a\\$"], tokenize_header_value("\"\\a\\$\"")),
    ?assertEqual(["abc def", "foo, bar", "12345", ""],
                 tokenize_header_value("\"abc def\" \"foo, bar\" , 12345, \"\"")),
    ?assertEqual(undefined,
                 tokenize_header_value(undefined)),
    ?assertEqual(undefined,
                 tokenize_header_value("umatched quote\"")),
    ?assertEqual(undefined,
                 tokenize_header_value("\"unmatched quote")).

-endif.