%% @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]).
-export([default/3, enter_from_list/2, default_from_list/2]).
-export([to_list/1, make/1]).
-export([test/0]).

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

%% @spec test() -> ok
%% @doc Run tests for this module.
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),
    ok.

%% @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 tuple is already mochiweb_headers.
make(T) when is_tuple(T) ->
    T.

%% @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 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

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).