%% @author Bob Ippolito <bob@mochimedia.com>
%% @copyright 2007 Mochi Media, Inc.
%%
%% Permission is hereby granted, free of charge, to any person obtaining a
%% copy of this software and associated documentation files (the "Software"),
%% to deal in the Software without restriction, including without limitation
%% the rights to use, copy, modify, merge, publish, distribute, sublicense,
%% and/or sell copies of the Software, and to permit persons to whom the
%% Software is furnished to do so, subject to the following conditions:
%%
%% The above copyright notice and this permission notice shall be included in
%% all copies or substantial portions of the Software.
%%
%% THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
%% IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
%% FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
%% THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
%% LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
%% FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
%% DEALINGS IN THE SOFTWARE.

%% @doc Yet another JSON (RFC 4627) library for Erlang. mochijson2 works
%%      with binaries as strings, arrays as lists (without an {array, _})
%%      wrapper and it only knows how to decode UTF-8 (and ASCII).
%%
%%      JSON terms are decoded as follows (javascript -> erlang):
%%      <ul>
%%          <li>{"key": "value"} ->
%%              {struct, [{&lt;&lt;"key">>, &lt;&lt;"value">>}]}</li>
%%          <li>["array", 123, 12.34, true, false, null] ->
%%              [&lt;&lt;"array">>, 123, 12.34, true, false, null]
%%          </li>
%%      </ul>
%%      <ul>
%%          <li>Strings in JSON decode to UTF-8 binaries in Erlang</li>
%%          <li>Objects decode to {struct, PropList}</li>
%%          <li>Numbers decode to integer or float</li>
%%          <li>true, false, null decode to their respective terms.</li>
%%      </ul>
%%      The encoder will accept the same format that the decoder will produce,
%%      but will also allow additional cases for leniency:
%%      <ul>
%%          <li>atoms other than true, false, null will be considered UTF-8
%%              strings (even as a proplist key)
%%          </li>
%%          <li>{json, IoList} will insert IoList directly into the output
%%              with no validation
%%          </li>
%%          <li>{array, Array} will be encoded as Array
%%              (legacy mochijson style)
%%          </li>
%%          <li>A non-empty raw proplist will be encoded as an object as long
%%              as the first pair does not have an atom key of json, struct,
%%              or array
%%          </li>
%%      </ul>

-module(mochijson2).
-author('bob@mochimedia.com').
-export([encoder/1, encode/1]).
-export([decoder/1, decode/1, decode/2]).

%% This is a macro to placate syntax highlighters..
-define(Q, $\").
-define(ADV_COL(S, N), S#decoder{offset=N+S#decoder.offset,
                                 column=N+S#decoder.column}).
-define(INC_COL(S), S#decoder{offset=1+S#decoder.offset,
                              column=1+S#decoder.column}).
-define(INC_LINE(S), S#decoder{offset=1+S#decoder.offset,
                               column=1,
                               line=1+S#decoder.line}).
-define(INC_CHAR(S, C),
        case C of
            $\n ->
                S#decoder{column=1,
                          line=1+S#decoder.line,
                          offset=1+S#decoder.offset};
            _ ->
                S#decoder{column=1+S#decoder.column,
                          offset=1+S#decoder.offset}
        end).
-define(IS_WHITESPACE(C),
        (C =:= $\s orelse C =:= $\t orelse C =:= $\r orelse C =:= $\n)).

-ifdef(map_unavailable).
-define(IS_MAP(_), false).
-else.
-define(IS_MAP(X), is_map(X)).
-endif.

%% @type json_string() = atom | binary()
%% @type json_number() = integer() | float()
%% @type json_array() = [json_term()]
%% @type json_object() = {struct, [{json_string(), json_term()}]}
%% @type json_eep18_object() = {[{json_string(), json_term()}]}
%% @type json_iolist() = {json, iolist()}
%% @type json_term() = json_string() | json_number() | json_array() |
%%                     json_object() | json_eep18_object() | json_iolist()

-record(encoder, {handler=null,
                  utf8=false}).

-record(decoder, {object_hook=null,
                  offset=0,
                  line=1,
                  column=1,
                  state=null}).

%% @spec encoder([encoder_option()]) -> function()
%% @doc Create an encoder/1 with the given options.
%% @type encoder_option() = handler_option() | utf8_option()
%% @type utf8_option() = boolean(). Emit unicode as utf8 (default - false)
encoder(Options) ->
    State = parse_encoder_options(Options, #encoder{}),
    fun (O) -> json_encode(O, State) end.

%% @spec encode(json_term()) -> iolist()
%% @doc Encode the given as JSON to an iolist.
encode(Any) ->
    json_encode(Any, #encoder{}).

%% @spec decoder([decoder_option()]) -> function()
%% @doc Create a decoder/1 with the given options.
decoder(Options) ->
    State = parse_decoder_options(Options, #decoder{}),
    fun (O) -> json_decode(O, State) end.

%% @spec decode(iolist(), [{format, proplist | eep18 | struct | map}]) -> json_term()
%% @doc Decode the given iolist to Erlang terms using the given object format
%%      for decoding, where proplist returns JSON objects as [{binary(), json_term()}]
%%      proplists, eep18 returns JSON objects as {[binary(), json_term()]},
%%      map returns JSON objects as #{binary() => json_term()}, and struct
%%      returns them as-is.
decode(S, Options) ->
    json_decode(S, parse_decoder_options(Options, #decoder{})).

%% @spec decode(iolist()) -> json_term()
%% @doc Decode the given iolist to Erlang terms.
decode(S) ->
    json_decode(S, #decoder{}).

%% Internal API

parse_encoder_options([], State) ->
    State;
parse_encoder_options([{handler, Handler} | Rest], State) ->
    parse_encoder_options(Rest, State#encoder{handler=Handler});
parse_encoder_options([{utf8, Switch} | Rest], State) ->
    parse_encoder_options(Rest, State#encoder{utf8=Switch}).

parse_decoder_options([], State) ->
    State;
parse_decoder_options([{object_hook, Hook} | Rest], State) ->
    parse_decoder_options(Rest, State#decoder{object_hook=Hook});
parse_decoder_options([{format, map} | Rest], State) ->
    Hook = make_object_hook_for_map(),
    parse_decoder_options(Rest, State#decoder{object_hook=Hook});
parse_decoder_options([{format, Format} | Rest], State)
  when Format =:= struct orelse Format =:= eep18 orelse Format =:= proplist ->
    parse_decoder_options(Rest, State#decoder{object_hook=Format}).

-ifdef(map_unavailable).
make_object_hook_for_map() ->
    exit({json_decode, {bad_format, map_unavailable}}).
-else.
make_object_hook_for_map() ->
    fun ({struct, P}) -> maps:from_list(P) end.
-endif.


json_encode(true, _State) ->
    <<"true">>;
json_encode(false, _State) ->
    <<"false">>;
json_encode(null, _State) ->
    <<"null">>;
json_encode(I, _State) when is_integer(I) ->
    integer_to_list(I);
json_encode(F, _State) when is_float(F) ->
    mochinum:digits(F);
json_encode(S, State) when is_binary(S); is_atom(S) ->
    json_encode_string(S, State);
json_encode([{K, _}|_] = Props, State) when (K =/= struct andalso
                                             K =/= array andalso
                                             K =/= json) ->
    json_encode_proplist(Props, State);
json_encode({struct, Props}, State) when is_list(Props) ->
    json_encode_proplist(Props, State);
json_encode({Props}, State) when is_list(Props) ->
    json_encode_proplist(Props, State);
json_encode({}, State) ->
    json_encode_proplist([], State);
json_encode(Array, State) when is_list(Array) ->
    json_encode_array(Array, State);
json_encode({array, Array}, State) when is_list(Array) ->
    json_encode_array(Array, State);
json_encode(M, State) when ?IS_MAP(M) ->
    json_encode_map(M, State);
json_encode({json, IoList}, _State) ->
    IoList;
json_encode(Bad, #encoder{handler=null}) ->
    exit({json_encode, {bad_term, Bad}});
json_encode(Bad, State=#encoder{handler=Handler}) ->
    json_encode(Handler(Bad), State).

json_encode_array([], _State) ->
    <<"[]">>;
json_encode_array(L, State) ->
    F = fun (O, Acc) ->
                [$,, json_encode(O, State) | Acc]
        end,
    [$, | Acc1] = lists:foldl(F, "[", L),
    lists:reverse([$\] | Acc1]).

json_encode_proplist([], _State) ->
    <<"{}">>;
json_encode_proplist(Props, State) ->
    F = fun ({K, V}, Acc) ->
                KS = json_encode_string(K, State),
                VS = json_encode(V, State),
                [$,, VS, $:, KS | Acc]
        end,
    [$, | Acc1] = lists:foldl(F, "{", Props),
    lists:reverse([$\} | Acc1]).

-ifdef(map_unavailable).
json_encode_map(Bad, _State) ->
  %% IS_MAP definition guarantees that this branch is dead
  exit({json_encode, {bad_term, Bad}}).
-else.
json_encode_map(Map, _State) when map_size(Map) =:= 0 ->
    <<"{}">>;
json_encode_map(Map, State) ->
    F = fun(K, V, Acc) ->
                KS = json_encode_string(K, State),
                VS = json_encode(V, State),
                [$,, VS, $:, KS | Acc]
          end,
    [$, | Acc1] = maps:fold(F, "{", Map),
    lists:reverse([$\} | Acc1]).
-endif.

json_encode_string(A, State) when is_atom(A) ->
    json_encode_string(atom_to_binary(A, latin1), State);
json_encode_string(B, State) when is_binary(B) ->
    case json_bin_is_safe(B) of
        true ->
            [?Q, B, ?Q];
        false ->
            json_encode_string_unicode(unicode:characters_to_list(B), State, [?Q])
    end;
json_encode_string(I, _State) when is_integer(I) ->
    [?Q, integer_to_list(I), ?Q];
json_encode_string(L, State) when is_list(L) ->
    case json_string_is_safe(L) of
        true ->
            [?Q, L, ?Q];
        false ->
            json_encode_string_unicode(L, State, [?Q])
    end.

json_string_is_safe([]) ->
    true;
json_string_is_safe([C | Rest]) ->
    case C of
        ?Q ->
            false;
        $\\ ->
            false;
        $\b ->
            false;
        $\f ->
            false;
        $\n ->
            false;
        $\r ->
            false;
        $\t ->
            false;
        C when C >= 0, C < $\s; C >= 16#7f, C =< 16#10FFFF ->
            false;
        C when C < 16#7f ->
            json_string_is_safe(Rest);
        _ ->
            exit({json_encode, {bad_char, C}})
    end.

json_bin_is_safe(<<>>) ->
    true;
json_bin_is_safe(<<C, Rest/binary>>) ->
    case C of
        ?Q ->
            false;
        $\\ ->
            false;
        $\b ->
            false;
        $\f ->
            false;
        $\n ->
            false;
        $\r ->
            false;
        $\t ->
            false;
        C when C >= 0, C < $\s; C >= 16#7f ->
            false;
        C when C < 16#7f ->
            json_bin_is_safe(Rest)
    end.

json_encode_string_unicode([], _State, Acc) ->
    lists:reverse([$\" | Acc]);
json_encode_string_unicode([C | Cs], State, Acc) ->
    Acc1 = case C of
               ?Q ->
                   [?Q, $\\ | Acc];
               %% Escaping solidus is only useful when trying to protect
               %% against "</script>" injection attacks which are only
               %% possible when JSON is inserted into a HTML document
               %% in-line. mochijson2 does not protect you from this, so
               %% if you do insert directly into HTML then you need to
               %% uncomment the following case or escape the output of encode.
               %%
               %% $/ ->
               %%    [$/, $\\ | Acc];
               %%
               $\\ ->
                   [$\\, $\\ | Acc];
               $\b ->
                   [$b, $\\ | Acc];
               $\f ->
                   [$f, $\\ | Acc];
               $\n ->
                   [$n, $\\ | Acc];
               $\r ->
                   [$r, $\\ | Acc];
               $\t ->
                   [$t, $\\ | Acc];
               C when C >= 0, C < $\s ->
                   [unihex(C) | Acc];
               C when C >= 16#7f, C =< 16#10FFFF, State#encoder.utf8 ->
                   [unicode:characters_to_binary([C]) | Acc];
               C when  C >= 16#7f, C =< 16#10FFFF, not State#encoder.utf8 ->
                   [unihex(C) | Acc];
               C when C < 16#7f ->
                   [C | Acc];
               _ ->
                   %% json_string_is_safe guarantees that this branch is dead
                   exit({json_encode, {bad_char, C}})
           end,
    json_encode_string_unicode(Cs, State, Acc1).

hexdigit(C) when C >= 0, C =< 9 ->
    C + $0;
hexdigit(C) when C =< 15 ->
    C + $a - 10.

unihex(C) when C < 16#10000 ->
    <<D3:4, D2:4, D1:4, D0:4>> = <<C:16>>,
    Digits = [hexdigit(D) || D <- [D3, D2, D1, D0]],
    [$\\, $u | Digits];
unihex(C) when C =< 16#10FFFF ->
    N = C - 16#10000,
    S1 = 16#d800 bor ((N bsr 10) band 16#3ff),
    S2 = 16#dc00 bor (N band 16#3ff),
    [unihex(S1), unihex(S2)].

json_decode(L, S) when is_list(L) ->
    json_decode(iolist_to_binary(L), S);
json_decode(B, S) ->
    {Res, S1} = decode1(B, S),
    {eof, _} = tokenize(B, S1#decoder{state=trim}),
    Res.

decode1(B, S=#decoder{state=null}) ->
    case tokenize(B, S#decoder{state=any}) of
        {{const, C}, S1} ->
            {C, S1};
        {start_array, S1} ->
            decode_array(B, S1);
        {start_object, S1} ->
            decode_object(B, S1)
    end.

make_object(V, #decoder{object_hook=N}) when N =:= null orelse N =:= struct ->
    V;
make_object({struct, P}, #decoder{object_hook=eep18}) ->
    {P};
make_object({struct, P}, #decoder{object_hook=proplist}) ->
    P;
make_object(V, #decoder{object_hook=Hook}) ->
    Hook(V).

decode_object(B, S) ->
    decode_object(B, S#decoder{state=key}, []).

decode_object(B, S=#decoder{state=key}, Acc) ->
    case tokenize(B, S) of
        {end_object, S1} ->
            V = make_object({struct, lists:reverse(Acc)}, S1),
            {V, S1#decoder{state=null}};
        {{const, K}, S1} ->
            {colon, S2} = tokenize(B, S1),
            {V, S3} = decode1(B, S2#decoder{state=null}),
            decode_object(B, S3#decoder{state=comma}, [{K, V} | Acc])
    end;
decode_object(B, S=#decoder{state=comma}, Acc) ->
    case tokenize(B, S) of
        {end_object, S1} ->
            V = make_object({struct, lists:reverse(Acc)}, S1),
            {V, S1#decoder{state=null}};
        {comma, S1} ->
            decode_object(B, S1#decoder{state=key}, Acc)
    end.

decode_array(B, S) ->
    decode_array(B, S#decoder{state=any}, []).

decode_array(B, S=#decoder{state=any}, Acc) ->
    case tokenize(B, S) of
        {end_array, S1} ->
            {lists:reverse(Acc), S1#decoder{state=null}};
        {start_array, S1} ->
            {Array, S2} = decode_array(B, S1),
            decode_array(B, S2#decoder{state=comma}, [Array | Acc]);
        {start_object, S1} ->
            {Array, S2} = decode_object(B, S1),
            decode_array(B, S2#decoder{state=comma}, [Array | Acc]);
        {{const, Const}, S1} ->
            decode_array(B, S1#decoder{state=comma}, [Const | Acc])
    end;
decode_array(B, S=#decoder{state=comma}, Acc) ->
    case tokenize(B, S) of
        {end_array, S1} ->
            {lists:reverse(Acc), S1#decoder{state=null}};
        {comma, S1} ->
            decode_array(B, S1#decoder{state=any}, Acc)
    end.

tokenize_string(B, S=#decoder{offset=O}) ->
    case tokenize_string_fast(B, O) of
        {escape, O1} ->
            Length = O1 - O,
            S1 = ?ADV_COL(S, Length),
            <<_:O/binary, Head:Length/binary, _/binary>> = B,
            tokenize_string(B, S1, lists:reverse(binary_to_list(Head)));
        O1 ->
            Length = O1 - O,
            <<_:O/binary, String:Length/binary, ?Q, _/binary>> = B,
            {{const, String}, ?ADV_COL(S, Length + 1)}
    end.

tokenize_string_fast(B, O) ->
    case B of
        <<_:O/binary, ?Q, _/binary>> ->
            O;
        <<_:O/binary, $\\, _/binary>> ->
            {escape, O};
        <<_:O/binary, C1, _/binary>> when C1 < 128 ->
            tokenize_string_fast(B, 1 + O);
        <<_:O/binary, C1, C2, _/binary>> when C1 >= 194, C1 =< 223,
                C2 >= 128, C2 =< 191 ->
            tokenize_string_fast(B, 2 + O);
        <<_:O/binary, C1, C2, C3, _/binary>> when C1 >= 224, C1 =< 239,
                C2 >= 128, C2 =< 191,
                C3 >= 128, C3 =< 191 ->
            tokenize_string_fast(B, 3 + O);
        <<_:O/binary, C1, C2, C3, C4, _/binary>> when C1 >= 240, C1 =< 244,
                C2 >= 128, C2 =< 191,
                C3 >= 128, C3 =< 191,
                C4 >= 128, C4 =< 191 ->
            tokenize_string_fast(B, 4 + O);
        _ ->
            throw(invalid_utf8)
    end.

tokenize_string(B, S=#decoder{offset=O}, Acc) ->
    case B of
        <<_:O/binary, ?Q, _/binary>> ->
            {{const, iolist_to_binary(lists:reverse(Acc))}, ?INC_COL(S)};
        <<_:O/binary, "\\\"", _/binary>> ->
            tokenize_string(B, ?ADV_COL(S, 2), [$\" | Acc]);
        <<_:O/binary, "\\\\", _/binary>> ->
            tokenize_string(B, ?ADV_COL(S, 2), [$\\ | Acc]);
        <<_:O/binary, "\\/", _/binary>> ->
            tokenize_string(B, ?ADV_COL(S, 2), [$/ | Acc]);
        <<_:O/binary, "\\b", _/binary>> ->
            tokenize_string(B, ?ADV_COL(S, 2), [$\b | Acc]);
        <<_:O/binary, "\\f", _/binary>> ->
            tokenize_string(B, ?ADV_COL(S, 2), [$\f | Acc]);
        <<_:O/binary, "\\n", _/binary>> ->
            tokenize_string(B, ?ADV_COL(S, 2), [$\n | Acc]);
        <<_:O/binary, "\\r", _/binary>> ->
            tokenize_string(B, ?ADV_COL(S, 2), [$\r | Acc]);
        <<_:O/binary, "\\t", _/binary>> ->
            tokenize_string(B, ?ADV_COL(S, 2), [$\t | Acc]);
        <<_:O/binary, "\\u", C3, C2, C1, C0, Rest/binary>> ->
            C = erlang:list_to_integer([C3, C2, C1, C0], 16),
            if C > 16#D7FF, C < 16#DC00 ->
                %% coalesce UTF-16 surrogate pair
                <<"\\u", D3, D2, D1, D0, _/binary>> = Rest,
                D = erlang:list_to_integer([D3,D2,D1,D0], 16),
                Acc1 = [unicode:characters_to_binary(
                            <<C:16/big-unsigned-integer,
                              D:16/big-unsigned-integer>>,
                            utf16)
                       | Acc],
                tokenize_string(B, ?ADV_COL(S, 12), Acc1);
            true ->
                Acc1 = [unicode:characters_to_binary([C]) | Acc],
                tokenize_string(B, ?ADV_COL(S, 6), Acc1)
            end;
        <<_:O/binary, C1, _/binary>> when C1 < 128 ->
            tokenize_string(B, ?INC_CHAR(S, C1), [C1 | Acc]);
        <<_:O/binary, C1, C2, _/binary>> when C1 >= 194, C1 =< 223,
                C2 >= 128, C2 =< 191 ->
            tokenize_string(B, ?ADV_COL(S, 2), [C2, C1 | Acc]);
        <<_:O/binary, C1, C2, C3, _/binary>> when C1 >= 224, C1 =< 239,
                C2 >= 128, C2 =< 191,
                C3 >= 128, C3 =< 191 ->
            tokenize_string(B, ?ADV_COL(S, 3), [C3, C2, C1 | Acc]);
        <<_:O/binary, C1, C2, C3, C4, _/binary>> when C1 >= 240, C1 =< 244,
                C2 >= 128, C2 =< 191,
                C3 >= 128, C3 =< 191,
                C4 >= 128, C4 =< 191 ->
            tokenize_string(B, ?ADV_COL(S, 4), [C4, C3, C2, C1 | Acc]);
        _ ->
            throw(invalid_utf8)
    end.

tokenize_number(B, S) ->
    case tokenize_number(B, sign, S, []) of
        {{int, Int}, S1} ->
            {{const, list_to_integer(Int)}, S1};
        {{float, Float}, S1} ->
            {{const, list_to_float(Float)}, S1}
    end.

tokenize_number(B, sign, S=#decoder{offset=O}, []) ->
    case B of
        <<_:O/binary, $-, _/binary>> ->
            tokenize_number(B, int, ?INC_COL(S), [$-]);
        _ ->
            tokenize_number(B, int, S, [])
    end;
tokenize_number(B, int, S=#decoder{offset=O}, Acc) ->
    case B of
        <<_:O/binary, $0, _/binary>> ->
            tokenize_number(B, frac, ?INC_COL(S), [$0 | Acc]);
        <<_:O/binary, C, _/binary>> when C >= $1 andalso C =< $9 ->
            tokenize_number(B, int1, ?INC_COL(S), [C | Acc])
    end;
tokenize_number(B, int1, S=#decoder{offset=O}, Acc) ->
    case B of
        <<_:O/binary, C, _/binary>> when C >= $0 andalso C =< $9 ->
            tokenize_number(B, int1, ?INC_COL(S), [C | Acc]);
        _ ->
            tokenize_number(B, frac, S, Acc)
    end;
tokenize_number(B, frac, S=#decoder{offset=O}, Acc) ->
    case B of
        <<_:O/binary, $., C, _/binary>> when C >= $0, C =< $9 ->
            tokenize_number(B, frac1, ?ADV_COL(S, 2), [C, $. | Acc]);
        <<_:O/binary, E, _/binary>> when E =:= $e orelse E =:= $E ->
            tokenize_number(B, esign, ?INC_COL(S), [$e, $0, $. | Acc]);
        _ ->
            {{int, lists:reverse(Acc)}, S}
    end;
tokenize_number(B, frac1, S=#decoder{offset=O}, Acc) ->
    case B of
        <<_:O/binary, C, _/binary>> when C >= $0 andalso C =< $9 ->
            tokenize_number(B, frac1, ?INC_COL(S), [C | Acc]);
        <<_:O/binary, E, _/binary>> when E =:= $e orelse E =:= $E ->
            tokenize_number(B, esign, ?INC_COL(S), [$e | Acc]);
        _ ->
            {{float, lists:reverse(Acc)}, S}
    end;
tokenize_number(B, esign, S=#decoder{offset=O}, Acc) ->
    case B of
        <<_:O/binary, C, _/binary>> when C =:= $- orelse C=:= $+ ->
            tokenize_number(B, eint, ?INC_COL(S), [C | Acc]);
        _ ->
            tokenize_number(B, eint, S, Acc)
    end;
tokenize_number(B, eint, S=#decoder{offset=O}, Acc) ->
    case B of
        <<_:O/binary, C, _/binary>> when C >= $0 andalso C =< $9 ->
            tokenize_number(B, eint1, ?INC_COL(S), [C | Acc])
    end;
tokenize_number(B, eint1, S=#decoder{offset=O}, Acc) ->
    case B of
        <<_:O/binary, C, _/binary>> when C >= $0 andalso C =< $9 ->
            tokenize_number(B, eint1, ?INC_COL(S), [C | Acc]);
        _ ->
            {{float, lists:reverse(Acc)}, S}
    end.

tokenize(B, S=#decoder{offset=O}) ->
    case B of
        <<_:O/binary, C, _/binary>> when ?IS_WHITESPACE(C) ->
            tokenize(B, ?INC_CHAR(S, C));
        <<_:O/binary, "{", _/binary>> ->
            {start_object, ?INC_COL(S)};
        <<_:O/binary, "}", _/binary>> ->
            {end_object, ?INC_COL(S)};
        <<_:O/binary, "[", _/binary>> ->
            {start_array, ?INC_COL(S)};
        <<_:O/binary, "]", _/binary>> ->
            {end_array, ?INC_COL(S)};
        <<_:O/binary, ",", _/binary>> ->
            {comma, ?INC_COL(S)};
        <<_:O/binary, ":", _/binary>> ->
            {colon, ?INC_COL(S)};
        <<_:O/binary, "null", _/binary>> ->
            {{const, null}, ?ADV_COL(S, 4)};
        <<_:O/binary, "true", _/binary>> ->
            {{const, true}, ?ADV_COL(S, 4)};
        <<_:O/binary, "false", _/binary>> ->
            {{const, false}, ?ADV_COL(S, 5)};
        <<_:O/binary, "\"", _/binary>> ->
            tokenize_string(B, ?INC_COL(S));
        <<_:O/binary, C, _/binary>> when (C >= $0 andalso C =< $9)
                                         orelse C =:= $- ->
            tokenize_number(B, S);
        <<_:O/binary>> ->
            trim = S#decoder.state,
            {eof, S}
    end.
%%
%% Tests
%%
-ifdef(TEST).
-include_lib("eunit/include/eunit.hrl").


%% testing constructs borrowed from the Yaws JSON implementation.

%% Create an object from a list of Key/Value pairs.

obj_new() ->
    {struct, []}.

is_obj({struct, Props}) ->
    F = fun ({K, _}) when is_binary(K) -> true end,
    lists:all(F, Props).

obj_from_list(Props) ->
    Obj = {struct, Props},
    ?assert(is_obj(Obj)),
    Obj.

%% Test for equivalence of Erlang terms.
%% Due to arbitrary order of construction, equivalent objects might
%% compare unequal as erlang terms, so we need to carefully recurse
%% through aggregates (tuples and objects).

equiv({struct, Props1}, {struct, Props2}) ->
    equiv_object(Props1, Props2);
equiv(L1, L2) when is_list(L1), is_list(L2) ->
    equiv_list(L1, L2);
equiv(N1, N2) when is_number(N1), is_number(N2) -> N1 == N2;
equiv(B1, B2) when is_binary(B1), is_binary(B2) -> B1 == B2;
equiv(A, A) when A =:= true orelse A =:= false orelse A =:= null -> true.

%% Object representation and traversal order is unknown.
%% Use the sledgehammer and sort property lists.

equiv_object(Props1, Props2) ->
    L1 = lists:keysort(1, Props1),
    L2 = lists:keysort(1, Props2),
    Pairs = lists:zip(L1, L2),
    true = lists:all(fun({{K1, V1}, {K2, V2}}) ->
                             equiv(K1, K2) and equiv(V1, V2)
                     end, Pairs).

%% Recursively compare tuple elements for equivalence.

equiv_list([], []) ->
    true;
equiv_list([V1 | L1], [V2 | L2]) ->
    equiv(V1, V2) andalso equiv_list(L1, L2).

decode_test() ->
    [1199344435545.0, 1] = decode(<<"[1199344435545.0,1]">>),
    <<16#F0,16#9D,16#9C,16#95>> = decode([34,"\\ud835","\\udf15",34]).

e2j_vec_test() ->
    test_one(e2j_test_vec(utf8), 1).

test_one([], _N) ->
    %% io:format("~p tests passed~n", [N-1]),
    ok;
test_one([{E, J} | Rest], N) ->
    %% io:format("[~p] ~p ~p~n", [N, E, J]),
    true = equiv(E, decode(J)),
    true = equiv(E, decode(encode(E))),
    test_one(Rest, 1+N).

e2j_test_vec(utf8) ->
    [
     {1, "1"},
     {3.1416, "3.14160"}, %% text representation may truncate, trail zeroes
     {-1, "-1"},
     {-3.1416, "-3.14160"},
     {12.0e10, "1.20000e+11"},
     {1.234E+10, "1.23400e+10"},
     {-1.234E-10, "-1.23400e-10"},
     {10.0, "1.0e+01"},
     {123.456, "1.23456E+2"},
     {10.0, "1e1"},
     {<<"foo">>, "\"foo\""},
     {<<"foo", 5, "bar">>, "\"foo\\u0005bar\""},
     {<<"">>, "\"\""},
     {<<"\n\n\n">>, "\"\\n\\n\\n\""},
     {<<"\" \b\f\r\n\t\"">>, "\"\\\" \\b\\f\\r\\n\\t\\\"\""},
     {obj_new(), "{}"},
     {obj_from_list([{<<"foo">>, <<"bar">>}]), "{\"foo\":\"bar\"}"},
     {obj_from_list([{<<"foo">>, <<"bar">>}, {<<"baz">>, 123}]),
      "{\"foo\":\"bar\",\"baz\":123}"},
     {[], "[]"},
     {[[]], "[[]]"},
     {[1, <<"foo">>], "[1,\"foo\"]"},

     %% json array in a json object
     {obj_from_list([{<<"foo">>, [123]}]),
      "{\"foo\":[123]}"},

     %% json object in a json object
     {obj_from_list([{<<"foo">>, obj_from_list([{<<"bar">>, true}])}]),
      "{\"foo\":{\"bar\":true}}"},

     %% fold evaluation order
     {obj_from_list([{<<"foo">>, []},
                     {<<"bar">>, obj_from_list([{<<"baz">>, true}])},
                     {<<"alice">>, <<"bob">>}]),
      "{\"foo\":[],\"bar\":{\"baz\":true},\"alice\":\"bob\"}"},

     %% json object in a json array
     {[-123, <<"foo">>, obj_from_list([{<<"bar">>, []}]), null],
      "[-123,\"foo\",{\"bar\":[]},null]"}
    ].

%% test utf8 encoding
encoder_utf8_test() ->
    %% safe conversion case (default)
    <<"\"\\u0001\\u0442\\u0435\\u0441\\u0442\"">> =
        iolist_to_binary(encode(<<1,"\321\202\320\265\321\201\321\202">>)),

    %% raw utf8 output (optional)
    Enc = mochijson2:encoder([{utf8, true}]),
    <<34,"\\u0001",209,130,208,181,209,129,209,130,34>> =
        iolist_to_binary(Enc(<<1,"\321\202\320\265\321\201\321\202">>)).

input_validation_test() ->
    Good = [
        {16#00A3, <<?Q, 16#C2, 16#A3, ?Q>>}, %% pound
        {16#20AC, <<?Q, 16#E2, 16#82, 16#AC, ?Q>>}, %% euro
        {16#10196, <<?Q, 16#F0, 16#90, 16#86, 16#96, ?Q>>} %% denarius
    ],
    lists:foreach(fun({CodePoint, UTF8}) ->
        Expect = unicode:characters_to_binary([CodePoint]),
        Expect = decode(UTF8)
    end, Good),

    Bad = [
        %% 2nd, 3rd, or 4th byte of a multi-byte sequence w/o leading byte
        <<?Q, 16#80, ?Q>>,
        %% missing continuations, last byte in each should be 80-BF
        <<?Q, 16#C2, 16#7F, ?Q>>,
        <<?Q, 16#E0, 16#80,16#7F, ?Q>>,
        <<?Q, 16#F0, 16#80, 16#80, 16#7F, ?Q>>,
        %% we don't support code points > 10FFFF per RFC 3629
        <<?Q, 16#F5, 16#80, 16#80, 16#80, ?Q>>,
        %% escape characters trigger a different code path
        <<?Q, $\\, $\n, 16#80, ?Q>>
    ],
    lists:foreach(
      fun(X) ->
              ok = try decode(X) catch invalid_utf8 -> ok end,
              %% could be {ucs,{bad_utf8_character_code}} or
              %%          {json_encode,{bad_char,_}}
              {'EXIT', _} = (catch encode(X))
      end, Bad).

inline_json_test() ->
    ?assertEqual(<<"\"iodata iodata\"">>,
                 iolist_to_binary(
                   encode({json, [<<"\"iodata">>, " iodata\""]}))),
    ?assertEqual({struct, [{<<"key">>, <<"iodata iodata">>}]},
                 decode(
                   encode({struct,
                           [{key, {json, [<<"\"iodata">>, " iodata\""]}}]}))),
    ok.

big_unicode_test() ->
    UTF8Seq = unicode:characters_to_binary([16#0001d120]),
    ?assertEqual(
       <<"\"\\ud834\\udd20\"">>,
       iolist_to_binary(encode(UTF8Seq))),
    ?assertEqual(
       UTF8Seq,
       decode(iolist_to_binary(encode(UTF8Seq)))),
    ok.

custom_decoder_test() ->
    ?assertEqual(
       {struct, [{<<"key">>, <<"value">>}]},
       (decoder([]))("{\"key\": \"value\"}")),
    F = fun ({struct, [{<<"key">>, <<"value">>}]}) -> win end,
    ?assertEqual(
       win,
       (decoder([{object_hook, F}]))("{\"key\": \"value\"}")),
    ok.

atom_test() ->
    %% JSON native atoms
    [begin
         ?assertEqual(A, decode(atom_to_list(A))),
         ?assertEqual(iolist_to_binary(atom_to_list(A)),
                      iolist_to_binary(encode(A)))
     end || A <- [true, false, null]],
    %% Atom to string
    ?assertEqual(
       <<"\"foo\"">>,
       iolist_to_binary(encode(foo))),
    ?assertEqual(
       <<"\"\\ud834\\udd20\"">>,
       iolist_to_binary(
         encode(
           binary_to_atom(
             unicode:characters_to_binary([16#0001d120]), latin1)))),
    ok.

key_encode_test() ->
    %% Some forms are accepted as keys that would not be strings in other
    %% cases
    ?assertEqual(
       <<"{\"foo\":1}">>,
       iolist_to_binary(encode({struct, [{foo, 1}]}))),
    ?assertEqual(
       <<"{\"foo\":1}">>,
       iolist_to_binary(encode({struct, [{<<"foo">>, 1}]}))),
    ?assertEqual(
       <<"{\"foo\":1}">>,
       iolist_to_binary(encode({struct, [{"foo", 1}]}))),
	?assertEqual(
       <<"{\"foo\":1}">>,
       iolist_to_binary(encode([{foo, 1}]))),
    ?assertEqual(
       <<"{\"foo\":1}">>,
       iolist_to_binary(encode([{<<"foo">>, 1}]))),
    ?assertEqual(
       <<"{\"foo\":1}">>,
       iolist_to_binary(encode([{"foo", 1}]))),
    ?assertEqual(
       <<"{\"\\ud834\\udd20\":1}">>,
       iolist_to_binary(
         encode({struct, [{[16#0001d120], 1}]}))),
    ?assertEqual(
       <<"{\"1\":1}">>,
       iolist_to_binary(encode({struct, [{1, 1}]}))),
    ok.

unsafe_chars_test() ->
    Chars = "\"\\\b\f\n\r\t",
    [begin
         ?assertEqual(false, json_string_is_safe([C])),
         ?assertEqual(false, json_bin_is_safe(<<C>>)),
         ?assertEqual(<<C>>, decode(encode(<<C>>)))
     end || C <- Chars],
    ?assertEqual(
       false,
       json_string_is_safe([16#0001d120])),
    ?assertEqual(
       false,
       json_bin_is_safe(unicode:characters_to_binary([16#0001d120]))),
    ?assertEqual(
       [16#0001d120],
       unicode:characters_to_list(
         decode(
           encode(
             binary_to_atom(
               unicode:characters_to_binary([16#0001d120]),
               latin1))))),
    ?assertEqual(
       false,
       json_string_is_safe([16#10ffff])),
    ?assertEqual(
       false,
       json_bin_is_safe(unicode:characters_to_binary([16#10ffff]))),
    %% solidus can be escaped but isn't unsafe by default
    ?assertEqual(
       <<"/">>,
       decode(<<"\"\\/\"">>)),
    ok.

int_test() ->
    ?assertEqual(0, decode("0")),
    ?assertEqual(1, decode("1")),
    ?assertEqual(11, decode("11")),
    ok.

large_int_test() ->
    ?assertEqual(<<"-2147483649214748364921474836492147483649">>,
        iolist_to_binary(encode(-2147483649214748364921474836492147483649))),
    ?assertEqual(<<"2147483649214748364921474836492147483649">>,
        iolist_to_binary(encode(2147483649214748364921474836492147483649))),
    ok.

float_test() ->
    ?assertEqual(<<"-2147483649.0">>, iolist_to_binary(encode(-2147483649.0))),
    ?assertEqual(<<"2147483648.0">>, iolist_to_binary(encode(2147483648.0))),
    ok.

handler_test() ->
    ?assertEqual(
       {'EXIT',{json_encode,{bad_term,{x,y}}}},
       catch encode({x,y})),
    F = fun ({x,y}) -> [] end,
    ?assertEqual(
       <<"[]">>,
       iolist_to_binary((encoder([{handler, F}]))({x, y}))),
    ok.

encode_empty_test_() ->
    [{A, ?_assertEqual(<<"{}">>, iolist_to_binary(encode(B)))}
     || {A, B} <- [{"eep18 {}", {}},
                   {"eep18 {[]}", {[]}},
                   {"{struct, []}", {struct, []}}]].

encode_test_() ->
    P = [{<<"k">>, <<"v">>}],
    JSON = iolist_to_binary(encode({struct, P})),
    [{atom_to_list(F),
      ?_assertEqual(JSON, iolist_to_binary(encode(decode(JSON, [{format, F}]))))}
     || F <- [struct, eep18, proplist]].

format_test_() ->
    P = [{<<"k">>, <<"v">>}],
    JSON = iolist_to_binary(encode({struct, P})),
    [{atom_to_list(F),
      ?_assertEqual(A, decode(JSON, [{format, F}]))}
     || {F, A} <- [{struct, {struct, P}},
                   {eep18, {P}},
                   {proplist, P}]].

array_test() ->
    A = [<<"hello">>],
    ?assertEqual(A, decode(encode({array, A}))).

bad_char_test() ->
    ?assertEqual(
       {'EXIT', {json_encode, {bad_char, 16#110000}}},
       catch json_string_is_safe([16#110000])).

utf8_roundtrip_test_() ->
    %% These are the boundary cases for UTF8 encoding
    Codepoints = [%% 7 bits  -> 1 byte
                  16#00, 16#7f,
                  %% 11 bits -> 2 bytes
                  16#080, 16#07ff,
                  %% 16 bits -> 3 bytes
                  16#0800, 16#ffff,
                  16#d7ff, 16#e000,
                  %% 21 bits -> 4 bytes
                  16#010000, 16#10ffff],
    UTF8 = unicode:characters_to_binary(Codepoints),
    Encode = encoder([{utf8, true}]),
    [{"roundtrip escaped",
      ?_assertEqual(UTF8, decode(encode(UTF8)))},
     {"roundtrip utf8",
      ?_assertEqual(UTF8, decode(Encode(UTF8)))}].

utf8_non_character_test_() ->
    S = unicode:characters_to_binary([16#ffff, 16#fffe]),
    [{"roundtrip escaped", ?_assertEqual(S, decode(encode(S)))},
     {"roundtrip utf8", ?_assertEqual(S, decode((encoder([{utf8, true}]))(S)))}].

-ifndef(map_unavailable).

decode_map_test() ->
    Json = "{\"var1\": 3, \"var2\": {\"var3\": 7}}",
    M = #{<<"var1">> => 3,<<"var2">> => #{<<"var3">> => 7}},
    ?assertEqual(M, decode(Json, [{format, map}])).

encode_map_test() ->
    M = <<"{\"a\":1,\"b\":{\"c\":2}}">>,
    ?assertEqual(M, iolist_to_binary(encode(#{a => 1, b => #{ c => 2}}))).

encode_empty_map_test() ->
    ?assertEqual(<<"{}">>, encode(#{})).

-endif.

-endif.