%%
%% %CopyrightBegin%
%%
%% Copyright Ericsson AB 2000-2020. All Rights Reserved.
%%
%% Licensed under the Apache License, Version 2.0 (the "License");
%% you may not use this file except in compliance with the License.
%% You may obtain a copy of the License at
%%
%%     http://www.apache.org/licenses/LICENSE-2.0
%%
%% Unless required by applicable law or agreed to in writing, software
%% distributed under the License is distributed on an "AS IS" BASIS,
%% WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
%% See the License for the specific language governing permissions and
%% limitations under the License.
%%
%% %CopyrightEnd%
%%
-module(xref_reader).

-export([module/5]).

-import(lists, [keysearch/3, member/2, reverse/1]).

-record(xrefr,
	{module=[],
	 function=[],
	 def_at=[],
	 l_call_at=[],
	 x_call_at=[],
	 el=[],
	 ex=[],
	 x=[],
         df,
	 builtins_too=false,
         is_abstr,            % abstract module?
	 funvars=[],          % records variables bound to funs
			      % (for coping with list comprehension)
	 matches=[],          % records other bound variables
	 unresolved=[],       % unresolved calls, {{mfa(),mfa()},Line}
	 %% experimental; -xref(FunEdge) is recognized.
	 lattrs=[],            % local calls, {{mfa(),mfa()},Line}
	 xattrs=[],            % external calls, -"-
	 battrs=[],	       % badly formed xref attributes, term().
         on_load               % function name
	 }).

-include("xref.hrl").

%% The versions of the abstract code are as follows:
%% R7:  abstract_v1
%% R8:  abstract_v2
%% R9C: raw_abstract_v1

%% -> {ok, Module, {DefAt, LCallAt, XCallAt, LC, XC, X, Attrs, Depr, OL},
%%         Unresolved}} | EXIT
%% Attrs = {ALC, AXC, Bad}
%% ALC, AXC and Bad are extracted from the attribute 'xref'. An experiment.
module(Module, Forms, CollectBuiltins, X, DF) ->
    Attrs = [{Attr,V} || {attribute,_Anno,Attr,V} <- Forms],
    IsAbstract = xref_utils:is_abstract_module(Attrs),
    S = #xrefr{module = Module, builtins_too = CollectBuiltins,
               is_abstr = IsAbstract, x = X, df = DF},
    forms(Forms, S).

forms([F | Fs], S) ->
    S1 = form(F, S),
    forms(Fs, S1);
forms([], S) ->
    #xrefr{module = M, def_at = DefAt,
	   l_call_at = LCallAt, x_call_at = XCallAt,
	   el = LC, ex = XC, x = X, df = Depr, on_load = OnLoad,
	   lattrs = AL, xattrs = AX, battrs = B, unresolved = U} = S,
    OL = case OnLoad of
             undefined -> [];
             F ->
                 [{M, F, 0}]
         end,
    #xrefr{def_at = DefAt,
	   l_call_at = LCallAt, x_call_at = XCallAt,
	   el = LC, ex = XC, x = X, df = Depr, on_load = OnLoad,
	   lattrs = AL, xattrs = AX, battrs = B, unresolved = U} = S,
    Attrs = {lists:reverse(AL), lists:reverse(AX), lists:reverse(B)},
    {ok, M, {DefAt, LCallAt, XCallAt, LC, XC, X, Attrs, Depr, OL}, U}.

form({attribute, Anno, xref, Calls}, S) -> % experimental
    #xrefr{module = M, function = Fun,
	   lattrs = L, xattrs = X, battrs = B} = S,
    attr(Calls, erl_anno:line(Anno), M, Fun, L, X, B, S);
form({attribute, _, on_load, {F, 0}}, S) ->
    S#xrefr{on_load = F};
form({attribute, _Anno, _Attr, _Val}, S) ->
    S;
form({function, _, module_info, 0, _Clauses}, S) ->
    S;
form({function, _, module_info, 1, _Clauses}, S) ->
    S;
form({function, Anno, Name, Arity, Clauses}, S) ->
    case {Name, Arity, erl_anno:location(Anno)} of
        {behaviour_info, 1, 0} ->
            S; % generated
        _ ->
            MFA0 = {S#xrefr.module, Name, Arity},
            MFA = adjust_arity(S, MFA0),
            S1 = S#xrefr{function = MFA},
            Line = erl_anno:line(Anno),
            S2 = S1#xrefr{def_at = [{MFA,Line} | S#xrefr.def_at]},
            S3 = clauses(Clauses, S2),
            S3#xrefr{function = []}
    end;
form(_, S) ->
    %% OTP 20. Other uninteresting forms such as {eof, _} and {warning, _}.
    %% Exposed because sys_pre_expand is no longer run.
    S.


clauses(Cls, S) ->
    #xrefr{funvars = FunVars, matches = Matches} = S,
    clauses(Cls, FunVars, Matches, S).

clauses([{clause, _Anno, _H, G, B} | Cs], FunVars, Matches, S) ->
    S1 = case S#xrefr.builtins_too of
	     true -> expr(G, S);
	     false -> S
	 end,
    S2 = expr(B, S1),
    S3 = S2#xrefr{funvars = FunVars, matches = Matches},
    clauses(Cs, S3);
clauses([], _FunVars, _Matches, S) ->
    S.

attr(NotList, Ln, M, Fun, AL, AX, B, S) when not is_list(NotList) ->
    attr([NotList], Ln, M, Fun, AL, AX, B, S);
attr([E={From, To} | As], Ln, M, Fun, AL, AX, B, S) ->
    case mfa(From, M) of
	{_, _, MFA} when MFA =:= Fun; [] =:= Fun ->
	    attr(From, To, Ln, M, Fun, AL, AX, B, S, As, E);
	{_, _, _} ->
	    attr(As, Ln, M, Fun, AL, AX, [E | B], S);
	_ ->
	    attr(Fun, E, Ln, M, Fun, AL, AX, B, S, As, E)
    end;
attr([To | As], Ln, M, Fun, AL, AX, B, S) ->
    attr(Fun, To, Ln, M, Fun, AL, AX, B, S, As, To);
attr([], _Ln, _M, _Fun, AL, AX, B, S) ->
    S#xrefr{lattrs = AL, xattrs = AX, battrs = B}.

attr(From, To, Ln, M, Fun, AL, AX, B, S, As, E) ->
    case {mfa(From, M), mfa(To, M)} of
	{{true,_,F}, {_,external,T}} ->
	    attr(As, Ln, M, Fun, AL, [{{F,T},Ln} | AX], B, S);
	{{true,_,F}, {_,local,T}} ->
	    attr(As, Ln, M, Fun, [{{F,T},Ln} | AL], AX, B, S);
	_ -> attr(As, Ln, M, Fun, AL, AX, [E | B], S)
    end.

mfa({F,A}, M) when is_atom(F), is_integer(A) ->
    {true, local, {M,F,A}};
mfa(MFA={M,F,A}, M1) when is_atom(M), is_atom(F), is_integer(A) ->
    {M=:=M1, external, MFA};
mfa(_, _M) -> false.

expr({'if', _Anno, Cs}, S) ->
    clauses(Cs, S);
expr({'case', _Anno, E, Cs}, S) ->
    S1 = expr(E, S),
    clauses(Cs, S1);
expr({'receive', _Anno, Cs}, S) ->
    clauses(Cs, S);
expr({'receive', _Anno, Cs, To, ToEs}, S) ->
    S1 = expr(To, S),
    S2 = expr(ToEs, S1),
    clauses(Cs, S2);
expr({'try',_Anno,Es,Scs,Ccs,As}, S) ->
    S1 = expr(Es, S),
    S2 = clauses(Scs, S1),
    S3 = clauses(Ccs, S2),
    expr(As, S3);
expr({'fun', Anno, {function, {atom,_,Mod},
		    {atom,_,Name},
		    {integer,_,Arity}}}, S) ->
    %% New format in R15. M:F/A (literals).
    As = lists:duplicate(Arity, {atom, Anno, foo}),
    external_call(Mod, Name, As, Anno, false, S);
expr({'fun', Anno, {function, Mod, Name, {integer,_,Arity}}}, S) ->
    %% New format in R15. M:F/A (one or more variables).
    As = lists:duplicate(Arity, {atom, Anno, foo}),
    external_call(erlang, apply, [Mod, Name, list2term(As)], Anno, true, S);
expr({'fun', Anno, {function, Mod, Name, _Arity}}, S) ->
    %% New format in R15. M:F/A (one or more variables).
    As = {var, Anno, '_'},
    external_call(erlang, apply, [Mod, Name, As], Anno, true, S);
%% Only abstract_v1 and abstract_v2.
expr({'fun', Anno, {function, Name, Arity}, _Extra}, S) ->
    %% Added in R8.
    handle_call(local, S#xrefr.module, Name, Arity, Anno, S);
expr({'fun', _Anno, {clauses, Cs}, _Extra}, S) ->
    clauses(Cs, S);
%% End abstract_v1 and abstract_v2.
expr({'fun', Anno, {function, Name, Arity}}, S) ->
    %% Added in OTP 20.
    handle_call(local, S#xrefr.module, Name, Arity, Anno, S);
expr({'fun', _Anno, {clauses, Cs}}, S) ->
    clauses(Cs, S);
expr({named_fun, _Anno, '_', Cs}, S) ->
    clauses(Cs, S);
expr({named_fun, _Anno, Name, Cs}, S) ->
    S1 = S#xrefr{funvars = [Name | S#xrefr.funvars]},
    clauses(Cs, S1);
expr({call, Anno, {atom, _, Name}, As}, S) ->
    S1 = handle_call(local, S#xrefr.module, Name, length(As), Anno, S),
    expr(As, S1);
expr({call, Anno, {remote, _Anno, {atom,_,Mod}, {atom,_,Name}}, As}, S) ->
    external_call(Mod, Name, As, Anno, false, S);
expr({call, Anno, {remote, _Anno, Mod, Name}, As}, S) ->
    %% Added in R8.
    external_call(erlang, apply, [Mod, Name, list2term(As)], Anno, true, S);
expr({call, Anno, F, As}, S) ->
    external_call(erlang, apply, [F, list2term(As)], Anno, true, S);
expr({match, _Anno, {var,_,Var}, {'fun', _, {clauses, Cs}, _Extra}}, S) ->
    %% This is what is needed in R7 to avoid warnings for the functions
    %% that are passed around by the "expansion" of list comprehension.
    S1 = S#xrefr{funvars = [Var | S#xrefr.funvars]},
    clauses(Cs, S1);
expr({match, _Anno, {var,_,Var}, {'fun', _, {clauses, Cs}}}, S) ->
    %% OTP 20. Exposed because sys_pre_expand is no longer run.
    S1 = S#xrefr{funvars = [Var | S#xrefr.funvars]},
    clauses(Cs, S1);
expr({match, _Anno, {var,_,Var}, {named_fun, _, _, _} = Fun}, S) ->
    %% OTP 20. Exposed because sys_pre_expand is no longer run.
    S1 = S#xrefr{funvars = [Var | S#xrefr.funvars]},
    expr(Fun, S1);
expr({match, _Anno, {var,_,Var}, E}, S) ->
    %% Used for resolving code like
    %%     Args = [A,B], apply(m, f, Args)
    S1 = S#xrefr{matches = [{Var, E} | S#xrefr.matches]},
    expr(E, S1);
expr({op, _Anno, 'orelse', Op1, Op2}, S) ->
    expr([Op1, Op2], S);
expr({op, _Anno, 'andalso', Op1, Op2}, S) ->
    expr([Op1, Op2], S);
expr({op, Anno, Op, Operand1, Operand2}, S) ->
    external_call(erlang, Op, [Operand1, Operand2], Anno, false, S);
expr({op, Anno, Op, Operand}, S) ->
    external_call(erlang, Op, [Operand], Anno, false, S);
expr(T, S) when is_tuple(T) ->
    expr(tuple_to_list(T), S);
expr([E | Es], S) ->
    expr(Es, expr(E, S));
expr(_E, S) ->
    S.

%% Mod and Fun may not correspond to something in the abstract code,
%% which is signalled by X =:= true.
external_call(Mod, Fun, ArgsList, Anno, X, S) ->
    Arity = length(ArgsList),
    W = case xref_utils:is_funfun(Mod, Fun, Arity) of
	    true when erlang =:= Mod, apply =:= Fun, 2 =:= Arity -> apply2;
	    true when erts_debug =:= Mod, apply =:= Fun,4 =:= Arity -> debug4;
	    true when erlang =:= Mod, spawn_opt =:= Fun -> Arity - 1;
	    true -> Arity;
	    false when Mod =:= erlang ->
		case erl_internal:type_test(Fun, Arity) of
		    true -> type;
		    false -> false
		end;
	    false -> false
	end,
    S1 = if
	     W =:= type; X ->
		 S;
	     true ->
		 handle_call(external, Mod, Fun, Arity, Anno, S)
	 end,
    case {W, ArgsList} of
	{false, _} ->
	    expr(ArgsList, S1);
	{type, _} ->
	    expr(ArgsList, S1);
	{apply2, [{tuple, _, [M,F]}, ArgsTerm]} ->
	    eval_args(M, F, ArgsTerm, Anno, S1, ArgsList, []);
	{1, [{tuple, _, [M,F]} | R]} ->	% R = [] unless spawn_opt
	    eval_args(M, F, list2term([]), Anno, S1, ArgsList, R);
	{2, [Node, {tuple, _, [M,F]} | R]} -> % R = [] unless spawn_opt
	    eval_args(M, F, list2term([]), Anno, S1, ArgsList, [Node | R]);
	{3, [M, F, ArgsTerm | R]} -> % R = [] unless spawn_opt
	    eval_args(M, F, ArgsTerm, Anno, S1, ArgsList, R);
	{4, [Node, M, F, ArgsTerm | R]} -> % R = [] unless spawn_opt
	    eval_args(M, F, ArgsTerm, Anno, S1, ArgsList, [Node | R]);
	{debug4, [M, F, ArgsTerm, _]} ->
	    eval_args(M, F, ArgsTerm, Anno, S1, ArgsList, []);
	_Else -> % apply2, 1 or 2
	    check_funarg(W, ArgsList, Anno, S1)
    end.

eval_args(Mod, Fun, ArgsTerm, Anno, S, ArgsList, Extra) ->
    {IsSimpleCall, M, F} = mod_fun(Mod, Fun),
    case term2list(ArgsTerm, [], S) of
	undefined ->
	    S1 = unresolved(M, F, -1, Anno, S),
	    expr(ArgsList, S1);
	ArgsList2 when not IsSimpleCall ->
	    S1 = unresolved(M, F, length(ArgsList2), Anno, S),
	    expr(ArgsList, S1);
	ArgsList2 when IsSimpleCall ->
	    S1 = expr(Extra, S),
	    external_call(M, F, ArgsList2, Anno, false, S1)
    end.

mod_fun({atom,_,M1}, {atom,_,F1}) -> {true, M1, F1};
mod_fun({atom,_,M1}, _) -> {false, M1, ?VAR_EXPR};
mod_fun(_, {atom,_,F1}) -> {false, ?MOD_EXPR, F1};
mod_fun(_, _) -> {false, ?MOD_EXPR, ?VAR_EXPR}.

check_funarg(W, ArgsList, Anno, S) ->
    {FunArg, Args} = fun_args(W, ArgsList),
    S1 = case funarg(FunArg, S) of
	     true ->
		 S;
	     false when is_integer(W) -> % 1 or 2
		 unresolved(?MOD_EXPR, ?VAR_EXPR, 0, Anno, S);
	     false -> % apply2
		 N = case term2list(Args, [], S) of
			 undefined -> -1;
			 As -> length(As)
		     end,
		 unresolved(?MOD_EXPR, ?VAR_EXPR, N, Anno, S)
	 end,
    expr(ArgsList, S1).

funarg({'fun', _, _Clauses, _Extra}, _S) -> true;
funarg({'fun', _, {clauses, _}}, _S) ->
    %% OTP 20. sys_pre_expand not run.
    true;
funarg({'fun', _, {function, _, _}}, _S) ->
    %% OTP 20. sys_pre_expand not run.
    true;
funarg({'fun', _, {function,_,_,_}}, _S) ->
    %% New abstract format for fun M:F/A in R15.
    true;
funarg({named_fun, _, _, _}, _S) ->
    %% OTP 20. sys_pre_expand not run.
    true;
funarg({var, _, Var}, S) -> member(Var, S#xrefr.funvars);
funarg(_, _S) -> false.

fun_args(apply2, [FunArg, Args]) -> {FunArg, Args};
fun_args(1, [FunArg | Args]) -> {FunArg, Args};
fun_args(2, [_Node, FunArg | Args]) -> {FunArg, Args}.

list2term(L) ->
    A = erl_anno:new(0),
    list2term(L, A).

list2term([A | As], Anno) ->
    {cons, Anno, A, list2term(As)};
list2term([], Anno) ->
    {nil, Anno}.

term2list({cons, _Anno, H, T}, L, S) ->
    term2list(T, [H | L], S);
term2list({nil, _Anno}, L, _S) ->
    reverse(L);
term2list({var, _, Var}, L, S) ->
    case keysearch(Var, 1, S#xrefr.matches) of
	{value, {Var, E}} ->
	    term2list(E, L, S);
	false ->
	    undefined
    end;
term2list(_Else, _L, _S) ->
    undefined.

unresolved(M, F, A, Anno, S) ->
    handle_call(external, {M,F,A}, Anno, S, true).

handle_call(Locality, Module, Name, Arity, Anno, S) ->
    case xref_utils:is_builtin(Module, Name, Arity) of
	true when not S#xrefr.builtins_too -> S;
	_Else ->
	    To = {Module, Name, Arity},
	    handle_call(Locality, To, Anno, S, false)
    end.

handle_call(Locality, To0, Anno, S, IsUnres) ->
    From = S#xrefr.function,
    To = adjust_arity(S, To0),
    Call = {From, To},
    Line = erl_anno:line(Anno),
    CallAt = {Call, Line},
    S1 = if
             IsUnres ->
                 S#xrefr{unresolved = [CallAt | S#xrefr.unresolved]};
             true ->
                 S
         end,
    case Locality of
        local ->
            S1#xrefr{el = [Call | S1#xrefr.el],
                     l_call_at = [CallAt | S1#xrefr.l_call_at]};
        external ->
            S1#xrefr{ex = [Call | S1#xrefr.ex],
                     x_call_at = [CallAt | S1#xrefr.x_call_at]}
    end.

adjust_arity(#xrefr{is_abstr = true, module = M}, {M, F, A} = MFA) ->
    case xref_utils:is_static_function(F, A) of
        true ->
            MFA;
        false ->
            {M,F,A-1}
    end;
adjust_arity(_S, MFA) ->
    MFA.
