%%
%% %CopyrightBegin%
%%
%% SPDX-License-Identifier: Apache-2.0
%%
%% Copyright Ericsson AB 2000-2025. 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_utils).
-moduledoc false.

%% Avoid warning for local function error/1 clashing with autoimported BIF.
-compile({no_auto_import,[error/1]}).
-export([xset/2]).

-export([is_directory/1, file_info/1, fa_to_mfa/2]).

-export([is_string/2, is_path/1]).

-export([module_filename/2, application_filename/1, application_filename/2]).

-export([release_directory/3, select_application_directories/2, 
	 filename_to_application/1, select_last_application_version/1,
	 split_filename/2, scan_directory/4, list_path/2]).

-export([predefined_functions/0, is_funfun/3, is_builtin/3]).

-export([is_static_function/2, is_abstract_module/1]).

-export([closure/1, components/1, condensation/1, path/2, use/2, call/2]).

-export([regexpr/2]).

-export([relation_to_graph/1]).

-export([find_beam/1]).

-export([options/2]).

-export([format_error/1]).

-import(lists, [append/1, delete/2, filter/2, foldl/3, foreach/2, 
		keydelete/3, keysearch/3, keysort/2, last/1, map/2, 
		member/2, reverse/1, sort/1]).

-import(sofs, 
	[difference/2, domain/1, family/1,
	 family_to_relation/1, from_external/2, from_term/2, 
	 intersection/2, partition/2, relation/1, relation_to_family/1, 
	 restriction/2, set/1, to_external/1, type/1]).

-include_lib("kernel/include/file.hrl").

%%
%%  Exported functions
%%

xset(L, T) when is_list(L) ->
    from_external(lists:usort(L), T);
xset(S, T) ->
    from_external(S, T).

%% -> true | false | {error, ?MODULE, Reason}
%is_directory(F) ->
%    filelib:is_dir(F);
is_directory(F) ->
    case file:read_file_info(F) of
	{ok, Info} -> 
	    Info#file_info.type =:= directory;
	{error, Error} -> 
	    file_error(F, Error)
    end.

%% file_info(FileName) -> {ok, FileInfo} | {error, ?MODULE, Reason}
%%   FileInfo = {FileName, DirOrFile, Readable, ModificationTime}
%%   DirOrFile = directory | file
%%   Readable = readable | unreadable
%%   ModificationTime = {{Year, Month, Day}, {Hour, Minute, Second}}
%%
%% DirOrFile is equal to 'directory' ('file') if FileName is a
%% directory (regular file).
%% Readable is equal 'readable' ('unreadable') if FileName is readable
%% (unreadable).
%% ModificationTime is copied from file_info.mtime.
%%
file_info(F) ->
    case file:read_file_info(F) of
	{ok, Info} -> 
	    Readable = case Info#file_info.access of
			   Access when Access =:= read; 
                                       Access =:= read_write ->
			       readable;
			   _ ->
			       unreadable
		       end,
	    Type = case Info#file_info.type of
		       directory -> directory;
		       regular -> file;
		       _ -> error
		   end,
	    case Type of 
		error -> error({unrecognized_file, F});
		_ -> {ok, {F, Type, Readable, Info#file_info.mtime}}
	    end;
	{error, Error} -> 
	    file_error(F, Error)
    end.
    

fa_to_mfa(FAs, Mod) ->
    fa_to_mfa(FAs, Mod, []).

fa_to_mfa([{F,A} | MFs], Mod, L) ->
    fa_to_mfa(MFs, Mod, [{Mod,F,A} | L]);
fa_to_mfa([], _Mod, L) ->
    reverse(L).

module_filename(Dir, Module) ->
    filename:join(Dir, to_list(Module) ++ code:objfile_extension()).

application_filename(AppName) ->
    to_list(AppName) ++ ".app".

application_filename(Dir, AppName) ->
    filename:join(to_list(Dir), application_filename(AppName)).

%% -> bool()
is_string([], _) ->
    false;
is_string(Term, C) ->
    is_string1(Term, C).

is_string1([H | T], C) when H > C ->
    is_string1(T, C);
is_string1([], _) -> 
    true;
is_string1(_, _) -> 
    false.
    
%% -> bool()
is_path([S | Ss]) ->
    case is_string(S, 31) of
	true -> 
	    is_path(Ss);
	false ->
	    false
    end;
is_path([]) -> 
    true;
is_path(_) -> 
    false.

%====================================
% Release and application functions.
%====================================

%%% ApplDir = {ApplicationName,NumericApplicationVersion,ApplicationDirectory}
%%% ApplicationName = atom()
%%% ApplicationDirectory = string()
%%% NumericApplicationVersion = [integer()] ("3.1.7" becomes [3,1,7]).
%%% [] means that the application has no version...
%%%
%%% ModuleName = ModuleFileName = string()
%%% ReleaseName = atom()

%% release_directory(Directory, CheckLib, SubDirectory) -> 
%%     {ok, ReleaseName, AppDir, [ApplDir]} | {error, ?MODULE, Reason}
%%   CheckLib = bool()
%%   AppDir = string()
%%   SubDirectory = string()
%%
%% Returns all sub directories of a given directory, assuming all sub
%% directories are application directories. If a sub directory has a
%% sub directory SubDirectory, that one is chosen as application
%% directory. If Directory has a sub directory 'lib' and CheckLib is
%% equal to 'true', applications are looked for on that
%% directory. ApplDir is the directory where applications reside. In
%% any case, the returned ReleaseName is the basename of the given
%% directory.
%%
release_directory(Dir, UseLib, SubDir) ->
    SDir = subdir(Dir, "lib", UseLib),
    case file:list_dir(SDir) of
	{ok, FileNames} ->
            Files = [filename:join(SDir, File) || File <- FileNames],
	    case select_application_directories(Files, SubDir) of
		{ok, ApplDirs} ->
		    {ok, list_to_atom(filename:basename(Dir)), SDir, ApplDirs};
		Error ->
		    Error
	    end;
	{error, Error} ->
	    file_error(SDir, Error)
    end.

%% select_application_directories([FileName], SubDirectory) -> 
%%               {ok, [ApplDir]} | {error, ?MODULE, Error}
%%   SubDirectory = string()
%%
%% For each filename that is a directory, the filename is split into
%% an application name and an application version, if possible, using
%% '-' as separator. If not possible, the empty version - [] - is
%% used. If a directory has a sub directory called SubDirectory, that
%% one is returned as application directory rather than the directory
%% itself.
%%  
select_application_directories(FileNames, Dir) ->
    select_application_directories(FileNames, Dir, Dir =/= [], []).

%% filename_to_application(FileName) -> 
%%          {ApplicationName,NumbericApplicationVersion}
%%
%% Interprets a filename as an application name and an application
%% version. If the filename (the basename actually) cannot be split
%% into two components using '-' as separator, the whole basename is
%% used as application name, and the version returned is [].
%%
filename_to_application(FileName) ->
    Basename = filename:basename(FileName),
    case catch filename2appl(Basename) of
	{'EXIT',_} ->
	    {list_to_atom(Basename),[]};
	Split ->
	    Split
    end.
    
%% select_last_application_version([ApplDir]) -> [ApplDir]
%%
%% For each application that occurs with more than one version in the
%% input list, only the one with the last version is kept.
%%
select_last_application_version(AppVs) ->
    TL = to_external(partition(1, relation(AppVs))),
    [last(keysort(2, L)) || L <- TL].

-record(scan, {collected = [], errors = [], seen = [], unreadable = []}).

%% scan_directory(Directory, Recurse, Collect, Watch) -> 
%%     {Collected, Errors, Seen, Unreadable}
%%
%%   Watch = Collect = [string()]
%%   Directory = string() | atom()
%%   Recurse = bool()
%%   Collected = [{Dir,Basename}]
%%   Dir = Basename = Seen = Unreadable = [string()]
%% 
%% Collected (Seen) contains those regular files with extension
%% occurring in Collect (Watch). Watch is tried only if a filename
%% does not match Collect. Only readable files occur in Collected, the
%% unreadable files (with extension matching Collect) go into
%% Unreadable.
%%
scan_directory(File, Recurse, Collect, Watch) ->
    Init = #scan{},
    S = find_files_dir(File, Recurse, Collect, Watch, Init),
    #scan{collected = L, errors = E, seen = J, unreadable = U} = S,
    {reverse(L), reverse(E), reverse(J), reverse(U)}.

%% {Dir, Basename} | false
split_filename(File, Extension) ->
    case catch begin 
		   Dir = filename:dirname(File),
		   Basename = filename:basename(File, Extension),
		   {Dir, Basename++Extension}
	       end of
	{'EXIT', _} ->
	    false;
	R ->
	    R
    end.

%% list_path(Path, Extensions) -> 
%%    {[{Module, {integer(), Directory, Basename}}], [error()]}
%%
%%    Path = [Directory]
%%    Extensions = [string()]
%%    Module = atom()
%%    Directory = Basename = string()
%%
%% Files with any of the given extensions are searched for among
%% the given directories (Path). Directories "below" some of the given
%% directories are not searched (unless enumerated in Path). If some
%% file is found on more than one directory, the first one found is
%% returned (Path is searched from the beginning).
%%
list_path(P, Extensions) ->
    list_dirs(P, 1, Extensions, [], []).

list_dirs([D | Ds], I, Exts, CL, E) ->
    Fun = fun(X, A) -> 
		  File = filename:join(D, X),
		  case is_directory(File) of
		      false ->
			  Ext = filename:extension(X),
			  case member(Ext, Exts) of
			      true ->
				  M = list_to_atom(filename:basename(X, Ext)),
				  [{M, {I,D,X}} | A];
			      false ->
				  A
			  end;
		      true ->
			  A;
		      _Else ->
			  A
		  end
	   end,
    {NCL, NE} = case file:list_dir(D) of
		    {ok, C0} ->
			{foldl(Fun, CL, C0), E};
		    {error, Error} ->
			{CL, [file_error(D, Error) | E]}
		end,
    list_dirs(Ds, I+1, Exts, NCL, NE);
list_dirs([], _I, _Exts, C, E) -> 
    {C, E}.

%% Returns functions that are present in all modules.
predefined_functions() ->
    [{module_info,0}, {module_info,1}, {behaviour_info,1}].

%% Returns true if an MFA takes functional arguments.
is_funfun(erlang, apply, 2) -> true;
is_funfun(erlang, apply, 3) -> true;
is_funfun(erlang, spawn, 1) -> true;
is_funfun(erlang, spawn, 2) -> true;
is_funfun(erlang, spawn, 3) -> true;
is_funfun(erlang, spawn, 4) -> true;
is_funfun(erlang, spawn_link, 1) -> true;
is_funfun(erlang, spawn_link, 2) -> true;
is_funfun(erlang, spawn_link, 3) -> true;
is_funfun(erlang, spawn_link, 4) -> true;
is_funfun(erlang, spawn_opt, 2) -> true;
is_funfun(erlang, spawn_opt, 3) -> true;
is_funfun(erlang, spawn_opt, 4) -> true;
is_funfun(erlang, spawn_opt, 5) -> true;
is_funfun(erts_debug, apply, 4) -> true;
is_funfun(_, _, _) -> false.

is_builtin(erts_debug, apply, 4) -> true;
is_builtin(M, F, A) ->
    erlang:is_builtin(M, F, A).

is_abstract_module(Attributes) ->
    case keysearch(abstract, 1, Attributes) of
        {value, {abstract, true}} ->
            true;
        {value, {abstract, Vals}} when is_list(Vals) ->
            member(true, Vals);
        _ ->
            false
    end.

%% A "static function" is a function in an abstract module that may be
%% called directly.
is_static_function(module_info, 0) ->
    true;
is_static_function(module_info, 1) ->
    true;
is_static_function(new, _) ->
    true;
is_static_function(instance, _) ->
    true;
is_static_function(_F, _A) ->
    false.

%%% The following functions implement some of the operators recognized
%%% in xref_compiler.erl.

closure(S) ->
    relation_to_graph(S).

components(G) ->
    %% Returns a plain set of sets.
    from_term(digraph_utils:cyclic_strong_components(G), [[atom]]).

condensation(G) ->
    G2 = digraph_utils:condensation(G),
    %% A relation. The result can be only be used by a few set operations.
    R = graph_to_relation(G2),
    true = digraph:delete(G2),
    R.

path(G, [E]) ->
    path(G, [E,E]);
path(G, P=[E1 | _]) ->
    path(P, G, [[E1]]).

use(G, V) ->
    neighbours(to_external(V), G, reaching_neighbours, type(V)).

call(G, V) ->
    neighbours(to_external(V), G, reachable_neighbours, type(V)).

regexpr({regexpr, RExpr}, Var) ->
    Xs = match_list(to_external(Var), RExpr),
    xset(Xs, type(Var));
regexpr({ModExpr, FunExpr, ArityExpr}, Var) ->
    Type = type(Var),
    V1 = case {ModExpr,Type} of
	     {{atom, Mod},[{ModType, _}]} ->
		 restriction(Var, xset([Mod], [ModType]));
	     {{regexpr, MExpr},[{ModType, _}]} ->
		 Mods = match_list(to_external(domain(Var)), MExpr),
		 restriction(Var, xset(Mods, [ModType]));
	     {variable,_} ->
		 Var;
             {_,_} -> % Var is the empty set
                 Var
	 end,
    V2 = case FunExpr of
	     {atom, FunName} ->
		 V1L = to_external(V1),
		 xset(match_one(V1L, FunName, 2), Type);
	     {regexpr, FExpr} ->
		 V1L = to_external(V1),
		 xset(match_many(V1L, FExpr, 2), Type);
	     variable ->
		 V1
	 end,
    case ArityExpr of 
	{integer, Arity} ->
	    V2L = to_external(V2),
	    xset(match_one(V2L, Arity, 3), Type);
	{regexpr, Expr} ->
	    V2L = to_external(V2),
	    xset(match_many(V2L, Expr, 3), Type);
	variable ->
	    V2
    end.

%% -> digraph:graph()
relation_to_graph(S) ->
    G = digraph:new(),
    Fun = fun({From, To}) -> 
		  digraph:add_vertex(G, From),
		  digraph:add_vertex(G, To),
		  digraph:add_edge(G, From, To)
	  end,
    foreach(Fun, to_external(S)),
    G.

%% -> {ok, FileName} | Error | fault()
%% Finds a module's BEAM file.
find_beam(Module) when is_atom(Module) ->
    case code:which(Module) of
	non_existing ->
	    error({no_such_module, Module});
	preloaded ->
	    {Module, {_M, _Bin, File}} = 
                {Module, code:get_object_code(Module)},
	    {ok, File};
        cover_compiled ->
	    error({cover_compiled, Module});
	File ->
	    {ok, File}
    end;
find_beam(Culprit) ->
    erlang:error(badarg, [Culprit]).

%% options(Options, ValidOptions) -> {OptionValues, InvalidOptions}
%%
%% Options = [Option] | Option
%% ValidOptions = [atom() | {OptionName, ValidValues}]
%% OptionValues = [bool() | {OptionName, [term()]}]
%% OptionName = atom()
%% InvalidOptions = [Option]
%% Option = OptionName | {OptionName, term()}
%% ValidValues = [] | [DefaultValue | [ValidValue]] | [DefaultValue, Tester]
%% ValidValue = DefaultValue = term()
%% Tester = fun([term()]) -> bool()
%%
%% A Boolean Option has a name (an atom). A Value Option has a name
%% (an atom) and a value (a term).
%%
%% ValidOptions enumerates allowed options - a Boolean Option is
%% enumerated with its name, and a Value Option is enumerated with a
%% pair {Name, Values}, where Name is the option's name and Values is
%% a list of allowed values for the Value Option, the first one being
%% the default value (by convention). An empty list of allowed values
%% means that all terms are allowed as value (and that there is no
%% default value). Also if the only allowed value is the default
%% value, all terms are allowed as value. A function argument (Tester)
%% may be used for testing the supplied values (useful for a path...)
%% An allowed option must not be enumerated more than once, but
%% allowed values may be duplicated.
%%
%% OptionValues is a list of option values, where member i is the
%% value of option i in ValidOptions. The value of a Boolean Option is
%% 'true' if the option name is mentioned in Options, otherwise
%% 'false'. The value of a Value Option is a list of the option values
%% mentioned in Options for the Value Option. If the Value Option is
%% not mentioned in Options, the list contains the default value (if
%% there is no default value, the list is empty), and if it is
%% mentioned more than once, the values are sorted in standard order.
%%
%% InvalidOptions is a list of those options present in Options that
%% do not match any allowed option mentioned in ValidOptions.
%%
options(Options, Valid) ->
    split_options(Options, [], [], [], Valid).

format_error({error, Module, Error}) ->
    Module:format_error(Error);
format_error({file_error, FileName, Reason}) ->
    io_lib:format("~ts: ~tp~n", [FileName, file:format_error(Reason)]);
format_error({unrecognized_file, FileName}) ->
    io_lib:format("~tp is neither a regular file nor a directory~n", 
		  [FileName]);
format_error({no_such_module, Module}) ->
    io_lib:format("Cannot find module ~tp using the code path~n", [Module]);
format_error({interpreted, Module}) ->
    io_lib:format("Cannot use BEAM code of interpreted module ~tp~n", [Module]);
format_error(E) ->
    io_lib:format("~tp~n", [E]).

%%
%%  Local functions
%%

to_list(X) when is_atom(X) -> atom_to_list(X);
to_list(X) when is_list(X) -> X.

select_application_directories([FileName|FileNames], Dir, Flag, L) ->
    case is_directory(FileName) of
	true ->
	    File = filename:basename(FileName),
	    {Name, Vsn} = filename_to_application(File),
	    ApplDir = {Name, Vsn, subdir(FileName, Dir, Flag)},
	    select_application_directories(FileNames, Dir, Flag, [ApplDir|L]);
	false ->
	    select_application_directories(FileNames, Dir, Flag, L);
	Error ->
	    Error
    end;
select_application_directories([], _Dir, _Flag, L) ->
    {ok,reverse(L)}.

subdir(Dir, _, false) ->
    Dir;
subdir(Dir, SubDir, true) ->
    EDir = filename:join(Dir, SubDir),
    case is_directory(EDir) of
	true -> EDir;
	_FalseOrError -> Dir
    end.

%% Avoid "App-01.01" - the zeroes will be lost.
filename2appl(File) ->
    [ApplName, V] = string:split(File, "-", trailing),
    true = string:length(V) > 0,
    VsnT = string:lexemes(V, "."),
    Vsn = [list_to_integer(Vsn) || Vsn <- VsnT],
    {list_to_atom(ApplName),Vsn}.

find_files_dir(Dir, Recurse, Collect, Watch, L) ->
    case file:list_dir(Dir) of
	{ok, Files} ->
	    find_files(sort(Files), Dir, Recurse, Collect, Watch, L);
	{error, Error} ->
            L#scan{errors = [file_error(Dir, Error)|L#scan.errors]}
    end.

find_files([F | Fs], Dir, Recurse, Collect, Watch, L) ->
    File = filename:join(Dir, F),
    L1 = case file_info(File) of
	     {ok, {_, directory, readable, _}} when Recurse ->
		 find_files_dir(File, Recurse, Collect, Watch, L);
             {ok, {_, directory, _, _}} ->
		 L;
	     Info ->
                 #scan{collected = B, errors = E,
                       seen = J, unreadable = U} = L,
		 Ext = filename:extension(File),
		 C = member(Ext, Collect),
		 case C of
		     true ->
			 case Info of
			     {ok, {_, file, readable, _}} ->
                                 L#scan{collected = [{Dir,F} | B]};
			     {ok, {_, file, unreadable, _}} ->
                                 L#scan{unreadable = [File|U]};
			     Error ->
                                 L#scan{errors = [Error|E]}
			 end;
		     false ->
			 case member(Ext, Watch) of
                             true -> L#scan{seen = [File|J]};
			     false -> L
			 end
		 end
	 end,
    find_files(Fs, Dir, Recurse, Collect, Watch, L1);
find_files([], _Dir, _Recurse, _Collect, _Watch, L) ->
    L.

graph_to_relation(G) ->
    Fun = fun(E) -> {_E, V1, V2, _Label} = digraph:edge(G, E), {V1, V2} end,
    from_term(map(Fun, digraph:edges(G)), [{[atom],[atom]}]).

path([E1, E2 | P], G, L) ->
    case digraph:get_short_path(G, E1, E2) of
	false ->
	    false;
	[_V | Vs] ->
	    path([E2 | P], G, [Vs | L])
    end;
path([_], _G, L) ->
    append(reverse(L)).

neighbours(Vs, G, Fun, VT) ->
    neighbours(Vs, G, Fun, VT, []).

neighbours([V | Vs], G, Fun, VT, L) ->
    Ns = digraph_utils:Fun([V], G),
    neighbours(Ns, G, Fun, VT, L, V, Vs);
neighbours([], _G, _Fun, [VT], L) ->
    xset(L, [{VT,VT}]).

neighbours([N | Ns], G, Fun, VT, L, V, Vs) when Fun =:= reachable_neighbours ->
    neighbours(Ns, G, Fun, VT, [{V, N} | L], V, Vs);
neighbours([N | Ns], G, Fun, VT, L, V, Vs) ->
    neighbours(Ns, G, Fun, VT, [{N, V} | L], V, Vs);
neighbours([], G, Fun, VT, L, _V, Vs) ->
    neighbours(Vs, G, Fun, VT, L).

match_list(L, RExpr) ->
    {ok, Expr} = re:compile(RExpr, [unicode]),
    filter(fun(E) -> match(E, Expr) end, L).

match_one(VarL, Con, Col) ->
    select_each(VarL, fun(E) -> Con =:= element(Col, E) end).

match_many(VarL, RExpr, Col) ->
    {ok, Expr} = re:compile(RExpr, [unicode]),
    select_each(VarL, fun(E) -> match(element(Col, E), Expr) end).

match(I, Expr) when is_integer(I) ->
    S = integer_to_list(I),
    {match, [{0,length(S)}]} =:= re:run(S, Expr, [{capture, first}]);
match(A, Expr) when is_atom(A) ->
    S = atom_to_list(A),
    case re:run(S, Expr, [{capture, first}]) of
        {match, [{0,Size}]} ->
            Size =:= byte_size(unicode:characters_to_binary(S));
        _ ->
            false
    end.

select_each([{Mod,Funs} | L], Pred) ->
    case filter(Pred, Funs) of
        [] ->
             select_each(L, Pred);
        NFuns ->
             [{Mod,NFuns} | select_each(L, Pred)]
    end;
select_each([], _Pred) ->
    [].

split_options([O | Os], A, P, I, V) when is_atom(O) ->
    split_options(Os, [O | A], P, I, V);
split_options([O={Name,_} | Os], A, P, I, V) when is_atom(Name) ->
    split_options(Os, A, [O | P], I, V);
split_options([O | Os], A, P, I, V) ->
    split_options(Os, A, P, [O | I], V);
split_options([], A, P, I, V) ->
    Atoms = to_external(set(A)),
    Pairs = to_external(relation_to_family(relation(P))),
    option_values(V, Atoms, Pairs, I, []);
split_options(O, A, P, I, V) ->
    split_options([O], A, P, I, V).

option_values([O | Os], A, P, I, Vs) when is_atom(O) ->
    option_values(Os, delete(O, A), P, I, [member(O, A) | Vs]);    
option_values([{Name, AllowedValues} | Os], A, P, I, Vs) ->
    case keysearch(Name, 1, P) of
	{value, {_, Values}} ->
	    option_value(Name, AllowedValues, Values, A, P, I, Vs, Os);
	false when AllowedValues =:= [] ->
	    option_values(Os, A, P, I, [[] | Vs]);
	false ->
	    [Default | _] = AllowedValues,
	    option_values(Os, A, P, I, [[Default] | Vs])
    end;
option_values([], A, P, Invalid, Values) ->
    I2 = to_external(family_to_relation(family(P))),
    {reverse(Values), Invalid ++ A ++ I2}.

option_value(Name, [_Deflt, Fun], Vals, A, P, I, Vs, Os) 
                                                  when is_function(Fun) ->
    P1 = keydelete(Name, 1, P),
    case Fun(Vals) of
	true ->
	    option_values(Os, A, P1, I, [Vals | Vs]);
	false ->
	    option_values(Os, A, [{Name,Vals} | P1], I, [[] | Vs])
    end;
option_value(Name, AllowedValues, Values, A, P, I, Vs, Os) ->
    P1 = keydelete(Name, 1, P),
    VS = set(Values),
    AVS = set(AllowedValues),
    V1 = to_external(intersection(VS, AVS)),
    {V, NP} = case to_external(difference(VS, AVS)) of
		  _ when AllowedValues =:= [] -> {Values,P1};
		  [] -> {V1,P1};
		  _ when length(AllowedValues) =:= 1 -> 
		      {Values,P1};
 		  I1 -> {V1,[{Name,I1} | P1]}
	      end,
    option_values(Os, A, NP, I, [V | Vs]).

file_error(File, Error) ->
    error({file_error, File, Error}).

error(Error) ->
    {error, ?MODULE, Error}.
