File: settings.pl

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/*  Part of SWI-Prolog

    Author:        Jan Wielemaker
    E-mail:        J.Wielemaker@vu.nl
    WWW:           http://www.swi-prolog.org
    Copyright (c)  2007-2016, University of Amsterdam
                              VU University Amsterdam
    All rights reserved.

    Redistribution and use in source and binary forms, with or without
    modification, are permitted provided that the following conditions
    are met:

    1. Redistributions of source code must retain the above copyright
       notice, this list of conditions and the following disclaimer.

    2. Redistributions in binary form must reproduce the above copyright
       notice, this list of conditions and the following disclaimer in
       the documentation and/or other materials provided with the
       distribution.

    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
    "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
    LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
    FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
    COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
    INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
    BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
    LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
    CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
    LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
    ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
    POSSIBILITY OF SUCH DAMAGE.
*/

:- module(settings,
          [ setting/4,                  % :Name, +Type, +Default, +Comment
            setting/2,                  % :Name, ?Value
            set_setting/2,              % :Name, +Value
            set_setting_default/2,      % :Name, +Value
            restore_setting/1,          % :Name
            load_settings/1,            % +File
            load_settings/2,            % +File, +Options
            save_settings/0,
            save_settings/1,            % +File
            current_setting/1,          % Module:Name
            setting_property/2,         % ?Setting, ?Property
            list_settings/0,
            list_settings/1,            % +Module

            convert_setting_text/3      % +Type, +Text, -Value
          ]).
:- use_module(library(error)).
:- use_module(library(broadcast)).
:- use_module(library(debug)).
:- use_module(library(option)).
:- use_module(library(arithmetic)).
:- set_prolog_flag(generate_debug_info, false).

/** <module> Setting management

This library allows management  of   configuration  settings  for Prolog
applications. Applications define settings  in   one  or  multiple files
using the directive setting/4 as illustrated below:

==
:- use_module(library(settings)).

:- setting(version, atom,   '1.0', 'Current version').
:- setting(timeout, number,    20, 'Timeout in seconds').
==

The directive is subject to   term_expansion/2,  which guarantees proper
synchronisation of the  database  if   source-files  are  reloaded. This
implies it is *not* possible to call setting/4 as a predicate.

Settings are local to a  module.  This   implies  they  are defined in a
two-level namespace. Managing settings  per   module  greatly simplifies
assembling large applications from multiple   modules that configuration
through  settings.  This  settings  management  library  ensures  proper
access, loading and saving of settings.

@see    library(config) distributed with XPCE provides an alternative
        aimed at graphical applications.
@author Jan Wielemaker
*/

:- dynamic
    st_value/3,                     % Name, Module, Value
    st_default/3,                   % Name, Module, Value
    local_file/1.                   % Path

:- multifile
    current_setting/6.              % Name, Module, Type, Default, Comment, Source

:- meta_predicate
    setting(:, +, +, +),
    setting(:, ?),
    set_setting(:, +),
    set_setting_default(:, +),
    current_setting(:),
    restore_setting(:).

:- predicate_options(load_settings/2, 2, [undefined(oneof([load,error]))]).

curr_setting(Name, Module, Type, Default, Comment, Src) :-
    current_setting(Name, Module, Type, Default0, Comment, Src),
    (   st_default(Name, Module, Default1)
    ->  Default = Default1
    ;   Default = Default0
    ).

%!  setting(:Name, +Type, +Default, +Comment) is det.
%
%   Define a  setting.  Name denotes  the name of the  setting, Type
%   its type.  Default is the  value before it is  modified. Default
%   can  refer  to  environment  variables and  can  use  arithmetic
%   expressions as defined by eval_default/4.
%
%   If a second declaration for  a   setting  is  encountered, it is
%   ignored  if  Type  and  Default  are    the  same.  Otherwise  a
%   permission_error is raised.
%
%   @param Name     Name of the setting (an atom)
%   @param Type     Type for setting.  One of =any= or a type defined
%                   by must_be/2.
%   @param Default  Default value for the setting.
%   @param Comment  Atom containing a (short) descriptive note.


setting(Name, Type, Default, Comment) :-
    throw(error(context_error(nodirective,
                              setting(Name, Type, Default, Comment)),
                _)).

:- multifile
    system:term_expansion/2.

system:term_expansion((:- setting(QName, Type, Default, Comment)),
                    Expanded) :-
    \+ current_prolog_flag(xref, true),
    prolog_load_context(module, M0),
    strip_module(M0:QName, Module, Name),
    must_be(atom, Name),
    to_atom(Comment, CommentAtom),
    eval_default(Default, Module, Type, Value),
    check_type(Type, Value),
    source_location(File, Line),
    (   current_setting(Name, Module, OType, ODef, _, OldLoc),
        (   OType \=@= Type
        ;    ODef \=@= Default
        ),
        OldLoc \= (File:_)
    ->  format(string(Message),
               'Already defined at: ~w', [OldLoc]),
        throw(error(permission_error(redefine, setting, Module:Name),
                    context(Message, _)))
    ;   Expanded = settings:current_setting(Name, Module, Type, Default,
                                            CommentAtom, File:Line)
    ).

to_atom(Atom, Atom) :-
    atom(Atom),
    !.
to_atom(String, Atom) :-
    format(atom(Atom), '~s', String).

%!  setting(:Name, ?Value) is nondet.
%
%   True when Name is a currently   defined setting with Value. Note
%   that setting(Name, Value) only enumerates   the  settings of the
%   current  module.  All  settings   can    be   enumerated   using
%   setting(Module:Name, Value). This predicate is  =det= if Name is
%   ground.
%
%   @error  existence_error(setting, Name)

setting(Module:Name, Value) :-
    (   nonvar(Name), nonvar(Module)
    ->  (   st_value(Name, Module, Value0)
        ->  Value = Value0
        ;   curr_setting(Name, Module, Type, Default, _, _)
        ->  eval_default(Default, Module, Type, Value)
        ;   existence_error(setting, Module:Name)
        )
    ;   current_setting(Name, Module, _, _, _, _),
        setting(Module:Name, Value)
    ).


:- dynamic
    setting_cache/3.
:- volatile
    setting_cache/3.

%!  clear_setting_cache is det.
%
%   Clear the cache for evaluation of default values.

clear_setting_cache :-
    retractall(setting_cache(_,_,_)).

%!  eval_default(+Default, +Module, +Type, -Value) is det.
%
%   Convert the settings default value. The notation allows for some
%   `function-style' notations to make the library more generic:
%
%           * env(Name)
%           Get value from the given environment variable. The value
%           is handed to convert_setting_text/3 to convert the
%           textual representation into a Prolog term.  Raises an
%           existence_error of the variable is not defined.
%
%           * env(Name, Default)
%           As env(Name), but uses the value Default if the variable
%           is not defined.
%
%           * setting(Name)
%           Ask the value of another setting.
%
%           * Expression
%           If Type is numeric, evaluate the expression.  env(Var)
%           evaluates to the value of an environment variable.
%           If Type is =atom=, concatenate A+B+....  Elements of the
%           expression can be env(Name).

:- multifile
    eval_default/3.                 % +Default, +Type, -Value

eval_default(Default, _, _Type, Value) :-
    var(Default),
    !,
    Value = Default.
eval_default(Default, _, Type, Value) :-
    eval_default(Default, Type, Val),
    !,
    Value = Val.
eval_default(Default, _, _, Value) :-
    atomic(Default),
    !,
    Value = Default.
eval_default(Default, _, Type, Value) :-
    setting_cache(Default, Type, Val),
    !,
    Value = Val.
eval_default(env(Name), _, Type, Value) :-
    !,
    (   getenv(Name, TextValue)
    ->  convert_setting_text(Type, TextValue, Val),
        assert(setting_cache(env(Name), Type, Val)),
        Value = Val
    ;   existence_error(environment_variable, Name)
    ).
eval_default(env(Name, Default), _, Type, Value) :-
    !,
    (   getenv(Name, TextValue)
    ->  convert_setting_text(Type, TextValue, Val)
    ;   Val = Default
    ),
    assert(setting_cache(env(Name), Type, Val)),
    Value = Val.
eval_default(setting(Name), Module, Type, Value) :-
    !,
    strip_module(Module:Name, M, N),
    setting(M:N, Value),
    must_be(Type, Value).
eval_default(Expr, _, Type, Value) :-
    numeric_type(Type, Basic),
    !,
    arithmetic_expression_value(Expr, Val0),
    (   Basic == float
    ->  Val is float(Val0)
    ;   Basic = integer
    ->  Val is round(Val0)
    ;   Val = Val0
    ),
    assert(setting_cache(Expr, Type, Val)),
    Value = Val.
eval_default(A+B, Module, atom, Value) :-
    !,
    phrase(expr_to_list(A+B, Module), L),
    atomic_list_concat(L, Val),
    assert(setting_cache(A+B, atom, Val)),
    Value = Val.
eval_default(List, Module, list(Type), Value) :-
    !,
    eval_list_default(List, Module, Type, Val),
    assert(setting_cache(List, list(Type), Val)),
    Value = Val.
eval_default(Default, _, _, Default).


%!  eval_list_default(+List, +Module, +ElementType, -DefaultList)
%
%   Evaluate the default for a list of values.

eval_list_default([], _, _, []).
eval_list_default([H0|T0], Module, Type, [H|T]) :-
    eval_default(H0, Module, Type, H),
    eval_list_default(T0, Module, Type, T).

%!  expr_to_list(+Expression, +Module)// is det.
%
%   Process the components to create an  atom. Atom concatenation is
%   expressed as A+B. Components may refer to envrionment variables.

expr_to_list(A+B, Module) -->
    !,
    expr_to_list(A, Module),
    expr_to_list(B, Module).
expr_to_list(env(Name), _) -->
    !,
    (   { getenv(Name, Text) }
    ->  [Text]
    ;   { existence_error(environment_variable, Name) }
    ).
expr_to_list(env(Name, Default), _) -->
    !,
    (   { getenv(Name, Text) }
    ->  [Text]
    ;   [Default]
    ).
expr_to_list(setting(Name), Module) -->
    !,
    { strip_module(Module:Name, M, N),
      setting(M:N, Value)
    },
    [ Value ].
expr_to_list(A, _) -->
    [A].

%!  env(+Name:atom, -Value:number) is det.
%!  env(+Name:atom, +Default:number, -Value:number) is det
%
%   Evaluate  environment  variables   on    behalf   of  arithmetic
%   expressions.

:- arithmetic_function(env/1).
:- arithmetic_function(env/2).

env(Name, Value) :-
    (   getenv(Name, Text)
    ->  convert_setting_text(number, Text, Value)
    ;   existence_error(environment_variable, Name)
    ).
env(Name, Default, Value) :-
    (   getenv(Name, Text)
    ->  convert_setting_text(number, Text, Value)
    ;   Value = Default
    ).


%!  numeric_type(+Type, -BaseType)
%
%   True if Type is a numeric type   and  BaseType is the associated
%   basic Prolog type. BaseType is  one   of  =integer=,  =float= or
%   =number=.

numeric_type(integer, integer).
numeric_type(nonneg, integer).
numeric_type(float, float).
numeric_type(between(L,_), Type) :-
    ( integer(L) -> Type = integer ; Type = float ).


%!  set_setting(:Name, +Value) is det.
%
%   Change a setting. Performs existence   and type-checking for the
%   setting. If the effective value  of   the  setting is changed it
%   broadcasts the event below.
%
%           settings(changed(Module:Name, Old, New))
%
%   @error  existence_error(setting, Name)
%   @error  type_error(Type, Value)

set_setting(QName, Value) :-
    strip_module(QName, Module, Name),
    must_be(atom, Name),
    (   curr_setting(Name, Module, Type, Default0, _Comment, _Src),
        eval_default(Default0, Module, Type, Default)
    ->  setting(Module:Name, Old),
        (   Value == Default
        ->  retract_setting(Module:Name)
        ;   st_value(Name, Module, Value)
        ->  true
        ;   check_type(Type, Value)
        ->  retract_setting(Module:Name),
            assert_setting(Module:Name, Value)
        ),
        (   Old == Value
        ->  true
        ;   broadcast(settings(changed(Module:Name, Old, Value))),
            clear_setting_cache     % might influence dependent settings
        )
    ;   existence_error(setting, Name)
    ).

retract_setting(Module:Name) :-
    retractall(st_value(Name, Module, _)).

assert_setting(Module:Name, Value) :-
    assert(st_value(Name, Module, Value)).

%!  restore_setting(:Name) is det.
%
%   Restore the value of setting Name   to  its default. Broadcast a
%   change like set_setting/2 if  the  current   value  is  not  the
%   default.

restore_setting(QName) :-
    strip_module(QName, Module, Name),
    must_be(atom, Name),
    (   st_value(Name, Module, Old)
    ->  retract_setting(Module:Name),
        setting(Module:Name, Value),
        (   Old \== Value
        ->  broadcast(settings(changed(Module:Name, Old, Value)))
        ;   true
        )
    ;   true
    ).

%!  set_setting_default(:Name, +Default) is det.
%
%   Change the default for a setting.  The   effect  is  the same as
%   set_setting/2, but the new value is  considered the default when
%   saving and restoring  a  setting.  It   is  intended  to  change
%   application defaults in a particular context.

set_setting_default(QName, Default) :-
    strip_module(QName, Module, Name),
    must_be(atom, Name),
    (   current_setting(Name, Module, Type, Default0, _Comment, _Src)
    ->  retractall(settings:st_default(Name, Module, _)),
        retract_setting(Module:Name),
        (   Default == Default0
        ->  true
        ;   assert(settings:st_default(Name, Module, Default))
        ),
        eval_default(Default, Module, Type, Value),
        set_setting(Module:Name, Value)
    ;   existence_error(setting, Module:Name)
    ).


                 /*******************************
                 *             TYPES            *
                 *******************************/

%!  check_type(+Type, +Term)
%
%   Type  checking  for  settings.  Currently  simply  forwarded  to
%   must_be/2.

check_type(Type, Term) :-
    must_be(Type, Term).


                 /*******************************
                 *             FILE             *
                 *******************************/

%!  load_settings(File) is det.
%!  load_settings(File, +Options) is det.
%
%   Load local settings from File. Succeeds  if File does not exist,
%   setting the default save-file to File.  Options are:
%
%     * undefined(+Action)
%     Define how to handle settings that are not defined.  When
%     =error=, an error is printed and the setting is ignored.
%     when =load=, the setting is loaded anyway, waiting for a
%     definition.

load_settings(File) :-
    load_settings(File, []).

load_settings(File, Options) :-
    absolute_file_name(File, Path,
                       [ access(read),
                         file_errors(fail)
                       ]),
    !,
    assert(local_file(Path)),
    open(Path, read, In, [encoding(utf8)]),
    read_setting(In, T0),
    call_cleanup(load_settings(T0, In, Options), close(In)),
    clear_setting_cache.
load_settings(File, _) :-
    absolute_file_name(File, Path,
                       [ access(write),
                         file_errors(fail)
                       ]),
    !,
    assert(local_file(Path)).
load_settings(_, _).

load_settings(end_of_file, _, _) :- !.
load_settings(Setting, In, Options) :-
    catch(store_setting(Setting, Options), E,
          print_message(warning, E)),
    read_setting(In, Next),
    load_settings(Next, In, Options).

read_setting(In, Term) :-
    read_term(In, Term,
              [ syntax_errors(dec10)
              ]).

%!  store_setting(Term, +Options)
%
%   Store setting loaded from file in the Prolog database.

store_setting(setting(Module:Name, Value), _) :-
    curr_setting(Name, Module, Type, Default0, _Commentm, _Src),
    !,
    eval_default(Default0, Module, Type, Default),
    (   Value == Default
    ->  true
    ;   check_type(Type, Value)
    ->  retractall(st_value(Name, Module, _)),
        assert(st_value(Name, Module, Value)),
        broadcast(settings(changed(Module:Name, Default, Value)))
    ).
store_setting(setting(Module:Name, Value), Options) :-
    !,
    (   option(undefined(load), Options, load)
    ->  retractall(st_value(Name, Module, _)),
        assert(st_value(Name, Module, Value))
    ;   existence_error(setting, Module:Name)
    ).
store_setting(Term, _) :-
    type_error(setting, Term).

%!  save_settings is det.
%!  save_settings(+File) is det.
%
%   Save modified settings to File.

save_settings :-
    local_file(File),
    !,
    save_settings(File).

save_settings(File) :-
    absolute_file_name(File, Path,
                       [ access(write)
                       ]),
    !,
    open(Path, write, Out,
         [ encoding(utf8),
           bom(true)
         ]),
    write_setting_header(Out),
    forall(current_setting(Name, Module, _, _, _, _),
           save_setting(Out, Module:Name)),
    close(Out).


write_setting_header(Out) :-
    get_time(Now),
    format_time(string(Date), '%+', Now),
    format(Out, '/*  Saved settings~n', []),
    format(Out, '    Date: ~w~n', [Date]),
    format(Out, '*/~n~n', []).

save_setting(Out, Module:Name) :-
    curr_setting(Name, Module, Type, Default, Comment, _Src),
    (   st_value(Name, Module, Value),
        \+ ( eval_default(Default, Module, Type, DefValue),
             debug(setting, '~w <-> ~w~n', [DefValue, Value]),
             DefValue =@= Value
           )
    ->  format(Out, '~n%\t~w~n', [Comment]),
        format(Out, 'setting(~q:~q, ~q).~n', [Module, Name, Value])
    ;   true
    ).

%!  current_setting(?Setting) is nondet.
%
%   True if Setting is a currently defined setting

current_setting(Setting) :-
    ground(Setting),
    !,
    strip_module(Setting, Module, Name),
    current_setting(Name, Module, _, _, _, _).
current_setting(Module:Name) :-
    current_setting(Name, Module, _, _, _, _).

%!  setting_property(+Setting, +Property) is det.
%!  setting_property(?Setting, ?Property) is nondet.
%
%   Query currently defined settings.  Property is one of
%
%           * comment(-Atom)
%           * type(-Type)
%           Type of the setting.
%           * default(-Default)
%           Default value.  If this is an expression, it is
%           evaluated.
%           * source(-File:-Line)
%           Location where the setting is defined.

setting_property(Setting, Property) :-
    ground(Setting),
    !,
    Setting = Module:Name,
    curr_setting(Name, Module, Type, Default, Comment, Src),
    !,
    setting_property(Property, Module, Type, Default, Comment, Src).
setting_property(Setting, Property) :-
    Setting = Module:Name,
    curr_setting(Name, Module, Type, Default, Comment, Src),
    setting_property(Property, Module, Type, Default, Comment, Src).

setting_property(type(Type), _, Type, _, _, _).
setting_property(default(Default), M, Type, Default0, _, _) :-
    eval_default(Default0, M, Type, Default).
setting_property(comment(Comment), _, _, _, Comment, _).
setting_property(source(Src), _, _, _, _, Src).

%!  list_settings is det.
%!  list_settings(+Module) is det.
%
%   List settings to =current_output=. The   second  form only lists
%   settings on the matching module.
%
%   @tbd    Compute the required column widths

list_settings :-
    list_settings(_).

list_settings(Spec) :-
    spec_term(Spec, Term),
    TS1 = 25,
    TS2 = 40,
    format('~`=t~72|~n'),
    format('~w~t~*| ~w~w~t~*| ~w~n',
           ['Name', TS1, 'Value (*=modified)', '', TS2, 'Comment']),
    format('~`=t~72|~n'),
    forall(current_setting(Term),
           list_setting(Term, TS1, TS2)).

spec_term(M:S, M:S) :- !.
spec_term(M, M:_).


list_setting(Module:Name, TS1, TS2) :-
    curr_setting(Name, Module, Type, Default0, Comment, _Src),
    eval_default(Default0, Module, Type, Default),
    setting(Module:Name, Value),
    (   Value \== Default
    ->  Modified = (*)
    ;   Modified = ''
    ),
    format('~w~t~*| ~q~w~t~*| ~w~n', [Module:Name, TS1, Value, Modified, TS2, Comment]).


                 /*******************************
                 *            TYPES             *
                 *******************************/

%!  convert_setting_text(+Type, +Text, -Value)
%
%   Converts from textual form to  Prolog   Value.  Used  to convert
%   values obtained from the environment.  Public to provide support
%   in user-interfaces to this library.
%
%   @error  type_error(Type, Value)

:- multifile
    convert_text/3.                 % +Type, +Text, -Value

convert_setting_text(Type, Text, Value) :-
    convert_text(Type, Text, Value),
    !.
convert_setting_text(atom, Value, Value) :-
    !,
    must_be(atom, Value).
convert_setting_text(boolean, Value, Value) :-
    !,
    must_be(boolean, Value).
convert_setting_text(integer, Atom, Number) :-
    !,
    term_to_atom(Term, Atom),
    Number is round(Term).
convert_setting_text(float, Atom, Number) :-
    !,
    term_to_atom(Term, Atom),
    Number is float(Term).
convert_setting_text(between(L,U), Atom, Number) :-
    !,
    (   integer(L)
    ->  convert_setting_text(integer, Atom, Number)
    ;   convert_setting_text(float, Atom, Number)
    ),
    must_be(between(L,U), Number).
convert_setting_text(Type, Atom, Term) :-
    term_to_atom(Term, Atom),
    must_be(Type, Term).


                 /*******************************
                 *            SANDBOX           *
                 *******************************/

:- multifile
    sandbox:safe_meta_predicate/1.

sandbox:safe_meta_predicate(settings:setting/2).