js_write.pl

/*  Part of SWI-Prolog

    Author:        Jan Wielemaker, Michiel Hildebrand
    E-mail:        J.Wielemaker@uva.nl
    WWW:           http://www.swi-prolog.org
    Copyright (c)  2010-2014, 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(javascript,
          [ js_script//1,               % +Content

            js_call//1,                 % +Function(Arg..)
            js_new//2,                  % +Id, +Function(+Args)
            js_expression//1,           % +Expression
            js_arg_list//1,             % +ListOfExpressions
            js_arg//1,                  % +Arg
            js_args//1,                 % +Args

            javascript/4                % Quasi Quotation handler
          ]).

:- use_module(library(http/html_write)).
:- use_module(library(http/json)).
:- use_module(library(apply)).
:- use_module(library(error)).
:- use_module(library(lists)).
:- use_module(library(debug)).
:- use_module(library(quasi_quotations)).
:- use_module(library(dcg/basics)).
:- use_module(js_grammar).

:- html_meta
    js_script(html, ?, ?).

:- quasi_quotation_syntax(javascript).

/** <module> Utilities for including JavaScript

This library is a supplement   to library(http/html_write) for producing
JavaScript fragments. Its main role is  to   be  able to call JavaScript
functions  with  valid  arguments  constructed  from  Prolog  data.  For
example, suppose you want to call a   JavaScript  functions to process a
list of names represented as Prolog atoms.   This  can be done using the
call below, while without this library you   would have to be careful to
properly escape special characters.

    ==
    numbers_script(Names) -->
        html(script(type('text/javascript'),
             [ \js_call('ProcessNumbers'(Names)
             ]),
    ==

The accepted arguments are described with js_expression//1.
*/

%!  js_script(+Content)// is det.
%
%   Generate a JavaScript =script= element with the given content.

js_script(Content) -->
    html(script(type('text/javascript'),
                Content)).


                 /*******************************
                 *        QUASI QUOTATION       *
                 *******************************/

%!  javascript(+Content, +Vars, +VarDict, -DOM) is det.
%
%   Quasi quotation parser for JavaScript  that allows for embedding
%   Prolog variables to substitude _identifiers_   in the JavaScript
%   snippet. Parameterizing a JavaScript string   is  achieved using
%   the JavaScript `+` operator, which   results in concatenation at
%   the client side.
%
%     ==
%         ...,
%         js_script({|javascript(Id, Config)||
%                     $(document).ready(function() {
%                        $("#"+Id).tagit(Config);
%                      });
%                    |}),
%         ...
%     ==
%
%   The current implementation tokenizes the   JavaScript  input and
%   yields syntax errors on unterminated  comments, strings, etc. No
%   further parsing is  implemented,  which   makes  it  possible to
%   produce syntactically incorrect and   partial JavaScript. Future
%   versions are likely to include a  full parser, generating syntax
%   errors.
%
%   The parser produces a  term  `\List`,   which  is  suitable  for
%   js_script//1 and html//1.  Embedded  variables   are  mapped  to
%   `\js_expression(Var)`, while the remaining  text   is  mapped to
%   atoms.
%
%   @tbd    Implement a full JavaScript parser. Users should _not_
%           rely on the ability to generate partial JavaScript
%           snippets.

javascript(Content, Vars, Dict, \Parts) :-
    include(qq_var(Vars), Dict, QQDict),
    phrase_from_quasi_quotation(
        js(QQDict, Parts),
        Content).

qq_var(Vars, _=Var) :-
    member(V, Vars),
    V == Var,
    !.

js(Dict, [Pre, Subst|More]) -->
    here(Here0),
    js_tokens(_),
    here(Here1),
    js_token(identifier(Name)),
    { memberchk(Name=Var, Dict),
      !,
      Subst = \js_expression(Var),
      diff_to_atom(Here0, Here1, Pre)
    },
    js(Dict, More).
js(_, [Last]) -->
    string(Codes),
    \+ [_],
    !,
    { atom_codes(Last, Codes) }.

js_tokens([]) --> [].
js_tokens([H|T]) -->
    js_token(H),
    js_tokens(T).


%       diff_to_atom(+Start, +End, -Atom)
%
%       True when Atom is an atom that represents the characters between
%       Start and End, where End must be in the tail of the list Start.

diff_to_atom(Start, End, Atom) :-
    diff_list(Start, End, List),
    atom_codes(Atom, List).

diff_list(Start, End, List) :-
    Start == End,
    !,
    List = [].
diff_list([H|Start], End, [H|List]) :-
    diff_list(Start, End, List).

here(Here, Here, Here).


                 /*******************************
                 *     PROLOG --> JAVASCRIPT    *
                 *******************************/

%!  js_call(+Term)// is det.
%
%   Emit a call to a Javascript function.  The Prolog functor is the
%   name of the function. The arguments are converted from Prolog to
%   JavaScript using js_arg_list//1. Please not that Prolog functors can
%   be quoted atom and thus the following is legal:
%
%       ==
%           ...
%           html(script(type('text/javascript'),
%                [ \js_call('x.y.z'(hello, 42))
%                ]),
%       ==

js_call(Term) -->
    { Term =.. [Function|Args] },
    html(Function), js_arg_list(Args), [';\n'].


%!  js_new(+Id, +Term)// is det.
%
%   Emit a call to a Javascript object declaration. This is the same
%   as:
%
%       ==
%       ['var ', Id, ' = new ', \js_call(Term)]
%       ==


js_new(Id, Term) -->
    { Term =.. [Function|Args] },
    html(['var ', Id, ' = new ', Function]), js_arg_list(Args), [';\n'].

%!  js_arg_list(+Expressions:list)// is det.
%
%   Write javascript (function) arguments.  This   writes  "(", Arg,
%   ..., ")".  See js_expression//1 for valid argument values.


js_arg_list(Args) -->
    ['('], js_args(Args), [')'].

js_args([]) -->
    [].
js_args([H|T]) -->
    js_expression(H),
    (   { T == [] }
    ->  []
    ;   html(', '),
        js_args(T)
    ).

%!  js_expression(+Expression)// is det.
%
%   Emit a single JSON argument.  Expression is one of:
%
%       $ Variable :
%       Emitted as Javascript =null=
%       $ List :
%       Produces a Javascript list, where each element is processed
%       by this library.
%       $ object(Attributes) :
%       Where Attributes is a Key-Value list where each pair can be
%       written as Key-Value, Key=Value or Key(Value), accommodating
%       all common constructs for this used in Prolog.
%       $ { K:V, ... }
%       Same as object(Attributes), providing a more JavaScript-like
%       syntax.  This may be useful if the object appears literally
%       in the source-code, but is generally less friendly to produce
%       as a result from a computation.
%       $ Dict :
%       Emit a dict as a JSON object using json_write_dict/3.
%       $ json(Term) :
%       Emits a term using json_write/3.
%       $ @(Atom) :
%       Emits these constants without quotes.  Normally used for the
%       symbols =true=, =false= and =null=, but can also be use for
%       emitting JavaScript symbols (i.e. function- or variable
%       names).
%       $ Number :
%       Emitted literally
%       $ symbol(Atom) :
%       Synonym for @(Atom).  Deprecated.
%       $ Atom or String :
%       Emitted as quoted JavaScript string.

js_expression(Expr) -->
    js_arg(Expr),
    !.
js_expression(Expr) -->
    { type_error(js(expression), Expr) }.

%!  js_arg(+Expression)// is semidet.
%
%   Same as js_expression//1, but fails if Expression is invalid,
%   where js_expression//1 raises an error.
%
%   @deprecated     New code should use js_expression//1.

js_arg(H) -->
    { var(H) },
    !,
    [null].
js_arg(object(H)) -->
    { is_list(H) },
    !,
    html([ '{', \js_kv_list(H), '}' ]).
js_arg({}(Attrs)) -->
    !,
    html([ '{', \js_kv_cslist(Attrs), '}' ]).
js_arg(@(Id)) --> js_identifier(Id).
js_arg(symbol(Id)) --> js_identifier(Id).
js_arg(json(Term)) -->
    { json_to_string(json(Term), String),
      debug(json_arg, '~w~n', String)
    },
    [ String ].
js_arg(Dict) -->
    { is_dict(Dict),
      !,
      with_output_to(string(String),
                     json_write_dict(current_output, Dict, [width(0)]))
    },
    [ String ].
js_arg(H) -->
    { is_list(H) },
    !,
    html([ '[', \js_args(H), ']' ]).
js_arg(H) -->
    { number(H) },
    !,
    [H].
js_arg(H) -->
    { atomic(H),
      !,
      js_quoted_string(H, Q)
    },
    [ '"', Q, '"'
    ].

js_kv_list([]) --> [].
js_kv_list([H|T]) -->
    (   js_kv(H)
    ->  (   { T == [] }
        ->  []
        ;   html(', '),
            js_kv_list(T)
        )
    ;   { type_error(javascript_key_value, H) }
    ).

js_kv(Key:Value) -->
    !,
    js_key(Key), [:], js_expression(Value).
js_kv(Key-Value) -->
    !,
    js_key(Key), [:], js_expression(Value).
js_kv(Key=Value) -->
    !,
    js_key(Key), [:], js_expression(Value).
js_kv(Term) -->
    { compound(Term),
      Term =.. [Key,Value]
    },
    !,
    js_key(Key), [:], js_expression(Value).

js_key(Key) -->
    (   { must_be(atom, Key),
          js_identifier(Key)
        }
    ->  [Key]
    ;   { js_quoted_string(Key, QKey) },
        html(['\'', QKey, '\''])
    ).

js_kv_cslist((A,B)) -->
    !,
    js_kv(A),
    html(', '),
    js_kv_cslist(B).
js_kv_cslist(A) -->
    js_kv(A).

%!  js_quoted_string(+Raw, -Quoted)
%
%   Quote text for use in JavaScript.  Quoted does _not_ include the
%   leading and trailing quotes.
%
%   @tbd    Join with json stuff.

js_quoted_string(Raw, Quoted) :-
    atom_codes(Raw, Codes),
    phrase(js_quote_codes(Codes), QuotedCodes),
    atom_codes(Quoted, QuotedCodes).

js_quote_codes([]) -->
    [].
js_quote_codes([0'\r,0'\n|T]) -->
    !,
    "\\n",
    js_quote_codes(T).
js_quote_codes([0'<,0'/|T]) -->        % Avoid XSS scripting hacks
    !,
    "<\\/",
    js_quote_codes(T).
js_quote_codes([H|T]) -->
    js_quote_code(H),
    js_quote_codes(T).

js_quote_code(0'') -->
    !,
    "\\'".
js_quote_code(0'") -->
    !,
    "\\\"".
js_quote_code(0'\\) -->
    !,
    "\\\\".
js_quote_code(0'\n) -->
    !,
    "\\n".
js_quote_code(0'\r) -->
    !,
    "\\r".
js_quote_code(0'\t) -->
    !,
    "\\t".
js_quote_code(C) -->
    [C].

%!  js_identifier(+Id:atom)// is det.
%
%   Emit an identifier if it is a valid one

js_identifier(Id) -->
    { must_be(atom, Id),
      js_identifier(Id)
    },
    !,
    [ Id ].
js_identifier(Id) -->
    { domain_error(js(identifier), Id)
    }.

%!  js_identifier(+Id:atom) is semidet.
%
%   True if Id is a  valid   identifier.  In traditional JavaScript,
%   this means it starts  with  [$_:letter:]   and  is  followed  by
%   [$_:letter:digit:]

js_identifier(Id) :-
    sub_atom(Id, 0, 1, _, First),
    char_type(First, csymf),
    forall(sub_atom(Id, _, 1, _, Char), char_type(Char, csym)).


%!  json_to_string(+JSONTerm, -String)
%
%   Write JSONTerm to String.

json_to_string(JSON, String) :-
    with_output_to(string(String),
                   json_write(current_output,JSON,[width(0)])).