=encoding utf8

=head1 NAME

Log::Report::Message - a piece of text to be translated

=head1 INHERITANCE

 Log::Report::Message is extended by
   Dancer2::Plugin::LogReport::Message

=head1 SYNOPSIS

 # Objects created by Log::Report's __ functions
 # Full feature description in the DETAILS section

 # no interpolation
 __"Hello, World";

 # with interpolation
 __x"age {years}", years => 12;

 # interpolation for one or many
 my $nr_files = @files;
 __nx"one file", "{_count} files", $nr_files;
 __nx"one file", "{_count} files", \@files;

 # interpolation of arrays
 __x"price-list: {prices%.2f}", prices => \@prices, _join => ', ';

 # white-spacing on msgid preserved
 print __"\tCongratulations,\n";
 print "\t", __("Congratulations,"), "\n";  # same

=head1 DESCRIPTION

Any use of a translation function exported by L<Log::Report|Log::Report>, like
C<__()> (the function is named underscore-underscore) or C<__x()>
(underscore-underscore-x) will result in this object.  It will capture
some environmental information, and delay the translation until it
is needed.

Creating an object first and translating it later, is slower than
translating it immediately.  However, on the location where the message
is produced, we do not yet know in what language to translate it to:
that depends on the front-end, the log dispatcher.

=head1 METHODS

=head2 Constructors

=over 4

=item $obj-E<gt>B<clone>(%options, $variables)

Returns a new object which copies info from original, and updates it
with the specified %options and $variables.  The advantage is that the
cached translations are shared between the objects.

example: use of clone()

 my $s = __x "found {nr} files", nr => 5;
 my $t = $s->clone(nr => 3);
 my $t = $s->(nr => 3);      # equivalent
 print $s;     # found 5 files
 print $t;     # found 3 files

=item Log::Report::Message-E<gt>B<fromTemplateToolkit>($domain, $msgid, $params)

See L<Log::Report::Extract::Template|Log::Report::Extract::Template> on the details how to integrate
Log::Report translations with Template::Toolkit (version 1 and 2)

=item Log::Report::Message-E<gt>B<new>(%options)

B<End-users: do not use this method directly>, but use L<Log::Report::__()|Log::Report/"Language Translations">
and friends.  The %options is a mixed list of object initiation parameters
(all with a leading underscore) and variables to be filled in into the
translated C<_msgid> string.

 -Option   --Default
  _append    undef
  _category  undef
  _class     []
  _classes   []
  _context   undef
  _count     undef
  _domain    <from "use Log::Report">
  _expand    false
  _join      $" $LIST_SEPARATOR
  _lang      <from locale>
  _msgid     undef
  _plural    undef
  _prepend   undef
  _to        <undef>

=over 2

=item _append => STRING|MESSAGE

Text as STRING or MESSAGE object to be displayed after the display
of this message.

=item _category => INTEGER

The category when the real gettext library is used, for instance
LC_MESSAGES.

=item _class => STRING|ARRAY

When messages are used for exception based programming, you add
C<_class> parameters to the argument list.  Later, with for instance
L<Log::Report::Dispatcher::Try::wasFatal(class)|Log::Report::Dispatcher::Try/"Status">, you can check the
category of the message.

One message can be part of multiple classes.  The STRING is used as
comma- and/or blank separated list of class tokens (barewords), the
ARRAY lists all tokens separately. See L<classes()|Log::Report::Message/"Accessors">.

=item _classes => STRING|ARRAY

Alternative for C<_class>, which cannot be used at the same time.

=item _context => WORDS|ARRAY

[1.00] Set keywords which can be used to select alternatives
between translations.  Read the DETAILS section in
L<Log::Report::Translator::Context|Log::Report::Translator::Context>

=item _count => INTEGER|ARRAY|HASH

When defined, the C<_plural> need to be defined as well.  When an
ARRAY is provided, the length of the ARRAY is taken.  When a HASH
is given, the number of keys in the HASH is used.

=item _domain => STRING

The text-domain (translation table) to which this C<_msgid> belongs.

With this parameter, your can "borrow" translations from other textdomains.
Be very careful with this (although there are good use-cases)  The xgettext
msgid extractor may add the used msgid to this namespace as well.  To
avoid that, add a harmless '+':

  print __x(+"errors", _domain => 'global');

The extractor will not take the msgid when it is an expression.  The '+'
has no effect on the string at runtime.

=item _expand => BOOLEAN

Indicates whether variables are to be filled-in.

=item _join => STRING

Which STRING to be used then an ARRAY is being filled-in.

=item _lang => ISO

[1.00] Override language setting from locale, for instance because that
is not configured correctly (yet).  This does not extend to prepended
or appended translated message object.

=item _msgid => MSGID

The message label, which refers to some translation information.
Usually a string which is close the English version of the message.
This will also be used if there is no translation possible/known.

Leading white-space C<\s> will be added to C<_prepend>.  Trailing
white-space will be added before C<_append>.

=item _plural => MSGID

Can be used together with C<_count>.  This plural form of the C<_msgid>
text is used to simplify the work of translators, and as fallback when
no translation is possible: therefore, this can best resemble an
English message.

White-space at the beginning and end of the string are stripped off.
The white-space provided by the C<_msgid> will be used.

=item _prepend => STRING|MESSAGE

Text as STRING or MESSAGE object to be displayed before the display
of this message.

=item _to => NAME

Specify the NAME of a dispatcher as destination explicitly. Short
for  C<< report {to => NAME}, ... >>  See L<to()|Log::Report::Message/"Accessors">

=back

=back

=head2 Accessors

=over 4

=item $obj-E<gt>B<append>()

Returns the string or L<Log::Report::Message|Log::Report::Message> object which is appended
after this one.  Usually C<undef>.

=item $obj-E<gt>B<classes>()

Returns the LIST of classes which are defined for this message; message
group indicators, as often found in exception-based programming.

=item $obj-E<gt>B<context>()

Returns an HASH if there is a context defined for this message.

=item $obj-E<gt>B<count>()

Returns the count, which is used to select the translation
alternatives.

=item $obj-E<gt>B<domain>()

Returns the domain of the first translatable string in the structure.

=item $obj-E<gt>B<msgid>()

Returns the msgid which will later be translated.

=item $obj-E<gt>B<prepend>()

Returns the string which is prepended to this one.  Usually C<undef>.

=item $obj-E<gt>B<to>( [$name] )

Returns the $name of a dispatcher if explicitly specified with
the '_to' key. Can also be used to set it.  Usually, this will
return undef, because usually all dispatchers get all messages.

=item $obj-E<gt>B<valueOf>($parameter)

Lookup the named $parameter for the message.  All pre-defined names
have their own method which should be used with preference.

example: 

When the message was produced with

  my @files = qw/one two three/;
  my $msg = __xn "found one file: {file}"
               , "found {nrfiles} files: {files}"
               , scalar @files
               , file    => $files[0]
               , files   => \@files
               , nrfiles => @files+0
               , _class  => 'IO, files'
               , _join   => ', ';

then the values can be takes from the produced message as

  my $files = $msg->valueOf('files');  # returns ARRAY reference
  print @$files;              # 3
  my $count = $msg->count;    # 3
  my @class = $msg->classes;  # 'IO', 'files'
  if($msg->inClass('files'))  # true

Simplified, the above example can also be written as:

  local $" = ', ';
  my $msg  = __xn "found one file: {files}"
                , "found {_count} files: {files}"
                , @files      # has scalar context
                , files   => \@files
                , _class  => 'IO, files';

=back

=head2 Processing

=over 4

=item $obj-E<gt>B<concat>( STRING|$object, [$prepend] )

This method implements the overloading of concatenation, which is needed
to delay translations even longer.  When $prepend is true, the STRING
or $object (other C<Log::Report::Message>) needs to prepended, otherwise
it is appended.

example: of concatenation

 print __"Hello" . ' ' . __"World!";
 print __("Hello")->concat(' ')->concat(__"World!")->concat("\n");

=item $obj-E<gt>B<inClass>($class|Regexp)

Returns true if the message is in the specified $class (string) or
matches the Regexp.  The trueth value is the (first matching) class.

=item $obj-E<gt>B<toHTML>( [$locale] )

[1.11] Translate the message, and then entity encode HTML volatile characters.

=item $obj-E<gt>B<toString>( [$locale] )

Translate a message.  If not specified, the default locale is used.

=item $obj-E<gt>B<untranslated>()

Return the concatenation of the prepend, msgid, and append strings.  Variable
expansions within the msgid is not performed.

=back

=head1 DETAILS

=head2 OPTIONS and VARIABLES

The L<Log::Report|Log::Report> functions which define translation request can all
have OPTIONS.  Some can have VARIABLES to be interpolated in the string as
well.  To distinguish between the OPTIONS and VARIABLES (both a list
of key-value pairs), the keys of the OPTIONS start with an underscore C<_>.
As result of this, please avoid the use of keys which start with an
underscore in variable names.  On the other hand, you are allowed to
interpolate OPTION values in your strings.

=head3 Interpolating

With the C<__x()> or C<__nx()>, interpolation will take place on the
translated MSGID string.  The translation can contain the VARIABLE
and OPTION names between curly brackets.  Text between curly brackets
which is not a known parameter will be left untouched.

 fault __x"cannot open open {filename}", filename => $fn;

 print __xn"directory {dir} contains one file"
          ,"directory {dir} contains {nr_files} files"
          , scalar(@files)            # (1) (2)
          , nr_files => scalar @files # (3)
          , dir      => $dir;

(1) this required third parameter is used to switch between the different
plural forms.  English has only two forms, but some languages have many
more.

(2) the "scalar" keyword is not needed, because the third parameter is
in SCALAR context.  You may also pass C< \@files > there, because ARRAYs
will be converted into their length.  A HASH will be converted into the
number of keys in the HASH.

(3) the C<scalar> keyword is required here, because it is LIST context:
otherwise all filenames will be filled-in as parameters to C<__xn()>.
See below for the available C<_count> valure, to see how the C<nr_files>
parameter can disappear.

=head3 Interpolation of VARIABLES

C<Log::Report> uses L<String::Print> to interpolate values in(translated)
messages.  This is a very powerful syntax, and you should certainly read
that manual-page.  Here, we only described additional features, specific
to the usage of C<String::Print> in C<Log::Report::Message> objects.

There is no way of checking beforehand whether you have provided all
required values, to be interpolated in the translated string.

For interpolating, the following rules apply:

=over 4

=item *

Simple scalar values are interpolated "as is"

=item *

References to SCALARs will collect the value on the moment that the
output is made.  The C<Log::Report::Message> object which is created with
the C<__xn> can be seen as a closure.  The translation can be reused.
See example below.

=item *

Code references can be used to create the data "under fly".  The
C<Log::Report::Message> object which is being handled is passed as
only argument.  This is a hash in which all OPTIONS and VARIABLES
can be found.

=item *

When the value is an ARRAY, all members will be interpolated with C<$">
between the elements.  Alternatively (maybe nicer), you can pass an
interpolation parameter via the C<_join> OPTION.

=back

 local $" = ', ';
 error __x"matching files: {files}", files => \@files;

 error __x"matching files: {files}", files => \@files, _join => ', ';

=head3 Interpolation of OPTIONS

You are permitted the interpolate OPTION values in your string.  This may
simplify your coding.  The useful names are:

=over 4

=item _msgid

The MSGID as provided with L<Log::Report::__()|Log::Report/"Language Translations"> and L<Log::Report::__x()|Log::Report/"Language Translations">

=item _plural, _count

The PLURAL MSGIDs, respectively the COUNT as used with
L<Log::Report::__n()|Log::Report/"Language Translations"> and L<Log::Report::__nx()|Log::Report/"Language Translations">

=item _textdomain

The label of the textdomain in which the translation takes place.

=item _class or _classes

Are to be used to group reports, and can be queried with L<inClass()|Log::Report::Message/"Processing">,
L<Log::Report::Exception::inClass()|Log::Report::Exception/"Processing">, or
L<Log::Report::Dispatcher::Try::wasFatal()|Log::Report::Dispatcher::Try/"Status">.

=back

=head3 Handling white-spaces

In above examples, the msgid and plural form have a trailing new-line.
In general, it is much easier to write

   print __x"Hello, World!\n";

than

   print __x("Hello, World!") . "\n";

For the translation tables, however, that trailing new-line is "over
information"; it is an layout issue, not a translation issue.

Therefore, the first form will automatically be translated into the
second.  All leading and trailing white-space (blanks, new-lines, tabs,
...) are removed from the msgid befor the look-up, and then added to
the translated string.

Leading and trailing white-space on the plural form will also be
removed.  However, after translation the spacing of the msgid will
be used.

=head3 Avoiding repetative translations

This way of translating is somewhat expensive, because an object to
handle the C<__x()> is created each time.

 for my $i (1..100_000)
 {   print __x "Hello World {i}\n", i => $i;
 }

The suggestion that Locale::TextDomain makes to improve performance,
is to get the translation outside the loop, which only works without
interpolation:

 use Locale::TextDomain;
 my $i = 42;
 my $s = __x("Hello World {i}\n", i => $i);
 foreach $i (1..100_000)
 {   print $s;
 }

Oops, not what you mean because the first value of C<$i> is captured
in the initial message object.  With Log::Report, you can do it (except
when you use contexts)

 use Log::Report;
 my $i;
 my $s = __x("Hello World {i}\n", i => \$i);
 foreach $i (1..100_000)
 {   print $s;
 }

Mind you not to write: C<for my $i> in above case!!!!

You can also write an incomplete translation:

 use Log::Report;
 my $s = __x "Hello World {i}\n";
 foreach my $i (1..100_000)
 {   print $s->(i => $i);
 }

In either case, the translation will be looked-up only once.

=head1 OVERLOADING

=over 4

=item overload: B<as $function>

When the object is used to call as $function, a new object is
created with the data from the original one but updated with the
new parameters.  Implemented in C<clone()>.

=item overload: B<concatenation>

An (accidental) use of concatenation (a dot where a comma should be
used) would immediately stringify the object.  This is avoided by
overloading that operation.

=item overload: B<stringification>

When the object is used in string context, it will get translated.
Implemented as L<toString()|Log::Report::Message/"Processing">.

=back

=head1 SEE ALSO

This module is part of Log-Report distribution version 1.11,
built on January 18, 2016. Website: F<http://perl.overmeer.net/log-report/>

=head1 LICENSE

Copyrights 2007-2016 by [Mark Overmeer]. For other contributors see ChangeLog.

This program is free software; you can redistribute it and/or modify it
under the same terms as Perl itself.
See F<http://www.perl.com/perl/misc/Artistic.html>

