=encoding utf8

=head1 NAME

Log::Report::Template - Template Toolkit with translations

=head1 INHERITANCE

 Log::Report::Template
   is a Template

=head1 SYNOPSIS

  use Log::Report::Template;
  my $templater = Log::Report::Template->new(%config);
  $templater->addTextdomain(name => "Tic", lexicons => ...);
  $templater->process('template_file.tt', \%vars, \$output);

=head1 DESCRIPTION

This module extends Template, which is the core of Template Toolkit.
The main addition is support for translations via the translation
framework offered by L<Log::Report|Log::Report>.

You add translations to a template system, by adding calls to some
translation function (by default called C<loc()>) to your template text.
That function will perform dark magic to collect the translation from
translation tables, and fill in values.  For instance:

  [% price = 3.14 %]
  <div>Price: [% price %]</div>          # no translation
  <div>[% loc("Price: {price}") %]</div> # translation optional

It's quite a lot of work to make your templates translatable.
Please read the L</DETAILS> section before you start using this module.

=head1 METHODS

=head2 Constructors

=over 4

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

Create a new translator object.  You may pass the C<%options> as HASH or
PAIRS.  By convension, all basic Template Toolkit options are in capitals.
Read Template::Config about what they mean.  Extension options provided
by this module are all in lower-case.

In a web-environment, you want to start this before your webserver starts
forking.

 -Option           --Default
  modifiers          []
  processing_errors  'NATIVE'
  template_syntax    'HTML'
  textdomain_class   Log::Report::Template::Textdomain
  translate_to       undef

=over 2

=item modifiers => ARRAY

Add a list of modifiers to the default set.  Modifiers are part of the
formatting process, when values get inserted in the translated string.
Read L</"Formatter value modifiers">.

=item processing_errors => 'NATIVE'|'EXCEPTION'

The Template Toolkit infrastructure handles errors carefully: C<undef> is
returned and you need to call L<error()|Log::Report::Template/"Template (Toolkit) base-class"> to collect it.

=item template_syntax => 'UNKNOWN'|'HTML'

Linked to L<String::Print::new(encode_for)|String::Print/"Constructors">: the output of the translation
is HTML encoded unless the inserted value name ends on C<_html>.
Read L</"Translation into HTML">

=item textdomain_class => CLASS

Use your own extension to L<Log::Report::Template::Textdomain|Log::Report::Template::Textdomain>.

=item translate_to => LANGUAGE

Globally set the output language of template processing.  Usually, this
is derived from the logged-in user setting or browser setting.
See L<translateTo()|Log::Report::Template/"Attributes">.

=back

=back

=head2 Attributes

=over 4

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

Get the C<String::Print> object which formats the messages.

=item $obj-E<gt>B<translateTo>( [$language] )

=back

=head2 Handling text domains

=over 4

=item $obj-E<gt>B<addTextdomain>(%options)

Create a new L<Log::Report::Template::Textdomain|Log::Report::Template::Textdomain> object.
See its C<new()> method for the options.

Additional facts about the options: you may specify C<only_in_directory>
as a path. Those directories must be in the INCLUDE_PATH as well.
The (domain) C<name> must be unique, and the C<function> not yet in use.

When the code also uses this textdomain, then that configuration will
get extended with this configuration.

example: 

  my $domain = $templater->addTextdomain(
    name     => 'my-project',
    function => 'loc',   # default
  );

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

Returns the textdomain with the specified C<$name>.

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

Returns a LIST with all defined textdomains, unsorted.

=item $obj-E<gt>B<extract>(%options)

Extract message ids from the templates, and register them to the lexicon.
Read section L</"Extracting PO-files"> how to use this method.

Show statistics will be show when the Log::Report more is VERBOSE or
DEBUG.

 -Option        --Default
  charset         'UTF-8'
  filename_match  qr/\.tt2?$/
  filenames       undef
  write_tables    <true>

=over 2

=item charset => CHARSET

=item filename_match => RegEx

Process all files from the INCLUDE_PATH directories which match this
regular expression.

=item filenames => FILENAME|ARRAY

By default, all filenames from the INCLUDE_PATH directories which match
the C<filename_match> are processed, but you may explicitly create a
subset by hand.

=item write_tables => BOOLEAN

When false, the po-files will not get updated.

=back

=back

=head2 Template filters

Some common activities in templates are harder when translation is
needed.  A few TT filters are provided to easy the process.

=over 4

=item Filter: cols

A typical example of an HTML component which needs translation is

  <tr><td>Price:</td><td>20 £</td></tr>

Both the price text as value need to be translated.  In plain perl
(with Log::Report) you would write

  __x"Price: {price £}", price => $product->price   # or
  __x"Price: {p.price £}", p => $product;

In HTML, there seems to be the need for two separate translations,
may in the program code.  This module (actually L<String::Print|String::Print>)
can be trained to convert money during translation, because '£'
is a modifier.  The translation for Dutch (via a PO table) could be

   "Prijs: {p.price €}"

SO: we want to get both table fields in one translation.  Try this:

  <tr>[% loc("Price:\t{p.price £}" | cols %]</tr>

In the translation table, you have to place the tabs (backslash-t) as
well.

There are two main forms of C<cols>.  The first form is the containerizer:
pass 'cols' a list of container names.  The fields in the input string
(as separated by tabs) are wrapped in the named container.  The last
container name will be reused for all remaining columns.  By default,
everything is wrapped in 'td' containers.

  "a\tb\tc" | cols             <td>a</td><td>b</td><td>c</td>
  "a\tb\tc" | cols('td')       same
  "a\tb\tc" | cols('th', 'td') <th>a</th><td>b</td><td>c</td>
  "a"       | cols('div')      <div>a</div>
  loc("a")  | cols('div')      <div>xxxx</div>

The second form has one pattern, which contains (at least one) '$1'
replacement positions.  Missing columns for positional parameters
will be left blank.

  "a\tb\tc" | cols('#$3#$1#')  #c#a#
  "a"       | cols('#$3#$1#')  ##a#
  loc("a")  | cols('#$3#$1#')  #mies#aap#

=item Filter: br

Some translations will produce more than one line of text.  Add
'<br>' after each of them.

  [% loc('intro-text') | br %]
  [% | br %][% intro_text %][% END %]
  [% FILTER br %][% intro_text %][% END %]

=back

=head2 Formatter value modifiers

Modifiers simplify the display of values.  Read the section about
modifiers in L<String::Print|String::Print>.  Here, only some examples are shown.

You can achieve the same transformation with TT vmethods, or with the
perl code which drives your website.  The advantange is that you can
translate them.  And they are quite readible.

=over 4

=item POSIX format C<%-10s>, C<%2.4f>, etc

Exactly like format of the perl's internal C<printf()> (which is
actually being called to do the formatting)

Examples:

 # pi in two decimals
 [% loc("π = {pi %.2f}", pi => 3.14157) %]

 # show int, no fraction. filesize is a template variable
 [% loc("file size {size %d}", size => filesize + 0.5) %]

=item BYTES

Convert a file size into a nice human readible format.

Examples:

  # filesize and fn are passed as variables to the templater
  [% loc("downloaded {size BYTES} {fn}\n", size => fs, fn => fn) %]
  # may produce:   "  0 B", "25 MB", "1.5 GB", etc

=item Time-formatting YEAR, DATE, TIME, DT

Accept various time syntaxes as value, and translate them into
standard formats: year only, date in YYYY-MM-DD, time as 'HH::MM::SS',
and various DateTime formats:

Examples:

  # shows 'Copyright 2017'
  [% loc("Copyright {today YEAR}", today => '2017-06-26') %]
 
  # shows 'Created: 2017-06-26'
  [% loc("Created: {now DATE}", now => '2017-06-26 00:24:15') %]
  
  # shows 'Night: 00:24:15'
  [% loc("Night: {now TIME}", now => '2017-06-26 00:24:15') %]
  
  # shows 'Mon Jun 26 00:28:50 CEST 2017'
  [% loc("Stamp: {now DT(ASC)}", now => 1498429696) %]

=item Default //"string", //'string', or //word

When a parameter has no value or is an empty string, the word or
string will take its place.

  [% loc("visitors: {count //0}", count => 3) %]
  [% loc("published: {date DT//'not yet'}", date => '') %]
  [% loc("copyright: {year//2017 YEAR}", year => '2018') %]
  [% loc("price: {price//5 EUR}", price => product.price %]
  [% loc("price: {price EUR//unknown}", price => 3 %]

=back

=head2 Template (Toolkit) base-class

The details of the following functions can be found in the Template
manual page.  They are included here for reference only.

=over 4

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

If the 'processing_errors' option is 'NATIVE' (default), you have to
collect the error like this:

  $tt->process($template_fn, $vars, ...)
     or die $tt->error;

When the 'procesing_errors' option is set to 'EXCEPTION', the error is
translated into a L<Log::Report::Exception|Log::Report::Exception>:

  use Log::Report;
  try { $tt->process($template_fn, $vars, ...) };
  print $@->wasFatal if $@;

In the latter solution, the try() is probably only on the level of the
highest level: the request handler which catches all kinds of serious
errors at once.

=item $obj-E<gt>B<process>( $template, [\%vars, $output, \%options] )

Process the C<$template> into C<$output>, filling in the C<%vars>.

=back

=head1 DETAILS

=head2 Textdomains

This module uses standard gettext PO-translation tables via the
L<Log::Report::Lexicon|Log::Report::Lexicon> distribution.  An important role here is
for the 'textdomain': the name of the set of translation tables.

For code, you say "use Log::Report '<textdomain>;" in each related
module (pm file).  We cannot do achieve comparible syntax with
Template Toolkit: you must specify the textdomain before the
templates get processed.

Your website may contain multiple separate sets of templates.  For
instance, a standard website implementation with some local extensions.
The only way to get that to work, is by using different translation
functions: one textdomain may use 'loc()', where an other uses 'L()'.

=head3 Integration with Template::Toolkit

Instead of Template, from Template::Toolkit, you use its extension
L<Log::Report::Template|Log::Report::Template>.

  # during initiation of the webserver, once in your script (before fork)
  my $lexicons   = 'some-directory-for-translation-tables';
  my $pots = Log::Report::Translator::POT->new(lexicons => $lexicons);

  my $templater  = Log::Report::Template->new(...);
  my $domain     = $templater->addTextdomain(
      name     => $domainname,
      function => 'loc',
  );
  $domain->configure(translator => $pots);

  # part of the processing per page
  $vars{translate_to} = 'nl_NL.utf8';
  $templater->process($template, \%vars, \$output);

When you use the same domain for both templates as source code, then be
aware that there is only one place where you can configure the domain.
This may be in the code.  When you use a separate domain for the templates,
then you configure as shown above.

=head3 Template::Toolkit in Dancer2

When you use Dancer2, you need to connect the text domain with

  my $domain = (engine 'template')->addTextdomain(
      name       => 'isaas',
      function   => 'loc',
  );

And in file C<config.ini>:

  template: "TTLogReport"
  engines:
    template:
      TTLogReport:

This "TTLogReport" refers to module L<Dancer2::Template::TTLogReport|Dancer2::Template::TTLogReport>, which is
part of distribution C<Log-Report>.

=head2 Supported syntax

=head3 Translation syntax

Let say that your translation function is called 'loc', which is the
default name.  Then, you can use that name as simple function.

In these examples, C<PAIRS> is a list of values to be inserted in the
C<msgid> string. When the C<msgid> is specified with a C<plural> alternative,
then a C<COUNTER> value is required to indicate which alternative is
required.

  [% loc("msgid", PAIRS) %]
  [% loc('msgid', PAIRS) %]
  [% loc("msgid|plural", COUNTER, PAIRS) %]
  [% loc("msgid|plural", _count => COUNTER, PAIRS) %]
 
  [% INCLUDE
       title = loc('something')
   %]

But also as filter.  Although filters and functions work differently
internally in Template Toolkit, it is convenient to permit both syntaxes.

  [% | loc(PAIRS) %]msgid[% END %]
  [% 'msgid' | loc(PAIRS) %]
  [% "msgid" | loc(PAIRS) %]
  
  [% "msgid|plural" | loc(COUNTER, PAIRS) %]
  [% "msgid|plural" | loc(_count => COUNTER, PAIRS) %]
  [% FILTER loc %]msgid[% END %]
  [% FILTER loc(COUNTER, PAIRS) %]msgid|plural[% END %]

As examples

  [% loc("hi {n}", n => name) %]
  [% | loc(n => name) %]hi {n}[% END %]
  [% "hi {n}" | loc(n => name) %]
  [% loc("one person|{_count} people", size) %]
  [% | loc(size) %]one person|{_count} people[% END %]
  [% 'one person|{_count} people' | loc(size) %]

These syntaxes work exacly like translations with Log::Report for your
Perl programs.  Compare this with:

  __x"hi {n}", n => name;    # equivalent to
  __x("hi {n}", n => name);  # replace __x() by loc()

=head3 Translation syntax, more magic

With TT, we can add a simplificition which we cannot offer for Perl
translations: TT variables are dynamic and stored in the stash which
we can access.  Therefore, we can lookup "accidentally" missed parameters.

  [% SET name = 'John Doe' %]
  [% loc("Hi {name}", name => name) %]  # looks silly
  [% loc("Hi {name}") %]                # uses TT stash directly

Sometimes, computation of objects is expensive: you never know.  So, you
may try to avoid repeated computation.  In the follow example, "soldOn"
is collected/computed twice:

  [% IF product.soldOn %]
  <td>[% loc("Sold on {product.soldOn DATE}")</td>
  [% END %]

The performance is predictable optimal with:

  [% sold_on = product.soldOn; IF sold_on %]
  <td>[% loc("Sold on {sold_on DATE}")</td>
  [% END %]

=head3 Translation into HTML

Usually, when data is passed from the program's internal to the template,
it should get encoded into HTML to escape some characters.  Typical TT
code:

  Title&gt; [% title | html %]

When your insert is produced by the localizer, you can do this as well
(set C<template_syntax> to 'UNKNOWN' first)

  [% loc("Title> {t}", t => title) | html %]

The default TT syntax is 'HTML', which will circumvent the need to
use the html filter.  In that default case, you only say:

  [% loc("Title> {t}", t => title) %]
  [% loc("Title> {title}") %]  # short form, see previous section

When the title is already escaped for HTML, you can circumvent that
by using tags which end on 'html':

  [% loc("Title> {t_html}", t_html => title) %]

  [% SET title_html = html(title) %]
  [% loc("Title> {title_html}") %]

=head2 Extracting PO-files

You may define a textdomain without doing any translations (yet)  However,
when you start translating, you will need to maintain translation tables
which are in PO-format.  PO-files can be maintained with a wide variety
of tools, for instance poedit, Pootle, virtaal, GTranslator, Lokalize,
or Webtranslateit.

=head3 Setting-up translations

Start with desiging a domain structure.  Probably, you want to create
a separate domain for the templates (external texts in many languages)
and your Perl program (internal texts with few languages).

Pick a lexicon directory, which is also inside your version control setup,
for instance your GIT repository.  Some po-editors can work together
with various version control systems.

Now, start using this module.  There are two ways: either by creating it
as object, or by extension.

  ### As object
  # Somewhere in your code
  use Log::Report::Template;
  my $templater = Log::Report::Template->new(%config);
  $templater->addTextdomain(...);

  $templater->process('template_file.tt', \%vars); # runtime
  $templater->extract(...);    # rarely, "off-line"

Some way or another, you want to be able to share the creation of the
templater and configuration of the textdomain between the run-time use
and the irregular (off-line) extraction of msgids.

The alternative is via extension:

  ### By extension
  # Somewhere in your code:
  use My::Template;
  my $templater = My::Template->new;
  $templater->process('template_file.tt', \%vars);
  
  # File lib/My/Template.pm
  package My::Template;
  use parent 'Log::Report::Template';

  sub init($) {
     my ($self, $args) = @_;
     # add %config into %$args
     $self->SUPER::init($args);
     $self->addTextdomain(...);
     $self;
  }

  1;

The second solution requires a little bit of experience with OO, but is
easier to maintain and to share.

=head3 adding a new language

The first time you run L<extract()|Log::Report::Template/"Handling text domains">, you will see a file being created
in C<$lexicon/$textdomain-$charset.po>.  That file will be left empty:
copy it to start a new translation.

There are many ways to structure PO-files.  Which structure used, is
detected automatically by L<Log::Report::Lexicon|Log::Report::Lexicon>.  My personal preference 
is C<$lexicon/$textdomain/$language-$charset.po>.  On Unix-like systems,
you would do:

  # Start a new language
  mkdir mylexicon/mydomain
  cp mylexicon/mydomain-utf8.po mylexicon/mydomain/nl_NL-utf8.po 
  
  # fill the nl_NL-utf8.po file with the translation
  poedit mylexicon/mydomain/nl_NL-utf8.po
  
  # add the file to your version control system
  git add mylexicon/mydomain/nl_NL-utf8.po
  
Now, when your program sets the locale to 'nl-NL', it should start
translating to Dutch.  If it doesn't, it is not always easy to
figure-out what is wrong...

=head3 Keeping translations up to date

You have to call L<extract()|Log::Report::Template/"Handling text domains"> when msgids have changed or added,
to have the PO-tables updated.  The language specific tables will
get updated automatically... look for msgids which are 'fuzzy'
(need update)

You may also use the external program C<xgettext-perl>, which is
shipped with the L<Log::Report::Lexicon|Log::Report::Lexicon> distribution.

=head3 More performance via MO-files

PO-files are quite large.  You can reduce the translation table size by
creating a binary "MO"-file for each of them. L<Log::Report::Lexicon|Log::Report::Lexicon>
will prefer mo files, if it encounters them, but generation is not (yet)
organized via Log::Report components.  Search for "msgfmt" as separate
tool or CPAN module.

=head1 SEE ALSO

This module is part of Log-Report-Template distribution version 1.02,
built on July 29, 2025. Website: F<http://perl.overmeer.net/CPAN/>

=head1 LICENSE

Copyrights 2017-2025 by [Mark Overmeer <markov@cpan.org>]. 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://dev.perl.org/licenses/>

