=head1 NAME

Template::Provider - repository for compiled templates, loaded from disk.

=head1 SYNOPSIS

    $provider = Template::Provider->new(\%options);

    ($template, $error) = $provider->fetch($name);

=head1 DESCRIPTION

The Template::Provider is used to load, parse, compile and cache template
documents.  This object may be sub-classed to provide more specific 
facilities for loading, or otherwise providing access to templates.

The Template::Context objects maintain a list of Template::Provider 
objects which are polled in turn (via fetch()) to return a requested
template.  Each may return a compiled template, raise an error, or 
decline to serve the reqest, giving subsequent providers a chance to
do so.

This is the "Chain of Responsiblity" pattern.  See 'Design Patterns' for
further information.

This documentation needs work.

=head1 PUBLIC METHODS

=head2 new(\%options) 

Constructor method which instantiates and returns a new Template::Provider
object.  The optional parameter may be a hash reference containing any of
the following items:

=over 4


=item INCLUDE_PATH

The INCLUDE_PATH is used to specify one or more directories in which
template files are located.  When a template is requested that isn't
defined locally as a BLOCK, each of the INCLUDE_PATH directories is
searched in turn to locate the template file.  Multiple directories
can be specified as a reference to a list or as a single string where
each directory is delimited by ':'. The DELIMITER option can be set
to redefine the delimiter value.

    my $provider = Template::Provider->new({
        INCLUDE_PATH => '/usr/local/templates',
    });
  
    my $provider = Template::Provider->new({
        INCLUDE_PATH => '/usr/local/templates:/tmp/my/templates',
    });
  
    my $provider = Template::Provider->new({
        INCLUDE_PATH => [ '/usr/local/templates', 
                          '/tmp/my/templates' ],
    });

=item DELIMITER

Used to provide an alternative delimiter character sequence for 
separating paths specified in the INCLUDE_PATH.  May be useful for 
operating systems that permit the use of ':' in file names.

    # tolerate Silly Billy's file system conventions
    my $provider = Template::Provider->new({
	DELIMITER    => ' ',
        INCLUDE_PATH => 'C:/HERE/NOW D:/THERE/THEN',
    });

    # better solution: install Linux!  :-)

=item ABSOLUTE

The ABSOLUTE flag is used to indicate if templates specified with
absolute filenames (e.g. '/foo/bar') should be processed.  It is
disabled by default and any attempt to load a template by such a
name will cause a 'file' exception to be raised.

    my $provider = Template::Provider->new({
	ABSOLUTE => 1,
    });

    # this is why it's disabled by default
    [% INSERT /etc/passwd %]

=item RELATIVE

The RELATIVE flag is used to indicate if templates specified with
filenames relative to the current directory (e.g. './foo/bar' or
'../../some/where/else') should be loaded.  It is also disabled by
default, and will raise a 'file' error if such template names are
encountered.  

    my $provider = Template::Provider->new({
	RELATIVE => 1,
    });

    [% INCLUDE ../logs/error.log %]

=item DEFAULT

The DEFAULT option can be used to specify a default template which should 
be used whenever a specified template can't be found in the INCLUDE_PATH.

    my $provider = Template::Provider->new({
	DEFAULT => 'notfound.html',
    });

If a non-existant template is requested through the Template process()
method, or by an INCLUDE, PROCESS or WRAPPER directive, then the
DEFAULT template will instead be processed, if defined.  Note that the
DEFAULT template is not used when templates are specified with
absolute or relative filenames, or as a reference to a input file
handle or text string.

=item CACHE_SIZE

The Template::Provider module caches compiled templates to avoid the need
to re-parse template files or blocks each time they are used.  The CACHE_SIZE
option is used to limit the number of compiled templates that the module
should cache.

By default, the CACHE_SIZE is undefined and all compiled templates are
cached.  When set to any positive value, the cache will be limited to
storing no more than that number of compiled templates.  When a new
template is loaded and compiled and the cache is full (i.e. the number
of entries == CACHE_SIZE), the least recently used compiled template
is discarded to make room for the new one.

The CACHE_SIZE can be set to 0 to disable caching altogether.

    my $provider = Template::Provider->new({
	CACHE_SIZE => 64,   # only cache 64 compiled templates
    });

    my $provider = Template::Provider->new({
	CACHE_SIZE => 0,   # don't cache any compiled templates
    });

=item COMPILE_EXT

From version 2 onwards, the Template Toolkit has the ability to
compile templates to Perl code and save them to disk for subsequent
use (i.e. cache persistance).  The COMPILE_EXT option may be
provided to specify a filename extension for compiled template files.
It is undefined by default and no attempt will be made to read or write 
any compiled template files.

    my $provider = Template::Provider->new({
	COMPILE_EXT => '.ttc',
    });

If COMPILE_EXT is defined (and COMPILE_DIR isn't, see below) then compiled
template files with the COMPILE_EXT extension will be written to the same
directory from which the source template files were loaded.

Compiling and subsequent reuse of templates happens automatically
whenever the COMPILE_EXT or COMPILE_DIR options are set.  The Template
Toolkit will automatically reload and reuse compiled files when it 
finds them on disk.  If the corresponding source file has been modified
since the compiled version as written, then it will load and re-compile
the source and write a new compiled version to disk.  

This form of cache persistance offers significant benefits in terms of 
time and resources required to reload templates.  Compiled templates can
be reloaded by a simple call to Perl's require(), leaving Perl to handle
all the parsing and compilation.  This is a Good Thing.

=item COMPILE_DIR

The COMPILE_DIR option is used to specify an alternate directory root
under which compiled template files should be saved.  

    my $provider = Template::Provider->new({
	COMPILE_DIR => '/tmp/ttc',
    });

The COMPILE_EXT option may also be specified to have a consistent file
extension added to these files.  

    my $provider1 = Template::Provider->new({
	COMPILE_DIR => '/tmp/ttc',
	COMPILE_EXT => '.ttc1',
    });

    my $provider2 = Template::Provider->new({
	COMPILE_DIR => '/tmp/ttc',
	COMPILE_EXT => '.ttc2',
    });


When COMPILE_EXT is undefined, the compiled template files have the
same name as the original template files, but reside in a different
directory tree.

Each directory in the INCLUDE_PATH is replicated in full beneath the 
COMPILE_DIR directory.  This example:

    my $provider = Template::Provider->new({
	COMPILE_DIR  => '/tmp/ttc',
	INCLUDE_PATH => '/home/abw/templates:/usr/share/templates',
    });

would create the following directory structure:

    /tmp/ttc/home/abw/templates/
    /tmp/ttc/usr/share/templates/

Files loaded from different INCLUDE_PATH directories will have their
compiled forms save in the relevant COMPILE_DIR directory.

=item TOLERANT

The TOLERANT flag is used by the various Template Toolkit provider
modules (Template::Provider, Template::Plugins, Template::Filters) to
control their behaviour when errors are encountered.  By default, any
errors are reported as such, with the request for the particular
resource (template, plugin, filter) being denied and an exception
raised.  When the TOLERANT flag is set to any true values, errors will
be silently ignored and the provider will instead return
STATUS_DECLINED.  This allows a subsequent provider to take
responsibility for providing the resource, rather than failing the
request outright.  If all providers decline to service the request,
either through tolerated failure or a genuine disinclination to
comply, then a '<resource> not found' exception is raised.

=item PARSER

The Template::Parser module implements a parser object for compiling
templates into Perl code which can then be executed.  A default object
of this class is created automatically and then used by the
Template::Provider whenever a template is loaded and requires 
compilation.  The PARSER option can be used to provide a reference to 
an alternate parser object.

    my $provider = Template::Provider->new({
	PARSER => MyOrg::Template::Parser->new({ ... }),
    });

=back

=head2 fetch($name)

Returns a compiled template for the name specified.  If the template 
cannot be found then (undef, STATUS_DECLINED) is returned.  If an error
occurs (e.g. read error, parse error) then ($error, STATUS_ERROR) is 
returned, where $error is the error message generated.  If the TOLERANT
flag is set the the method returns (undef, STATUS_DECLINED) instead of
returning an error.

=head2 store($name, $template)

Stores the compiled template, $template, in the cache under the name, 
$name.  Susbequent calls to fetch($name) will return this template in
preference to any disk-based file.

=head2 include_path(\@newpath))

Accessor method for the INCLUDE_PATH setting.  If called with an
argument, this method will replace the existing INCLUDE_PATH with
the new value.

=head1 AUTHOR

Andy Wardley E<lt>abw@kfs.orgE<gt>

    http://www.template-toolkit.org/
    http://www.kfs.org/~abw/

=head1 REVISION

$Revision: 1.1 $

=head1 COPYRIGHT

    Copyright (C) 1996-2000 Andy Wardley.  All Rights Reserved.
    Copyright (C) 1998-2000 Canon Research Centre Europe Ltd.

This module is free software; you can redistribute it and/or
modify it under the same terms as Perl itself.


=head1 SEE ALSO


L<Template|Template>