package SQL::Translator::Producer::TT::Base;

=pod

=head1 NAME

SQL::Translator::Producer::TT::Base - TT (Template Toolkit) based Producer base
class.

=cut

use strict;
use warnings;

our @EXPORT_OK;
our $VERSION = '1.59';

use Template;
use Data::Dumper;
use IO::Handle;
use Exporter;
use base qw(Exporter);
@EXPORT_OK = qw(produce);

use SQL::Translator::Utils 'debug';

# Hack to convert the produce call into an object. ALL sub-classes need todo
# this so that the correct class gets created.
sub produce {
    return __PACKAGE__->new( translator => shift )->run;
};

sub new {
    my $proto = shift;
    my $class = ref $proto || $proto;
    my %args  = @_;

    my $me = bless {}, $class;
    $me->{translator} = delete $args{translator} || die "Need a translator.";

    return $me;
}

sub translator { shift->{translator}; }
sub schema     { shift->{translator}->schema(@_); }

# Util args access method.
# No args - Return hashref (the actual hash in Translator) or hash of args.
# 1 arg   - Return that named args value.
# Args    - List of names. Return values of the given arg names in list context
#           or return as hashref in scalar context. Any names given that don't
#           exist in the args are returned as undef.
sub args {
    my $me = shift;

    # No args
    unless (@_) {
        return wantarray
            ? %{ $me->{translator}->producer_args }
            : $me->{translator}->producer_args
        ;
    }

    # 1 arg. Return the value whatever the context.
    return $me->{translator}->producer_args->{$_[0]} if @_ == 1;

    # More args so return values list or hash ref
    my %args = %{ $me->{translator}->producer_args };
    return wantarray ? @args{@_} : { map { ($_=>$args{$_}) } @_ };
}

# Run the produce and return the result.
sub run {
    my $me = shift;
    my $scma = $me->schema;
    my %args = %{$me->args};
    my $tmpl = $me->tt_schema or die "No template!";

    debug "Processing template $tmpl\n";
    my $out;
    my $tt = Template->new(
        #DEBUG    => $me->translator->debug,
        ABSOLUTE => 1,  # Set so we can use from the command line sensibly
        RELATIVE => 1,  # Maybe the cmd line code should set it! Security!
        $me->tt_config, # Hook for sub-classes to add config
        %args,          # Allow any TT opts to be passed in the producer_args
    ) || die "Failed to initialize Template object: ".Template->error;

    $tt->process( $tmpl, {
        $me->tt_default_vars,
        $me->tt_vars,          # Sub-class hook for adding vars
    }, \$out )
    or die "Error processing template '$tmpl': ".$tt->error;

    return $out;
}


# Sub class hooks
#-----------------------------------------------------------------------------

sub tt_config { () };

sub tt_schema {
    my $me = shift;
    my $class = ref $me;

    my $file = $me->args("ttfile");
    return $file if $file;

    no strict 'refs';
    my $ref = *{"$class\:\:DATA"}{IO};
    if ( $ref->opened ) {
        local $/ = undef; # Slurp mode
        return \<$ref>;
    }

    undef;
};

sub tt_default_vars {
    my $me = shift;
    return (
        translator => $me->translator,
        schema     => $me->pre_process_schema($me->translator->schema),
    );
}

sub pre_process_schema { $_[1] }

sub tt_vars   { () };

1;

=pod

=head1 SYNOPSIS

 # Create a producer using a template in the __DATA__ section.
 package SQL::Translator::Producer::Foo;

 use base qw/SQL::Translator::Producer::TT::Base/;

 # Convert produce call into a method call on our new class
 sub produce { return __PACKAGE__->new( translator => shift )->run; };

 # Configure the Template object.
 sub tt_config { ( INTERPOLATE => 1 ); }

 # Extra vars to add to the template
 sub tt_vars { ( foo => "bar" ); }

 # Put template in DATA section (or use file with ttfile producer arg)
 __DATA__
 Schema

 Database: [% schema.database %]
 Foo: $foo
 ...

=head1 DESCRIPTION

A base class producer designed to be sub-classed to create new TT based
producers cheaply - by simply giving the template to use and sprinkling in some
extra template variables and config.

You can find an introduction to this module in L<SQL::Translator::Manual>.

The 1st thing the module does is convert the produce sub routine call we get
from SQL::Translator into a method call on an object, which we can then
sub-class. This is done with the following code which needs to appear in B<all>
sub classes.

 # Convert produce call into an object method call
 sub produce { return __PACKAGE__->new( translator => shift )->run; };

See L<PRODUCER OBJECT> below for details.

The upshot of this is we can make new template producers by sub classing this
base class, adding the above snippet and a template.
The module also provides a number of hooks into the templating process,
see L<SUB CLASS HOOKS> for details.

See the L<SYNOPSIS> above for an example of creating a simple producer using
a single template stored in the producers DATA section.

=head1 SUB CLASS HOOKS

Sub-classes can override these methods to control the templating by giving
the template source, adding variables and giving config to the Tempate object.

=head2 tt_config

 sub tt_config { ( INTERPOLATE => 1 ); }

Return hash of Template config to add to that given to the L<Template> C<new>
method.

=head2 tt_schema

 sub tt_schema { "foo.tt"; }
 sub tt_schema { local $/ = undef; \<DATA>; }

The template to use, return a file name or a scalar ref of TT
source, or an L<IO::Handle>. See L<Template> for details, as the return from
this is passed on to it's C<produce> method.

The default implementation uses the producer arg C<ttfile> as a filename to read
the template from. If the arg isn't there it will look for a C<__DATA__> section
in the class, reading it as template source if found. Returns undef if both
these fail, causing the produce call to fail with a 'no template!' error.

=head2 tt_vars

 sub tt_vars { ( foo => "bar" ); }

Return hash of template vars to use in the template. Nothing added here
by default, but see L<tt_default_vars> for the variables you get for free.

=head2 tt_default_vars

Return a hash-ref of the default vars given to the template.
You wouldn't normally over-ride this, just inherit the default implementation,
to get the C<translator> & C<schema> variables, then over-ride L<tt_vars> to add
your own.

The current default variables are:

=over 4

=item schema

The schema to template.

=item translator

The L<SQL::Translator> object.

=back

=head2 pre_process_schema

WARNING: This method is Experimental so may change!

Called with the L<SQL::Translator::Schema> object and should return one (it
doesn't have to be the same one) that will become the C<schema> variable used
in the template.

Gets called from tt_default_vars.

=head1 PRODUCER OBJECT

The rest of the methods in the class set up a sub-classable producer object.
You normally just inherit them.

=head2 new

 my $tt_producer = TT::Base->new( translator => $translator );

Construct a new TT Producer object. Takes a single, named arg of the
L<SQL::Translator> object running the translation. Dies if this is not given.

=head2 translator

Return the L<SQL::Translator> object.

=head2 schema

Return the L<SQL::Translator::Schema> we are translating. This is equivalent
to C<< $tt_producer->translator->schema >>.

=head2 run

Called to actually produce the output, calling the sub class hooks. Returns the
produced text.

=head2 args

Util wrapper method around C<< TT::Base->translator->producer_args >> for
(mostly) readonly access to the producer args. How it works depends on the
number of arguments you give it and the context.

 No args - Return hashref (the actual hash in Translator) or hash of args.
 1 arg   - Return value of the arg with the passed name.
 2+ args - List of names. In list context returns values of the given arg
           names, returns as a hashref in scalar context. Any names given
           that don't exist in the args are returned as undef.

This is still a bit messy but is a handy way to access the producer args when
you use your own to drive the templating.

=head1 SEE ALSO

L<perl>,
L<SQL::Translator>,
L<Template>.

=head1 TODO

- Add support for a sqlf template repository, set as an INCLUDE_PATH,
so that sub-classes can easily include file based templates using relative
paths.

- Pass in template vars from the producer args and command line.

- Merge in TT::Table.

- Hooks to pre-process the schema and post-process the output.

=head1 AUTHOR

Mark Addison E<lt>grommit@users.sourceforge.netE<gt>.

=cut
