use 5.008008;
use strict;
use warnings;
use ExtUtils::MakeMaker;

# Now care for our 'conf' files and others
our $additional =    {
    # In toplevel directory 'conf', take these 'files', install into 'target'
    # and eventually set permission for them.
    conf    =>  {
        files   =>  [qw(
            conf/foo.ini
            conf/bar.conf
            conf/template.txt
        )],
        target  =>  '$(INSTALLSITELIB)/../conf', # Relative to site lib
        perms   =>  644,
    },
};

# Then the WriteMakefile call
WriteMakefile(
    NAME              => 'Foo::Bar',
    AUTHOR            => 'Me <me@my.com>',
    ABSTRACT_FROM     => 'lib/Foo/Bar.pm',
    VERSION_FROM      => 'bin/footsie', # finds $VERSION
    PREREQ_PM         => {
        'Carp'              =>  0,
        'Cwd'               =>  0,
        'Data::Dumper'      =>  0,
    ...
};

package MY;

#-------------------------
# I use the $additional hashref to write the values.
# By overriding post_constants I create my own variables into the makefile.
# These are (e.g. if we use files of toplevel directory 'key'):
# INSTALL_KEY_DIR = target_stanza_of_$additional_for_key
# KEY_FILES = files_stanza_of_$additional_for_key
sub MY::post_constants {
    my $return_string;
    foreach my $add_dir ( keys %$additional ){
        my @files   =   @{ $additional->{$add_dir}->{'files'} };
        my $target  =   $additional->{$add_dir}->{'target'};
        $return_string .= 'INSTALL_' . uc($add_dir) . '_DIR = ' . $target . "\n"
                        . uc($add_dir) . "_FILES = @files\n";
    };
    return $return_string;
};

#-------------------------
# The postamble stores for each toplevel directory 'key' mentioned as key
# in variable $additional the following entry:
#   install :: install.keyfiles
#
#   install.keyfiles :: $(KEY_FILES)
#       $(MKPATH) $(INSTALL_KEY_DIR)
#       $(CP) $(KEY_FILES) $(INSTALL_KEY_DIR)
#       $(CHMOD) 644 $(INSTALL_KEY_DIR)/*
sub MY::postamble {
    my $self = shift;
    my $return_string;
    foreach my $add_dir ( keys %$additional ){
        my $identifyer  =   'install.' . lc $add_dir . 'files'; # Like install.conffiles
        my $target_dir  =   'INSTALL_' . uc($add_dir) . '_DIR'; # Like INSTALL_CONF_DIR
        my $files       =   uc($add_dir) . "_FILES";            # Like CONF_FILES
        $return_string .=   "install :: $identifyer\n\n"
                        .   $identifyer . ' :: $(' . $files . ')' . "\n"
                        .   "\t\$(MKPATH) \$($target_dir)\n"
                        .   "\t\$(CP) \$($files) \$($target_dir)\n";

        # If we find a permission to set => do it.
        if ( exists $additional->{$add_dir}->{'perms'} ){
            my $perm = $additional->{$add_dir}->{'perms'};
            $return_string .=   "\t\$(CHMOD) $perm \$($target_dir)/*\n";
        };
    };
    return $return_string;
};

##</code><code>##

# --- MakeMaker post_constants section:
INSTALL_CONF_DIR = $(INSTALLSITELIB)/../conf
CONF_FILES = conf/foo.ini conf/bar.conf conf/template.txt

# --- MakeMaker postamble section:
install :: install.conffiles

install.conffiles :: $(CONF_FILES)
    $(MKPATH) $(INSTALL_CONF_DIR)
    $(CP) $(CONF_FILES) $(INSTALL_CONF_DIR)
    $(CHMOD) 644 $(INSTALL_CONF_DIR)/*