#!/usr/bin/env perl

use Carp;
use DBI;
use strict;
use warnings;

eval {
    my $DBH=DBI->connect('dbi:SQLite:Library.sqlite','','',{ PrintError=>1, RaiseError=>1 });
    $DBH->do("DROP TABLE IF EXISTS packages;");
    $DBH->do("CREATE TABLE packages (
                package text,
                body text,
                unique (package)
                );");
    my $STH=$DBH->prepare("INSERT INTO packages (package,body) VALUES (?,?);");
    print "Inserting package 'A'\n";
    $STH->execute('A',<<'__A__');
package A;

use Carp;
use strict;
use warnings;
use A::B;

sub sub_a {
    Carp::cluck '...';
    A::B::sub_b();
    }
    1;
__A__
    print "Inserting package 'A::B'\n";
    $STH->execute('A::B',<<'__A::B__');
package A::B;

use Carp;
use strict;
use warnings;

sub sub_b {
    Carp::cluck '...';
    };

    1;
__A::B__
    $STH->finish;
    $DBH->disconnect;
    };
if (my $error=$@) {
    Carp::confess $error;
    };

print "$0 completed."
__END__

##</code><code>##

package A;

use Carp;
use strict;
use warnings;
use A::B;

sub sub_a {
    Carp::cluck '...';
    A::B::sub_b();
    }
    1;

##</code><code>##

package A::B;

use Carp;
use strict;
use warnings;

sub sub_b {
    Carp::cluck '...';
    };

    1;

##</code><code>##

package dbLoader;

use Carp;
use Data::Dumper;
use DBI;
use Scalar::Util;
use strict;
use warnings;
use feature 'state';

    sub import {
        my $self=shift;
        return;
        }; # import:

my $KNOWN_PACKAGES_HREF;
my ($DBH,$STH);

{ # INTERNALS:
    sub _dbLoader {
        my (undef,$path_S)=@_;

        s{[/\\]}{::}g, s{\.pm$}{}
            for (my $package_s=$path_S);

        return # unless the package is in the this library
           unless (exists $KNOWN_PACKAGES_HREF->{$package_s});
        warn Data::Dumper->Dump([\$path_S,\$package_s],[qw(*path *package)]),' ';

        my $body_sref;
        eval {
            $STH->execute($package_s);
            if(my $value_aref=$STH->fetchrow_arrayref()) {
                chomp($value_aref->[0]);
                $body_sref=\$value_aref->[0];
                warn "fetched - ",Data::Dumper->Dump([\$body_sref],[qw(*body)]),'';
                $INC{$path_S}="DBI:Pg:$path_S";
                };
            };
        if (my $error=$@) {
            Carp::confess $@;
            }
        elsif (!defined $body_sref) {
            return;
            }
        else {
            open my $fh,'<',$body_sref
                or Carp::confess "Couldn't open string for reading! $!";
            return (
                    sub { #Carp::cluck 'In anonymous sub';
                        if ($_=<$fh>) {
                            warn Data::Dumper->Dump([\$_],[qw(*_)]),' ';
                            return 1;
                            }
                        else {
                            return 0;
                            };
                        } # Anonymous sub:
                    );
            };
        }; # _dbLoader:

    } # INTERNALS:

BEGIN {
    eval {
        $DBH=DBI->connect('dbi:SQLite:Library.sqlite','','',{ PrintError=>1, RaiseError=>1 });

        # Create a (global) hashref of packages/prefixes
        $STH=$DBH->prepare(<<"__SQL__");
            SELECT package FROM packages;
__SQL__
        $STH->execute();
        my $field_aref=$STH->{NAME_lc};
        while (my $value_aref=$STH->fetchrow_arrayref()) {
            my %_h;
            @_h{@$field_aref}=@$value_aref;
            $KNOWN_PACKAGES_HREF->{$_h{package}}=undef;
            };
        $STH->finish();
        warn Data::Dumper->Dump([\$KNOWN_PACKAGES_HREF],[qw(*KNOWN_PACKAGES)]),' ';
        # Statement handle for fetching source(s)
        $STH=$DBH->prepare(<<"__SQL__");
            SELECT body FROM packages WHERE package = ?;
__SQL__
        warn "SELECT prepared";
        unshift @INC,\&_dbLoader;
        warn "Prepended \&_dbLoader to \@INC";
        };
    if (my $error=$@) {
        Carp::confess $@;
        };
    }; # BEGIN:
END {
    print STDERR sprintf("%40s\t%s\n",$_,$INC{$_})
        for (sort grep { $INC{$_} !~ m{^([A-Za-z]:|/)}} keys %INC);
    }; # END:

    1;

##</code><code>##

#!/usr/bin/env perl

use strict;
use warnings;
# Note the order ... "A::B", "A" - this works!
use A::B;
use A;

A::sub_a();
A::B::sub_b();
exit;

##</code><code>##

#!/usr/bin/env perl

use strict;
use warnings;
# Note the order ... "A" with the implicit requir'ing of "A::B" by "A" - this does NOT work
use A;

A::sub_a();
A::B::sub_b();
exit;

##</code><code>##

... at DBI:Pg:A.pm line 8.
        require A.pm called at WorksNot.plx line 6
        main::BEGIN() called at DBI:Pg:A.pm line 0
        eval {...} called at DBI:Pg:A.pm line 0
Can't locate object method "b_b" via package "1" (perhaps you forgot to load "1"?) at DBI:Pg:A.pm line 7.
Compilation failed in require at WorksNot.plx line 6.
BEGIN failed--compilation aborted at WorksNot.plx line 6.
##</code><code>##

            return (
                    $body_sref
                    );

##</code><code>##

            return (
                    $fh,
                   );

##</code><code>##

            return (
                    sub { #Carp::cluck 'In anonymous sub';
                        if ($_=<$fh>) {
                            warn Data::Dumper->Dump([\$_],[qw(*_)]),' ';
                            return 1;
                            }
                        else {
                            return 0;
                            };
                        } # Anonymous sub:
                    );