# For internal Module::CoreList use only.
package Module::CoreList::TieHashDelta;
use strict;
use vars qw($VERSION);

$VERSION = "3.03";

sub TIEHASH {
my ($class, $changed, $removed, $parent) = @_;

return bless {
changed => $changed,
removed => $removed,
parent => $parent,
keys_inflated => 0,
}, $class;
}

sub FETCH {
my ($self, $key) = @_;

if (exists $self->{changed}{$key}) {
return $self->{changed}{$key};
} elsif (exists $self->{removed}{$key}) {
return undef;
} elsif (defined $self->{parent}) {
return $self->{parent}{$key};
}
return undef;
}

sub EXISTS {
my ($self, $key) = @_;

if (exists $self->{changed}{$key}) {
return 1;
} elsif (exists $self->{removed}{$key}) {
return '';
} elsif (defined $self->{parent}) {
return exists $self->{parent}{$key};
}
return '';
}

sub FIRSTKEY {
my ($self) = @_;

if (not $self->{keys_inflated}) {
# This inflates the whole set of hashes... Somewhat expensive, but saves
# many tied hash calls later.
my @parent_keys;
if (defined $self->{parent}) {
@parent_keys = keys %{$self->{parent}};
}

@parent_keys = grep !exists $self->{removed}{$_}, @parent_keys;
for my $key (@parent_keys) {
next if exists $self->{changed}->{$key};
$self->{changed}{$key} = $self->{parent}{$key};
}

$self->{keys_inflated} = 1;
}

keys %{$self->{changed}}; # reset each
$self->NEXTKEY;
}

sub NEXTKEY {
my ($self) = @_;
each %{$self->{changed}};
}

1;