sub Min { my $min=shift; $_<$min and $min=$_ for @_; $min }
sub Max { my $max=shift; $_>$max and $max=$_ for @_; $max }
sub CalcNavigation {
    my %P = ref($_[0]) eq "HASH" ? %{ $_[0] } : ();
    $P{DefaultCount}    = 20 unless defined $P{DefaultCount};
    $P{PrevPages}       = 10 unless defined $P{PrevPages};
    $P{NextPages}       = 10 unless defined $P{NextPages};
    $P{$_}              = 0 for grep {! defined $P{$_}} 
        qw(From Count Records);
    $P{$_} = int($P{$_}) for
        qw(DefaultCount PrevPages NextPages From Count Records);
    $P{DefaultCount}    = Max($P{DefaultCount}, 1);
    $P{Records} = 0 unless $P{Records} > 0;
    $P{From} = Min(Max($P{From}, 1), Max($P{Records}, 1));
    $P{Count}= Max($P{Count}, 0) || $P{DefaultCount};
    $P{Page} = int(($P{From}-1)/$P{Count})+1;
    $P{From} = ($P{Page}-1)*$P{Count}+1;
    $P{To}   = Min($P{From}+$P{Count}-1, $P{Records});
    $P{Prev} = Max($P{From}-$P{Count}, 1);
    $P{Prev} = undef if $P{From} == 1;
    $P{Next} = $P{From}+$P{Count};
    $P{Next} = undef if $P{Next} > $P{Records};
    $P{Pages}= [ map {{
                        Page    => $_,
                        From    => ($_-1)*$P{Count}+1,
                        To      => Min($_*$P{Count}, $P{Records}) 
        }} Max(1, $P{Page}-$P{PrevPages}) .. 
        Min($P{Page}+$P{NextPages}, ($P{Records}-1)/$P{Count}+1) ];
    return \%P;
}