use strict;
use warnings;
use feature 'state', 'say';
use Test::More;
use JSON;

sub calc_rev {
    state %price_by_qty = (
         1 => 15,
         3 => 10,
         6 => 8,
        10 => 5,
    );

    my $qty = shift;
    return 0 if ! $qty;

    for my $level ( sort { $b <=> $a } keys %price_by_qty ) {
        return $qty * $price_by_qty{ $level } if $qty >= $level;
    }
}

#
# mock getting an aref of rows for this test file
my $json = do { local $/; <DATA> };
my $rows = decode_json( $json );
#

my $revenue = 0;

for my $row ( @{ $rows } ) {
    $revenue += calc_rev($row->{total});
}

is( $revenue, 123, 'Revenue is 123. Mwahahahaa!');

done_testing;

__DATA__
[
  {"total":3},
  {"total":6},
  {"total":1},
  {"total":2}
]