#!/usr/bin/env perl
use strict;
use warnings;

my $usage = "Usage: $0 [-r] pool/dataset\n  -r    include snapshots of child datasets (recursive)\n";
my $recurse = 0;
my $dataset;

while (@ARGV) {
  my $a = shift @ARGV;
  if ($a eq '-r') { $recurse = 1; next }
  if (defined $dataset) { die $usage }
  $dataset = $a;
}

die $usage unless defined $dataset;

my @cmd = ('zfs','list','-t','snapshot','-o','name,used','-H');
push @cmd, '-r' if $recurse;
push @cmd, $dataset;

open my $fh, "-|", @cmd or die "Failed to run zfs: $!\n";

sub parse_size {
  my ($s) = @_;
  return 0 unless defined $s && length $s;
  $s =~ s/,//g;
  if ($s =~ /([0-9.]+)\s*([BKMGTP]?)$/i) {
    my ($n,$u) = ($1, uc $2);
    my %m = ('B' => 1, ''=>1, 'K'=>1024, 'M'=>1024**2, 'G'=>1024**3, 'T'=>1024**4, 'P'=>1024**5);
    return int($n * $m{$u});
  }
  # fallback: try to interpret as integer bytes
  return int($s);
}

sub human {
  my ($n) = @_;
  return "0 B" if $n == 0;
  my @units = qw(B K M G T P);
  my $i = 0;
  while ($n >= 1024 && $i < @units-1) { $n /= 1024; $i++ }
  return sprintf("%.2f %s", $n, $units[$i]);
}

my $sum = 0;
while (my $line = <$fh>) {
  chomp $line;
  next unless $line =~ /\S/;
  my ($name, $used) = split /\s+/, $line, 2;
  $used =~ s/^\s+|\s+$//g if defined $used;
  $sum += parse_size($used);
}
close $fh;

printf "%s (%d bytes)\n", human($sum), $sum;
exit 0