#!/usr/bin/perl

use strict;
use warnings;

use File::Basename;
use List::MoreUtils qw(firstidx);

my $VM_STAT = "/usr/bin/vm_stat";

my $vm_stat = 0;
my $human = 0;    # TODO: -h
my $scale;
my $unit = 1024;  # TODO: --si
my $page_size;
my %mem = ( );

if (basename($0) eq "vm_stat") {
    $vm_stat = 1;
}

if (@ARGV > 0) {
    # TODO: use Getopt::Long
    # TODO: add --help, --version
    # TODO: add --old, --total, --lohi, --seconds, --count
    # TODO: add --bytes, --kilo, --mega, --giga
    my @params = qw(-b -k -m -g --tera);
    my $idx = firstidx { $_ eq $ARGV[0] } @params;
    if ($idx == -1) { $idx = 1 };
    $scale = $unit ** $idx;
}

if ($vm_stat && !defined $scale) {
    exec $VM_STAT or die;
}

unless ($scale) {
    $scale = $unit;
}

open(PIPE, "-|", $VM_STAT);
my %vm = ( );

while(<PIPE>) {
    /page size of (\d+)/ and $page_size = $1;

    if ($vm_stat) {
        /Pages\s+([^:]+)[^\d]+(\d+)/ and printf("%-16s % 16d\n", "$1:", $2 * $page_size / $scale);
    } else {
        my @keys = ( "free", "active", "inactive", "speculative", "wired down" );
        foreach my $key (@keys) {
            /Pages $key[^\d]+(\d+)/ and $vm{$key} = $1 * $page_size;
        }

    }
}

close(PIPE);

unless ($vm_stat) {
    `sysctl hw.memsize` =~ /(\d+)/ and $mem{total} = $1;
    $mem{free}             = $vm{free} + $vm{speculative};
    $mem{used}             = $vm{'wired down'} + $vm{active} + $vm{inactive};
    $mem{shared}           = 0;
    $mem{buffers}          = 0;
    $mem{cached}           = $vm{inactive};
    $mem{no_cache_used}    = $vm{'wired down'} + $vm{active};
    $mem{no_cache_free}    = $mem{total} - $mem{no_cache_used};

    # alternative for total
    #while (my $swapfile = </private/var/vm/swapfile*>) {
    #    $mem{swap_total}      += (stat($swapfile))[7];
    #}

    foreach my $key ( qw(total used free) ) {
        if (`sysctl vm.swapusage` =~ /$key = ([0-9.]+)/) {
            $mem{"swap_$key"} = $1 * 1048576;
        }
    }

    foreach my $key ( keys %mem ) {
        $mem{$key} /= $scale;
    }

    my @keys = qw(total used free shared buffers cached);
    printf("%7s", "");
    foreach my $key (@keys) {
        printf("%11s", $key);
    }
    print("\n");

    printf("%7s", "Mem:");
    foreach my $key (@keys) {
        printf("%11d", $mem{$key});
    }
    print("\n");

    print("+/- buffers/cache:");
    printf("%11d", $mem{no_cache_used});
    printf("%11d", $mem{no_cache_free});
    print("\n");

    printf("%7s", "Swap:");
    printf("%11d", $mem{swap_total});
    printf("%11d", $mem{swap_used});
    printf("%11d", $mem{swap_free});
    print("\n");

}