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

use MIME::Base64 qw(encode_base64);
use File::Basename qw(basename);

sub usage {
    die "Usage: $0 --to TO --from FROM --subject SUBJECT --body BODY file1 [file2 ...]\n";
}

my ($to, $from, $subject, $body);
my @files;

while (@ARGV) {
    my $a = shift @ARGV;

    if ($a eq '--to')       { $to       = shift @ARGV // usage(); }
    elsif ($a eq '--from') { $from     = shift @ARGV // usage(); }
    elsif ($a eq '--subject') { $subject = shift @ARGV // usage(); }
    elsif ($a eq '--body') { $body     = shift @ARGV // usage(); }
    else { push @files, $a; }
}

usage() unless defined $to && defined $from && defined $subject && defined $body;
usage() unless @files >= 1;

my $boundary = "BOUNDARY_" . time . "_" . int(rand(1_000_000));

print "From: $from\n";
print "To: $to\n";
print "Subject: $subject\n";
print "MIME-Version: 1.0\n";
print "Content-Type: multipart/mixed; boundary=\"$boundary\"\n\n";

print "--$boundary\n";
print "Content-Type: text/plain; charset=UTF-8\n\n";
print "$body\n\n";

for my $file (@files) {
    if (!-f $file) {
        warn "Skipping missing file: $file\n";
        next;
    }

    my $fname = basename($file);
    open(my $fh, "<", $file) or die "Cannot open $file: $!";
    binmode($fh);
    local $/;
    my $raw = <$fh>;
    close($fh);

    my $b64 = encode_base64($raw, ""); # no newlines

    print "--$boundary\n";
    print "Content-Type: application/octet-stream; name=\"$fname\"\n";
    print "Content-Disposition: attachment; filename=\"$fname\"\n";
    print "Content-Transfer-Encoding: base64\n\n";
    print $b64;
    print "\n\n";
}

print "--$boundary--\n";