#!/usr/bin/perl

use strict;
use warnings qw /all/;

# Program picks up files in one directory, and moves them round robin
# to a set of other directories.
# It's required to keep track of directory a file was moved to last.
    
use Fcntl qw /:DEFAULT :flock :seek/;

my $pickup   = "/tmp/main";
my @targets  = map {"/tmp/target/$_"} qw /dir1 dir2 dir3 dir4 dir5 dir
+6/;
my $state    = "/tmp/state";


# Open the state file for read/write, creating it as necessary.
sysopen my $state_h => $state, O_RDWR | O_CREAT, 0666
     or die "Failed to sysopen $state: $!\n";

# Lock the file exclusively. This has the additional effect no other
# invokation will try to move the same files we do.
flock $state_h => LOCK_EX or die "Failed to flock $state: $!\n";
    
# Read the state. If the file didn't exist, this will return undef.
my $last_dir = <$state_h>;
 
# If defined, chomp, and rotate the target directories until we found
# the directory the last file was written to. If not defined, roll one
# directory in the opposite direction.   
if (defined $last_dir) {
    chomp $last_dir;
    push @targets => shift @targets while $last_dir ne $targets [0];
}
else {
    unshift @targets => pop @targets;
}

# Open the pickup directory and read its content.
opendir my $pickup_h => $pickup or die "Failed to opendir $pickup: $!\
+n";
my @files = grep {$_ ne "." && $_ ne ".."} readdir $pickup_h;
closedir $pickup_h;

# For all the files to be moved, roll the target directories so we get
# the next one, and then move the file to the destination. We're assum
+ing
# we work on the same file system and we can use 'rename'.
foreach my $file (@files) {
    push @targets => shift @targets;
    rename "$pickup/$file" => "$targets[0]/$file"
        or  die "Failed to rename $pickup/$file\n";  
}

# Record the last directory we wrote into, and close the file;
# closing the file will release the lock.
seek  $state_h => SEEK_SET, 0 or die "Failed to seek $state: $!\n";
print $state_h $targets [0], "\n";
close $state_h or die "Failed to close $state: $!\n";

exit;
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