=head1 NAME

AnyEvent::MP::Global - network backbone services

=head1 SYNOPSIS

   use AnyEvent::MP::Global;

=head1 DESCRIPTION

This module is usually run (or started on) seed nodes and provides a
variety of services to connected nodes, such as the distributed database.

The global nodes form a fully-meshed network, that is, all global nodes
currently maintain connections to all other global nodes.

Loading this module (e.g. as a service) transforms the local node into a
global node. There are no user-servicable parts inside.

For a limited time, this module also exports some AEMP 1.x compatibility
functions (C<grp_reg>, C<grp_get> and C<grp_mon>).

=cut

package AnyEvent::MP::Global;

use common::sense;
use Carp ();

use AnyEvent ();

use AnyEvent::MP;
use AnyEvent::MP::Kernel;

AE::log 7 => "starting global service.";

#############################################################################
# node protocol parts for global nodes

package AnyEvent::MP::Kernel;

# TODO: this is ugly (classical use vars vs. our),
# maybe this should go into MP::Kernel

our %NODE;
our $NODE;

our $GLOBAL;
our $MASTER;
our $MASTER_MON;
our $MASTER_TIMER;

our %GLOBAL_SLAVE;

our %GLOBAL_DB; # global db
our %LOCAL_DBS; # local databases of other global nodes
our %LOCAL_DB;  # this node database

our $SRCNODE; # the origin node id
our %NODE_REQ;

# only in global code
our %GLOBAL_MON; # monitors {family}

sub other_globals() {
   grep $_ ne $NODE && node_is_up $_, keys %{ $GLOBAL_DB{"'g"} }
}

# broadcasts a message to all other global nodes
sub g_broadcast {
   snd $_, @_
      for other_globals;
}

# add/replace/del inside a family in the database
# @$dle must not contain any key in %$set
sub g_upd {
   my ($node, $family, $set, $del) = @_;

   my $ldb = $LOCAL_DBS{$node}{$family} ||= {};
   my $gdb = $GLOBAL_DB       {$family} ||= {};

   # add/replace keys
   while (my ($k, $v) = each %$set) {
      $ldb->{$k} =
      $gdb->{$k} = $v;
   }

   my @del; # actual deletes

   # take care of deletes
   keydel:
   for my $k (@$del) {
      delete $ldb->{$k};
      delete $gdb->{$k};

      # check if some other node still has the key, then we don't delete, but change
      for (values %LOCAL_DBS) {
         if (exists $_->{$family}{$k}) {
            $set->{$k} = $gdb->{$k} = $_->{$family}{$k};

            next keydel;
         }
      }

      push @del, $k;
   }

   # family could be empty now
   delete $GLOBAL_DB{$family} unless %$gdb;
   delete $LOCAL_DBS{$node}{$family} unless %$ldb;

   g_broadcast g_upd => $family, $set, \@del
      if exists $GLOBAL_SLAVE{$node};

   # tell subscribers we have changed the family
   snd $_ => g_chg2 => $family, $set, \@del
      for keys %{ $GLOBAL_MON{$family} };
}

# set the whole (node-local) database - previous value must be empty
sub g_set($$) {
   my ($node, $db) = @_;

   while (my ($f, $k) = each %$db) {
      g_upd $node, $f, $k;
   }
}

# delete all keys from a database
sub g_clr($) {
   my ($node) = @_;

   my $db = $LOCAL_DBS{$node};

   while (my ($f, $k) = each %$db) {
      g_upd $node, $f, undef, [keys %$k];
   }

   delete $LOCAL_DBS{$node};
}

# gather node databases from slaves

# other node wants to make us the master
$NODE_REQ{g_slave} = sub {
   my ($db) = @_
      or return; # empty g_slave is used to start global service

   my $node = $SRCNODE;
   undef $GLOBAL_SLAVE{$node};
   g_set $node, $db;
};

$NODE_REQ{g_set} = sub {
   &g_set ($SRCNODE, @_);
};

$NODE_REQ{g_upd} = sub {
   &g_upd ($SRCNODE, @_);
};

$NODE_REQ{g_find} = sub {
   my ($node) = @_;

   snd $SRCNODE, g_found => $node, $GLOBAL_DB{"'l"}{$node};
};

$NODE_REQ{g_db_family} = sub {
   my ($family, $id) = @_;
   snd $SRCNODE, g_reply => $id, $GLOBAL_DB{$family} || {};
};

$NODE_REQ{g_db_keys} = sub {
   my ($family, $id) = @_;
   snd $SRCNODE, g_reply => $id, [keys %{ $GLOBAL_DB{$family} } ];
};

$NODE_REQ{g_db_values} = sub {
   my ($family, $id) = @_;
   snd $SRCNODE, g_reply => $id, [values %{ $GLOBAL_DB{$family} } ];
};

# monitoring

sub g_slave_disconnect($) {
   my ($node) = @_;

   g_clr $node;

   if (my $mon = delete $GLOBAL_SLAVE{$node}) {
      while (my ($f, $fv) = each %$mon) {
         delete $GLOBAL_MON{$f}{$_}
            for keys %$fv;

         delete $GLOBAL_MON{$f}
            unless %{ $GLOBAL_MON{$f} };
      }
   }
}

# g_mon0 family - stop monitoring
$NODE_REQ{g_mon0} = sub {
   delete $GLOBAL_MON{$_[0]}{$SRCNODE};
   delete $GLOBAL_MON{$_[0]} unless %{ $GLOBAL_MON{$_[0]} };

   delete $GLOBAL_SLAVE{$SRCNODE}{$_[0]};
};

# g_mon1 family key - start monitoring
$NODE_REQ{g_mon1} = sub {
   undef $GLOBAL_SLAVE{$SRCNODE}{$_[0]};
   undef $GLOBAL_MON{$_[0]}{$SRCNODE};

   snd $SRCNODE, g_chg1 => $_[0], $GLOBAL_DB{$_[0]};
};

#############################################################################
# switch to global mode

# regularly try to connect to global nodes - maybe use seeding code?
$MASTER_TIMER = AE::timer 0, $AnyEvent::MP::Kernel::CONFIG->{monitor_timeout}, sub {
   (add_node $_)->connect
      for other_globals;
};

# instantly connect to other global nodes when we learn of them
# so we don't have to wait for the timer.
#TODO
#   $GLOBAL_MON{"'g"}{""}{""} = sub {
#      (add_node $_[1])->connect;
#   };

# delete slaves on node-down
# clear slave db on node-down
$MASTER_MON = mon_nodes sub {
   g_slave_disconnect $_[0] unless $_[1];
};

# tell everybody who connects that we are a global node
push @AnyEvent::MP::Transport::HOOK_GREET, sub {
   $_[0]{local_greeting}{global} = 1;
};

# connect from a global node
sub g_global_connect {
   my ($node) = @_;

   # we need to set this currently, as to avoid race conditions
   # because it takes a while until the other global node tells us it is global.

   undef $GLOBAL_DB{"'g"}{$node};
   undef $LOCAL_DBS{$node}{"'g"}{$node};

   # global nodes send all local databases, merged,
   # as their local database to global nodes
   my %db;

   for (values %LOCAL_DBS) {
      while (my ($f, $fv) = each %$_) {
         while (my ($k, $kv) = each %$fv) {
            $db{$f}{$k} = $kv;
         }
      }
   }

   snd $node => g_set => \%db;
}

# send our database to every global node that connects
push @AnyEvent::MP::Transport::HOOK_CONNECT, sub {
   return unless $_[0]{remote_greeting}{global};

   g_global_connect $_[0]{remote_node};
};

# tell our master that we are global now
for (values %NODE) {
   if ($_->{transport} && $_->{transport}{remote_greeting}{global}) {
      snd $_->{id} => "g_global";
      g_global_connect $_->{id};
   }
}

$NODE_REQ{g_global} = sub {
   g_slave_disconnect $SRCNODE;

   my $node = $NODE{$SRCNODE};
   $node->{transport}{remote_greeting}{global} = 1;

   g_global_connect $SRCNODE;
};

# enable global mode
$GLOBAL = 1;

# global nodes are their own masters - this
# resends global requests and sets the local database.
master_set $NODE;

# now add us to the set of global nodes
db_set "'g" => $NODE => undef;

#############################################################################
# compatibility functions for aemp 1.0

package AnyEvent::MP::Global;

use base "Exporter";
our @EXPORT = qw(grp_reg grp_get grp_mon);

sub grp_reg($$) {
   &db_reg
}

sub grp_get($) {
   my @ports = keys %{ $AnyEvent::MP::Kernel::GLOBAL_DB{$_[0]} };

   @ports ? \@ports : undef
}

sub grp_mon($$) {
   my ($grp, $cb) = @_;

   db_mon $grp => sub {
      my ($ports, $add, $chg, $del) = @_;

      $cb->([keys %$ports], $add, $del);
   };
}

=head1 SEE ALSO

L<AnyEvent::MP>.

=head1 AUTHOR

 Marc Lehmann <schmorp@schmorp.de>
 http://home.schmorp.de/

=cut

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