observers

[scpubgit/DKit.git] / lib / DX / RuleSet.pm

package DX::RuleSet;

use Moo;
use DX::Op::CallRule;
use DX::Op::MemberOf;
use DX::Op::ApplyConstraint;
use DX::Op::Return;
use DX::Op::Cut;
use DX::Op::Observe;
use List::Util qw(reduce);

has rules => (is => 'ro', default => sub { {} });

sub add_rule {
  my ($self, $name, $vars, @body) = @_;
  my $full_name = join('/', $name, scalar @$vars);
  push @{$self->rules->{$full_name}}, $self->_make_rule($vars, @body);
  return $self;
}

sub _make_rule {
  my ($self, $vars, @body) = @_;
  my $head = reduce { $b->but(next => $a) }
               DX::Op::Return->new,
               reverse map $self->expand(@$_), @body;
  [ $vars, $head ];
}

sub expand {
  my ($self, $type, @rest) = @_;
  if ($self->can(my $expand_meth = "_expand_${type}")) {
    return $self->$expand_meth(@rest);
  }
  return $self->_expand_call($type, @rest);
}

sub _expand_call {
  my ($self, $name, @args) = @_;
  DX::Op::CallRule->new(rule_name => $name, rule_args => \@args);
}

sub _expand_cut { return DX::Op::Cut->new }

sub _expand_member_of {
  my ($self, $member_var, $coll_var) = @_;
  DX::Op::MemberOf->new(
    member_var => $member_var,
    coll_var => $coll_var,
  );
}

sub _expand_constrain {
  my ($self, $vars, $constraint) = @_;
  DX::Op::ApplyConstraint->new(
    vars => $vars,
    constraint => $constraint
  );
}

sub _expand_observe {
  my ($self, $vars, $builder) = @_;
  DX::Op::Observe->new(
    vars => $vars,
    builder => $builder,
  );
}

1;