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=head1 NAME

Mail::SpamAssassin::Plugin::AutoLearnThreshold - threshold-based discriminator for Bayes auto-learning

=head1 SYNOPSIS

  loadplugin     Mail::SpamAssassin::Plugin::AutoLearnThreshold

=head1 DESCRIPTION

This plugin implements the threshold-based auto-learning discriminator
for SpamAssassin's Bayes subsystem.  Auto-learning is a mechanism
whereby high-scoring mails (or low-scoring mails, for non-spam) are fed
into its learning systems without user intervention, during scanning.

Note that certain tests are ignored when determining whether a message
should be trained upon:

=over 4

=item * rules with tflags set to 'learn' (the Bayesian rules)

=item * rules with tflags set to 'userconf' (user configuration)

=item * rules with tflags set to 'noautolearn'

=back

Also note that auto-learning occurs using scores from either scoreset 0
or 1, depending on what scoreset is used during message check.  It is
likely that the message check and auto-learn scores will be different.

=cut

package Mail::SpamAssassin::Plugin::AutoLearnThreshold;

use Mail::SpamAssassin::Plugin;
use Mail::SpamAssassin::Logger;
use strict;
use warnings;
use bytes;
use re 'taint';

use vars qw(@ISA);
@ISA = qw(Mail::SpamAssassin::Plugin);

sub new {
  my $class = shift;
  my $mailsaobject = shift;

  $class = ref($class) || $class;
  my $self = $class->SUPER::new($mailsaobject);
  bless ($self, $class);

  $self->set_config($mailsaobject->{conf});

  return $self;
}

sub set_config {
  my($self, $conf) = @_;
  my @cmds;

=head1 USER OPTIONS

The following configuration settings are used to control auto-learning:

=over 4

=item bayes_auto_learn_threshold_nonspam n.nn   (default: 0.1)

The score threshold below which a mail has to score, to be fed into
SpamAssassin's learning systems automatically as a non-spam message.

=cut

  push (@cmds, {
    setting => 'bayes_auto_learn_threshold_nonspam',
    default => 0.1,
    type => $Mail::SpamAssassin::Conf::CONF_TYPE_NUMERIC
  });

=item bayes_auto_learn_threshold_spam n.nn      (default: 12.0)

The score threshold above which a mail has to score, to be fed into
SpamAssassin's learning systems automatically as a spam message.

Note: SpamAssassin requires at least 3 points from the header, and 3
points from the body to auto-learn as spam.  Therefore, the minimum
working value for this option is 6.

=cut

  push (@cmds, {
    setting => 'bayes_auto_learn_threshold_spam',
    default => 12.0,
    type => $Mail::SpamAssassin::Conf::CONF_TYPE_NUMERIC
  });

=item bayes_auto_learn_on_error (0 | 1)        (default: 0)

With C<bayes_auto_learn_on_error> off, autolearning will be performed
even if bayes classifier already agrees with the new classification (i.e.
yielded BAYES_00 for what we are now trying to teach it as ham, or yielded
BAYES_99 for spam). This is a traditional setting, the default was chosen
to retain backwards compatibility.

With C<bayes_auto_learn_on_error> turned on, autolearning will be performed
only when a bayes classifier had a different opinion from what the autolearner
is now trying to teach it (i.e. it made an error in judgement). This strategy
may or may not produce better future classifications, but usually works
very well, while also preventing unnecessary overlearning and slows down
database growth.

=cut

  push (@cmds, {
    setting => 'bayes_auto_learn_on_error',
    default => 0,
    type => $Mail::SpamAssassin::Conf::CONF_TYPE_BOOL
  });

  $conf->{parser}->register_commands(\@cmds);
}

sub autolearn_discriminator {
  my ($self, $params) = @_;

  my $scan = $params->{permsgstatus};
  my $conf = $scan->{conf};

  # Figure out min/max for autolearning.
  # Default to specified auto_learn_threshold settings
  my $min = $conf->{bayes_auto_learn_threshold_nonspam};
  my $max = $conf->{bayes_auto_learn_threshold_spam};

  # Find out what score we should consider this message to have ...
  my $score = $scan->get_autolearn_points();
  my $body_only_points = $scan->get_body_only_points();
  my $head_only_points = $scan->get_head_only_points();
  my $learned_points = $scan->get_learned_points();

  dbg("learn: auto-learn? ham=$min, spam=$max, ".
                "body-points=".$body_only_points.", ".
                "head-points=".$head_only_points.", ".
                "learned-points=".$learned_points);

  my $isspam;
  if ($score < $min) {
    $isspam = 0;
  } elsif ($score >= $max) {
    $isspam = 1;
  } else {
    dbg("learn: auto-learn? no: inside auto-learn thresholds, not considered ham or spam");
    return;
  }

  my $learner_said_ham_points = -1.0;
  my $learner_said_spam_points = 1.0;

  if ($isspam) {
    my $required_body_points = 3;
    my $required_head_points = 3;

    if ($body_only_points < $required_body_points) {
      dbg("learn: auto-learn? no: scored as spam but too few body points (".
          $body_only_points." < ".$required_body_points.")");
      return;
    }
    if ($head_only_points < $required_head_points) {
      dbg("learn: auto-learn? no: scored as spam but too few head points (".
          $head_only_points." < ".$required_head_points.")");
      return;
    }
    if ($learned_points < $learner_said_ham_points) {
      dbg("learn: auto-learn? no: scored as spam but learner indicated ham (".
          $learned_points." < ".$learner_said_ham_points.")");
      return;
    }

    if (!$scan->is_spam()) {
      dbg("learn: auto-learn? no: scored as ham but autolearn wanted spam");
      return;
    }

  } else {
    if ($learned_points > $learner_said_spam_points) {
      dbg("learn: auto-learn? no: scored as ham but learner indicated spam (".
          $learned_points." > ".$learner_said_spam_points.")");
      return;
    }

    if ($scan->is_spam()) {
      dbg("learn: auto-learn? no: scored as spam but autolearn wanted ham");
      return;
    }
  }

  if ($conf->{bayes_auto_learn_on_error}) {
    # learn-on-error strategy chosen:
    # only allow learning if the autolearning classifier was unsure or
    # had a different opinion from what we are trying to make it learn
    #
    my $tests = $scan->get_tag('TESTS');
    if (defined $tests && $tests ne 'none') {
      my %t = map { ($_,1) } split(/,/, $tests);
      if ($isspam && $t{'BAYES_99'} || !$isspam && $t{'BAYES_00'}) {
        dbg("learn: auto-learn? no: learn-on-error, %s, already classified ".
            "as such",  $isspam ? 'spam' : 'ham');
        return;
      }
    }
  }

  dbg("learn: auto-learn? yes, ".($isspam?"spam ($score > $max)":"ham ($score < $min)"));
  return $isspam;
}

1;

=back

=cut
