my $seq;    # a Bio::Seq object
  my $polyA = Bio::EnsEMBL::Utils::PolyA->new();

  # returns a new Bio::Seq object with the trimmed sequence
  my $trimmed_seq = $polyA->clip($seq);

  # cat put Ns in the place of the polyA/polyT tail
  my $masked_seq = $polyA->mask($seq);

  # can put in lower case the polyA/polyT using any flag:
  my $softmasked_seq = $poly->mask( $seq, 'soft' );

  It reads a Bio::Seq object, it first finds out whether it has a
  polyA or a polyT and then performs one operation in the seq string:
  clipping, masking or softmasking.  It then returns a new Bio::Seq
  object with the new sequence.

  my ($self,$clip) = @_;
  if (defined($clip)){
    $self->{_clip} = $clip;
  }
  return $self->{_clip};
}

############################################################

  my ($self, $seq) = @_;
  my $new_seq;
  my $length = length($seq);
  
  # is it a polyA or polyT?
  my $check_polyT = substr( $seq, 0, 6 );
  
  my $check_polyA = substr( $seq, -6 );
  
  my $t_count = $check_polyT =~ tr/Tt//;
  my $a_count = $check_polyA =~ tr/Aa//;
  
  #### polyA ####
  if ( $a_count >= 5 && $a_count > $t_count ){
    
    # we calculate the number of bases we want to chop
    my $length_to_mask = 0;
    
    # we start with 3 bases
    my ($piece, $count ) = (3,0);
    
    # count also the number of Ns, consider the Ns as potential As
    my $n_count = 0;

    # take 3 by 3 bases from the end
    while( $length_to_mask < $length ){
      my $chunk  = substr( $seq, ($length - ($length_to_mask + 3)), $piece);
      $count   = $chunk =~ tr/Aa//;
      $n_count = $chunk =~ tr/Nn//;
      if ( ($count + $n_count) >= 2*( $piece )/3 ){
	$length_to_mask += 3;
      }
      else{
	last;
      }
    }
    
    if ( $length_to_mask > 0 ){
      # do not mask the last base if it is not an A:
      my $last_base        = substr( $seq, ( $length - $length_to_mask    ), 1);
      my $previous_to_last = substr( $seq, ( $length - $length_to_mask - 1), 1);
      if ( !( $last_base eq 'A' || $last_base eq 'a') ){
	$length_to_mask--;
      }
      elsif( $previous_to_last eq 'A' || $previous_to_last eq 'a' ){
	$length_to_mask++;
      }
      my $clipped_seq = substr( $seq, 0, $length - $length_to_mask );
      my $mask;
      if ( $self->_clip ){
	$mask = "";
      }
      elsif( $self->_mask ){
	$mask    = "N" x ($length_to_mask);
      }
      elsif ( $self->_softmask ){
	$mask = lc substr( $seq, ( $length - $length_to_mask ) );
      }
      $new_seq =  $clipped_seq . $mask;
    }
    else{
      $new_seq = $seq;
    }	
  }
  #### polyT ####
  elsif( $t_count >=5 && $t_count > $a_count ){
    
    # calculate the number of bases to chop
    my $length_to_mask = -3;
    
    # we start with 3 bases:
    my ($piece, $count) = (3,3);
    
    # count also the number of Ns, consider the Ns as potential As
    my $n_count = 0;
    
    # take 3 by 3 bases from the beginning
    while ( $length_to_mask < $length ){
      my $chunk = substr( $seq, $length_to_mask + 3, $piece );
      #print STDERR "length to mask: $length_to_mask\n";
      #print "chunk: $chunk\n";
      $count = $chunk =~ tr/Tt//;
      $n_count = $chunk =~ tr/Nn//;
      if ( ($count+$n_count)  >= 2*( $piece )/3 ){
	$length_to_mask +=3;
      }
      else{
	last;
	
      }
    }
    if ( $length_to_mask >= 0 ){
      # do not chop the last base if it is not a A:
      #print STDERR "clipping sequence $seq\n";
      my $last_base        = substr( $seq, ( $length_to_mask + 3 - 1 ), 1 );
      my $previous_to_last = substr( $seq, ( $length_to_mask + 3     ), 1 );
      if ( !( $last_base eq 'T' || $last_base eq 't' ) ){
	$length_to_mask--;
      }
      elsif( $previous_to_last eq 'T' || $previous_to_last eq 't' ){
	$length_to_mask++;
      }
      my $clipped_seq = substr( $seq, $length_to_mask + 3);
      my $mask;
      if ( $self->_clip ){
	$mask = "";
      }
      elsif( $self->_mask ){
	$mask        = "N" x ($length_to_mask+3);
      }
      elsif ($self->_softmask){
	$mask = lc substr( $seq, 0, ($length_to_mask + 3) );
      }
      $new_seq     = $mask.$clipped_seq;
    }
    else{
      $new_seq = $seq;
    }
  }
  else{
    # we cannot be sure of what it is
    # do not clip
    $new_seq = $seq;
  }

  return $new_seq;
}

############################################################

  my ($self,$mask) = @_;
  if (defined($mask)){
    $self->{_mask} = $mask;
  }
  return $self->{_mask};
}

############################################################

  my ($self,$softmask) = @_;
  if (defined($softmask)){
    $self->{_softmask} = $softmask;
  }
  return $self->{_softmask};
}

############################################################

  my ($self, $bioseq) = @_;

  # print STDERR "past a $bioseq\n";
  my $seq = $bioseq->seq;
  $self->_clip(1);
  $self->_mask(0);
  $self->_softmask(0);
  my $new_seq = $self->_find_polyA($seq);
  my $cdna = Bio::Seq->new();
  if (length($new_seq) > 0){
    $cdna->seq($new_seq);
  } 
  else {
    print "While clipping the the polyA tail, sequence ".$bioseq->display_id." totally disappeared.\n";
    print "Returning undef\n";
    return undef;
  }
  $cdna->display_id( $bioseq->display_id );
  $cdna->desc( $bioseq->desc );
  
  return $cdna;
}

############################################################

  my ($self, $seq) = @_;
  my $new_seq;
  my $length = length($seq);
  
  # is it a polyA or polyT?
  my $check_polyT = substr( $seq, 0, 10 );
  
  my $check_polyA = substr( $seq, -10 );
  
  print STDERR "polyA: $check_polyA\n";

  my $t_count = $check_polyT =~ tr/Tt//;
  my $a_count = $check_polyA =~ tr/Aa//;
  
  ## testing with this short cut
  if ( $a_count >=7 || $t_count >=7 ){
    return 1;
  }
  else{
    return 0;
  }
}


################
1;

  my ($self, $bioseq, $flag ) = @_;
  
  my $seq = $bioseq->seq;
  $self->_clip(0);
  if ( $flag ){
    $self->_mask(0);
    $self->_softmask(1);
  }
  else{
    $self->_mask(1);
    $self->_softmask(0);
  }
  my $new_seq = $self->_find_polyA($seq);
  my $cdna = new Bio::Seq;
  $cdna->seq($new_seq);
  $cdna->display_id( $bioseq->display_id );
  $cdna->desc( $bioseq->desc );
  
  return $cdna;
}

############################################################




############################################################

  my ($class) = @_;
   if (ref($class)){
    $class = ref($class);
  }
  my $self = {};
  bless($self,$class);
  
  return $self;
}


############################################################

  Copyright (c) 1999-2009 The European Bioinformatics Institute and
  Genome Research Limited.  All rights reserved.

  This software is distributed under a modified Apache license.
  For license details, please see

    /info/about/code_licence.html

  Please email comments or questions to the public Ensembl
  developers list at <ensembl-dev@ebi.ac.uk>.

  Questions may also be sent to the Ensembl help desk at
  <helpdesk@ensembl.org>.