=head1 LICENSE

Copyright [1999-2015] Wellcome Trust Sanger Institute and the EMBL-European Bioinformatics Institute
Copyright [2016-2017] EMBL-European Bioinformatics Institute

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

     http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.

=cut


=head1 CONTACT

  Please email comments or questions to the public Ensembl
  developers list at <http://lists.ensembl.org/mailman/listinfo/dev>.

  Questions may also be sent to the Ensembl help desk at
  <http://www.ensembl.org/Help/Contact>.

=cut

=head1 NAME Bio::EnsEMBL::Intron - A class representing an Intron

=head1 SYNOPSIS

  $intron = Bio::EnsEMBL::Intron->new( exon1, exon2, $analysis );

=cut


package Bio::EnsEMBL::Intron;
use strict;
use warnings;

use Bio::EnsEMBL::Utils::Exception qw( warning throw );

use base qw(Bio::EnsEMBL::Feature);

=head2 new

  Arg [1]    : Bio::EnsEMBL::Exon The 5' exon for the intron; required
  Arg [2]    : Bio::EnsEMBL::Exon The 3' exon for the intron; required
  Arg [3]    : Bio::EnsEMBL::Analysis Analysis to link to this Intron
  Example    : $intron = new Bio::EnsEMBL::Intron($exon1, $exon2)
  Description: Create an Intron object from two exons and an optional analysis
  Returntype : Bio::EnsEMBL::Intron
  Exceptions : exons not on the same strand or slice.
  Caller     : general
  Status     : Stable

=cut

sub new {
  my ( $proto, $e1, $e2, $analysis ) = @_;

  my $class = ref $proto || $proto;

  my $self = $class->SUPER::new();

  if ( $e1->strand() == -1 ) {
    $self->{'end'}   = $e1->start() - 1;
    $self->{'start'} = $e2->end() + 1;
  } else {
    $self->{'start'} = $e1->end() + 1;
    $self->{'end'}   = $e2->start() - 1;
  }

  if ( $e1->strand() != $e2->strand() ) {
    #  throw("Exons on different strand. Not allowed");
  } else {
    $self->{'strand'} = $e1->strand();
  }

  if ( $e1->slice() != $e2->slice() ) {
    if ( ( $e1->slice()->seq_region_name() ne
           $e2->slice()->seq_region_name() )
         && ( $e1->slice()->coord_system_name() ne
              $e2->slice()->coord_system_name() ) )
    {
      throw("Exons on different slices. Not allowed");
    } else {
      warning("Exons have different slice references to the same seq_region");
    }
  } else {
    $self->{'slice'} = $e1->slice();
  }
  
  if($analysis) {
    $self->analysis($analysis);
  }

  $self->{'prev'} = $e1;
  $self->{'next'} = $e2;

  return $self;
} ## end sub new

=head2 length

  Args       : none
  Example    : $length = $intron->length();
  Description: Returns the length of this intron
  Returntype : Integer
  Exceptions : none
  Caller     : general
  Status     : Stable

=cut

sub length {
  my ($self) = @_;

  # TODO: Introns on circular slices, see Feature.pm but allow for
  # zero-length introns.

  return $self->{'end'} - $self->{'start'} + 1;
}


=head2 prev_Exon

  Args       : none
  Example    : $exon = $intron->prev_Exon
  Description: Returns the exon before this Intron
  Returntype : Bio::EnsEMBL::Exon
  Exceptions : none
  Caller     : general
  Status     : Stable

=cut

sub prev_Exon {
  my ($self) = shift;

  return $self->{'prev'};
}


=head2 next_Exon

  Args       : none
  Example    : $exon = $intron->next_Exon
  Description: Returns the exon after this Intron
  Returntype : Bio::EnsEMBL::Exon
  Exceptions : none
  Caller     : general
  Status     : Stable

=cut

sub next_Exon {
  my ($self) = shift;

  return $self->{'next'};
}

=head2 rank

  Args       : none
  Example    : $rank = $intron->rank
  Description: Returns the rank of this Intron
  Returntype : Integer
  Exceptions : none
  Caller     : general
  Status     : Stable

=cut

sub rank {
  my ($self, $transcript) = @_;

  return $self->prev_Exon->rank($transcript);
}

=head2 is_splice_canonical

  Example     : my $canonical = $intron->is_splice_canonical(); 
  Description : Indicates if the splice site is considered normal. This means
                splice site variants equal to (D == donor, A == acceptor)
                  GT (D) => AG (A) 
                  AT (D) => AC (A)
                  GC (D) => AG (A)
  Returntype  : Boolean indicating if the splice was as expected
  Exceptions  : See splice_seq

=cut

sub is_splice_canonical {
  my ($self) = @_;
  my $splice = join q{}, @{$self->splice_seq()}; 
  my $canonical = {
    'GTAG' => 1, 'ATAC' => 1, 'GCAG' => 1
  }->{$splice};
  return $canonical || 0;
}

=head2 splice_seq

  Example     : my ($donor, $acceptor) = @{$intron->splice_seq}; 
  Description : Get the donor and acceptor splice sites for this intron
  Returntype  : ArrayRef[String] The donor and acceptor sequences as Strings
  Exceptions  : Thrown if a feature Slice cannot be found

=cut

sub splice_seq {
  my ($self) = @_;
  my $slice = $self->feature_Slice();
  throw "Cannot retrieve feature_Slice() for this Intron" unless $slice;
  my $length = $self->length();
  my $donor_seq    = uc($slice->subseq(1,2));
  my $acceptor_seq = uc($slice->subseq($length - 1, $length));
  return [$donor_seq, $acceptor_seq];
}

1;


