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# $Id: BaseSAXHandler.pm,v 1.4.6.1 2006/10/02 23:10:22 sendu Exp $
#
# BioPerl module for BaseSAXHandler
#
# Cared for by Juguang Xiao, juguang@tll.org.sg
#
# Copyright Juguang Xiao 
#
# You may distribute this module under the same terms as perl itself
# POD documentation - main docs before the code
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=head1 NAME
Bio::OntologyIO::Handlers::BaseSAXHandler
=head1 DESCRIPTION
This module is an abstract module, serving as the base of any SAX Handler 
implementation. It tries to offer the framework that SAX handlers generally 
need, such as tag_stack, char_store, etc.
In the implementation handler, you can take advantage of this based module by
the following suggestions.
1) In start_element,
 sub start_element {
     my $self=shift;
     my $tag=$_[0]->{Name};
     my %args=%{$_[0]->{Attributes}};
     # Your code here.
     # Before you conclude the method, write these 2 line.
     $self->_visited_count_inc($tag);
     $self->_push_tag($tag);
 }
2) In end_element,
 sub end_element {
     my $self=shift;
     my $tag=shift->{Name};
     # Your code here.
     # Before you conclude the method, write these 2 lines.
     $self->_visited_count_dec($tag);
     $self->_pop_tag;
 }
3) In characters, or any other methods where you may use the tag
stack or count
 sub characters {
     my $self=shift;
     my $text=shift->{Data};
     $self->_chars_hash->{$self->_top_tag} .= $text;
 }
 $count = $self->_visited_count('myTag');
 $tag = $self->_top_tag;
=head1 AUTHOR
Juguang Xiao, juguang@tll.org.sg
=head2 APPENDIX
The rest of the documentation details each of the object methods.
Interal methods are usually preceded with a _
=cut
package Bio::OntologyIO::Handlers::BaseSAXHandler;
use strict;
use base qw(Bio::Root::Root);
sub new {
    my ($class, @args) = @_;
    my $self=$class->SUPER::new(@args);
    $self->_initialize(@args);
    return $self;
}
sub _initialize {
    my $self = shift;
    $self->{_tag_stack} = [];
    $self->{_visited_count} = {};
    $self->{_chars_hash} = {};
    $self->{_current_hash} = {};
}
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=head2 _tag_stack
  Title   : _tag_stack
  Usage   : @tags = $self->_tag_stack;
  Function: Get an array of tags that have been accessed but not enclosed.
  Return  : 
  Args    :    
=cut
sub _tag_stack {
    return @{shift->{_tag_stack}};
}
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=head2 _push_tag
=cut
sub _push_tag {
    my($self,$tag)=@_;
    push @{$self->{_tag_stack}}, $tag;
}
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=head2 _pop_tag
=cut
sub _pop_tag {
    my $self=shift;
    return pop @{$self->{_tag_stack}};
}
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=head2 _top_tag
  Title   : _top_tag
  Usage   : $top = $self->_top_tag;
  Function: get the top tag in the tag stack.
  Return  : a tag name
  Args    : [none]   
=cut
sub _top_tag {
    my $self = shift;
    my @stack=@{$self->{_tag_stack}};
    return $stack[-1];
# get the last element in an array while remaining it in. There are few  ways
# 1) $stack[-1]
# 2) $stack[$#stack]
# 3) $stack[@stack-1]
}
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=head2 _chars_hash
  Title   : _chars_hash
  Usage   : $hash= $self->_chars_hash;
  Function: return the character cache for the specific tag
  Return  : a hash reference, which is intent for character storage for tags
  Args    : [none]
=cut
sub _chars_hash {
    return shift->{_chars_hash};
}
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=head2 _current_hash
=cut
sub _current_hash {
    return  shift->{_current_hash};
}
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=head2 _visited_count_inc
  Title   : _vistied_count_inc
  Usage   : $self->vistied_count_inc($tag); # the counter for the tag increase
  Function: the counter for the tag increase
  Return  : the current count after this increment
  Args    : the tag name [scalar]
=cut
sub _visited_count_inc {
    my ($self, $tag) = @_;
    my $visited_count=$self->{_visited_count};
    if(exists $visited_count->{$tag}){
        $visited_count->{$tag}++;
    }else{
        $visited_count->{$tag}=1;
    }
    return $visited_count->{$tag};
}
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=head2 _visited_count_dec
  Title   : _visited_count_dec
  Usage   : $self->_visited_count_dec($tag);
  Function: the counter for the tag decreases by one
  Return  : the current count for the specific tag after the decrement
  Args    : the tag name [scalar]
=cut
sub _visited_count_dec {
    my ($self, $tag) = @_;
    my $visited_count=$self->{_visited_count};
    if(exists $visited_count->{$tag}){
        $visited_count->{$tag}--;
    }else{
        $self->throw("'$tag' has not been visited yet. How to decrease it?!");
    }
    return $visited_count->{$tag};
}
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=head2 _visited_count
  Title   : _visited_count
  Usage   : $count = $self->_visited_count
  Function: return the counter for the tag
  Return  : the current counter for the specific tag
  Args    : the tag name [scalar]
=cut
sub _visited_count {
    my ($self, $tag) = @_;
    return $self->{_visited_count}->{$tag};
}
1;