package Lingua::Sentence;

use 5.008008;
use strict;
use warnings;

use Carp qw(croak);
use File::ShareDir 'dist_dir';

our $VERSION = '1.04';


# Preloaded methods go here.

sub new {
	ref(my $class= shift) and croak "Class name needed";
	my $langid = shift;
	if($langid !~ /^[a-z][a-z]$/) {
		croak "Invalid language id: $langid";
	}
	my $prefixfile = shift;

	# Try loading nonbreaking prefix file specified in constructor
	my $dir = dist_dir('Lingua-Sentence');
	if(defined($prefixfile)) {
		if(!(-e $prefixfile)) {
			print STDERR "WARNING: Specified prefix file '$prefixfile' does not exist, attempting fall-back to $langid version...\n";
			$prefixfile = "$dir/nonbreaking_prefix.$langid";
		}
	}
	else {
		$prefixfile = "$dir/nonbreaking_prefix.$langid";
	}

	my %NONBREAKING_PREFIX;
	#default back to English if we don't have a language-specific prefix file
	if (!(-e $prefixfile)) {
		$prefixfile = "$dir/nonbreaking_prefix.en";
		print STDERR "WARNING: No known abbreviations for language '$langid', attempting fall-back to English version...\n";
		die ("ERROR: No abbreviations files found in $dir\n") unless (-e $prefixfile);
	}
	if (-e "$prefixfile") {
		open(PREFIX, "<:utf8", "$prefixfile");
		while (<PREFIX>) {
			my $item = $_;
			chomp($item);
			if (($item) && (substr($item,0,1) ne "#")) {
				if ($item =~ /(.*)[\s]+(\#NUMERIC_ONLY\#)/) {
					$NONBREAKING_PREFIX{$1} = 2;
				} else {
					$NONBREAKING_PREFIX{$item} = 1;
				}
			}
		}
		close(PREFIX);
	}

	my $self = { LangID => $langid, Nonbreaking => \%NONBREAKING_PREFIX };
	bless $self,$class;
	return $self;
}

sub split {
	my $self = shift;
	if(!ref $self) {
		return "Unnamed $self";
	}
	my $text = shift;
	if(!$text) {
	    return '';
	}
	return _preprocess($self,$text);
}

sub split_array {
	my $self = shift;
	if(!ref $self) {
		return "Unnamed $self";
	}
	my $text = shift;
	if(!$text) {
	    return ();
	}
	my $splittext = _preprocess($self,$text);
	chomp $splittext;
	return split(/\n/,$splittext);
}

sub _preprocess {
	my ($self,$text) = @_;

	#####add sentence breaks as needed#####
	
	#non-period end of sentence markers (?!) followed by sentence starters.
	$text =~ s/([?!]) +([\'\"\(\[\¿\¡\p{IsPi}]*[\p{IsUpper}])/$1\n$2/g;
		
	#multi-dots followed by sentence starters
	$text =~ s/(\.[\.]+) +([\'\"\(\[\¿\¡\p{IsPi}]*[\p{IsUpper}])/$1\n$2/g;
	
	# add breaks for sentences that end with some sort of punctuation inside a quote or parenthetical and are followed by a possible sentence starter punctuation and upper case
	$text =~ s/([?!\.][\ ]*[\'\"\)\]\p{IsPf}]+) +([\'\"\(\[\¿\¡\p{IsPi}]*[\ ]*[\p{IsUpper}])/$1\n$2/g;
		
	# add breaks for sentences that end with some sort of punctuation are followed by a sentence starter punctuation and upper case
	$text =~ s/([?!\.]) +([\'\"\(\[\¿\¡\p{IsPi}]+[\ ]*[\p{IsUpper}])/$1\n$2/g;
	
	# special punctuation cases are covered. Check all remaining periods.
	my $word;
	my $i;
	my @words = split(/ +/,$text);
	$text = "";
	for ($i=0;$i<(scalar(@words)-1);$i++) {
		if ($words[$i] =~ /([\p{IsAlnum}\.\-]*)([\'\"\)\]\%\p{IsPf}]*)(\.+)$/) {
			#check if $1 is a known honorific and $2 is empty, never break
			my $prefix = $1;
			my $starting_punct = $2;
			if($prefix && $self->{Nonbreaking}{$prefix} && $self->{Nonbreaking}{$prefix} == 1 && !$starting_punct) {
				#not breaking;
			} elsif ($words[$i] =~ /(\.)[\p{IsUpper}\-]+(\.+)$/) {
				#not breaking - upper case acronym	
			} elsif($words[$i+1] =~ /^([ ]*[\'\"\(\[\¿\¡\p{IsPi}]*[ ]*[\p{IsUpper}0-9])/) {
				#the next word has a bunch of initial quotes, maybe a space, then either upper case or a number
				$words[$i] = $words[$i]."\n" unless ($prefix && $self->{Nonbreaking}{$prefix} && $self->{Nonbreaking}{$prefix} == 2 && !$starting_punct && ($words[$i+1] =~ /^[0-9]+/));
				#we always add a return for these unless we have a numeric non-breaker and a number start
			}
			
		}
		$text = $text.$words[$i]." ";
	}
	
	#we stopped one token from the end to allow for easy look-ahead. Append it now.
	$text = $text.$words[$i];
	
	# clean up spaces at head and tail of each line as well as any double-spacing
	$text =~ s/ +/ /g;
	$text =~ s/\n /\n/g;
	$text =~ s/ \n/\n/g;
	$text =~ s/^ //g;
	$text =~ s/ $//g;
	
	#add trailing break
	$text .= "\n" unless $text =~ /\n$/;
	
	return $text;
}

1;
__END__

=head1 NAME

Lingua::Sentence - Perl extension for breaking text paragraphs into sentences

=head1 SYNOPSIS

	use Lingua::Sentence;

	my $splitter = Lingua::Sentence->new("en");

	my $text = 'This is a paragraph. It contains several sentences. "But why," you ask?';

	print $splitter->split($text);


=head1 DESCRIPTION

This module allows splitting of text paragraphs into sentences. It is based on scripts developed by Philipp Koehn and Josh Schroeder for processing the Europarl corpus (L<http://www.statmt.org/europarl/>).

The module uses punctuation and capitalization clues to split paragraphs into an newline-separated string with one sentence per line. For example:

	This is a paragraph. It contains several sentences. "But why," you ask?

goes to:

	This is a paragraph.
	It contains several sentences.
	"But why," you ask?

Languages currently supported by the module are:

=over


=item Catalan

=item Czech

=item Dutch

=item English

=item French

=item German

=item Greek

=item Hungarian

=item Icelandic

=item Italian

=item Latvian

=item Polish

=item Portuguese

=item Russian

=item Spanish

=item Slovak

=item Slovenian

=item Swedish

=back

=head2 Nonbreaking Prefixes Files

Nonbreaking prefixes are loosely defined as any word ending in a period that does NOT indicate an end of sentence marker. A basic example is Mr. and Ms. in English.

The sentence splitter module uses the nonbreaking prefix files included in this distribution.

To add a file for other languages, follow the naming convention nonbreaking_prefix.?? and use the two-letter language code you intend to use when creating a Lingua::Sentence object.

The sentence splitter module will first look for a file for the language it is processing, and fall back to English if a file
for that language is not found. 

For the splitter, normally a period followed by an uppercase word results in a sentence split. If the word preceeding the period
is a nonbreaking prefix, this line break is not inserted.

A special case of prefixes, NUMERIC_ONLY, is included for special cases where the prefix should be handled ONLY when before numbers.
For example, "Article No. 24 states this." the No. is a nonbreaking prefix. However, in "No. It is not true." No functions as a word.

See the example prefix files included in the distribution for more examples.

=head3 CREDITS

Thanks for the following individuals for supplying nonbreaking prefix files:
Bas Rozema (Dutch), HilE<aacute>rio Leal Fontes (Portuguese), JesE<uacute>s GimE<eacute>nez (Catalan & Spanish)

=head2 EXPORT

=over

=item new($lang_id)

Instantiate an object to split sentences in language $lang_id. If the language is not supported, a splitter object for English will be instantiated.

=item new($lang_id,$nonbreaking_prefix_file)

Instantiate an object to split sentences in language $lang_id and the nonbreaking prefix file $nonbreaking_prefix_file. If the file does not exist, a splitter object for English will be instantiated.

=item split($text)

Split sentences in $text by inserting newline characters at the sentence breaks. The resulting string is also terminated with a newline.

=item split_array($text)

Split sentences in $text into an array of sentences.

=back

=head1 SUPPORT

Bugs should always be submitted via the project hosting bug tracker

L<http://code.google.com/p/corpus-tools/issues/list>

For other issues, contact the maintainer.

=head1 SEE ALSO

L<Text::Sentence>, L<Lingua::EN::Sentence>, L<Lingua::DE::Sentence>, L<Lingua::HE::Sentence>

=head1 AUTHOR

Achim Ruopp, E<lt>achimru@gmail.comE<gt>

=head1 COPYRIGHT AND LICENSE

Copyright (C) 2010 by Digital Silk Road

Portions Copyright (C) 2005 by Philip Koehn and Josh Schroeder (used with permission)

This program is free software: you can redistribute it and/or modify
it under the terms of the GNU Lesser General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
 
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU Lesser General Public License for more details.
 
You should have received a copy of the GNU Lesser General Public License
along with this program.  If not, see <http://www.gnu.org/licenses/>.

=cut