=encoding utf-8

=head1 NAME

Unicode::LineBreak - UAX #14 Unicode Line Breaking Algorithm

=head1 SYNOPSIS

    use Unicode::LineBreak;
    $lb = Unicode::LineBreak->new();
    $broken = $lb->break($string);

=head1 DESCRIPTION

Unicode::LineBreak performs Line Breaking Algorithm described in
Unicode Standards Annex #14 [UAX #14].
East_Asian_Width informative properties defined by Annex #11 [UAX #11] will
be concerned to determin breaking positions.

=head2 Terminology

Following terms are used for convenience.

B<Mandatory break> is obligatory line breaking behavior defined by core
rules and performed regardless of surrounding characters.
B<Arbitrary break> is line breaking behavior allowed by core rules
and chosen by user to perform it.
Arbitrary break includes B<direct break> and B<indirect break>
defined by [UAX #14].

B<Alphabetic characters> are characters usually no line breaks are allowed
between pairs of them, except that other characters provide break
oppotunities.
B<Ideographic characters> are characters that usually allow line breaks
both before and after themselves.
[UAX #14] classifies most of alphabetic to AL and most of ideographic to ID
(These terms are inaccurate from the point of view by grammatology).
On several scripts, breaking positions are not obvious by each characters
therefore heuristic based on dictionary is used.

B<Number of columns> of a string is not always equal to the number of characters it contains:
Each of characters is either B<wide>, B<narrow> or nonspacing;
they occupy 2, 1 or 0 columns, respectively.
Several characters may be both wide and narrow by the contexts they are used.
Characters may have more various widths by customization.

=head1 PUBLIC INTERFACE

=head2 Line Breaking

=over 4

=item new ([KEY => VALUE, ...])

I<Constructor>.
About KEY => VALUE pairs see L</Options>.

=item $self->break (STRING)

I<Instance method>.
Break Unicode string STRING and returns it.

=item $self->break_partial (STRING)

I<Instance method>.
Same as break() but accepts incremental inputs.
Give C<undef> as STRING argument to specify that input was completed.

=item $self->config (KEY)

=item $self->config (KEY => VALUE, ...)

I<Instance method>.
Get or update configuration.  About KEY => VALUE pairs see L</Options>.

=item $self->copy

I<Copy constructor>.
Create a copy of object instance.

=begin comment

=item $self->reset

I<Undocumented>.

=end comment

=back

=head2 Getting Informations

=over 4

=item context ([Charset => CHARSET], [Language => LANGUAGE])

I<Function>.
Get language/region context used by character set CHARSET or
language LANGUAGE.

=item $self->eawidth (STRING)

I<Instance method>.
Get East_Asian_Width property of the first character of Unicode string
STRING.
See L</Constants> for returned value.
EA_Z means nonspacing (zero width) character.
Property value A (ambiguous) will be resolved to other appropriate values. 

=item $self->lbclass (STRING)

I<Instance method>.
Get line breaking property (class) of the first character of Unicode string
STRING.
See L</Constants> for returned value.
Classes AI, SA, SG and XX will be resolved to other
appropriate classes. 
However, when word segmentation for South East Asian writing systems is
enabled, characters of supported scripts (currently Thai only) will be kept SA.

=item $self->lbrule (BEFORE, AFTER)

I<Instance method>.
Get line breaking action between class BEFORE and class AFTER.
See L</Constants> for returned value.

B<Note>:
This method might not give appropriate value related to classes
BK, CM, CR, LF, NL and SP,
and won't give meaningful value related to classes
AI, SA, SG and XX. 

=item $self->strsize (LEN, PRE, SPC, STR)

=item $self->strsize (LEN, PRE, SPC, STR, MAX)

I<Instance method>.
When MAX is not specified, calculate I<number of columns> of Unicode string
PRE.SPC.STR based on character widths defined by [UAX #11].
When a positive value MAX is specified, return I<number of characters> of
SUBSTR, the longest substring of STR by which number of columns of
PRE.SPC.SUBSTR does not exceed MAX.

=back

=head2 Options

L</new> and L</config> methods accept following pairs.

=over 4

=item CharactersMax => NUMBER

Possible maximum number of characters in one line,
not counting trailing SPACEs and newline sequence.
Note that number of characters generally doesn't represent length of line.
Default is C<998>.
Should not be C<0>.

=item ColumnsMin => NUMBER

Minimum number of columns which line broken arbitrarily may include, not
counting trailing spaces and newline sequences.
Default is C<0>.

=item ColumnsMax => NUMBER

Maximum number of columns line may include not counting trailing spaces and
newline sequence.  In other words, maximum length of line.
Default is C<76>.

=back

See also L</UrgentBreaking> option and L</User-Defined Breaking Behaviors>.

=over 4

=item Context => CONTEXT

Specify language/region context.
Currently available contexts are C<"EASTASIAN"> and C<"NONEASTASIAN">.
Default context is C<"NONEASTASIAN">.

=item Format => METHOD

Specify the method to format broken lines.

=over 4

=item C<"DEFAULT">

Default method.
Just only insert newline at arbitrary breaking positions.

=item C<"NEWLINE">

Insert or replace newline sequences with that specified by L</Newline> option,
remove SPACEs leading newline sequences or end-of-text.  Then append newline
at end of text if it does not exist.

=item C<"TRIM">

Insert newline at arbitrary breaking positions. Remove SPACEs leading
newline sequences.

=item Subroutine reference

See L</Formatting Lines>.

=back

=item HangulAsAL => C<"YES"> | C<"NO">

Treat hangul syllables and conjoining jamos as alphabetic characters (AL).
Default is C<"NO">.

=item LegacyCM => C<"YES"> | C<"NO">

Treat combining characters lead by a SPACE as an isolated combining character
(ID).
As of Unicode 5.0, such use of SPACE is not recommended.
Default is C<"YES">.

=item Newline => STRING

Unicode string to be used for newline sequence.
Default is C<"\n">.

=item SizingMethod => METHOD

Specify method to calculate size of string.
Following options are available.

=over 4

=item C<"DEFAULT">

Default method.
strsize() will be used.

=item Subroutine reference

See L</Calculating String Size>.

=back

See also L</TailorEA> option.

=item TailorEA => C<[> ORD C<=E<gt>> CLASS, ... C<]>

Tailor classification of East_Asian_Width property.
ORD is UCS scalar value of character or array reference of them.
CLASS is one of East_Asian_Width property values N, Na, W, F and H
(See L</Constants>).

By default, no tailorings are available.
See also L</Tailoring Character Properties>.

=item TailorLB => C<[> ORD C<=E<gt>> CLASS, ... C<]>

Tailor classification of line breaking property.
ORD is UCS scalar value of character or array reference of them.
CLASS is one of line breaking classes (See L</Constants>).

By default, no tailorings are available.
See also L</Tailoring Character Properties>.

=item UrgentBreaking => METHOD

Specify method to handle excessing lines.
Following options are available.

=over 4

=item C<"CROAK">

Print error message and die.

=item C<"FORCE">

Force breaking excessing fragment.

=item C<"NONBREAK">

Default method.
Won't break excessing fragment.

=item Subroutine reference

See L</User-Defined Breaking Behaviors>.

=back

=item UserBreaking => C<[>METHOD, ...C<]>

Specify user-defined line breaking behavior(s).
Following methods are available.

=over 4

=item C<"NONBREAKURI">

Won't break URIs.

=item C<"BREAKURI">

Break URIs according to a rule suitable for printed materials.
For more details see [CMOS], sections 6.17 and 7.11.

=item C<[> REGEX, SUBREF C<]>

The sequences matching regular expression REGEX will be broken by
subroutine referred by SUBREF.
For more details see L</User-Defined Breaking Behaviors>.

=back

=back

=head2 Constants

=over 4

=item C<EA_Na>,	C<EA_N>, C<EA_A>, C<EA_W>, C<EA_H>, C<EA_F>, C<EA_Z>

Index values to specify 6 East_Asian_Width properties
defined by [UAX #11], and EA_Z to specify nonspacing.

=item C<LB_BK>, C<LB_CR>, C<LB_LF>, C<LB_NL>, C<LB_SP>, C<LB_OP>, C<LB_CL>, C<LB_CP>, C<LB_QU>, C<LB_GL>, C<LB_NS>, C<LB_EX>, C<LB_SY>, C<LB_IS>, C<LB_PR>, C<LB_PO>, C<LB_NU>, C<LB_AL>, C<LB_ID>, C<LB_IN>, C<LB_HY>, C<LB_BA>, C<LB_BB>, C<LB_B2>, C<LB_CB>, C<LB_ZW>, C<LB_CM>, C<LB_WJ>, C<LB_H2>, C<LB_H3>, C<LB_JL>, C<LB_JV>, C<LB_JT>, C<LB_SG>, C<LB_AI>, C<LB_SA>, C<LB_XX>

Index values to specify 37 line breaking properties (classes)
defined by [UAX #14].

B<Note>: Property value CP was introduced by Unicode 5.2.0.

=item C<MANDATORY>, C<DIRECT>, C<INDIRECT>, C<PROHIBITED>

4 values to specify line breaking behaviors:
Mandatory break; Both direct break and indirect break are allowed;
Indirect break is allowed but direct break is prohibited;
Prohibited break.

=item C<Unicode::LineBreak::SouthEastAsian::supported>

Flag to determin if word segmentation for South East Asian writing systems is
enabled.
If this feature was enabled, a non-empty string is set. 
Otherwise, C<undef> is set.

B<N.B.>: Current release supports Thai script of modern Thai language only.

=item C<UNICODE_VERSION>

A string to specify version of Unicode standard this module refers.

=back

=head1 CUSTOMIZATION

=head2 Formatting Lines

If you specify subroutine reference as a value of L</Format> option,
it should accept three arguments:

    MODIFIED = &subroutine(SELF, EVENT, STR);

SELF is a Unicode::LineBreak object,
EVENT is a string to determine the context that subroutine was called in,
and STR is a fragment of Unicode string leading or trailing breaking position.

    EVENT |When Fired           |Value of STR
    -----------------------------------------------------------------
    "sot" |Beginning of text    |Fragment of first line
    "sop" |After mandatory break|Fragment of next line
    "sol" |After arbitrary break|Fragment on sequel of line
    ""    |Just before any      |Complete line without trailing
          |breaks               |SPACEs
    "eol" |Arbitrary break      |SPACEs leading breaking position
    "eop" |Mandatory break      |Newline and its leading SPACEs
    "eot" |End of text          |SPACEs (and newline) at end of
          |                     |text
    -----------------------------------------------------------------

Subroutine should return modified text fragment or may return
C<undef> to express that no modification occurred.
Note that modification in the context of C<"sot">, C<"sop"> or C<"sol"> may
affect decision of successive breaking positions while in the others won't.

B<Note>:
As of release 1.003, string arguments are Unicode::GCString object.
See L<Unicode::GCString/CAVEAT>.

For example, following code folds lines removing trailing spaces:

    sub fmt {
        if ($_[1] =~ /^eo/) {
            return "\n";
        }
        return undef;
    }
    my $lb = Unicode::LineBreak->new(Format => \&fmt);
    $output = $lb->break($text);

=head2 User-Defined Breaking Behaviors

When a line generated by arbitrary break is expected to be beyond measure of
either CharactersMax, ColumnsMin or ColumnsMax, B<urgent break> may be
performed on successive string.
If you specify subroutine reference as a value of L</UrgentBreaking> option,
it should accept five arguments:

    BROKEN = &subroutine(SELF, LEN, PRE, SPC, STR);

SELF is a Unicode::LineBreak object, LEN is size of preceding string,
PRE is preceding Unicode string, SPC is additional SPACEs and STR is a
Unicode string to be broken.

Subroutine should return an array of broken string STR.

B<Note>:
As of release 1.003, string arguments are Unicode::GCString object.
See L<Unicode::GCString/CAVEAT>.

For example, following code inserts hyphen to the name of several chemical substances (such as Titin) so that it may be folded:

    sub hyphenize {
        return map {$_ =~ s/yl$/yl-/; $_} split /(\w+?yl(?=\w))/, $_[4];
    }
    my $lb = Unicode::LineBreak->new(UrgentBreaking => \&hyphenize);
    $output = $lb->break("Methionylthreonylthreonylglutaminylarginyl...");

If you specify [REGEX, SUBREF] array reference as an item of
L</UserBreaking> option,
subroutine should accept two arguments:

    BROKEN = &subroutine(SELF, STR);

SELF is a Unicode::LineBreak object and
STR is a Unicode string matched with REGEX.

Subroutine should return an array of broken string STR.

For example, following code will break HTTP URLs using [CMOS] rule.

    my $url = qr{http://[\x21-\x7E]+}i;
    sub breakurl {
        my $self = shift;
        my $str = shift;
        return split m{(?<=[/]) (?=[^/]) |
                       (?<=[^-.]) (?=[-~.,_?\#%=&]) |
                       (?<=[=&]) (?=.)}x, $str;
    }
    my $lb = Unicode::LineBreak->new(UserBreaking => [$url, \&breakurl]);
    $output = $lb->break($string);

=head2 Calculating String Size

If you specify subroutine reference as a value of L</SizingMethod> option,
it will be called with five or six arguments:

    COLS = &subroutine(SELF, LEN, PRE, SPC, STR);

    CHARS = &subroutine(SELF, LEN, PRE, SPC, STR, MAX);

SELF is a Unicode::LineBreak object, LEN is size of preceding string,
PRE is preceding Unicode string, SPC is additional SPACEs and STR is a
Unicode string to be processed.

By the first format, subroutine should return calculated number of columns of C<PRE.SPC.STR>.
The number of columns may not be an integer: Unit of the number may be freely chosen, however, it should be same as those of L</ColumnsMin> and L</ColumnsMax> option.

By the second format, subroutine should return maximum
I<number of Unicode characters> that substring of STR contains
by which number of columns PRE.SPC.SUBSTR contains may not exceed MAX.
This format will be used when L</UrgentBreaking> option is set to C<"FORCE">.
If you don't wish to implement latter format, C<undef> should be returned.

B<Note>:
As of release 1.003, string arguments are Unicode::GCString object.
See L<Unicode::GCString/CAVEAT>.

For example, following code processes lines with tab stops by each eight columns.

    sub tabbedsizing {
        my ($self, $cols, $pre, $spc, $str, $max) = @_;
        return undef if $max;
    
	my $spcstr = $spc.$str;
        while ($spcstr =~ s/^( *)(\t+)//) {
            $cols += length($1);
            $cols += length($2) * 8 - $cols % 8;
        }
        $cols += $self->strsize(0, '', '', $spcstr);
        return $cols;
    };
    my $lb = Unicode::LineBreak->new(TailorLB => [ord("\t") => LB_SP],
                                     SizingMethod => \&tabbedsizing);
    $output = $lb->break($string);

=head2 Tailoring Character Properties

Character properties may be tailored by L</TailorLB> and L</TailorEA>
options.  Some constants are defined for convenience of tailoring.

=head3 Line Breaking Properties

By default, several hiragana, katakana and characters corresponding to kana
are treated as nonstarters (NS).
When the following pair(s) are specified for value of L</TailorLB> option,
these characters are treated as normal ideographic characters (ID).

=over 4

=item C<KANA_NONSTARTERS() =E<gt> LB_ID>

All of characters below.

=item C<IDEOGRAPHIC_ITERATION MARKS() =E<gt> LB_ID>

Ideographic iteration marks.
U+3005 IDEOGRAPHIC ITERATION MARK, U+303B VERTICAL IDEOGRAPHIC ITERATION MARK, U+309D HIRAGANA ITERATION MARK, U+309E HIRAGANA VOICED ITERATION MARK, U+30FD KATAKANA ITERATION MARK and U+30FE KATAKANA VOICED ITERATION MARK.

N.B. Some of them are neither hiragana nor katakana.

=item C<KANA_SMALL_LETTERS() =E<gt> LB_ID>

=item C<KANA_PROLONGED_SOUND_MARKS() =E<gt> LB_ID>

Hiragana or katakana small letters:
Hiragana small letters U+3041 A, U+3043 I, U+3045 U, U+3047 E, U+3049 O, U+3063 TU, U+3083 YA, U+3085 YU, U+3087 YO, U+308E WA, U+3095 KA, U+3096 KE. 
Katakana small letters U+30A1 A, U+30A3 I, U+30A5 U, U+30A7 E, U+30A9 O, U+30C3 TU, U+30E3 YA, U+30E5 YU, U+30E7 YO, U+30EE WA, U+30F5 KA, U+30F6 KE.
Katakana phonetic extensions U+31F0 KU - U+31FF RO.
Halfwidth katakana small letters U+FF67 A - U+FF6F TU.

Hiragana or katakana prolonged sound marks:
U+30FC KATAKANA-HIRAGANA PROLONGED SOUND MARK and
U+FF70 HALFWIDTH KATAKANA-HIRAGANA PROLONGED SOUND MARK.

N.B. These letters are optionally treated either as nonstarter or
as normal ideographic.  See [JIS X 4051] 6.1.1.

N.B. U+3095, U+3096, U+30F5, U+30F6 are considered to be
neither hiragana nor katakana.

=item C<MASU_MARK() =E<gt> LB_ID>

U+303C MASU MARK.

N.B. Although this character is not kana, it is usually regarded as
abbreviation to sequence of hiragana C<"ます"> or katakana C<"マス">,
MA and SU.

N.B. This character is classified as nonstarter (NS) by [UAX #14]
and as Class 13 (corresponding to ID) by [JIS X 4051].

=back

=head3 East_Asian_Width Properties

Some particular letters of Latin, Greek and Cyrillic scripts have ambiguous
(A) East_Asian_Width property.  Thus, these characters are treated as wide
in C<"EASTASIAN"> context.
Specifying C<TailorEA =E<gt> [ AMBIGUOUS_>*C<() =E<gt> EA_N ]>,
those characters are always treated as narrow.

=over 4

=item C<AMBIGUOUS_ALPHABETICS() =E<gt> EA_N>

Treat all of characters below as East_Asian_Width neutral (N).

=item C<AMBIGUOUS_CYRILLIC() =E<gt> EA_N>

=item C<AMBIGUOUS_GREEK() =E<gt> EA_N>

=item C<AMBIGUOUS_LATIN() =E<gt> EA_N>

Treate letters having ambiguous (A) width of Cyrillic, Greek and Latin scripts
as neutral (N).

=back

On the other hand, despite several characters were occasionally rendered as wide characters by number of implementations for East Asian character sets, they are given narrow (Na) East_Asian_Width property just because they have fullwidth (F) compatibility characters.
Specifying C<TailorEA> as below, those characters are treated as ambiguous
--- wide on C<"EASTASIAN"> context.

=over 4

=item C<QUESTIONABLE_NARROW_SIGNS() =E<gt> EA_A>

U+00A2 CENT SIGN, U+00A3 POUND SIGN, U+00A5 YEN SIGN (or yuan sign),
U+00A6 BROKEN BAR, U+00AC NOT SIGN, U+00AF MACRON.

=back

=head2 Configuration File

Built-in defaults of option parameters for L</new> and L</config> method
can be overridden by configuration files:
F<Unicode/LineBreak/Defaults.pm>.
For more details read F<Unicode/LineBreak/Defaults.pm.sample>.

=head1 BUGS

Please report bugs or buggy behaviors to developer.

CPAN Request Tracker:
L<http://rt.cpan.org/Public/Dist/Display.html?Name=Unicode-LineBreak>.

=head1 VERSION

Consult $VERSION variable.

Development versions of this module may be found at 
L<http://hatuka.nezumi.nu/repos/Unicode-LineBreak/>.

=head2 Conformance to Standards

Character properties this module is based on are defined by
Unicode Standards version 6.0.0.

This module is intended to implement UAX14-C2.

=over 4

=item *

Some ideographic characters may be treated either as NS or as ID by choice.

=item *

Hangul syllables and conjoining jamos may be treated as
either ID or AL by choice.

=item *

Characters assigned to AI may be resolved to either AL or ID by choice.

=item *

Character(s) assigned to CB are not resolved.

=item *

When word segmentation for South East Asian writing systems is not supported,
characters assigned to SA are resolved to AL,
except that characters that have Grapheme_Cluster_Break property value
Extend or SpacingMark be resolved to CM.

=item *

Characters assigned to SG or XX are resolved to AL.

=item *

Code points of following UCS ranges are given fixed property values even
if they have not been assigned any characers.

    Ranges             | lbclass()  | eawidth()  | Description
    -------------------------------------------------------------
    U+3400..U+4DBF     | ID         | W          | CJK ideographs
    U+4E00..U+9FFF     | ID         | W          | CJK ideographs
    U+D800..U+DFFF     | AL (SG)    | N          | Surrogates
    U+E000..U+F8FF     | AL (XX)    | F or N (A) | Private use
    U+F900..U+FAFF     | ID         | W          | CJK ideographs
    U+20000..U+2FFFD   | ID         | W          | CJK ideographs
    U+30000..U+3FFFD   | ID         | W          | CJK ideographs
    U+F0000..U+FFFFD   | AL (XX)    | F or N (A) | Private use
    U+100000..U+10FFFD | AL (XX)    | F or N (A) | Private use
    Other unassigned   | AL (XX)    | N          | Unassigned
    -------------------------------------------------------------

=item *

Characters belonging to General Category Mn, Me, Cc, Cf, Zl or Zp have the
property value Z (nonspacing) defined by this module, regardless of
East_Asian_Width property values assigned by [UAX #11].

=back

=head1 REFERENCES

=over 4

=item [CMOS]

I<The Chicago Manual of Style>, 15th edition.
Chicago University Press, 2003.

=item [JIS X 4051]

JIS X 4051:2004
I<日本語文書の組版方法> (I<Formatting Rules for Japanese Documents>).
Japanese Standards Association, 2004.

=item [UAX #11]

A. Freytag (2008-2009).
I<Unicode Standard Annex #11: East Asian Width>, Revision 17-19.
L<http://unicode.org/reports/tr11/>.

=item [UAX #14]

A. Freytag and A. Heninger (2008-2010).
I<Unicode Standard Annex #14: Unicode Line Breaking Algorithm>, Revision 22-25.
L<http://unicode.org/reports/tr14/>.

=back

=head1 SEE ALSO

L<Text::LineFold>, L<Text::Wrap>.

=head1 AUTHOR

Copyright (C) 2009, 2010 Hatuka*nezumi - IKEDA Soji <hatuka(at)nezumi.nu>.

This program is free software; you can redistribute it and/or modify it 
under the same terms as Perl itself.

=cut
