package Font::TTF::Coverage;

=head1 TITLE

Font::TTF::Coverage - Opentype coverage and class definition objects

=head1 DESCRIPTION

Coverage tables and class definition objects are virtually identical concepts
in OpenType. Their difference comes purely in their storage. Therefore we can
say that a coverage table is a class definition in which the class definition
for each glyph is the corresponding index in the coverage table. The resulting
data structure is that a Coverage table has the following fields:

=item cover

A boolean to indicate whether this table is a coverage table (TRUE) or a
class definition (FALSE)

=item val

A hash of glyph ids against values (either coverage index or class value)

=item fmt

The storage format used is given here, but is recalculated when the table
is written out.

=head1 METHODS

=cut

=head2 new($isCover)

Creates a new coverage table or class definition table, depending upon the
value of $isCover

=cut

sub new
{
    my ($class, $isCover) = @_;
    my ($self) = {};

    $self->{'cover'} = $isCover;
    bless $self, $class;
}


=head2 read($fh)

Reads the coverage/class table from the given file handle

=cut

sub read
{
    my ($self, $fh) = @_;
    my ($dat, $fmt, $num, $i, $c);

    $fh->read($dat, 4);
    ($fmt, $num) = unpack("n2", $dat);
    $self->{'fmt'} = $fmt;

    if ($self->{'cover'})
    {
        if ($fmt == 1)
        {
            $fh->read($dat, $num << 1);
            map {$self->{'val'}{$_} = $i++} unpack("n*", $dat);
        } elsif ($fmt == 2)
        {
            $fh->read($dat, $num * 6);
            for ($i = 0; $i < $num; $i++)
            {
                ($first, $last, $c) = unpack("n3", substr($dat, $i * 6, 6));
                map {$self->{'val'}{$_} = $c++} ($first .. $last);
            }
        }
    } elsif ($fmt == 1)
    {
        $fh->read($dat, 2);
        $first = $num;
        ($num) = unpack("n", $dat);
        $fh->read($dat, $num << 1);
        map {$self->{'val'}{$first++} = $_} unpack("n*", $dat);
    } elsif ($fmt == 2)
    {
        $fh->read($dat, $num * 6);
        for ($i = 0; $i < $num; $i++)
        {
            ($first, $last, $c) = unpack("n3", substr($dat, $i * 6, 6));
            map {$self->{'val'}{$_} = $c} ($first .. $last);
        }
    }
    $self;
}


=head2 out($fh, $state)

Writes the coverage/class table to the given file handle. If $state is 1 then
the output string is returned rather than being output to a filehandle.

=cut

sub out
{
    my ($self, $fh, $state) = @_;
    my ($g, $eff, $grp, $out);
    my ($shipout) = ($state ? sub {$out .= $_[0];} : sub {$fh->print($_[0]);});
    my (@gids) = sort {$a <=> $b} keys %{$self->{'val'}};

    $fmt = 1; $grp = 1;
    for ($i = 1; $i <= $#gids; $i++)
    {
        if ($self->{'val'}{$gids[$i]} < $self->{'val'}{$gids[$i-1]} && $self->{'cover'})
        {
            $fmt = 2;
            last;
        } elsif ($gids[$i] == $gids[$i-1] + 1)
        { $eff++; }
        else
        { $grp++; }
    }
    if ($self->{'cover'})
    { $fmt = 2 if ($eff / $grp > 4); }
    else
    { $fmt = 2 if ($grp > 1); }
    
    if ($fmt == 1 && $self->{'cover'})
    {
        my ($last) = 0;
        &$shipout(pack('n2', 1, $self->{'val'}{$gids[-1]} + 1));
        &$shipout(pack('n*', @gids));
    } elsif ($fmt == 1)
    {
        my ($last) = $gids[0];
        &$shipout(pack("n3", 1, $last, $gids[-1] - $last + 1));
        foreach $g (@gids)
        {
            if ($g > $last + 1)
            { &$shipout(pack('n*', 0 x ($g - $last - 1))); }
            &$shipout(pack('n', $self->{'val'}{$g}));
            $last = $g;
        }
    } else
    {
        my ($start, $end, $ind, $numloc, $endloc, $num);
        &$shipout(pack("n2", 2, 0));
        $numloc = $fh->tell() - 2 unless $state;

        $start = 0; $end = 0; $num = 0;
        while ($end < $#gids)
        {
            if ($gids[$end + 1] == $gids[$end] + 1
                && $self->{'val'}{$gids[$end + 1]}
                        == $self->{'val'}{$gids[$end]}
                           + ($self->{'cover'} ? 1 : 0))
            {
                $end++;
                next;
            }

            &$shipout(pack("n3", $gids[$start], $gids[$end],
                    $self->{'val'}{$gids[$start]}));
            $start = $end + 1;
            $end++;
            $num++;
        }
        &$shipout(pack("n3", $gids[$start], $gids[$end],
                $self->{'val'}{$gids[$start]}));
        $num++;
        if ($state)
        { substr($out, 2, 2) = pack('n', $num); }
        else
        {
            $endloc = $fh->tell();
            $fh->seek($numloc, 0);
            $fh->print(pack("n", $num));
            $fh->seek($endloc, 0);
        }
    }
    return ($state ? $out : $self);
}


=head2 $c->out_xml($context)

Outputs this coverage/class in XML

=cut

sub out_xml
{
    my ($self, $context, $depth) = @_;
    my ($fh) = $context->{'fh'};

    $fh->print("$depth<" . ($self->{'cover'} ? 'coverage' : 'class') . ">\n");
    foreach $gid (sort {$a <=> $b} keys %{$self->{'val'}})
    {
        $fh->printf("$depth$context->{'indent'}<gref glyph='%s' val='%s'/>\n", $gid, $self->{'val'}{$gid});
    }
    $fh->print("$depth</" . ($self->{'cover'} ? 'coverage' : 'class') . ">\n");
    $self;
}

=head1 AUTHOR

Martin Hosken Martin_Hosken@sil.org. See L<Font::TTF::Font> for copyright and
licensing.

=cut

1;

