+ Subtitle::SSA->style_usage

lib/Subtitle/SSA.pm

@@ -187,4 +187,34 @@ sub build {
   return join($self->{eol}, @lines);
 }
 
+sub style_usage {
+  my ($self) = @_;
+
+  my $styles = {};
+  foreach my $s (@{ $self->{styles} }) {
+    $styles->{ $s->{name} } = 0;
+  }
+
+  my $stats = {};
+  foreach my $e (@{ $self->{events} }) {
+    my $sn = $e->{style} || 'Default';
+    if ($sn eq '*Default') {
+      # even libass author not knows what really '*' means
+      $sn = 'Default';
+    }
+    $stats->{$sn} //= 0;
+    $stats->{$sn}++;
+    next if exists $styles->{$sn};
+    my $msg = sprintf "Event uses style named '%s' but it's not defined", $sn;
+    $self->log(warn => $msg);
+  }
+
+  my @unused = grep { $stats->{$_} == 0 } keys %{ $stats };
+  foreach my $u (@unused) {
+    $self->log(warn => "Style '$u' not used by any event");
+  }
+
+  return $stats;
+}
+
 1;