# First encode possible HTML, because the text is 
# supposed to be plain text
use HTML::Entities();
$text = HTML::Entities::encode($text);

# Convert Windows or Mac line terminators to Unix single \n
$text =~ s/\r\n|\n\r/\n/g;

# Remove leading and trailing white space
$text =~ s/^\s*//;
$text =~ s/\s*$//g

# Convert all double line breaks to para tags
$text =~ s|\n\s*\n|</p><p>|g

# Convert any single line breaks to br tags
$text =~ s|\n\s*|<br />|g

# If text is more than just white space, add opening and
# closing para tags
$text = "<p>$text</p>" if $text;