Markdown.pl: format fancy checkboxes

Unordered list items that begin with '[ ]' or '[x]' and
a space will be formatted to display a fancy checkbox
(and checkmark for "x") when the fancy style sheet is
included in the output.

Without the fancy stylesheet everything will still look
fine, but the fancy stuff won't be there.

A new "--show-stylesheet" option is added to show the
style sheet at the beginning of the output.  When combined
with no arguments and redirecting standard input to
/dev/null it can be used to show just the style sheet.

And, since we're adding a stylesheet, add an item to
make the "code" blocks look a bit nicer too.

Signed-off-by: Kyle J. McKay <mackyle@gmail.com>

Markdown.pl

@@ -46,8 +46,9 @@ exit(&_main(@ARGV)||0) unless caller;
 #
 # Global default settings:
 #
-my ($g_empty_element_suffix, $g_indent_width, $g_tab_width);
+my ($g_style_prefix, $g_empty_element_suffix, $g_indent_width, $g_tab_width);
 BEGIN {
+    $g_style_prefix = "_markdown-";	# Prefix for markdown css class styles
     $g_empty_element_suffix = " />";	# Change to ">" for HTML output
     $g_indent_width = 4;		# Number of spaces considered new level
     $g_tab_width = 4;			# Legacy even though it's wrong
@@ -58,6 +59,9 @@ BEGIN {
 # Globals:
 #
 
+# Style sheet template
+my $g_style_sheet;
+
 # Permanent block id table
 my %g_perm_block_ids;
 
@@ -257,6 +261,7 @@ sub _main {
 	'htmlroot|r=s',
 	'imageroot|i=s',
 	'tabwidth|tab-width=s',
+	'stylesheet|style-sheet',
     );
     if ($cli_opts{'help'}) {
 	pod2usage(-verbose => 2, -exitval => 0);
@@ -289,8 +294,17 @@ sub _main {
     if ($cli_opts{'imageroot'}) {	 # Use image URL prefix
 	$options{img_prefix} = $cli_opts{'imageroot'};
     }
+    if ($cli_opts{'stylesheet'}) {  # Display the style sheet
+	$options{show_styles} = 1;
+    }
     $options{tab_width} = 8 unless defined($options{tab_width});
 
+    #### Show the style sheet if requested
+    if ($options{show_styles}) {
+	my $stylesheet = $g_style_sheet;
+	$stylesheet =~ s/%\(base\)/$g_style_prefix/g;
+	print $stylesheet;
+    }
 
     #### Process incoming text: ###########################
     for (;;) {
@@ -322,6 +336,7 @@ sub Markdown {
     # hashref or a list of name, value paurs.
     %opt = (
 	# set initial defaults
+	style_prefix		=> $g_style_prefix,
 	empty_element_suffix	=> $g_empty_element_suffix,
 	tab_width		=> $g_tab_width,
 	indent_width		=> $g_indent_width,
@@ -382,7 +397,8 @@ sub Markdown {
 
     $text = _UnescapeSpecialChars($text);
 
-    return $text . "\n";
+    $text .= "\n" unless $text eq "";
+    return $text;
 }
 
 
@@ -409,7 +425,8 @@ sub _HashBTCodeBlocks {
 	    $codeblock =~ s/\A\n+//; # trim leading newlines
 	    $codeblock =~ s/\s+\z//; # trim trailing whitespace
 	    $codeblock = _EncodeCode($codeblock); # or run highlighter here
-	    $codeblock = "<div><dl></dl><pre><code>" . $codeblock . "\n</code></pre></div>";
+	    $codeblock = "<div class=\"$opt{style_prefix}code-bt\"><dl></dl><pre><code>"
+		. $codeblock . "\n</code></pre></div>";
 
 	    my $key = block_id($codeblock);
 	    $g_html_blocks{$key} = $codeblock;
@@ -1024,7 +1041,7 @@ sub _DoLists {
 		# Turn double returns into triple returns, so that we can make a
 		# paragraph for the last item in a list, if necessary:
 		$list =~ s/\n\n/\n\n\n/g;
-		my $result = _ProcessListItems($list, $marker_any);
+		my $result = _ProcessListItems($list_type, $list, $marker_any);
 		$result = "<$list_type>\n" . $result . "</$list_type>\n";
 		$result;
 	    }egmx;
@@ -1050,7 +1067,7 @@ sub _DoLists {
 		# Turn double returns into triple returns, so that we can make a
 		# paragraph for the last item in a list, if necessary:
 		$list =~ s/\n\n/\n\n\n/g;
-		my $result = _ProcessListItems($list, $marker_any);
+		my $result = _ProcessListItems($list_type, $list, $marker_any);
 		$result = "<$list_type>\n" . $result . "</$list_type>\n";
 		$result;
 	    }egmx;
@@ -1067,6 +1084,7 @@ sub _ProcessListItems {
 #   into individual list items.
 #
 
+    my $list_type = shift;
     my $list_str = shift;
     my $marker_any = shift;
 
@@ -1097,18 +1115,33 @@ sub _ProcessListItems {
     # trim trailing blank lines:
     $list_str =~ s/\n{2,}\z/\n/;
 
-
     $list_str =~ s{
 	(\n)?				# leading line = $1
 	(^[ ]*)				# leading whitespace = $2
-	($marker_any) [ ]+		# list marker = $3
+	($marker_any) [ ] ([ ]*)	# list marker = $3 leading item space = $4
-	((?s:.+?)			# list item text   = $4
+	((?s:.+?)			# list item text = $5
-	(\n{1,2}))
+	 (?:\n{1,2}))
 	(?= \n* (?: \z | \2 $marker_any [ ]))
     }{
-	my $item = $4;
+	my $item = $5;
 	my $leading_line = $1;
 	my $leading_space = $2;
+	my $leading_item_space = $4;
+	my $liclass = '';
+	my $checkbox = '';
+
+	if ($list_type eq "ul" && !$leading_item_space && $item =~ /^\[([ xX])\] +(.*)$/s) {
+	    my $checkmark = lc $1;
+	    $item = $2;
+	    my ($checkbox_class, $checkbox_val);
+	    if ($checkmark eq "x") {
+		($checkbox_class, $checkbox_val) = ("checkbox-on", "x");
+	    } else {
+		($checkbox_class, $checkbox_val) = ("checkbox-off", "&#160;");
+	    }
+	    $liclass = " class=\"$opt{style_prefix}$checkbox_class\"";
+	    $checkbox = "<span><span></span></span><span></span><span>[<tt>$checkbox_val</tt>]&#160;</span>";
+	}
 
 	if ($leading_line or ($item =~ m/\n{2,}/)) {
 	    $item = _RunBlockGamut(_Outdent($item));
@@ -1120,7 +1153,7 @@ sub _ProcessListItems {
 	    $item = _RunSpanGamut($item);
 	}
 
-	"<li>" . $item . "</li>\n";
+	"<li$liclass>" . $checkbox . $item . "</li>\n";
     }egmx;
 
     $g_list_level--;
@@ -1153,7 +1186,8 @@ sub _DoCodeBlocks {
 	    $codeblock =~ s/\A\n+//; # trim leading newlines
 	    $codeblock =~ s/\s+\z//; # trim trailing whitespace
 
-	    my $result = "<div><dl></dl><pre><code>" . $codeblock . "\n</code></pre></div>";
+	    my $result = "<div class=\"$opt{style_prefix}code\"><dl></dl><pre><code>"
+		. $codeblock . "\n</code></pre></div>";
 	    my $key = block_id($result);
 	    $g_code_blocks{$key} = $result;
 	    "\n\n" . $key . "\n\n";
@@ -1530,12 +1564,107 @@ sub _PrefixURL {
 }
 
 
-1;
+BEGIN {
+    $g_style_sheet = <<'STYLESHEET';
+
+<style type="text/css">
+/* <![CDATA[ */
+
+/* Markdown.pl fancy style sheet
+** Copyright (C) 2017 Kyle J. McKay.
+** All rights reserved.
+**
+** Redistribution and use in source and binary forms, with or without
+** modification, are permitted provided that the following conditions are met:
+**
+**   1. Redistributions of source code must retain the above copyright notice,
+**      this list of conditions and the following disclaimer.
+**
+**   2. Redistributions in binary form must reproduce the above copyright
+**      notice, this list of conditions and the following disclaimer in the
+**      documentation and/or other materials provided with the distribution.
+**
+**   3. Neither the name of the copyright holder nor the names of its
+**      contributors may be used to endorse or promote products derived from
+**      this software without specific prior written permission.
+**
+** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+** AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+** IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+** ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
+** LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+** CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+** SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+** INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+** CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+** ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+** POSSIBILITY OF SUCH DAMAGE.
+*/
+
+div.%(base)code-bt > pre, div.%(base)code > pre {
+	margin: 0 3ex;
+	padding: 1ex;
+	background-color: #eee;
+	overflow: auto;
+}
 
-__DATA__
+li.%(base)checkbox-on,
+li.%(base)checkbox-off {
+	list-style-type: none;
+	display: block;
+}
+li.%(base)checkbox-on > span:first-child + span + span,
+li.%(base)checkbox-off > span:first-child + span + span {
+	position: absolute;
+	clip: rect(0,0,0,0);
+}
+li.%(base)checkbox-on > span:first-child,
+li.%(base)checkbox-off > span:first-child,
+li.%(base)checkbox-on > span:first-child + span,
+li.%(base)checkbox-off > span:first-child + span {
+	display: block;
+	position: absolute;
+	margin-left: -3ex;
+	width: 1em;
+	height: 1em;
+}
+li.%(base)checkbox-on > span:first-child > span:first-child,
+li.%(base)checkbox-off > span:first-child > span:first-child {
+	display: block;
+	position: absolute;
+	left: 0.75pt; top: 0.75pt; right: 0.75pt; bottom: 0.75pt;
+}
+li.%(base)checkbox-on > span:first-child > span:first-child:before,
+li.%(base)checkbox-off > span:first-child > span:first-child:before {
+	display: inline-block;
+	position: relative;
+	right: 1pt;
+	width: 100%;
+	height: 100%;
+	border: 1pt solid;
+	content: "";
+}
+li.%(base)checkbox-on > span:first-child + span:before {
+	position: relative;
+	left: 2pt;
+	bottom: 1pt;
+	font-size: 125%;
+	line-height: 80%;
+	content: "\2713";
+}
 
+/* ]]> */
+</style>
 
-=pod
+STYLESHEET
+    $g_style_sheet =~ s/^\s+//g;
+    $g_style_sheet =~ s/\s+$//g;
+    $g_style_sheet .= "\n";
+}
+
+1;
+
+__DATA__
 
 =head1 NAME
 
@@ -1545,7 +1674,7 @@ Markdown.pl - convert Markdown format text files to HTML
 
 B<Markdown.pl> [B<--help>] [B<--html4tags>] [B<--htmlroot>=I<prefix>]
     [B<--imageroot>=I<prefix>] [B<--version>] [B<--shortversion>]
-    [B<--tabwidth>=I<num>] [--] [I<file>...]
+    [B<--tabwidth>=I<num>] [B<--stylesheet>] [--] [I<file>...]
 
  Options:
    -h                                   show short usage help
@@ -1559,6 +1688,7 @@ B<Markdown.pl> [B<--help>] [B<--html4tags>] [B<--htmlroot>=I<prefix>]
    -V | --version                       show version, authors, license
                                         and copyright
    -s | --shortversion                  show just the version number
+   --stylesheet                         output the fancy style sheet
    --                                   end options and treat next
                                         argument as file
 
@@ -1632,6 +1762,16 @@ Display Markdown's version number and copyright information.
 Display the short-form version number.
 
 
+=item B<--stylesheet>
+
+Include the fancy style sheet at the beginning of the output.  This style
+sheet makes fancy checkboxes and list numbering work.  Without it things
+will still look fine except that the fancy stuff won't be there.
+
+Use this option with no other arguments and redirect standard input to
+/dev/null to get just the style sheet and nothing else.
+
+
 =item B<-h>, B<--help>
 
 Display Markdown's help.  With B<--help> full help is shown, with B<-h> only