Markdown.pl: modularize for reusability

Options may now be passed in to the Markdown function and it
may be called multiple times with different options on different
texts with no unwanted interaction between the calls.

Simply `require "Markdown.pl"` and then call Markdown::Markdown.

Or something like this will import the `Markdown` function
regardless of whether it's available in Markdown.pl or Markdown.pm:

  BEGIN {eval {require "Markdown.pl"}}
  use Markdown qw(Markdown);

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

Markdown.pl

@@ -14,11 +14,18 @@ use strict;
 use warnings;
 close(DATA) if fileno(DATA);
 
+require Exporter;
 use Digest::MD5 qw(md5_hex);
-use vars qw($VERSION);
+use File::Basename qw(basename);
+use vars qw($VERSION @ISA @EXPORT_OK);
+@ISA = qw(Exporter);
+@EXPORT_OK = qw(Markdown);
+$INC{__PACKAGE__.'.pm'} = $INC{basename(__FILE__)} unless exists $INC{__PACKAGE__.'.pm'};
+
 $VERSION = '1.0.3';
 # Sun 06 Sep 2015
 
+
 ## Disabled; causes problems under Perl 5.6.1:
 # use utf8;
 # binmode( STDOUT, ":utf8" );  # c.f.: http://acis.openlib.org/dev/perl-unicode-struggle.html
@@ -28,8 +35,6 @@ $VERSION = '1.0.3';
 # Global default settings:
 #
 my $g_empty_element_suffix = " />";	# Change to ">" for HTML output
-my $g_url_prefix = "";			# Prefixed to non-absolute URLs
-my $g_img_prefix = "";			# Prefixed to non-absolute image URLs
 my $g_tab_width = 4;
 
 
@@ -62,6 +67,7 @@ foreach my $char (split //, "\\\`*_{}[]()>#+-.!~") {
 my %g_urls;
 my %g_titles;
 my %g_html_blocks;
+my %opt;
 
 # Used to track when we're inside an ordered or unordered list
 # (see _ProcessListItems() for details):
@@ -191,6 +197,7 @@ elsif (!caller) {
 	use warnings;
 
 	#### Check for command-line switches: #################
+	my %options = ();
 	my %cli_opts;
 	use Getopt::Long;
 	Getopt::Long::Configure('pass_through');
@@ -216,13 +223,13 @@ elsif (!caller) {
 	    exit 0;
 	}
 	if ($cli_opts{'html4tags'}) {		# Use HTML tag style instead of XHTML
-	    $g_empty_element_suffix = ">";
+	    $options{empty_element_suffix} = ">";
 	}
 	if ($cli_opts{'htmlroot'}) {		# Use URL prefix
-	    $g_url_prefix = $cli_opts{'htmlroot'};
+	    $options{url_prefix} = $cli_opts{'htmlroot'};
 	}
 	if ($cli_opts{'imageroot'}) {		# Use image URL prefix
-	    $g_img_prefix = $cli_opts{'imageroot'};
+	    $options{img_prefix} = $cli_opts{'imageroot'};
 	}
 
 
@@ -232,7 +239,7 @@ elsif (!caller) {
 	    local $/;		    # Slurp the whole file
 	    $text = <>;
 	}
-	print Markdown($text);
+	print Markdown($text, \%options);
     }
 }
 
@@ -246,15 +253,35 @@ sub Markdown {
 # and <img> tags get encoded.
 #
     my $text = shift;
+    defined $text or $text='';
+
+    # Any remaining arguments after the first are options; either a single
+    # hashref or a list of name, value paurs.
+    %opt = (
+	# set initial defaults
+	empty_element_suffix	=> $g_empty_element_suffix,
+	tab_width		=> $g_tab_width,
+	url_prefix		=> "",	# Prefixed to non-absolute URLs
+	img_prefix		=> "",	# Prefixed to non-absolute image URLs
+    );
+    my %args = ();
+    if (ref($_[0]) eq "HASH") {
+	%args = %{$_[0]};
+    } else {
+	%args = @_;
+    }
+    while (my ($k,$v) = each %args) {
+	$opt{$k} = $v;
+    }
 
-    # Clear the global hashes. If we don't clear these, you get conflicts
+    # Clear the globals. If we don't clear these, you get conflicts
     # from other articles when generating a page which contains more than
     # one article (e.g. an index page that shows the N most recent
     # articles):
     %g_urls = ();
     %g_titles = ();
     %g_html_blocks = ();
-
+    $g_list_level = 0;
 
     # Standardize line endings:
     $text =~ s{\r\n}{\n}g;  # DOS to Unix
@@ -292,7 +319,7 @@ sub _StripLinkDefinitions {
 # hash references.
 #
     my $text = shift;
-    my $less_than_tab = $g_tab_width - 1;
+    my $less_than_tab = $opt{tab_width} - 1;
 
     # Link defs are in the form: ^[id]: url "optional title"
     while ($text =~ s{
@@ -327,7 +354,7 @@ sub _StripLinkDefinitions {
 
 sub _HashHTMLBlocks {
     my $text = shift;
-    my $less_than_tab = $g_tab_width - 1;
+    my $less_than_tab = $opt{tab_width} - 1;
 
     # Hashify HTML blocks:
     # We only want to do this for block-level HTML tags, such as headers,
@@ -445,9 +472,9 @@ sub _RunBlockGamut {
     $text = _DoHeaders($text);
 
     # Do Horizontal Rules:
-    $text =~ s{^[ ]{0,2}([ ]?\*[ ]?){3,}[ \t]*$}{\n<hr$g_empty_element_suffix\n}gmx;
+    $text =~ s{^[ ]{0,2}([ ]?\*[ ]?){3,}[ \t]*$}{\n<hr$opt{empty_element_suffix}\n}gmx;
-    $text =~ s{^[ ]{0,2}([ ]? -[ ]?){3,}[ \t]*$}{\n<hr$g_empty_element_suffix\n}gmx;
+    $text =~ s{^[ ]{0,2}([ ]? -[ ]?){3,}[ \t]*$}{\n<hr$opt{empty_element_suffix}\n}gmx;
-    $text =~ s{^[ ]{0,2}([ ]? _[ ]?){3,}[ \t]*$}{\n<hr$g_empty_element_suffix\n}gmx;
+    $text =~ s{^[ ]{0,2}([ ]? _[ ]?){3,}[ \t]*$}{\n<hr$opt{empty_element_suffix}\n}gmx;
 
     $text = _DoLists($text);
 
@@ -493,7 +520,7 @@ sub _RunSpanGamut {
     $text = _DoItalicsAndBoldAndStrike($text);
 
     # Do hard breaks:
-    $text =~ s/ {2,}\n/ <br$g_empty_element_suffix\n/g;
+    $text =~ s/ {2,}\n/ <br$opt{empty_element_suffix}\n/g;
 
     return $text;
 }
@@ -678,7 +705,7 @@ sub _DoImages {
 		$title =~ s!  ~ !$g_escape_table{'~'}!gx;
 		$result .=  " title=\"$title\"";
 	    }
-	    $result .= $g_empty_element_suffix;
+	    $result .= $opt{empty_element_suffix};
 	}
 	else {
 	    # If there's no such link ID, leave intact:
@@ -732,7 +759,7 @@ sub _DoImages {
 	    $title =~ s!  ~ !$g_escape_table{'~'}!gx;
 	    $result .=	" title=\"$title\"";
 	}
-	$result .= $g_empty_element_suffix;
+	$result .= $opt{empty_element_suffix};
 
 	$result;
     }xsge;
@@ -795,7 +822,7 @@ sub _DoLists {
 # Form HTML ordered (numbered) and unordered (bulleted) lists.
 #
     my $text = shift;
-    my $less_than_tab = $g_tab_width - 1;
+    my $less_than_tab = $opt{tab_width} - 1;
 
     # Re-usable patterns to match list item bullets and number markers:
     my $marker_ul  = qr/[*+-]/;
@@ -957,11 +984,11 @@ sub _DoCodeBlocks {
 	    (?:\n\n|\A)
 	    (		    # $1 = the code block -- one or more lines, starting with a space/tab
 	      (?:
-		(?:[ ]{$g_tab_width} | \t)  # Lines must start with a tab or a tab-width of spaces
+		(?:[ ]{$opt{tab_width}} | \t)  # Lines must start with a tab or a tab-width of spaces
 		.*\n+
 	      )+
 	    )
-	    ((?=^[ ]{0,$g_tab_width}\S)|\Z) # Lookahead for non-space at line-start, or end of doc
+	    ((?=^[ ]{0,$opt{tab_width}}\S)|\Z) # Lookahead for non-space at line-start, or end of doc
 	}{
 	    my $codeblock = $1;
 	    my $result; # return value
@@ -1364,7 +1391,7 @@ sub _Outdent {
 #
     my $text = shift;
 
-    $text =~ s/^(\t|[ ]{1,$g_tab_width})//gm;
+    $text =~ s/^(\t|[ ]{1,$opt{tab_width}})//gm;
     return $text;
 }
 
@@ -1376,7 +1403,7 @@ sub _Detab {
 #
     my $text = shift;
 
-    $text =~ s{(.*?)\t}{$1.(' ' x ($g_tab_width - length($1) % $g_tab_width))}ge;
+    $text =~ s{(.*?)\t}{$1.(' ' x ($opt{tab_width} - length($1) % $opt{tab_width}))}ge;
     return $text;
 }
 
@@ -1387,11 +1414,11 @@ sub _PrefixURL {
 #
     my $url = shift;
 
-    return $url unless $g_url_prefix ne '' || $g_img_prefix ne '';
+    return $url unless $opt{url_prefix} ne '' || $opt{img_prefix} ne '';
     return $url if $url =~ m,^//, || $url =~ /^[A-Za-z][A-Za-z0-9+.-]*:/;
-    my $ans = $g_url_prefix;
+    my $ans = $opt{url_prefix};
-    $ans = $g_img_prefix
+    $ans = $opt{img_prefix}
-        if $g_img_prefix ne '' && $url =~ /\.(?:png|gif|jpe?g|svg?z)$/i;
+        if $opt{img_prefix} ne '' && $url =~ /\.(?:png|gif|jpe?g|svg?z)$/i;
     return $url unless $ans ne '';
     $ans .= '/' if substr($ans, -1, 1) ne '/';
     $ans .= substr($url, 0, 1) eq '/' ? substr($url, 1) : $url;