Lazy footnotes for Markdown, based on TidBits lazy link style

lazyfootnotes.rb

#!/usr/bin/env ruby
# encoding: utf-8
=begin

http://marked2app.com

Marked 2 preprocessor - "Lazy" footnotes.
Allows use  of `[^]` or `†` footnote references
where the next  [^]: or †: note defines the text of the footnote.

† - Option-T
^ - Shift-6

Footnotes are given random prefixes to avoid duplication of ids within
a page.

Example:

Lorem ipsum dolor sit amet[^], consectetur adipisicing elit, sed do
eiusmod tempor† incididunt ut labore et dolore magna aliqua. Ut enim
ad minim veniam, quis nostrud exercitation[^] ullamco laboris nisi ut
aliquip ex ea commodo consequat.

[^]: This footnote will replace the first `[^]` found in the text.

†: This one will replace the first `†`. The syntaxes are auto-detected
and interchangeable.

[^]: This one replaces the second instance.

Inspired by [tidbits][^] and Carl Johnson†

[^]: http://tidbits.com

†: http://blog.carlsensei.com/
=end

# Marked sends the Markdown text to STDIN when calling the script.
if RUBY_VERSION.to_f > 1.8
	input = STDIN.read.force_encoding('UTF-8')
else
	input = STDIN.read
end

# random prefix and footnote counter
rand = rand(100000) + 100000
counter = 0


def replace_caret(input, prefix, counter)
	input.sub(/(\[)\^(\].*?\[)\^\]:/m) {
		%Q{#{$1}^fn#{prefix}-#{counter.to_s}#{$2}^fn#{prefix}-#{counter.to_s}]:}
	}
end

def replace_cross(input, prefix, counter)
	input.sub(/([^†]+)†(.*?)†:/m) {
		%Q{#{$1}[^fn#{prefix}-#{counter.to_s}]#{$2}[^fn#{prefix}-#{counter.to_s}]:}
	}
end

while input =~ /(\[\^\].*?\[\^\]:|†.*?†:)/m
	idx_caret = input.index(/\[\^\].*?\[\^\]:/m) || false
	idx_cross = input.index(/†.*?†:/m) || false

	break if !idx_caret && !idx_cross

	if ((idx_caret && idx_cross && idx_caret < idx_cross) || (idx_caret && !idx_cross))
		input = replace_caret(input, rand, counter += 1)
	elsif (idx_cross)
		input = replace_cross(input, rand, counter += 1)
	end
end

print input