shitty_markdown.rb

# This class renders an undefined subset of Markdown to HTML

class Markdown

	def initialize(fileName)
		@input = preprocess(File.read(fileName))
		@line_count = @input.lines.count
		@line_state = []
		@line_flags = {
			isCodeBlock: false
		}
		@line_text = []
		
		@tokenMap = { # This should be put somewhere else
			"#" => :h1,
			"##" => :h2,
			"###" => :h3,
			"*" => :bullet
		}
		
		@tagOpen = { # This should be put somewhere else
			:h1 => "<h1>",
			:h2 => "<h2>",
			:h3 => "<h3>",
			:codeBlock => "<pre><code>",
			:lineBreak => "</p>\n",
			:quote => "<blockquote><p>",
			:rule => "<hr>\n",
			:bullet => "<ul>"
		}
		
		@tagClose = { # This should be put somewhere else
			:h1 => "</h1>",
			:h2 => "</h2>",
			:h3 => "</h3>",
			:codeBlock => "</code></pre>",
			:lineBreak => "<p>",
			:quote => "</p></blockquote>",
			:rule => "",
			:bullet => "</ul>"
		}
		
		@escapees = "\\*[]()`"
	end

	def render() # Returns an HTML string of the rendered Markdown.
		parse()
		return renderHTML()
	end
	
private

	def preprocess(str)
		return str.gsub(/^###include \".+\"$/) do |s| ###include so doesn't conflict with code that may exist
			filename = s[/(?<=\").+(?=\")/] #" not the best way of doing this?
			replacement = File.read(filename)
			preprocess(replacement) if filename[/\.md$/] # recursive preprocessing TODO: test this...
			replacement
		end
	end

	def parse
		index = -1
		@input.each_line do |line|
			index += 1
			@line_state[index] = []
			line.chomp!
			
			if (line == "") then
				@line_state[index] = [:lineBreak]
				next
			elsif (line == "```") then
				@line_flags[:isCodeBlock] = !@line_flags[:isCodeBlock]
				next
			elsif (line == "---") then
				@line_state[index] = [:rule]
				next
			end
				
			if (@line_flags[:isCodeBlock]) then
				@line_state[index].push(:codeBlock)
				@line_text[index] = escapeInline(line)
				next
			end
					
			prefixTokens = line[/^\W*/].delete(" ") # extract tokens that occur at the start of a line ie >, #, * etc.
			prefixTokens = prefixTokens.scan(/((.)\2*)/).map(&:first) # split into runs of the same token i.e "###>>" => ["###", ">>"]
			
			@line_text[index] = line[/\w.*$/] # content of the line, not including initial tokens
			
			prefixTokens.each do |token|
				if (token[0] == ">")
					token.length.times { @line_state[index].push(:quote) }
				else
					@line_state[index].push(@tokenMap[token])
				end
			end
			
			@line_state[index].push(:lineBreak) if (@line_text[index][-3..-1] == "  ")
		end
		
	end
	
	def parseLine(line) # TODO decouple parsing and rendering
		line = escapeHTML(line)
		
		# my syntax highlighter really hates these regexps
		line.gsub!(/(?<!\\)`.+?[^\\]`/){|s| "<code>#{escapeInline(s[1..-2])}</code>"} #" inline code
		line.gsub!(/\[.+?\]\(.+?\)/){|s| "<a href=\"#{s.split("](")[1][0..-2]}\">#{s.split("](")[0][1..-1]}</a>"} # hyperlink
		line.gsub!(/(?<!\\)\*\*.+?[^\\]\*\*/){|s| "<strong>#{s[2..-3]}</strong>"} # bold
		line.gsub!(/(?<!\\)\*.+?[^\\]\*/){|s| "<em>#{s[1..-2]}</em>"} # italics

		return unescapeMarkdown(line)
	end
	
	def escapeHTML(str)
		str.gsub!("&", "&amp;")
		str.gsub!("<", "&lt;")
		str.gsub!(">", "&gt;")
		return str
	end
	
	def escapeInline(str) # escape inline markdown
		@escapees.each_char do |c|
			str.gsub!(c, "\\\\" + c) # I'm not sure why I need four backslashes here...
		end
		return str
	end
	
	def unescapeMarkdown(str)
		@escapees.each_char do |c|
			str.gsub!("\\" + c, c)
		end
		return str
	end
	
	def renderHTML
		output = "<p>"
	
		@line_count.times do |index|
			prevState = @line_state[index-1] || []
		
			diffIndex = 0
			while (prevState[diffIndex] == @line_state[index][diffIndex] && prevState[diffIndex] != nil) do
				diffIndex += 1
			end
			
			closedTags = prevState[diffIndex..-1].reverse # close tags in reverse order
			openedTags = @line_state[index][diffIndex..-1]
		
			closedTags.each do |tag|
				output += @tagClose[tag]
			end
			
			output += "\n"
			
			openedTags.each do |tag|
				output +=  @tagOpen[tag]
			end
			
			lineOut = parseLine(@line_text[index] || "")
			
			if @line_state[index].include? :bullet then
				lineOut = "<li>#{lineOut}</li>"
			end
			
			output += lineOut
		
		end
		
		output += "</p>"
		
		return output
		
	end
	
end

Example usage:

require_relative "../markdown"
md = Markdown.new("test.md")
puts md.render()