mdtoc.rb

#!/usr/bin/env ruby

TOP = 2; MAX = 4

def usage
  puts <<-EOF
Usage: #{$0} FILE.md [TOP [MAX]] [-h]
     FILE.md          Markdown source document
     TOP              top-level Markdown heading level (default #{TOP})
     MAX              maximum heading level (default #{MAX})
EOF
  exit 1
end

class ToCWriter
  def initialize(source_file, top=TOP, max=MAX)
    @source_file = source_file
    @top = top.to_i
    @max = max.to_i
    @count = 1
    @level  = ""
    @header = ""
    @start  = ""
    @anchor = ""
    @seen = []
  end

  def write
    puts "#### Table of contents\n\n"

    File.open(@source_file).each_line do |line|
      next unless line.match(/^#/)

      @level, @header = line.match(/^(#+) *(.*) *$/).captures
      next if ignore_this_header?

      set_anchor
      set_start

      puts "#{@start} [#{@header}](##{@anchor})"
    end
  end

 private

  def ignore_this_header?
    @header == "Table of contents" || \
      @level.length < @top || \
      @level.length > @max
  end

  def set_anchor
    @anchor = @header
      .downcase
      .gsub(/[^a-z\d_\- ]+/, "")
      .gsub(/ /, "-")
    update_if_seen
  end

  def update_if_seen
    inc = 2
    while @seen.include?(@anchor)
      if inc == 2
        @anchor += "-" + inc.to_s
      else
        @anchor.sub!(/-\d+$/, "-" + inc.to_s)
      end
      inc += 1
    end
    @seen << @anchor
  end

  def set_start
    len = @level.length
    if len == @top
      @start = "#{@count}."
      @count += 1
    else
      bullet = len % 2 == 0 ? "-" : "*"
      @start = "    " * (len - @top) + bullet
    end
  end
end

usage if ARGV.length == 0
usage if ARGV[0] == "-h"

if $0 == __FILE__
  ToCWriter.new(*ARGV).write
end