Generate changelog from git based on tags

changelog.rb

#!/usr/bin/env ruby
#
# This file generates a full changelog from your git history based on your tags.
#
# @example
#   ruby changelog.rb
#
# @example Write to file
#   ruby changelog.rb > CHANGELOG.md

require 'time'

class Changelog
  FORMAT = "%ci [%an] : %s"

  def initialize(depth = 3)
    @depth = depth

    @tags = `git for-each-ref refs/tags --sort=authordate --format='%(refname) | %(authordate)'`
    @tags = @tags.gsub( "refs/tags/", '' ).split("\n").reverse
  end

  def output
    changelog = []
    previous = nil

    tags.each do |tag|
      current, date = tag.split(' | ')

      unless previous.nil?
        # Get the commits between the current and previous tag
        commits = `git log --pretty="format:#{FORMAT}" #{current}...#{previous}`
        commits = commits.split("\n")

        # compose the changelog
        diff = ["# #{current} (#{Time.parse(date) rescue nil})", *commits, "\n"]
        changelog += diff
      end

      previous = current
    end

    changelog
  end

  def each(&block)
    output.each(&block)
  end


  private

  def tags
    @tags[0, @depth]
  end
end

class Tickets
  TICKET_REGEX = /([FBC]).*\[\#(\w+-\d+)\]\s*(.*)$/

  def initialize(changelog)
    @changelog = changelog
  end

  def output
    tickets.keys.sort.map do |id|
      ticket = tickets[id]

      # "%-7s [%s]\n  %s" % [id, ticket[:type], ticket[:messages].join("\n  ")]
      # "%s [%s]\n  %s" % [ticket[:type], id, ticket[:messages].join("\n  ")]
      "%s [%s]" % [ticket[:type], id]
    end
  end

  private

  def tickets
    list = {}

    @changelog.each do |log|
      match = log.match(TICKET_REGEX)
      next if match.nil?

      # line.match(/(?:\w+\/|#)(\d+)/)[1] rescue nil
      # line.match(/\#([0-9A-Z\-]+)/)[1] rescue nil
      type, id, message = match.captures

      if list.key?(id)
        list[id][:messages] << message.strip
      else
        list[id] = {type: type, messages: [message.strip]}
      end
    end

    list
  end
end

changelog = Changelog.new
puts changelog.output

tickets = Tickets.new(changelog)
puts *tickets.output