#!/usr/bin/env ruby
require 'octokit'

class PullRequest
  attr_reader :gh, :num

  def initialize(gh, num)
    @gh = gh
    @num = num
  end

  def entry
    pr = gh.pull_request('cucumber/cucumber-ruby', num)
    username = pr['user']['login']
    url = pr['html_url']
    title = pr['title']
    "#{title} ([##{num}](#{url}) [@#{username}](https://github.com/#{username}))"
  end

  def labels
    gh.labels_for_issue('cucumber/cucumber-ruby', num).map { |label| label['name'] }
  end

  def type_label
    types = labels.select { |label| label =~ /^type: / }
    raise('This pull request does not have a \'type\' label on it. Please add one.') if types.empty?

    raise('This pull request has more than one \'type\' label on it. Please choose just one.') if types.length > 1

    types.first
  end
end

class Changelog
  def self.open(path, &block)
    full_path = File.expand_path("#{File.dirname(__FILE__)}/#{path}/CHANGELOG.md")
    log = new(File.read(full_path))
    log.instance_exec(&block)
    File.write(full_path, log.body)
  end

  attr_reader :lines

  def initialize(body)
    @lines = body.lines
  end

  def insert(label, entry)
    section_index = lines.index { |line| line.strip == heading_for(label) }
    raise("Unable to find matching heading in CHANGELOG.md for '#{label}' (#{heading_for(label)})") unless section_index

    lines.insert(section_index + 2, "* #{entry}\n")
  end

  def heading_for(label)
    text = {
      'type: new feature' => 'Added',
      'type: bug' => 'Fixed',
      'type: refactoring / developer experience' => 'Changed'
    }.fetch(label)
    "### #{text}"
  end

  def body
    lines.join
  end
end

begin
  token = ENV['GITHUB_TOKEN'] || raise('You need to set GITHUB_TOKEN')
  num = (ARGV[0] || raise("syntax: #{$PROGRAM_NAME} <PULL-REQUEST-NUMBER>")).to_i

  gh = Octokit::Client.new(access_token: token)
  pr = PullRequest.new(gh, num)

  Changelog.open('..') do
    insert(pr.type_label, pr.entry)
  end
rescue StandardError => e
  abort e.message
end