server.rb

require 'sinatra'
require 'octokit'
require 'dotenv'
require 'pdfkit'

module MarkdownToPDF
  class App < Sinatra::Base
    configure :development do
      Dotenv.load
    end

    configure :production do
      require 'wkhtmltopdf-heroku'
      require 'rack-ssl-enforcer'
      use Rack::SslEnforcer
    end

    def nwo
      "#{params['owner']}/#{params['repo']}"
    end

    def path
      params['splat'].join('/').gsub(/\.pdf$/, '.md')
    end

    def ref
      params['ref']
    end

    def client
      @client ||= Octokit::Client.new access_token: ENV['GITHUB_TOKEN']
    end

    def markdown
      @markdown ||= begin
        response = client.contents nwo, path: path, ref: ref
        Base64.decode64(response.content).force_encoding('utf-8')
      end
    end

    def html
      @html ||= client.markdown markdown, context: nwo
    end

    def stylesheet
      File.expand_path 'public/bootstrap/dist/css/bootstrap.css'
    end

    def kit
      @kit ||= begin
        kit = PDFKit.new(html, page_size: 'Letter')
        kit.stylesheets << stylesheet
        kit
      end
    end

    get '/:owner/:repo/blob/:ref/*' do
      content_type 'application/pdf'
      kit.to_pdf
    end
  end
end