all_versions = [ '~> 1.8.1' ]
before_2_2_0 = [ '~> 1.7.7', '~> 1.6.8', '~> 1.5.5' ]
before_2_0_0 = [ '~> 1.4.6', '~> 1.2.4', '~> 1.1.9' ]
before_1_9_2 = [ '1.1.2' ]

json_gems = all_versions.dup
json_gems += before_2_2_0 if RUBY_VERSION < '2.2.0'
json_gems += before_2_0_0 if RUBY_VERSION < '2.0.0'
json_gems += before_1_9_2 if RUBY_VERSION < '1.9.2'

if defined?(RUBY_ENGINE) && RUBY_ENGINE == "rbx"
  json_gems.delete('~> 1.7.7')
end

if defined?(RUBY_ENGINE) && RUBY_ENGINE == "jruby"
  json_gems.delete('~> 1.2.4')
  json_gems.delete('~> 1.1.9')
end

json_gems.each do |version|
  gemfile <<-RB
    gem 'rack'
    gem 'json', '#{version}'
  RB
end