require "tmpdir"
require "digest/md5"
require "benchmark"
require "rubygems"
require "language_pack"
require "language_pack/base"
require "language_pack/ruby_version"
require "language_pack/helpers/nodebin"
require "language_pack/helpers/node_installer"
require "language_pack/helpers/yarn_installer"
require "language_pack/helpers/layer"
require "language_pack/helpers/binstub_check"
require "language_pack/version"

# base Ruby Language Pack. This is for any base ruby app.
class LanguagePack::Ruby < LanguagePack::Base
  NAME                 = "ruby"
  LIBYAML_VERSION      = "0.1.7"
  LIBYAML_PATH         = "libyaml-#{LIBYAML_VERSION}"
  RBX_BASE_URL         = "http://binaries.rubini.us/heroku"
  NODE_BP_PATH         = "vendor/node/bin"

  Layer = LanguagePack::Helpers::Layer

  # detects if this is a valid Ruby app
  # @return [Boolean] true if it's a Ruby app
  def self.use?
    instrument "ruby.use" do
      File.exist?("Gemfile")
    end
  end

  def self.bundler
    @@bundler ||= LanguagePack::Helpers::BundlerWrapper.new.install
  end

  def bundler
    self.class.bundler
  end

  def initialize(*args)
    super(*args)
    @fetchers[:mri]    = LanguagePack::Fetcher.new(VENDOR_URL, @stack)
    @fetchers[:rbx]    = LanguagePack::Fetcher.new(RBX_BASE_URL, @stack)
    @node_installer    = LanguagePack::Helpers::NodeInstaller.new
    @yarn_installer    = LanguagePack::Helpers::YarnInstaller.new
  end

  def name
    "Ruby"
  end

  def default_addons
    instrument "ruby.default_addons" do
      add_dev_database_addon
    end
  end

  def default_config_vars
    instrument "ruby.default_config_vars" do
      vars = {
        "LANG" => env("LANG") || "en_US.UTF-8",
      }

      ruby_version.jruby? ? vars.merge({
        "JRUBY_OPTS" => default_jruby_opts
      }) : vars
    end
  end

  def default_process_types
    instrument "ruby.default_process_types" do
      {
        "rake"    => "bundle exec rake",
        "console" => "bundle exec irb"
      }
    end
  end

  def best_practice_warnings
    if bundler.has_gem?("asset_sync")
      warn(<<-WARNING)
You are using the `asset_sync` gem.
This is not recommended.
See https://devcenter.heroku.com/articles/please-do-not-use-asset-sync for more information.
WARNING
    end
  end

  def compile
    instrument 'ruby.compile' do
      # check for new app at the beginning of the compile
      new_app?
      Dir.chdir(build_path)
      remove_vendor_bundle
      warn_bundler_upgrade
      warn_bad_binstubs
      install_ruby(slug_vendor_ruby, build_ruby_path)
      setup_language_pack_environment(
        ruby_layer_path: File.expand_path("."),
        gem_layer_path: File.expand_path("."),
        bundle_path: "vendor/bundle",
        bundle_default_without: "development:test"
      )
      allow_git do
        install_bundler_in_app(slug_vendor_base)
        load_bundler_cache
        build_bundler
        post_bundler
        create_database_yml
        install_binaries
        run_assets_precompile_rake_task
      end
      config_detect
      best_practice_warnings
      warn_outdated_ruby
      setup_profiled(ruby_layer_path: "$HOME", gem_layer_path: "$HOME") # $HOME is set to /app at run time
      setup_export
      cleanup
      super
    end
  rescue => e
    warn_outdated_ruby
    raise e
  end


  def build
    new_app?
    remove_vendor_bundle
    warn_bad_binstubs
    ruby_layer = Layer.new(@layer_dir, "ruby", launch: true)
    install_ruby("#{ruby_layer.path}/#{slug_vendor_ruby}")
    ruby_layer.metadata[:version] = ruby_version.version
    ruby_layer.metadata[:patchlevel] = ruby_version.patchlevel if ruby_version.patchlevel
    ruby_layer.metadata[:engine] = ruby_version.engine.to_s
    ruby_layer.metadata[:engine_version] = ruby_version.engine_version
    ruby_layer.write

    gem_layer = Layer.new(@layer_dir, "gems", launch: true, cache: true, build: true)
    setup_language_pack_environment(
      ruby_layer_path: ruby_layer.path,
      gem_layer_path: gem_layer.path,
      bundle_path: "#{gem_layer.path}/vendor/bundle",
      bundle_default_without: "development:test"
    )
    allow_git do
      # TODO install bundler in separate layer
      topic "Loading Bundler Cache"
      gem_layer.validate! do |metadata|
        valid_bundler_cache?(gem_layer.path, gem_layer.metadata)
      end
      install_bundler_in_app("#{gem_layer.path}/#{slug_vendor_base}")
      build_bundler
      # TODO post_bundler might need to be done in a new layer
      bundler.clean
      gem_layer.metadata[:gems] = Digest::SHA2.hexdigest(File.read("Gemfile.lock"))
      gem_layer.metadata[:stack] = @stack
      gem_layer.metadata[:ruby_version] = run_stdout(%q(ruby -v)).strip
      gem_layer.metadata[:rubygems_version] = run_stdout(%q(gem -v)).strip
      gem_layer.metadata[:buildpack_version] = BUILDPACK_VERSION
      gem_layer.write

      create_database_yml
      # TODO replace this with multibuildpack stuff? put binaries in their own layer?
      install_binaries
      run_assets_precompile_rake_task
    end
    setup_profiled(ruby_layer_path: ruby_layer.path, gem_layer_path: gem_layer.path)
    setup_export(gem_layer)
    config_detect
    best_practice_warnings
    cleanup

    super
  end

  def cleanup
  end

  def config_detect
  end

private

  # A bad shebang line looks like this:
  #
  # ```
  # #!/usr/bin/env ruby2.5
  # ```
  #
  # Since `ruby2.5` is not a valid binary name
  #
  def warn_bad_binstubs
    check = LanguagePack::Helpers::BinstubCheck.new(app_root_dir: Dir.pwd, warn_object: self)
    check.call
  end

  def default_malloc_arena_max?
    return true if @metadata.exists?("default_malloc_arena_max")
    return @metadata.touch("default_malloc_arena_max") if new_app?

    return false
  end

  def warn_bundler_upgrade
    old_bundler_version  = @metadata.read("bundler_version").strip if @metadata.exists?("bundler_version")

    if old_bundler_version && old_bundler_version != bundler.version
      warn(<<-WARNING, inline: true)
Your app was upgraded to bundler #{ bundler.version }.
Previously you had a successful deploy with bundler #{ old_bundler_version }.

If you see problems related to the bundler version please refer to:
https://devcenter.heroku.com/articles/bundler-version#known-upgrade-issues

WARNING
    end
  end

  # For example "vendor/bundle/ruby/2.6.0"
  def self.slug_vendor_base
    @slug_vendor_base ||= begin
      command = %q(ruby -e "require 'rbconfig';puts \"vendor/bundle/#{RUBY_ENGINE}/#{RbConfig::CONFIG['ruby_version']}\"")
      out = run_no_pipe(command, user_env: true).strip
      error "Problem detecting bundler vendor directory: #{out}" unless $?.success?
      out
    end
  end

  # the relative path to the bundler directory of gems
  # @return [String] resulting path
  def slug_vendor_base
    instrument 'ruby.slug_vendor_base' do
      @slug_vendor_base ||= self.class.slug_vendor_base
    end
  end

  # the relative path to the vendored ruby directory
  # @return [String] resulting path
  def slug_vendor_ruby
    "vendor/#{ruby_version.version_without_patchlevel}"
  end

  # the absolute path of the build ruby to use during the buildpack
  # @return [String] resulting path
  def build_ruby_path
    "/tmp/#{ruby_version.version_without_patchlevel}"
  end

  # fetch the ruby version from bundler
  # @return [String, nil] returns the ruby version if detected or nil if none is detected
  def ruby_version
    instrument 'ruby.ruby_version' do
      return @ruby_version if @ruby_version
      new_app           = !File.exist?("vendor/heroku")
      last_version_file = "buildpack_ruby_version"
      last_version      = nil
      last_version      = @metadata.read(last_version_file).strip if @metadata.exists?(last_version_file)

      @ruby_version = LanguagePack::RubyVersion.new(bundler.ruby_version,
        is_new:       new_app,
        last_version: last_version)
      return @ruby_version
    end
  end

  def set_default_web_concurrency
    <<-EOF
case $(ulimit -u) in
256)
  export HEROKU_RAM_LIMIT_MB=${HEROKU_RAM_LIMIT_MB:-512}
  export WEB_CONCURRENCY=${WEB_CONCURRENCY:-2}
  ;;
512)
  export HEROKU_RAM_LIMIT_MB=${HEROKU_RAM_LIMIT_MB:-1024}
  export WEB_CONCURRENCY=${WEB_CONCURRENCY:-4}
  ;;
16384)
  export HEROKU_RAM_LIMIT_MB=${HEROKU_RAM_LIMIT_MB:-2560}
  export WEB_CONCURRENCY=${WEB_CONCURRENCY:-8}
  ;;
32768)
  export HEROKU_RAM_LIMIT_MB=${HEROKU_RAM_LIMIT_MB:-6144}
  export WEB_CONCURRENCY=${WEB_CONCURRENCY:-16}
  ;;
*)
  ;;
esac
EOF
  end

  # default JRUBY_OPTS
  # return [String] string of JRUBY_OPTS
  def default_jruby_opts
    "-Xcompile.invokedynamic=false"
  end

  # sets up the environment variables for the build process
  def setup_language_pack_environment(ruby_layer_path:, gem_layer_path:, bundle_path:, bundle_default_without:)
    instrument 'ruby.setup_language_pack_environment' do
      if ruby_version.jruby?
        ENV["PATH"] += ":bin"
        ENV["JRUBY_OPTS"] = env('JRUBY_BUILD_OPTS') || env('JRUBY_OPTS')
      end
      setup_ruby_install_env(ruby_layer_path)

      # By default Node can address 1.5GB of memory, a limitation it inherits from
      # the underlying v8 engine. This can occasionally cause issues during frontend
      # builds where memory use can exceed this threshold.
      #
      # This passes an argument to all Node processes during the build, so that they
      # can take advantage of all available memory on the build dynos.
      ENV["NODE_OPTIONS"] ||= "--max_old_space_size=2560"

      # TODO when buildpack-env-args rolls out, we can get rid of
      # ||= and the manual setting below
      default_config_vars.each do |key, value|
        ENV[key] ||= value
      end

      paths = []
      gem_path = "#{gem_layer_path}/#{slug_vendor_base}"
      ENV["GEM_PATH"] = gem_path
      ENV["GEM_HOME"] = gem_path

      ENV["DISABLE_SPRING"] = "1"

      # Rails has a binstub for yarn that doesn't work for all applications
      # we need to ensure that yarn comes before local bin dir for that case
      paths << yarn_preinstall_bin_path if yarn_preinstalled?

      # Need to remove `./bin` folder since it links to the wrong --prefix ruby binstubs breaking require in Ruby 1.9.2 and 1.8.7.
      # Because for 1.9.2 and 1.8.7 there is a "build" ruby and a non-"build" Ruby
      paths << "#{File.expand_path(".")}/bin" unless ruby_version.ruby_192_or_lower?

      paths << "#{gem_layer_path}/#{bundler_binstubs_path}" # Binstubs from bundler, eg. vendor/bundle/bin
      paths << "#{gem_layer_path}/#{slug_vendor_base}/bin"  # Binstubs from rubygems, eg. vendor/bundle/ruby/2.6.0/bin
      paths << ENV["PATH"]

      ENV["PATH"] = paths.join(":")

      ENV["BUNDLE_WITHOUT"] = env("BUNDLE_WITHOUT") || bundle_default_without
      if ENV["BUNDLE_WITHOUT"].include?(' ')
        ENV["BUNDLE_WITHOUT"] = ENV["BUNDLE_WITHOUT"].tr(' ', ':')

        warn("Your BUNDLE_WITHOUT contains a space, we are converting it to a colon `:` BUNDLE_WITHOUT=#{ENV["BUNDLE_WITHOUT"]}", inline: true)
      end
      ENV["BUNDLE_PATH"] = bundle_path
      ENV["BUNDLE_BIN"] = bundler_binstubs_path
      ENV["BUNDLE_DEPLOYMENT"] = "1"
      ENV["BUNDLE_GLOBAL_PATH_APPENDS_RUBY_SCOPE"] = "1" if bundler.needs_ruby_global_append_path?
    end
  end

  # Sets up the environment variables for subsequent processes run by
  # muiltibuildpack. We can't use profile.d because $HOME isn't set up
  def setup_export(layer = nil)
    instrument 'ruby.setup_export' do
      if layer
        paths = ENV["PATH"]
      else
        paths = ENV["PATH"].split(":").map do |path|
          /^\/.*/ !~ path ? "#{build_path}/#{path}" : path
        end.join(":")
      end

      # TODO ensure path exported is correct
      set_export_path "PATH", paths, layer

      if layer
        gem_path = "#{layer.path}/#{slug_vendor_base}"
      else
        gem_path = "#{build_path}/#{slug_vendor_base}"
      end
      set_export_path "GEM_PATH", gem_path, layer
      set_export_default "LANG", "en_US.UTF-8", layer

      # TODO handle jruby
      if ruby_version.jruby?
        set_export_default "JRUBY_OPTS", default_jruby_opts
      end

      set_export_default "BUNDLE_PATH", ENV["BUNDLE_PATH"], layer
      set_export_default "BUNDLE_WITHOUT", ENV["BUNDLE_WITHOUT"], layer
      set_export_default "BUNDLE_BIN", ENV["BUNDLE_BIN"], layer
      set_export_default "BUNDLE_GLOBAL_PATH_APPENDS_RUBY_SCOPE", ENV["BUNDLE_GLOBAL_PATH_APPENDS_RUBY_SCOPE"], layer if bundler.needs_ruby_global_append_path?
      set_export_default "BUNDLE_DEPLOYMENT", ENV["BUNDLE_DEPLOYMENT"], layer if ENV["BUNDLE_DEPLOYMENT"] # Unset on windows since we delete the Gemfile.lock
    end
  end

  # sets up the profile.d script for this buildpack
  def setup_profiled(ruby_layer_path: , gem_layer_path: )
    instrument 'setup_profiled' do
      profiled_path = []

      # Rails has a binstub for yarn that doesn't work for all applications
      # we need to ensure that yarn comes before local bin dir for that case
      if yarn_preinstalled?
        profiled_path << yarn_preinstall_bin_path.gsub(File.expand_path("."), "$HOME")
      elsif has_yarn_binary?
        profiled_path << "#{ruby_layer_path}/vendor/#{@yarn_installer.binary_path}"
      end
      profiled_path << "$HOME/bin" # /app in production
      profiled_path << "#{gem_layer_path}/#{bundler_binstubs_path}" # Binstubs from bundler, eg. vendor/bundle/bin
      profiled_path << "#{gem_layer_path}/#{slug_vendor_base}/bin"  # Binstubs from rubygems, eg. vendor/bundle/ruby/2.6.0/bin
      profiled_path << "$PATH"

      set_env_default  "LANG",     "en_US.UTF-8"
      set_env_override "GEM_PATH", "#{gem_layer_path}/#{slug_vendor_base}:$GEM_PATH"
      set_env_override "PATH",      profiled_path.join(":")
      set_env_override "DISABLE_SPRING", "1"

      set_env_default "MALLOC_ARENA_MAX", "2"     if default_malloc_arena_max?

      web_concurrency = env("SENSIBLE_DEFAULTS") ? set_default_web_concurrency : ""
      add_to_profiled(web_concurrency, filename: "WEB_CONCURRENCY.sh", mode: "w") # always write that file, even if its empty (meaning no defaults apply), for interop with other buildpacks - and we overwrite the file rather than appending (which is the default)

      # TODO handle JRUBY
      if ruby_version.jruby?
        set_env_default "JRUBY_OPTS", default_jruby_opts
      end

      set_env_default "BUNDLE_PATH", ENV["BUNDLE_PATH"]
      set_env_default "BUNDLE_WITHOUT", ENV["BUNDLE_WITHOUT"]
      set_env_default "BUNDLE_BIN", ENV["BUNDLE_BIN"]
      set_env_default "BUNDLE_GLOBAL_PATH_APPENDS_RUBY_SCOPE", ENV["BUNDLE_GLOBAL_PATH_APPENDS_RUBY_SCOPE"] if bundler.needs_ruby_global_append_path?
      set_env_default "BUNDLE_DEPLOYMENT", ENV["BUNDLE_DEPLOYMENT"] if ENV["BUNDLE_DEPLOYMENT"] # Unset on windows since we delete the Gemfile.lock
    end
  end

  def warn_outdated_ruby
    return unless defined?(@outdated_version_check)

    @warn_outdated ||= begin
      @outdated_version_check.join

      warn_outdated_minor
      warn_outdated_eol
      warn_stack_upgrade
      true
    end
  end

  def warn_stack_upgrade
    return unless defined?(@ruby_download_check)
    return unless @ruby_download_check.next_stack(current_stack: stack)
    return if @ruby_download_check.exists_on_next_stack?(current_stack: stack)

    warn(<<~WARNING)
      Your Ruby version is not present on the next stack

      You are currently using #{ruby_version.version_for_download} on #{stack} stack.
      This version does not exist on #{@ruby_download_check.next_stack(current_stack: stack)}. In order to upgrade your stack you will
      need to upgrade to a supported Ruby version.

      For a list of supported Ruby versions see:
        https://devcenter.heroku.com/articles/ruby-support#supported-runtimes

      For a list of the oldest Ruby versions present on a given stack see:
        https://devcenter.heroku.com/articles/ruby-support#oldest-available-runtimes
    WARNING
  end

  def warn_outdated_eol
    return unless @outdated_version_check.maybe_eol?

    if @outdated_version_check.eol?
      warn(<<~WARNING)
        EOL Ruby Version

        You are using a Ruby version that has reached its End of Life (EOL)

        We strongly suggest you upgrade to Ruby #{@outdated_version_check.suggest_ruby_eol_version} or later

        Your current Ruby version no longer receives security updates from
        Ruby Core and may have serious vulnerabilities. While you will continue
        to be able to deploy on Heroku with this Ruby version you must upgrade
        to a non-EOL version to be eligible to receive support.

        Upgrade your Ruby version as soon as possible.

        For a list of supported Ruby versions see:
          https://devcenter.heroku.com/articles/ruby-support#supported-runtimes
      WARNING
    else
      # Maybe EOL
      warn(<<~WARNING)
        Potential EOL Ruby Version

        You are using a Ruby version that has either reached its End of Life (EOL)
        or will reach its End of Life on December 25th of this year.

        We suggest you upgrade to Ruby #{@outdated_version_check.suggest_ruby_eol_version} or later

        Once a Ruby version becomes EOL, it will no longer receive
        security updates from Ruby core and may have serious vulnerabilities.

        Please upgrade your Ruby version.

        For a list of supported Ruby versions see:
          https://devcenter.heroku.com/articles/ruby-support#supported-runtimes
      WARNING
    end
  end

  def warn_outdated_minor
    return if @outdated_version_check.latest_minor_version?

    warn(<<~WARNING)
      There is a more recent Ruby version available for you to use:

      #{@outdated_version_check.suggested_ruby_minor_version}

      The latest version will include security and bug fixes. We always recommend
      running the latest version of your minor release.

      Please upgrade your Ruby version.

      For all available Ruby versions see:
        https://devcenter.heroku.com/articles/ruby-support#supported-runtimes
    WARNING
  end

  # install the vendored ruby
  # @return [Boolean] true if it installs the vendored ruby and false otherwise
  def install_ruby(install_path, build_ruby_path = nil)
    instrument 'ruby.install_ruby' do
      # Could do a compare operation to avoid re-downloading ruby
      return false unless ruby_version
      installer = LanguagePack::Installers::RubyInstaller.installer(ruby_version).new(@stack)

      @ruby_download_check = LanguagePack::Helpers::DownloadPresence.new(ruby_version.file_name)
      @ruby_download_check.call

      if ruby_version.build?
        installer.fetch_unpack(ruby_version, build_ruby_path, true)
      end

      installer.install(ruby_version, install_path)

      @outdated_version_check = LanguagePack::Helpers::OutdatedRubyVersion.new(
        current_ruby_version: ruby_version,
        fetcher: installer.fetcher
      )
      @outdated_version_check.call

      @metadata.write("buildpack_ruby_version", ruby_version.version_for_download)

      topic "Using Ruby version: #{ruby_version.version_for_download}"
      if !ruby_version.set
        warn(<<~WARNING)
          You have not declared a Ruby version in your Gemfile.

          To declare a Ruby version add this line to your Gemfile:

          ```
          ruby "#{LanguagePack::RubyVersion::DEFAULT_VERSION_NUMBER}"
          ```

          For more information see:
            https://devcenter.heroku.com/articles/ruby-versions
        WARNING
      end

      if ruby_version.warn_ruby_26_bundler?
        warn(<<~WARNING, inline: true)
          There is a known bundler bug with your version of Ruby

          Your version of Ruby contains a problem with the built-in integration of bundler. If
          you encounter a bundler error you need to upgrade your Ruby version. We suggest you upgrade to:

          #{@outdated_version_check.suggested_ruby_minor_version}

          For more information see:
            https://devcenter.heroku.com/articles/bundler-version#known-upgrade-issues
        WARNING
      end
    end

    true
  rescue LanguagePack::Fetcher::FetchError
    if @ruby_download_check.does_not_exist?
      message = <<~ERROR
        The Ruby version you are trying to install does not exist: #{ruby_version.version_for_download}
      ERROR
    else
      message = <<~ERROR
        The Ruby version you are trying to install does not exist on this stack.

        You are trying to install #{ruby_version.version_for_download} on #{stack}.

        Ruby #{ruby_version.version_for_download} is present on the following stacks:

          - #{@ruby_download_check.valid_stack_list.join("\n  - ")}
      ERROR

      if env("CI")
        message << <<~ERROR

          On Heroku CI you can set your stack in the `app.json`. For example:

          ```
          "stack": "heroku-20"
          ```
        ERROR
      end
    end

    message << <<~ERROR

      Heroku recommends you use the latest supported Ruby version listed here:
        https://devcenter.heroku.com/articles/ruby-support#supported-runtimes

      For more information on syntax for declaring a Ruby version see:
        https://devcenter.heroku.com/articles/ruby-versions
    ERROR

    error message
  end

  # TODO make this compatible with CNB
  def new_app?
    @new_app ||= !File.exist?("vendor/heroku")
  end

  # find the ruby install path for its binstubs during build
  # @return [String] resulting path or empty string if ruby is not vendored
  def ruby_install_binstub_path(ruby_layer_path = ".")
    @ruby_install_binstub_path ||=
      if ruby_version.build?
        "#{build_ruby_path}/bin"
      elsif ruby_version
        "#{ruby_layer_path}/#{slug_vendor_ruby}/bin"
      else
        ""
      end
  end

  # setup the environment so we can use the vendored ruby
  def setup_ruby_install_env(ruby_layer_path = ".")
    instrument 'ruby.setup_ruby_install_env' do
      ENV["PATH"] = "#{File.expand_path(ruby_install_binstub_path(ruby_layer_path))}:#{ENV["PATH"]}"
    end
  end

  # installs vendored gems into the slug
  def install_bundler_in_app(bundler_dir)
    instrument 'ruby.install_language_pack_gems' do
      FileUtils.mkdir_p(bundler_dir)
      Dir.chdir(bundler_dir) do |dir|
        `cp -R #{bundler.bundler_path}/. .`
      end

      # write bundler shim, so we can control the version bundler used
      # Ruby 2.6.0 started vendoring bundler
      write_bundler_shim("vendor/bundle/bin") if ruby_version.vendored_bundler?
    end
  end

  # default set of binaries to install
  # @return [Array] resulting list
  def binaries
    add_node_js_binary + add_yarn_binary
  end

  # vendors binaries into the slug
  def install_binaries
    instrument 'ruby.install_binaries' do
      binaries.each {|binary| install_binary(binary) }
      Dir["bin/*"].each {|path| run("chmod +x #{path}") }
    end
  end

  # vendors individual binary into the slug
  # @param [String] name of the binary package from S3.
  #   Example: https://s3.amazonaws.com/language-pack-ruby/node-0.4.7.tgz, where name is "node-0.4.7"
  def install_binary(name)
    topic "Installing #{name}"
    bin_dir = "bin"
    FileUtils.mkdir_p bin_dir
    Dir.chdir(bin_dir) do |dir|
      if name.match(/^node\-/)
        @node_installer.install
        # need to set PATH here b/c `node-gyp` can change the CWD, but still depends on executing node.
        # the current PATH is relative, but it needs to be absolute for this.
        # doing this here also prevents it from being exported during runtime
        node_bin_path = File.absolute_path(".")
        # this needs to be set after so other binaries in bin/ don't take precedence"
        ENV["PATH"] = "#{ENV["PATH"]}:#{node_bin_path}"
      elsif name.match(/^yarn\-/)
        FileUtils.mkdir_p("../vendor")
        Dir.chdir("../vendor") do |vendor_dir|
          @yarn_installer.install
          yarn_path = File.absolute_path("#{vendor_dir}/#{@yarn_installer.binary_path}")
          ENV["PATH"] = "#{yarn_path}:#{ENV["PATH"]}"
        end
      else
        @fetchers[:buildpack].fetch_untar("#{name}.tgz")
      end
    end
  end

  # removes a binary from the slug
  # @param [String] relative path of the binary on the slug
  def uninstall_binary(path)
    FileUtils.rm File.join('bin', File.basename(path)), :force => true
  end

  def load_default_cache?
    new_app? && ruby_version.default?
  end

  # loads a default bundler cache for new apps to speed up initial bundle installs
  def load_default_cache
    instrument "ruby.load_default_cache" do
      if false # load_default_cache?
        puts "New app detected loading default bundler cache"
        patchlevel = run("ruby -e 'puts RUBY_PATCHLEVEL'").strip
        cache_name  = "#{LanguagePack::RubyVersion::DEFAULT_VERSION}-p#{patchlevel}-default-cache"
        @fetchers[:buildpack].fetch_untar("#{cache_name}.tgz")
      end
    end
  end

  # remove `vendor/bundle` that comes from the git repo
  # in case there are native ext.
  # users should be using `bundle pack` instead.
  # https://github.com/heroku/heroku-buildpack-ruby/issues/21
  def remove_vendor_bundle
    if File.exists?("vendor/bundle")
      warn(<<-WARNING)
Removing `vendor/bundle`.
Checking in `vendor/bundle` is not supported. Please remove this directory
and add it to your .gitignore. To vendor your gems with Bundler, use
`bundle pack` instead.
WARNING
      FileUtils.rm_rf("vendor/bundle")
    end
  end

  def bundler_binstubs_path
    "vendor/bundle/bin"
  end

  def bundler_path
    @bundler_path ||= "#{slug_vendor_base}/gems/#{bundler.dir_name}"
  end

  def write_bundler_shim(path)
    FileUtils.mkdir_p(path)
    shim_path = "#{path}/bundle"
    File.open(shim_path, "w") do |file|
      file.print <<-BUNDLE
#!/usr/bin/env ruby
require 'rubygems'

version = "#{bundler.version}"

if ARGV.first
  str = ARGV.first
  str = str.dup.force_encoding("BINARY") if str.respond_to? :force_encoding
  if str =~ /\A_(.*)_\z/ and Gem::Version.correct?($1) then
    version = $1
    ARGV.shift
  end
end

if Gem.respond_to?(:activate_bin_path)
load Gem.activate_bin_path('bundler', 'bundle', version)
else
gem "bundler", version
load Gem.bin_path("bundler", "bundle", version)
end
BUNDLE
    end
    FileUtils.chmod(0755, shim_path)
  end

  # runs bundler to install the dependencies
  def build_bundler
    instrument 'ruby.build_bundler' do
      log("bundle") do
        if File.exist?("#{Dir.pwd}/.bundle/config")
          warn(<<~WARNING, inline: true)
            You have the `.bundle/config` file checked into your repository
             It contains local state like the location of the installed bundle
             as well as configured git local gems, and other settings that should
            not be shared between multiple checkouts of a single repo. Please
            remove the `.bundle/` folder from your repo and add it to your `.gitignore` file.

            https://devcenter.heroku.com/articles/bundler-configuration
          WARNING
        end

        if bundler.windows_gemfile_lock?
          log("bundle", "has_windows_gemfile_lock")

          File.unlink("Gemfile.lock")
          ENV.delete("BUNDLE_DEPLOYMENT")

          warn(<<~WARNING, inline: true)
            Removing `Gemfile.lock` because it was generated on Windows.
            Bundler will do a full resolve so native gems are handled properly.
            This may result in unexpected gem versions being used in your app.
            In rare occasions Bundler may not be able to resolve your dependencies at all.

            https://devcenter.heroku.com/articles/bundler-windows-gemfile
          WARNING
        end

        bundle_command = String.new("")
        bundle_command << "BUNDLE_WITHOUT='#{ENV["BUNDLE_WITHOUT"]}' "
        bundle_command << "BUNDLE_PATH=#{ENV["BUNDLE_PATH"]} "
        bundle_command << "BUNDLE_BIN=#{ENV["BUNDLE_BIN"]} "
        bundle_command << "BUNDLE_DEPLOYMENT=#{ENV["BUNDLE_DEPLOYMENT"]} " if ENV["BUNDLE_DEPLOYMENT"] # Unset on windows since we delete the Gemfile.lock
        bundle_command << "BUNDLE_GLOBAL_PATH_APPENDS_RUBY_SCOPE=#{ENV["BUNDLE_GLOBAL_PATH_APPENDS_RUBY_SCOPE"]} " if bundler.needs_ruby_global_append_path?
        bundle_command << "bundle install -j4"

        topic("Installing dependencies using bundler #{bundler.version}")

        bundler_output = String.new("")
        bundle_time    = nil
        env_vars = {}
        Dir.mktmpdir("libyaml-") do |tmpdir|
          libyaml_dir = "#{tmpdir}/#{LIBYAML_PATH}"

          # need to setup compile environment for the psych gem
          yaml_include   = File.expand_path("#{libyaml_dir}/include").shellescape
          yaml_lib       = File.expand_path("#{libyaml_dir}/lib").shellescape
          pwd            = Dir.pwd
          bundler_path   = "#{pwd}/#{slug_vendor_base}/gems/#{bundler.dir_name}/lib"

          # we need to set BUNDLE_CONFIG and BUNDLE_GEMFILE for
          # codon since it uses bundler.
         env_vars["BUNDLE_GEMFILE"] = "#{pwd}/Gemfile"
          env_vars["BUNDLE_CONFIG"] = "#{pwd}/.bundle/config"
          env_vars["CPATH"] = noshellescape("#{yaml_include}:$CPATH")
          env_vars["CPPATH"] = noshellescape("#{yaml_include}:$CPPATH")
          env_vars["LIBRARY_PATH"] = noshellescape("#{yaml_lib}:$LIBRARY_PATH")
          env_vars["RUBYOPT"] = syck_hack
          env_vars["NOKOGIRI_USE_SYSTEM_LIBRARIES"] = "true"
          env_vars["BUNDLE_DISABLE_VERSION_CHECK"] = "true"
          env_vars["BUNDLER_LIB_PATH"]             = "#{bundler_path}" if ruby_version.ruby_version == "1.8.7"
          env_vars["BUNDLE_DISABLE_VERSION_CHECK"] = "true"

          puts "Running: #{bundle_command}"
          instrument "ruby.bundle_install" do
            bundle_time = Benchmark.realtime do
              bundler_output << pipe("#{bundle_command} --no-clean", out: "2>&1", env: env_vars, user_env: true)
            end
          end
        end

        if $?.success?
          puts "Bundle completed (#{"%.2f" % bundle_time}s)"
          log "bundle", :status => "success"
          puts "Cleaning up the bundler cache."
          instrument "ruby.bundle_clean" do
            # Only show bundle clean output when not using default cache
            if load_default_cache?
              run("bundle clean > /dev/null", user_env: true, env: env_vars)
            else
              pipe("bundle clean", out: "2> /dev/null", user_env: true, env: env_vars)
            end
          end
          @bundler_cache.store

          # Keep gem cache out of the slug
          FileUtils.rm_rf("#{slug_vendor_base}/cache")
        else
          mcount "fail.bundle.install"
          log "bundle", :status => "failure"
          error_message = "Failed to install gems via Bundler."
          puts "Bundler Output: #{bundler_output}"
          if bundler_output.match(/An error occurred while installing sqlite3/)
            mcount "fail.sqlite3"
            error_message += <<~ERROR

              Detected sqlite3 gem which is not supported on Heroku:
              https://devcenter.heroku.com/articles/sqlite3
            ERROR
          end

          if bundler_output.match(/but your Gemfile specified/)
            mcount "fail.ruby_version_mismatch"
            error_message += <<~ERROR

              Detected a mismatch between your Ruby version installed and
              Ruby version specified in Gemfile or Gemfile.lock. You can
              correct this by running:

                  $ bundle update --ruby
                  $ git add Gemfile.lock
                  $ git commit -m "update ruby version"

              If this does not solve the issue please see this documentation:

              https://devcenter.heroku.com/articles/ruby-versions#your-ruby-version-is-x-but-your-gemfile-specified-y
            ERROR
          end

          error error_message
        end
      end
    end
  end

  def post_bundler
    instrument "ruby.post_bundler" do
      Dir[File.join(slug_vendor_base, "**", ".git")].each do |dir|
        FileUtils.rm_rf(dir)
      end
      bundler.clean
    end
  end

  # RUBYOPT line that requires syck_hack file
  # @return [String] require string if needed or else an empty string
  def syck_hack
    instrument "ruby.syck_hack" do
      syck_hack_file = File.expand_path(File.join(File.dirname(__FILE__), "../../vendor/syck_hack"))
      rv             = run_stdout('ruby -e "puts RUBY_VERSION"').strip
      # < 1.9.3 includes syck, so we need to use the syck hack
      if Gem::Version.new(rv) < Gem::Version.new("1.9.3")
        "-r#{syck_hack_file}"
      else
        ""
      end
    end
  end

  # writes ERB based database.yml for Rails. The database.yml uses the DATABASE_URL from the environment during runtime.
  def create_database_yml
    instrument 'ruby.create_database_yml' do
      return false unless File.directory?("config")
      return false if  bundler.has_gem?('activerecord') && bundler.gem_version('activerecord') >= Gem::Version.new('4.1.0.beta1')

      log("create_database_yml") do
        topic("Writing config/database.yml to read from DATABASE_URL")
        File.open("config/database.yml", "w") do |file|
          file.puts <<-DATABASE_YML
<%

require 'cgi'
require 'uri'

begin
  uri = URI.parse(ENV["DATABASE_URL"])
rescue URI::InvalidURIError
  raise "Invalid DATABASE_URL"
end

raise "No RACK_ENV or RAILS_ENV found" unless ENV["RAILS_ENV"] || ENV["RACK_ENV"]

def attribute(name, value, force_string = false)
  if value
    value_string =
      if force_string
        '"' + value + '"'
      else
        value
      end
    "\#{name}: \#{value_string}"
  else
    ""
  end
end

adapter = uri.scheme
adapter = "postgresql" if adapter == "postgres"

database = (uri.path || "").split("/")[1]

username = uri.user
password = uri.password

host = uri.host
port = uri.port

params = CGI.parse(uri.query || "")

%>

<%= ENV["RAILS_ENV"] || ENV["RACK_ENV"] %>:
  <%= attribute "adapter",  adapter %>
  <%= attribute "database", database %>
  <%= attribute "username", username %>
  <%= attribute "password", password, true %>
  <%= attribute "host",     host %>
  <%= attribute "port",     port %>

<% params.each do |key, value| %>
  <%= key %>: <%= value.first %>
<% end %>
          DATABASE_YML
        end
      end
    end
  end

  def rake
    @rake ||= begin
      rake_gem_available = bundler.has_gem?("rake") || ruby_version.rake_is_vendored?
      raise_on_fail      = bundler.gem_version('railties') && bundler.gem_version('railties') > Gem::Version.new('3.x')

      topic "Detecting rake tasks"
      rake = LanguagePack::Helpers::RakeRunner.new(rake_gem_available)
      rake.load_rake_tasks!({ env: rake_env }, raise_on_fail)
      rake
    end
  end

  def rake_env
    if database_url
      { "DATABASE_URL" => database_url }
    else
      {}
    end.merge(user_env_hash)
  end

  def database_url
    env("DATABASE_URL") if env("DATABASE_URL")
  end

  # executes the block with GIT_DIR environment variable removed since it can mess with the current working directory git thinks it's in
  # @param [block] block to be executed in the GIT_DIR free context
  def allow_git(&blk)
    git_dir = ENV.delete("GIT_DIR") # can mess with bundler
    blk.call
    ENV["GIT_DIR"] = git_dir
  end

  # decides if we need to enable the dev database addon
  # @return [Array] the database addon if the pg gem is detected or an empty Array if it isn't.
  def add_dev_database_addon
    pg_adapters.any? {|a| bundler.has_gem?(a) } ? ['heroku-postgresql'] : []
  end

  def pg_adapters
    [
      "pg",
      "activerecord-jdbcpostgresql-adapter",
      "jdbc-postgres",
      "jdbc-postgresql",
      "jruby-pg",
      "rjack-jdbc-postgres",
      "tgbyte-activerecord-jdbcpostgresql-adapter"
    ]
  end

  # decides if we need to install the node.js binary
  # @note execjs will blow up if no JS RUNTIME is detected and is loaded.
  # @return [Array] the node.js binary path if we need it or an empty Array
  def add_node_js_binary
    return [] if node_js_preinstalled?

    if Pathname(build_path).join("package.json").exist? ||
         bundler.has_gem?('execjs') ||
         bundler.has_gem?('webpacker')
      [@node_installer.binary_path]
    else
      []
    end
  end

  def add_yarn_binary
    return [] if yarn_preinstalled?
|
    if Pathname(build_path).join("yarn.lock").exist? || bundler.has_gem?('webpacker')
      [@yarn_installer.name]
    else
      []
    end
  end

  def has_yarn_binary?
    add_yarn_binary.any?
  end

  # checks if node.js is installed via the official heroku-buildpack-nodejs using multibuildpack
  # @return String if it's detected and false if it isn't
  def node_preinstall_bin_path
    return @node_preinstall_bin_path if defined?(@node_preinstall_bin_path)

    legacy_path = "#{Dir.pwd}/#{NODE_BP_PATH}"
    path        = run("which node").strip
    if path && $?.success?
      @node_preinstall_bin_path = path
    elsif run("#{legacy_path}/node -v") && $?.success?
      @node_preinstall_bin_path = legacy_path
    else
      @node_preinstall_bin_path = false
    end
  end
  alias :node_js_preinstalled? :node_preinstall_bin_path

  def node_not_preinstalled?
    !node_js_preinstalled?
  end

  # Example: tmp/build_8523f77fb96a956101d00988dfeed9d4/.heroku/yarn/bin/ (without the `yarn` at the end)
  def yarn_preinstall_bin_path
    (yarn_preinstall_binary_path || "").chomp("/yarn")
  end

  # Example `tmp/build_8523f77fb96a956101d00988dfeed9d4/.heroku/yarn/bin/yarn`
  def yarn_preinstall_binary_path
    return @yarn_preinstall_binary_path if defined?(@yarn_preinstall_binary_path)

    path = run("which yarn").strip
    if path && $?.success?
      @yarn_preinstall_binary_path = path
    else
      @yarn_preinstall_binary_path = false
    end
  end

  def yarn_preinstalled?
    yarn_preinstall_binary_path
  end

  def yarn_not_preinstalled?
    !yarn_preinstalled?
  end

  def run_assets_precompile_rake_task
    instrument 'ruby.run_assets_precompile_rake_task' do

      precompile = rake.task("assets:precompile")
      return true unless precompile.is_defined?

      topic "Precompiling assets"
      precompile.invoke(env: rake_env)
      if precompile.success?
        puts "Asset precompilation completed (#{"%.2f" % precompile.time}s)"
      else
        precompile_fail(precompile.output)
      end
    end
  end

  def precompile_fail(output)
    mcount "fail.assets_precompile"
    log "assets_precompile", :status => "failure"
    msg = "Precompiling assets failed.\n"
    if output.match(/(127\.0\.0\.1)|(org\.postgresql\.util)/)
      msg << "Attempted to access a nonexistent database:\n"
      msg << "https://devcenter.heroku.com/articles/pre-provision-database\n"
    end

    sprockets_version = bundler.gem_version('sprockets')
    if output.match(/Sprockets::FileNotFound/) && (sprockets_version < Gem::Version.new('4.0.0.beta7') && sprockets_version > Gem::Version.new('4.0.0.beta4'))
      mcount "fail.assets_precompile.file_not_found_beta"
      msg << "If you have this file in your project\n"
      msg << "try upgrading to Sprockets 4.0.0.beta7 or later:\n"
      msg << "https://github.com/rails/sprockets/pull/547\n"
    end

    error msg
  end

  def bundler_cache
    "vendor/bundle"
  end

  def valid_bundler_cache?(path, metadata)
    full_ruby_version       = run_stdout(%q(ruby -v)).strip
    rubygems_version        = run_stdout(%q(gem -v)).strip
    old_rubygems_version    = nil

    old_rubygems_version = metadata[:ruby_version]
    old_stack = metadata[:stack]
    old_stack ||= DEFAULT_LEGACY_STACK

    stack_change = old_stack != @stack
    if !new_app? && stack_change
      return [false, "Purging Cache. Changing stack from #{old_stack} to #{@stack}"]
    end

    # fix bug from v37 deploy
    if File.exists?("#{path}/vendor/ruby_version")
      puts "Broken cache detected. Purging build cache."
      cache.clear("vendor")
      FileUtils.rm_rf("#{path}/vendor/ruby_version")
      return [false, "Broken cache detected. Purging build cache."]
      # fix bug introduced in v38
    elsif !metadata.include?(:buildpack_version) && metadata.include?(:ruby_version)
      puts "Broken cache detected. Purging build cache."
      return [false, "Broken cache detected. Purging build cache."]
    elsif (@bundler_cache.exists? || @bundler_cache.old?) && full_ruby_version != metadata[:ruby_version]
      return [false, <<-MESSAGE]
Ruby version change detected. Clearing bundler cache.
Old: #{metadata[:ruby_version]}
New: #{full_ruby_version}
MESSAGE
    end

    # fix git gemspec bug from Bundler 1.3.0+ upgrade
    if File.exists?(bundler_cache) && !metadata.include?(:bundler_version) && !run("find #{path}/vendor/bundle/*/*/bundler/gems/*/ -name *.gemspec").include?("No such file or directory")
      return [false, "Old bundler cache detected. Clearing bundler cache."]
    end

    # fix for https://github.com/heroku/heroku-buildpack-ruby/issues/86
    if (!metadata.include?(:rubygems_version) ||
        (old_rubygems_version == "2.0.0" && old_rubygems_version != rubygems_version)) &&
      metadata.include?(:ruby_version) && metadata[:ruby_version].strip.include?("ruby 2.0.0p0")
      return [false, "Updating to rubygems #{rubygems_version}. Clearing bundler cache."]
    end

    # fix for https://github.com/sparklemotion/nokogiri/issues/923
    if metadata.include?(:buildpack_version) && (bv = metadata[:buildpack_version].sub('v', '').to_i) && bv != 0 && bv <= 76
      return [false, <<-MESSAGE]
Fixing nokogiri install. Clearing bundler cache.
See https://github.com/sparklemotion/nokogiri/issues/923.
MESSAGE
    end

    # recompile nokogiri to use new libyaml
    if metadata.include?(:buildpack_version) && (bv = metadata[:buildpack_version].sub('v', '').to_i) && bv != 0 && bv <= 99 && bundler.has_gem?("psych")
      return [false, <<-MESSAGE]
Need to recompile psych for CVE-2013-6393. Clearing bundler cache.
See http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=737076.
MESSAGE
    end

    # recompile gems for libyaml 0.1.7 update
    if metadata.include?(:buildpack_version) && (bv = metadata[:buildpack_version].sub('v', '').to_i) && bv != 0 && bv <= 147 &&
        (metadata.include?(:ruby_version) && metadata[:ruby_version].match(/ruby 2\.1\.(9|10)/) ||
         bundler.has_gem?("psych")
        )
      return [false, <<-MESSAGE]
Need to recompile gems for CVE-2014-2014-9130. Clearing bundler cache.
See https://devcenter.heroku.com/changelog-items/1016.
MESSAGE
    end

    true
  end

  def load_bundler_cache
    instrument "ruby.load_bundler_cache" do
      cache.load "vendor"

      full_ruby_version       = run_stdout(%q(ruby -v)).strip
      rubygems_version        = run_stdout(%q(gem -v)).strip
      heroku_metadata         = "vendor/heroku"
      old_rubygems_version    = nil
      ruby_version_cache      = "ruby_version"
      buildpack_version_cache = "buildpack_version"
      bundler_version_cache   = "bundler_version"
      rubygems_version_cache  = "rubygems_version"
      stack_cache             = "stack"

      # bundle clean does not remove binstubs
      FileUtils.rm_rf("vendor/bundler/bin")

      old_rubygems_version = @metadata.read(ruby_version_cache).strip if @metadata.exists?(ruby_version_cache)
      old_stack = @metadata.read(stack_cache).strip if @metadata.exists?(stack_cache)
      old_stack ||= DEFAULT_LEGACY_STACK

      stack_change  = old_stack != @stack
      convert_stack = @bundler_cache.old?
      @bundler_cache.convert_stack(stack_change) if convert_stack
      if !new_app? && stack_change
        puts "Purging Cache. Changing stack from #{old_stack} to #{@stack}"
        purge_bundler_cache(old_stack)
      elsif !new_app? && !convert_stack
        @bundler_cache.load
      end

      # fix bug from v37 deploy
      if File.exists?("vendor/ruby_version")
        puts "Broken cache detected. Purging build cache."
        cache.clear("vendor")
        FileUtils.rm_rf("vendor/ruby_version")
        purge_bundler_cache
        # fix bug introduced in v38
      elsif !@metadata.include?(buildpack_version_cache) && @metadata.exists?(ruby_version_cache)
        puts "Broken cache detected. Purging build cache."
        purge_bundler_cache
      elsif (@bundler_cache.exists? || @bundler_cache.old?) && @metadata.exists?(ruby_version_cache) && full_ruby_version != @metadata.read(ruby_version_cache).strip
        puts "Ruby version change detected. Clearing bundler cache."
        puts "Old: #{@metadata.read(ruby_version_cache).strip}"
        puts "New: #{full_ruby_version}"
        purge_bundler_cache
      end

      # fix git gemspec bug from Bundler 1.3.0+ upgrade
      if File.exists?(bundler_cache) && !@metadata.exists?(bundler_version_cache) && !run("find vendor/bundle/*/*/bundler/gems/*/ -name *.gemspec").include?("No such file or directory")
        puts "Old bundler cache detected. Clearing bundler cache."
        purge_bundler_cache
      end

      # fix for https://github.com/heroku/heroku-buildpack-ruby/issues/86
      if (!@metadata.exists?(rubygems_version_cache) ||
          (old_rubygems_version == "2.0.0" && old_rubygems_version != rubygems_version)) &&
          @metadata.exists?(ruby_version_cache) && @metadata.read(ruby_version_cache).strip.include?("ruby 2.0.0p0")
        puts "Updating to rubygems #{rubygems_version}. Clearing bundler cache."
        purge_bundler_cache
      end

      # fix for https://github.com/sparklemotion/nokogiri/issues/923
      if @metadata.exists?(buildpack_version_cache) && (bv = @metadata.read(buildpack_version_cache).sub('v', '').to_i) && bv != 0 && bv <= 76
        puts "Fixing nokogiri install. Clearing bundler cache."
        puts "See https://github.com/sparklemotion/nokogiri/issues/923."
        purge_bundler_cache
      end

      # recompile nokogiri to use new libyaml
      if @metadata.exists?(buildpack_version_cache) && (bv = @metadata.read(buildpack_version_cache).sub('v', '').to_i) && bv != 0 && bv <= 99 && bundler.has_gem?("psych")
        puts "Need to recompile psych for CVE-2013-6393. Clearing bundler cache."
        puts "See http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=737076."
        purge_bundler_cache
      end

      # recompile gems for libyaml 0.1.7 update
      if @metadata.exists?(buildpack_version_cache) && (bv = @metadata.read(buildpack_version_cache).sub('v', '').to_i) && bv != 0 && bv <= 147 &&
          (@metadata.exists?(ruby_version_cache) && @metadata.read(ruby_version_cache).strip.match(/ruby 2\.1\.(9|10)/) ||
           bundler.has_gem?("psych")
          )
        puts "Need to recompile gems for CVE-2014-2014-9130. Clearing bundler cache."
        puts "See https://devcenter.heroku.com/changelog-items/1016."
        purge_bundler_cache
      end

      FileUtils.mkdir_p(heroku_metadata)
      @metadata.write(ruby_version_cache, full_ruby_version, false)
      @metadata.write(buildpack_version_cache, BUILDPACK_VERSION, false)
      @metadata.write(bundler_version_cache, bundler.version, false)
      @metadata.write(rubygems_version_cache, rubygems_version, false)
      @metadata.write(stack_cache, @stack, false)
      @metadata.save
    end
  end

  def purge_bundler_cache(stack = nil)
    instrument "ruby.purge_bundler_cache" do
      @bundler_cache.clear(stack)
      # need to reinstall language pack gems
      install_bundler_in_app(slug_vendor_base)
    end
  end
end