preserve_symlink.rb

class PreserveSymlink < Middleman::Extension
  def initialize(app, options_hash={}, &block)
    super
    setup_app! app, options_hash
    ext = self

    # callback
    app.after_build do |builder|
      ext.source_symlinks.each do |source_symlink_path|
       target_symlink_path =
         ext.convert_source_path_for_build(source_symlink_path)

       if target_symlink_path.exist?
         unless target_symlink_path.symlink?
           raise "Collupsion: symbolick link in source/ but file instance in build/"
         end

         next
       end

       builder.run(
         ext.symlink_command(
           source_symlink_path,
           target_symlink_path.dirname
         )
       )
      end
    end
  end

  # callback
  def after_configuration
    # Ignore symlinks on source/ and remove them on build/
    # only on build environment
    if app.build?
      source_symlinks.each do |source_symlink|
        ignore_path = source_symlink.relative_path_from(@_source_path)
        ignore_path = ignore_path.join("*") if source_symlink.directory?

        app.ignore ignore_path.to_s
      end

      # Middleman's clean process searches cleaning(remove) target file
      # regardless of it is in symlinked directory or not.
      # And then, it removes a file which in a symlink directory, and
      # deletes symlink itself becase symlink's directory is be empty.
      # To avoid to be deleted the file which placed on a symlink
      # referel directory, remove all symlink in a build dir manually.
      # This may be safe because normally there must not be symlinks
      # in Middleman's build directory.
      if @_build_path.exist?
        build_symlinks.each do |symlink_path|
          symlink_path.delete
        end
      end
    end
  end

  def setup_app!(app, options_hash)
    @_root_path = app.root_path
    @_source_path = @_root_path.join(app.source)
    @_build_path  = @_root_path.join(app.build_dir)

    # if options_hash[:preserve_symlinks]
    #   @_source_symlinks_ =
    #     options_hash[:preserve_symlinks].map do |preserve_path|
    #       Pathname(preserve_path).relative_path_from(@_source_path)
    #     end
    #
    #   @_build_symlinks_ =
    #     @_source_symlinks_.map{|path| convert_source_path_for_build(path) }
    # end
  end

  def build_symlinks(relative: false)
    @_build_symlinks_ ||= @_build_path.find.select(&:symlink?)

    if relative
      @_build_symlinks_.map{|t| t.relative_path_from(@_build_path) }
    else
      @_build_symlinks_
    end
  end

  def source_symlinks(relative: false)
    @_source_symlinks_ ||= @_source_path.find.select(&:symlink?)

    if relative
      @_source_symlinks_.map{|t| t.relative_path_from(@_source_path) }
    else
      @_source_symlinks_
    end
  end

  def convert_source_path_for_build(path)
    @_build_path.join(path.relative_path_from(@_source_path))
  end

  def symlink_command(source_symlink_path, target_directory)
    "ln -s #{source_symlink_path.readlink} #{target_directory}"
  end
end

::Middleman::Extensions.register(:preserve_symlink, PreserveSymlink)