Fix grape's incredible brokenness.

grapeish.rb

require 'sinatra/base'
require 'sinatra/namespace'
# You may need multi_json

class API < Sinatra::Base

  # Respond to all errors with JSON
  error do
    content_type :json
    e = env['sinatra.error']
    MultiJson.dump({:result => 'error', :message => e.message})
  end

  # Define some content helpers.
  helpers do

    def json(response)
      content_type :json
      if response.respond_to?(:entity) or response.respond_to?(:as_json)
        body MultiJson.dump(response.as_json)
      else
        body MultiJson.dump(response)
      end
    end

    # Moved (mostly) from Grape. Hate you, Grape.
    def present(object, options = {})
      content_type :json

      entity_class = options.delete(:with)

      object.class.ancestors.each do |potential|
        entity_class ||= (settings[:representations] || {})[potential]
      end

      entity_class ||= object.class.const_get(:Entity) if object.class.const_defined?(:Entity)

      root = options.delete(:root)

      representation = if entity_class
        entity_class.represent(object, embeds.merge(options))
      else
        object
      end

      representation = { root => representation } if root
      body representation.as_json.to_json
    end

  end

  namespace '/api/sheet' do

    post '/do-something-terrible' do
      raise 'Fail massively!'
    end

    get '/' do
      @sheet = Sheet.get(1)
      json @sheet # will call #entity -> #as_json on it, if defined.
    end

  end

end