class Grape::Middleware::Stack

def assert_index(index, where)
  i = index.is_a?(Integer) ? index : middlewares.index(index)
  i || raise("No such middleware to insert #{where}: #{index.inspect}")
end

def build
  builder = Rack::Builder.new
  others.shift(others.size).each { |m| merge_with(m) }
  middlewares.each { |m| m.build(builder) }
  builder
end

def concat(other_specs)
  use, not_use = other_specs.partition { |o| o.first == :use }
  others << not_use
  merge_with(use)
end

def initialize
  @middlewares = []
  @others = []
end

def insert(index, klass, *args, &block)
  index = assert_index(index, :before)
  middlewares.insert(index, self.class::Middleware.new(klass, args, block))
end

def insert_after(index, ...)
  index = assert_index(index, :after)
  insert(index + 1, ...)
end

def merge_with(middleware_specs)
  middleware_specs.each do |operation, klass, *args|
    if args.last.is_a?(Proc)
      last_proc = args.pop
      public_send(operation, klass, *args, &last_proc)
    else
      public_send(operation, klass, *args)
    end
  end
end

def use(klass, *args, &block)
  middleware = self.class::Middleware.new(klass, args, block)
  middlewares.push(middleware)
end