module Middleman::Sitemap::Extensions::Proxies::ResourceInstanceMethods

def content_type
  mime_type = super
  return mime_type if mime_type
  if proxy?
    proxied_to_resource.content_type
  else
    nil
  end
end

def get_source_file
  if proxy?
    proxied_to_resource.source_file
  else
    super
  end
end

def proxied_to
  @proxied_to
end

def proxied_to_resource
  proxy_resource = store.find_resource_by_path(proxied_to)
  unless proxy_resource
    raise "Path #{path} proxies to unknown file #{proxied_to}:#{store.resources.map(&:path)}"
  end
  if proxy_resource.proxy?
    raise "You can't proxy #{path} to #{proxied_to} which is itself a proxy."
  end
  proxy_resource
end

def proxy?
  !!@proxied_to
end

def proxy_to(target)
  target = ::Middleman::Util.normalize_path(target)
  raise "You can't proxy #{path} to itself!" if target == path
  @proxied_to = target
end