# frozen_string_literal: true

require "em_promise"

module Rack
	class Fiber
		def initialize(app)
			@app = app
		end

		def call(env)
			async_callback = env.delete("async.callback")
			run_fiber(env, async_callback)
			throw :async
		end

	protected

		def run_fiber(env, async_callback)
			# Use EMPromise to get a Fiber trampoline that can be shared by
			# other EMPromise down the stack. Also works as a normal Fiber if
			# no one uses EMPromise.
			EMPromise.resolve(nil).then {
				async_callback.call(@app.call(env))
			}.catch { |e|
				async_callback.call([500, {}, [e.to_s]])
			}
		end
	end
end