# frozen_string_literal: true

# Released under the MIT License.
# Copyright, 2024, by Samuel Williams.

require_relative '../reference'

require 'protocol/http/middleware'
require 'protocol/http/body/rewindable'

module Async
	module HTTP
		module Middleware
			# A client wrapper which transparently handles redirects to a given maximum number of hops.
			#
			# The default implementation will only follow relative locations (i.e. those without a scheme) and will switch to GET if the original request was not a GET.
			#
			# The best reference for these semantics is defined by the [Fetch specification](https://fetch.spec.whatwg.org/#http-redirect-fetch).
			#
			# | Redirect using GET                        | Permanent | Temporary |
			# |:-----------------------------------------:|:---------:|:---------:|
			# | Allowed                                   | 301       | 302       |
			# | Preserve original method                  | 308       | 307       |
			#
			# For the specific details of the redirect handling, see:
			# - <https://datatracker.ietf.org/doc/html/rfc7231#section-6-4-2> 301 Moved Permanently.
			# - <https://datatracker.ietf.org/doc/html/rfc7231#section-6-4-3> 302 Found.
			# - <https://datatracker.ietf.org/doc/html/rfc7538 308 Permanent Redirect.
			# - <https://datatracker.ietf.org/doc/html/rfc7231#section-6-4-7> 307 Temporary Redirect.
			#
			class LocationRedirector < ::Protocol::HTTP::Middleware
				class TooManyRedirects < StandardError
				end
				
				# Header keys which should be deleted when changing a request from a POST to a GET as defined by <https://fetch.spec.whatwg.org/#request-body-header-name>.
				PROHIBITED_GET_HEADERS = [
					'content-encoding',
					'content-language',
					'content-location',
					'content-type',
				]
				
				# maximum_hops is the max number of redirects. Set to 0 to allow 1 request with no redirects.
				def initialize(app, maximum_hops = 3)
					super(app)
					
					@maximum_hops = maximum_hops
				end
				
				# The maximum number of hops which will limit the number of redirects until an error is thrown.
				attr :maximum_hops
				
				def redirect_with_get?(request, response)
					# We only want to switch to GET if the request method is something other than get, e.g. POST.
					if request.method != GET
						# According to the RFC, we should only switch to GET if the response is a 301 or 302:
						return response.status == 301 || response.status == 302
					end
				end
				
				# Handle a redirect to a relative location.
				#
				# @parameter request [Protocol::HTTP::Request] The original request, which you can modify if you want to handle the redirect.
				# @parameter location [String] The relative location to redirect to.
				# @returns [Boolean] True if the redirect was handled, false if it was not.
				def handle_redirect(request, location)
					uri = URI.parse(location)
					
					if uri.absolute?
						return false
					end
					
					# Update the path of the request:
					request.path = Reference[request.path] + location
					
					# Follow the redirect:
					return true
				end
				
				def call(request)
					# We don't want to follow redirects for HEAD requests:
					return super if request.head?
					
					if body = request.body
						if body.respond_to?(:rewind)
							# The request body was already rewindable, so use it as is:
							body = request.body
						else
							# The request body was not rewindable, and we might need to resubmit it if we get a response status of 307 or 308, so make it rewindable:
							body = ::Protocol::HTTP::Body::Rewindable.new(body)
							request.body = body
						end
					end
					
					hops = 0
					
					while hops <= @maximum_hops
						response = super(request)
						
						if response.redirection?
							hops += 1
							
							# Get the redirect location:
							unless location = response.headers['location']
								return response
							end
							
							response.finish
							
							unless handle_redirect(request, location)
								return response
							end
							
							# Ensure the request (body) is finished and set to nil before we manipulate the request:
							request.finish
							
							if request.method == GET or response.preserve_method?
								# We (might) need to rewind the body so that it can be submitted again:
								body&.rewind
								request.body = body
							else
								# We are changing the method to GET:
								request.method = GET
								
								# We will no longer be submitting the body:
								body = nil
								
								# Remove any headers which are not allowed in a GET request:
								PROHIBITED_GET_HEADERS.each do |header|
									request.headers.delete(header)
								end
							end
						else
							return response
						end
					end
					
					raise TooManyRedirects, "Redirected #{hops} times, exceeded maximum!"
				end
			end
		end
	end
end