# Copyright, 2018, by Samuel G. D. Williams. <http://www.codeotaku.com>
# 
# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:
# 
# The above copyright notice and this permission notice shall be included in
# all copies or substantial portions of the Software.
# 
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
# THE SOFTWARE.

require 'async/http/client'
require 'protocol/http/headers'
require 'protocol/http/middleware'

module Falcon
	module BadRequest
		def self.call(request)
			return Protocol::HTTP::Response[400, {}, []]
		end
		
		def self.close
		end
	end
	
	class Proxy < Protocol::HTTP::Middleware
		FORWARDED = 'forwarded'.freeze
		X_FORWARDED_FOR = 'x-forwarded-for'.freeze
		X_FORWARDED_PROTO = 'x-forwarded-proto'.freeze
		
		VIA = 'via'.freeze
		CONNECTION = 'connection'.freeze
		
		HOP_HEADERS = [
			'connection',
			'keep-alive',
			'public',
			'proxy-authenticate',
			'transfer-encoding',
			'upgrade',
		]
		
		def initialize(app, hosts)
			super(app)
			
			@server_context = nil
			
			@hosts = hosts
			@clients = {}
			
			@count = 0
		end
		
		attr :count
		
		def close
			@clients.each_value(&:close)
			
			super
		end
		
		def connect(endpoint)
			@clients[endpoint] ||= Async::HTTP::Client.new(endpoint)
		end
		
		def lookup(request)
			# Trailing dot and port is ignored/normalized.
			if authority = request.authority&.sub(/(\.)?(:\d+)?$/, '')
				return @hosts[authority]
			end
		end
		
		def prepare_headers(headers)
			if connection = headers[CONNECTION]
				headers.extract(connection)
			end
			
			headers.extract(HOP_HEADERS)
		end
		
		def prepare_request(request, host)
			forwarded = []
			
			Async.logger.debug(self) do |buffer|
				buffer.puts "Request authority: #{request.authority}"
				buffer.puts "Host authority: #{host.authority}"
				buffer.puts "Request: #{request.method} #{request.path} #{request.version}"
				buffer.puts "Request headers: #{request.headers.inspect}"
			end
			
			# The authority of the request must match the authority of the endpoint we are proxying to, otherwise SNI and other things won't work correctly.
			request.authority = host.authority
			
			if address = request.remote_address
				request.headers.add(X_FORWARDED_FOR, address.ip_address)
				forwarded << "for=#{address.ip_address}"
			end
			
			if scheme = request.scheme
				request.headers.add(X_FORWARDED_PROTO, scheme)
				forwarded << "proto=#{scheme}"
			end
			
			unless forwarded.empty?
				request.headers.add(FORWARDED, forwarded.join(';'))
			end
			
			request.headers.add(VIA, "#{request.version} #{self.class}")
			
			self.prepare_headers(request.headers)
			
			return request
		end
		
		def call(request)
			if host = lookup(request)
				@count += 1
				
				request = self.prepare_request(request, host)
				
				client = connect(host.endpoint)
				
				client.call(request)
			else
				super
			end
		rescue
			Async.logger.error(self) {$!}
			return Protocol::HTTP::Response[502, {'content-type' => 'text/plain'}, ["#{$!.inspect}: #{$!.backtrace.join("\n")}"]]
		end
	end
end