require 'socket'
require 'openssl'

module CryptCheck
	module Tls
		module Engine
			SLOW_DOWN   = ENV.fetch('SLOW_DOWN', '0').to_i
			TCP_TIMEOUT = 10
			TLS_TIMEOUT = 2*TCP_TIMEOUT

			class TLSException < ::StandardError
			end
			class TLSNotAvailableException < TLSException
				def to_s
					'TLS seems not supported on this server'
				end
			end
			class MethodNotAvailable < TLSException
			end
			class CipherNotAvailable < TLSException
			end
			class InappropriateFallback < TLSException
			end
			class Timeout < ::StandardError
				def initialize(ip, port)
					@message = "Timeout when connecting to #{ip}:#{port} (max #{TCP_TIMEOUT.humanize})"
				end

				def to_s
					@message
				end
			end
			class TLSTimeout < Timeout
				def initialize(ip, port)
					@message = "Timeout when TLS connecting to #{ip}:#{port} (max #{TLS_TIMEOUT.humanize})"
				end
			end
			class ConnectionError < ::StandardError
			end

			attr_reader :hostname, :ip, :family, :port, :certs, :keys, :dh,
						:supported_methods, :supported_ciphers,
						:supported_curves, :curves_preference

			def initialize(hostname, ip, family, port)
				@hostname, @ip, @family, @port = hostname, ip, family, port
				@dh                            = []

				@name = "#@ip:#@port"
				@name += " [#@hostname]" if @hostname

				Logger.info { @name.colorize :blue }

				fetch_supported_methods
				fetch_supported_ciphers
				fetch_dh
				fetch_ciphers_preferences
				fetch_ecdsa_certs
				fetch_supported_curves
				fetch_curves_preference

				check_fallback_scsv

				verify_certs
			end

			def supported_method?(method)
				ssl_client method
				Logger.info { "  Method #{method}" }
				true
			rescue TLSException
				Logger.debug { "  Method #{method} : not supported" }
				false
			end

			def fetch_supported_methods
				Logger.info { '' }
				Logger.info { 'Supported methods' }
				@supported_methods = Method.select { |m| supported_method? m }
				raise TLSNotAvailableException if @supported_methods.empty?
			end

			def supported_cipher?(method, cipher)
				connection = ssl_client method, cipher
				Logger.info { "  Cipher #{cipher}" }
				dh = connection.tmp_key
				if dh
					Logger.info { "    PFS : #{dh}" }
				end
				connection
			rescue TLSException
				Logger.debug { "  Cipher #{cipher} : not supported" }
				nil
			end

			def fetch_supported_ciphers
				Logger.info { '' }
				Logger.info { 'Supported ciphers' }
				@supported_ciphers = @supported_methods.collect do |method|
					ciphers = Cipher[method].collect do |cipher|
						connection = supported_cipher? method, cipher
						next nil unless connection
						[cipher, connection]
					end.compact.to_h
					[method, ciphers]
				end.to_h
			end

			def fetch_ciphers_preferences
				Logger.info { '' }
				Logger.info { 'Cipher suite preferences' }

				@preferences = @supported_ciphers.collect do |method, ciphers|
					ciphers     = ciphers.keys
					preferences = if ciphers.size < 2
									  Logger.info { "  #{method}  : " + 'not applicable'.colorize(:unknown) }
									  nil
								  else
									  a, b, _ = ciphers
									  ab      = ssl_client(method, [a, b]).cipher.first
									  ba      = ssl_client(method, [b, a]).cipher.first
									  if ab != ba
										  Logger.info { "  #{method} : " + 'client preference'.colorize(:warning) }
										  :client
									  else
										  sort        = -> (a, b) do
											  connection = ssl_client method, [a, b]
											  cipher     = connection.cipher.first
											  cipher == a.name ? -1 : 1
										  end
										  preferences = ciphers.sort &sort
										  Logger.info { "  #{method}  : " + preferences.collect { |c| c.to_s :short }.join(', ') }
										  preferences
									  end
								  end
					[method, preferences]
				end.to_h
			end

			def fetch_dh
				@dh = @supported_ciphers.collect do |_, ciphers|
					ciphers.values.collect(&:tmp_key).select { |d| d.is_a? OpenSSL::PKey::DH }
				end.flatten.uniq &:fingerprint
			end

			def fetch_ecdsa_certs
				@ecdsa_certs = {}

				@supported_ciphers.each do |method, ciphers|
					ecdsa = ciphers.keys.detect &:ecdsa?
					next unless ecdsa

					@ecdsa_certs = Curve.collect do |curve|
						begin
							connection = ssl_client method, ecdsa, curves: curve
							[curve, connection]
						rescue TLSException
							nil
						end
					end.compact.to_h

					break
				end
			end

			def fetch_supported_curves
				Logger.info { '' }
				Logger.info { 'Supported elliptic curves' }
				@supported_curves = []

				ecdsa_curve = @ecdsa_certs.keys.first
				if ecdsa_curve
					# If we have an ECDSA cipher, we need at least the certificate curve to do handshake,
					# but with lowest priority to check for ECHDE and not just ECDSA

					@supported_ciphers.each do |method, ciphers|
						ecdsa = ciphers.keys.detect &:ecdsa?
						next unless ecdsa
						@supported_curves = Curve.select do |curve|
							if curve == ecdsa_curve
								# ECDSA curve is always supported
								Logger.info { "  ECC curve #{curve.name}" }
								next true
							end
							begin
								connection = ssl_client method, ecdsa, curves: [curve, ecdsa_curve]
								# Not too fast !!!
								# Handshake will **always** succeed, because ECDSA
								# curve is always supported.
								# So, we need to test for the real curve!
								# Treaky case : if server preference is enforced,
								# ECDSA curve can be prefered over ECDHE one and so
								# really supported curve can be detected as not supported :(

								dh               = connection.tmp_key
								negociated_curve = dh.curve
								supported        = ecdsa_curve != negociated_curve
								if supported
									Logger.info { "  ECC curve #{curve.name}" }
								else
									Logger.debug { "  ECC curve #{curve.name} : not supported" }
								end
								supported
							rescue TLSException
								false
							end
						end
						break
					end
				else
					# If we have no ECDSA ciphers, ECC supported are only ECDH ones
					# So peak an ECDH cipher and test all curves
					@supported_ciphers.each do |method, ciphers|
						ecdh = ciphers.keys.detect { |c| c.ecdh? or c.ecdhe? }
						next unless ecdh
						@supported_curves = Curve.select do |curve|
							begin
								ssl_client method, ecdh, curves: curve
								Logger.info { "  ECC curve #{curve.name}" }
								true
							rescue TLSException
								Logger.debug { "  ECC curve #{curve.name} : not supported" }
								false
							end
						end
						break
					end
				end
			end

			def fetch_curves_preference
				@curves_preference = if @supported_curves.size < 2
										 Logger.info { 'Curves preference : ' + 'not applicable'.colorize(:unknown) }
										 nil
									 else
										 method, cipher = @supported_ciphers.collect do |method, ciphers|
											 cipher = ciphers.keys.detect { |c| c.ecdh? or c.ecdhe? }
											 [method, cipher]
										 end.detect { |n| !n.nil? }

										 a, b, _ = @supported_curves
										 ab, ba  = [a, b], [b, a]
										 if cipher.ecdsa?
											 # In case of ECDSA, add the cert key at the end
											 # Or no negociation possible
											 ecdsa_curve = @ecdsa_certs.keys.first
											 ab << ecdsa_curve
											 ba << ecdsa_curve
										 end
										 ab = ssl_client(method, cipher, curves: ab).tmp_key.curve
										 ba = ssl_client(method, cipher, curves: ba).tmp_key.curve
										 if ab != ba
											 Logger.info { 'Curves preference : ' + 'client preference'.colorize(:warning) }
											 :client
										 else
											 sort        = lambda do |a, b|
												 curves = [a, b]
												 if cipher.ecdsa?
													 # In case of ECDSA, add the cert key at the end
													 # Or no negociation possible
													 curves << ecdsa_curve
												 end
												 connection = ssl_client method, cipher, curves: curves
												 curve      = connection.tmp_key.curve
												 a == curve ? -1 : 1
											 end
											 preferences = @supported_curves.sort &sort
											 Logger.info { 'Curves preference : ' + preferences.collect { |c| c.name }.join(', ') }
											 preferences
										 end
									 end
			end

			def check_fallback_scsv
				Logger.info { '' }

				@fallback_scsv = false
				if @supported_methods.size > 1
					# We will try to connect to the not better supported method
					method = @supported_methods[1]
					begin
						ssl_client method, fallback: true
					rescue InappropriateFallback,
							CipherNotAvailable # Seems some servers reply with "sslv3 alert handshake failure"...
						@fallback_scsv = true
					end
				else
					@fallback_scsv = nil
				end

				text, color = case @fallback_scsv
							  when true
								  ['supported', :good]
							  when false
								  ['not supported', :error]
							  when nil
								  ['not applicable', :unknown]
							  end
				Logger.info { 'Fallback SCSV : ' + text.colorize(color) }
			end

			Method.each do |method|
				class_eval <<-RUBY_EVAL, __FILE__, __LINE__ + 1
					def #{method.to_sym.downcase}?
						@supported_methods.detect { |m| m == :#{method.to_sym} }
					end
				RUBY_EVAL
			end

			Cipher::TYPES.each do |type, _|
				class_eval <<-RUBY_EVAL, __FILE__, __LINE__ + 1
					def #{type}?
						uniq_supported_ciphers.any? { |c| c.#{type}? }
					end
				RUBY_EVAL
			end

			private

			def connect(&block)
				socket   = ::Socket.new @family, sock_type
				sockaddr = ::Socket.sockaddr_in @port, @ip
				#Logger.trace { "Connecting to #{@ip}:#{@port}" }
				begin
					status = socket.connect_nonblock sockaddr
					#Logger.trace { "Connecting to #{@ip}:#{@port} status : #{status}" }
					raise ConnectionError, status unless status == 0
					#Logger.trace { "Connected to #{@ip}:#{@port}" }
					block_given? ? block.call(socket) : nil
				rescue ::IO::WaitReadable
					#Logger.trace { "Waiting for read to #{@ip}:#{@port}" }
					raise Timeout.new(@ip, @port) unless IO.select [socket], nil, nil, TCP_TIMEOUT
					retry
				rescue ::IO::WaitWritable
					#Logger.trace { "Waiting for write to #{@ip}:#{@port}" }
					raise Timeout.new(@ip, @port) unless IO.select nil, [socket], nil, TCP_TIMEOUT
					retry
				rescue Errno::ECONNREFUSED => e
					raise ConnectionError, e
				ensure
					socket.close
				end
			end

			def ssl_connect(socket, context, method, &block)
				ssl_socket          = ::OpenSSL::SSL::SSLSocket.new socket, context
				ssl_socket.hostname = @hostname if @hostname and method != :SSLv2
				#Logger.trace { "SSL connecting to #{name}" }
				begin
					ssl_socket.connect_nonblock
					#Logger.trace { "SSL connected to #{name}" }
					return block_given? ? block.call(ssl_socket) : nil
				rescue ::OpenSSL::SSL::SSLErrorWaitReadable
					#Logger.trace { "Waiting for SSL read to #{name}" }
					raise TLSTimeout.new(@ip, @port) unless IO.select [ssl_socket], nil, nil, TLS_TIMEOUT
					retry
				rescue ::OpenSSL::SSL::SSLErrorWaitWritable
					#Logger.trace { "Waiting for SSL write to #{name}" }
					raise TLSTimeout.new(@ip, @port) unless IO.select nil, [ssl_socket], nil, TLS_TIMEOUT
					retry
				rescue ::OpenSSL::SSL::SSLError => e
					case e.message
					when /state=SSLv2 read server hello A$/,
							/state=SSLv3 read server hello A$/,
							/state=SSLv3 read server hello A: wrong version number$/,
							/state=SSLv3 read server hello A: tlsv1 alert protocol version$/,
							/state=SSLv3 read server key exchange A: sslv3 alert handshake failure$/
						raise MethodNotAvailable, e
					when /state=SSLv2 read server hello A: peer error no cipher$/,
							/state=error: no ciphers available$/,
							/state=SSLv3 read server hello A: sslv3 alert handshake failure$/,
							/state=error: missing export tmp dh key$/,
							/state=error: wrong curve$/
						raise CipherNotAvailable, e
					when /state=SSLv3 read server hello A: tlsv1 alert inappropriate fallback$/
						raise InappropriateFallback, e
					end
					raise
				rescue ::SystemCallError => e
					case e.message
					when /^Connection reset by peer - SSL_connect$/
						raise TLSNotAvailableException, e
					end
					raise
				ensure
					ssl_socket.close
				end
			end

			def ssl_client(method, ciphers = nil, curves: nil, fallback: false, &block)
				sleep SLOW_DOWN if SLOW_DOWN > 0
				ssl_context = ::OpenSSL::SSL::SSLContext.new method.to_sym
				ssl_context.enable_fallback_scsv if fallback

				if ciphers
					ciphers = [ciphers] unless ciphers.is_a? Enumerable
					ciphers = ciphers.collect(&:name).join ':'
				else
					ciphers = Cipher::ALL
				end
				ssl_context.ciphers = ciphers

				if curves
					curves = [curves] unless curves.is_a? Enumerable
					# OpenSSL fails if the same curve is selected multiple times
					# So because Array#uniq preserves order, remove the less prefered ones
					curves                  = curves.collect(&:name).uniq.join ':'
					ssl_context.ecdh_curves = curves
				end

				Logger.trace { "Try method=#{method} / ciphers=#{ciphers} / curves=#{curves} / scsv=#{fallback}" }
				begin
					connect do |socket|
						ssl_connect socket, ssl_context, method do |ssl_socket|
							return block_given? ? block.call(ssl_socket) : ssl_socket
						end
					end
				rescue => e
					Logger.trace { "Error occurs : #{e}" }
					raise
				end
			end

			def verify_certs
				Logger.info { '' }
				Logger.info { 'Certificates' }

				# Let's begin the fun
				# First, collect "standard" connections
				# { method => { cipher => connection, ... }, ... }
				certs = @supported_ciphers.values.collect(&:values).flatten 1
				# Then, collect "ecdsa" connections
				# { curve => connection, ... }
				certs += @ecdsa_certs.values
				# For anonymous cipher, there is no certificate at all
				certs = certs.reject { |c| c.peer_cert.nil? }
				# Then, fetch cert
				certs = certs.collect { |c| Cert.new c }
				# Then, filter cert to keep uniq fingerprint
				@certs = certs.uniq { |c| c.fingerprint }

				@trusted = @valid = true
				@certs.each do |cert|
					key      = cert.key
					identity = cert.valid?(@hostname || @ip)
					trust    = cert.trusted?
					Logger.info { "  Certificate #{cert.subject} [#{cert.serial}] issued by #{cert.issuer}" }
					Logger.info { '    Key : ' + Tls.key_to_s(key) }
					if identity
						Logger.info { '    Identity : ' + 'valid'.colorize(:good) }
					else
						Logger.info { '    Identity : ' + 'invalid'.colorize(:error) }
						@valid = false
					end
					if trust == :trusted
						Logger.info { '    Trust : ' + 'trusted'.colorize(:good) }
					else
						Logger.info { '    Trust : ' + 'untrusted'.colorize(:error) + ' - ' + trust }
						@trusted = false
					end
				end
				@keys = @certs.collect &:key
			end

			private
			def uniq_supported_ciphers
				@uniq_supported_ciphers ||= @supported_ciphers.values.collect(&:keys).flatten.uniq
			end
		end
	end
end