# Copyright, 2018, by Samuel G. D. Williams. <http://www.codeotaku.com>
# Copyright, 2013, by Ilya Grigorik.
# 
# 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_relative 'frame'

module HTTP
	module Protocol
		module HTTP2
			# Certain frames can have padding:
			# https://http2.github.io/http2-spec/#padding
			#
			# +---------------+
			# |Pad Length? (8)|
			# +---------------+-----------------------------------------------+
			# |                            Data (*)                         ...
			# +---------------------------------------------------------------+
			# |                           Padding (*)                       ...
			# +---------------------------------------------------------------+
			#
			module Padded
				def padded?
					flag_set?(PADDED)
				end
				
				# We will round up frames to the given length:
				MODULUS = 0x0F
				
				def pack(data, modulus: MODULUS, padding_size: nil, maximum_size: nil)
					padding_size ||= (MODULUS - data.bytesize) % MODULUS
					
					if maximum_size
						maximum_padding_size = maximum_size - data.bytesize
						
						if padding_size > maximum_padding_size
							padding_size = maximum_padding_size
						end
					end
					
					if padding_size > 0
						set_flags(PADDED)
						
						buffer = String.new.b
						
						buffer << padding_size.chr
						buffer << data
						buffer << "\0" * padding_size
						
						super buffer
					else
						clear_flags(PADDED)
						
						super data
					end
				end
				
				def unpack
					if padded?
						padding_size = @payload[0].ord
						data_size = @payload.bytesize - 1 - padding_size
						
						if data_size < 0
							raise ProtocolError, "Invalid padding length: #{padding_size}"
						end
						
						return @payload.byteslice(1, data_size)
					else
						return @payload
					end
				end
			end
		end
	end
end