# frozen_string_literal: true

# 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/io/buffer'
require 'protocol/http/body/rewindable'

module Falcon
	module Adapters
		# Wraps a streaming input body into the interface required by `rack.input`.
		#
		# The input stream is an `IO`-like object which contains the raw HTTP POST data. When applicable, its external encoding must be `ASCII-8BIT` and it must be opened in binary mode, for Ruby 1.9 compatibility. The input stream must respond to `gets`, `each`, `read` and `rewind`.
		#
		# This implementation is not always rewindable, to avoid buffering the input when handling large uploads. See {Rewindable} for more details.
		class Input
			# Initialize the input wrapper.
			# @parameter body [Protocol::HTTP::Body::Readable]
			def initialize(body)
				@body = body
				
				# Will hold remaining data in `#read`.
				@buffer = nil
				@finished = @body.nil?
			end
			
			# The input body.
			# @attribute [Protocol::HTTP::Body::Readable]
			attr :body
			
			# Enumerate chunks of the request body.
			# @yields {|chunk| ...}
			# 	@parameter chunk [String]
			def each(&block)
				return to_enum unless block_given?
				
				while chunk = gets
					yield chunk
				end
			end
			
			# Rewind the input stream back to the start.
			#
			# `rewind` must be called without arguments. It rewinds the input stream back to the beginning. It must not raise Errno::ESPIPE: that is, it may not be a pipe or a socket. Therefore, handler developers must buffer the input data into some rewindable object if the underlying input stream is not rewindable.
			#
			# @returns [Boolean] Whether the body could be rewound.
			def rewind
				if @body and @body.respond_to? :rewind
					# If the body is not rewindable, this will fail.
					@body.rewind
					@buffer = nil
					@finished = false
					
					return true
				end
				
				return false
			end
			
			# Read data from the input stream.
			# 
			# `read` behaves like `IO#read`. Its signature is `read(length = nil, buffer = nil)`. If given, length must be a non-negative `Integer` (>= 0) or `nil`, and buffer must be a `String` and may not be nil. If `length` is given and not `nil`, then this method reads at most `length` bytes from the input stream. If `length` is not given or `nil`, then this method reads all data. When the end is reached, this method returns `nil` if `length` is given and not `nil`, or an empty `String` if `length` is not given or is `nil`. If `buffer` is given, then the read data will be placed into the `buffer` instead of a newly created `String` object.
			#
			# @parameter length [Integer] the amount of data to read
			# @parameter buffer [String] the buffer which will receive the data
			# @returns a buffer containing the data
			def read(length = nil, buffer = nil)
				buffer ||= Async::IO::Buffer.new
				buffer.clear
				
				until buffer.bytesize == length
					@buffer = read_next if @buffer.nil?
					break if @buffer.nil?
					
					remaining_length = length - buffer.bytesize if length
					
					if remaining_length && remaining_length < @buffer.bytesize
						# We know that we are not going to reuse the original buffer.
						# But byteslice will generate a hidden copy. So let's freeze it first:
						@buffer.freeze
						
						buffer << @buffer.byteslice(0, remaining_length)
						@buffer = @buffer.byteslice(remaining_length, @buffer.bytesize)
					else
						buffer << @buffer
						@buffer = nil
					end
				end
				
				return nil if buffer.empty? && length && length > 0
				
				return buffer
			end
			
			# Has the input stream been read completely?
			# @returns [Boolean]
			def eof?
				@finished and @buffer.nil?
			end
			
			# Read the next chunk of data from the input stream.
			#
			# `gets` must be called without arguments and return a `String`, or `nil` when the input stream has no more data.
			#
			# @returns [String | Nil] The next chunk from the body.
			def gets
				if @buffer.nil?
					return read_next
				else
					buffer = @buffer
					@buffer = nil
					return buffer
				end
			end
			
			# Close and discard the remainder of the input stream.
			def close
				@body&.close
			end
			
			private
			
			def read_next
				return nil if @finished
				
				if chunk = @body.read
					return chunk
				else
					@finished = true
					return nil
				end
			end
		end
	end
end