require 'socket'

class NntpClient
	attr_reader :host, :sock, :curgroup, :ydec
	def initialize(host = 'news.free.fr', curgroup = nil)
		@host = host
		@curgroup = curgroup
		@sock = nil
		@ydec = Ydec.new
	end

	def dl_bin(id, m=nil)
		retried = 0
		begin
			body(id) { |l| @ydec.parse_line l, m }
		rescue
			retried += 1
			raise if retried > 4
			@ydec.restart
			retry
		end
	end

	def reconnect
		@sock = TCPSocket.new @host, 'nntp'
		puts ' [+] connected'
		s = @sock.gets
		puts s if $VERBOSE
		mode 'reader'
		group @curgroup if @curgroup
	end

	def method_missing(*a)
		if a.first == :group
			@curgroup = a[1]
		end

		cmd = a * ' '

	begin
		begin
			@sock.puts cmd
		rescue
			return if a.first == :quit
			reconnect
			@sock.puts cmd
		end
		puts "> #{cmd}" if $VERBOSE
		str = @sock.gets.chomp! or raise 'partial read'
		puts str if $VERBOSE
	rescue
	retry
	end


		# no yield if response != 2xx
		if block_given?
			if str[0] == ?2
			loop do
				str = @sock.gets.chomp! or raise 'partial read'
				return if str == '.'
				str = str[1..-1] if str[0] == ?.
				yield str
			end
			else
				puts str
			end
		end
		str
	end
end

class Ydec
	def initialize
		restart
	end

	def restart
		@ybeginline = true
		@outfile = nil
		@outlen = nil
		@linelen = nil

		@ypartline = false
		@partoffset = nil
		@partsize = nil
		@partcrc = nil

		@curbuf = nil
		@specialchar = false
	end

	# returns true if you should pass the next line
	def parse_line(l, m=nil)
		l = l.chomp
		if @ybeginline
			parse_ybegin $1 if l =~ /^=ybegin\s+(.*?)\s*$/
			!@ybeginline
		elsif @ypartline
			parse_ypart  $1 if l =~ /^=ypart\s+(.*?)\s*$/
			!@ypartline
		elsif @curbuf
			if l =~ /^=yend\s+(.*?)\s*$/
				parse_yend $1, m
			else
				ydecode l
			end
			@curbuf
		end
	end

	def parse_ybegin(l)
		raise "invalid ybegin #{l.inspect}" unless l =~ /(.*) name=(.*)/
		l = $1
		@outfile = $2
		@ypartline = (l =~ /\bpart\b/)
		puts "ydec: decoding #{@outfile.inspect}#{' (part)' if @ypartline}" if $VERBOSE
		@outfile.gsub!(/[^a-zA-Z0-9_.+\-\[\]\(\)#'" ]/, '_')
		l.scan(/(\w+)=(\w+)/).each { |k, v|
			case k
			when 'line': @linelen = v.to_i
			when 'size': @outlen = v.to_i
			when 'part', 'total'
			else puts "unknown ybegin field #{k.inspect} = #{v.inspect}"
			end
		}
		@curbuf = ''
		@ybeginline = false
		true
	end
	
	def parse_ypart(l)
		l.scan(/(\w+)=(\w+)/).each { |k, v|
			case k
			when 'begin': @partoffset = v.to_i - 1
			when 'end':   @partsize = v.to_i - @partoffset
			else puts "unknown ypart field #{k.inspect} = #{v.inspect}"
			end
		}
		puts "ydec: decoding part: #@partsize o at #@partoffset" if $VERBOSE
		@curbuf = ''
		@ypartline = false
		true
	end

	def parse_yend(l, m=nil)
		sz = nil
		crc = nil
		pcrc = nil
		l.scan(/(\w+)=(\w+)/).each { |k, v|
			case k
			when 'size': sz = v.to_i
			when 'crc32': crc = v[0..7].hex
			when 'pcrc32': pcrc = v[0..7].hex
			when 'part'
			else puts "unknown yend field #{k.inspect} = #{v.inspect}"
			end
		}
		puts "ydec: finished" if $VERBOSE
		if @partsize
			m.lock if m
			File.open(@outfile, 'w') {} unless File.exist? @outfile
			File.open(@outfile, 'r+') { |fd| fd.seek @partoffset ; fd.write @curbuf }
			m.unlock if m
		else
			File.open(@outfile, 'w') { |fd| fd.write @curbuf }
		end
		@curbuf = nil
		@ybeginline = true
	end

	def ydecode(l)
		l.each_byte { |b|
			if @specialchar
				@specialchar = false
				@curbuf << ((b - 64 - 42) & 255)
			else
				case b
				when ?=
					@specialchar = true
				when ?\n, ?\r, ?\0
					puts "special char #{b.chr.inspect} in stream..."
				else
					@curbuf << ((b - 42) & 255)
				end
			end
		}
		if @specialchar
			puts "line ends with specialchar.."
			@specialchar = false
		end
	end
end