# code:
# * George Moschovitis  <gm@navel.gr>
#
# (c) 2004 Navel, all rights reserved.
# $Id: cluster.rb 104 2004-10-22 13:35:03Z gmosx $

$:.unshift "lib"

require "drb"
require "monitor"

require "n/application"
require "n/server"
require "n/utils/cache"
require "n/app/session"

module N

# = Cluster
#
# A Cluster manages the state of a collection of servers. The cluster 
# synchronizes the servers and distributes the state. An older version 
# used a polling system, ie: the servers polled the cluster to 
# obtain the state. This version uses a push system, ie when the 
# state is changed a delta is pushed to the clients.
#
# TODO: use Sync instead of Monitor
#
class Cluster < N::Application

	# = CHash ClusterHash
	#
	# The CHash 'endpoint' resides in the Cluster server
	#
	class CHash < Hash
		attr :mon
		
		# drbobject for this hash (local)
		attr_accessor :ldrb
		
		# the cluster, use a cluster to implement a set
		# (one server per drb_uri)
		attr_accessor :cluster
		
		#
		#
		def initialize(ldrb_uri = "druby://:8000")
			@mon = Monitor.new
			@ldrb = DRb.start_service(ldrb_uri, self)
			@cluster = {}
		end

		#  
		#		
		def join(sdrb_uri)
			@mon.synchronize {
				cluster[sdrb_uri] = DRbObject.new(nil, sdrb_uri)
			}
		end
		
		alias_method :old_set, :[]=

		# Not really usefull
		#		
		def []=(key, value)
			# store the value (useful on server restarts)
			@mon.synchronize {
				old_set(key, value)

				puts "CLUSTER #{key} = #{value}"
		
				cluster.each { |uri, sdrb|
					begin
						sdrb.server_sync(key, value)
					rescue => ex
						$log.error "Server at #{uri} is down, removing from cluster"
						cluster.delete(uri)
					end
				}
			}
		end
		
		# Use this, avoids syncing the original server, and avoids a 
		# nasty deadlock.
		#
		def cluster_sync(key, value, server_uri)
			# store the value (useful on server restarts)
			@mon.synchronize {
				old_set(key, value)

				puts "CLUSTER #{key} = #{value}"
		
				cluster.each { |uri, sdrb|
					begin
						sdrb.server_sync(key, value) unless uri == server_uri
					rescue => ex
						$log.error "Server at #{uri} is down, removing from cluster"
						cluster.delete(uri)
					end
				}
			}		
		end
		
		def [](key)
			@mon.synchronize {
				puts "LOOKUP #{key}"
				return super
			}
		end
		
	end
	
	# = SHash ServerHash
	#
	# The SHash 'endpoint' resides in the App server
	#
	class SHash < Hash
		attr :mon
	
		# drbobject for this hash (local)
		attr_accessor :ldrb
	
		# drb for the cluster hash
		attr_accessor :cdrb
		
		# ldrb = local drb uri
		# cdrb = cluster drb uri
		#
		def initialize(ldrb_uri = "druby://:9000", cdrb_uri = "druby://:8000")
			@mon = Monitor.new
			@ldrb_uri = ldrb_uri
			@ldrb = DRb.start_service(ldrb_uri, self)
			@cdrb = DRbObject.new(nil, cdrb_uri)
			@cdrb.join(ldrb_uri)
		end
		
		alias_method :old_set, :[]=
		
		#
		#
		def []=(key, value)
			# store the value in the local hash
			@mon.synchronize {
				puts "LOCAL #{key} = #{value}"
				old_set(key, value)
				@cdrb.cluster_sync(key, value, @ldrb_uri)
			}
		end
		
		# If the key is not found in the local hash, try the 
		# cluster hash.
		#
		def [](key)
			@mon.synchronize {
				unless value = super
					value = @cdrb[key]
					old_set(key, value)
				end
				return value
			}
		end
		
		# Called by the cluster
		#
		def server_sync(key, value)
			puts "SYNC #{key} = #{value}"
			@mon.synchronize {
				old_set(key, value)
			}
		end
			
	end

	# = Clm Cluster Last Modified Hash
	#
	class Clm < CHash
		def [](key)
			@mon.synchronize {
				unless value = super
					puts "INIT #{key}"
					value = Time.now.to_i
					old_set(key, value)
				end
				return value
			}
		end
	end
	
	# = Slm Server Last Modified Hash
	#
	class Slm < SHash
		def set!(key, lm = nil)
			lm = Time.now.to_i unless lm
			self[key] = lm
			return lm
		end
	end
	
	def initialize(name = "Cluster")
		super
	end
	
	def run
		N::Cluster::Clm.new
		DRb.start_service("druby://:8001", N::App::SessionManager.new)
	
		while true
			sleep(5000)
		end
		
		super
	end
	
end

end # module

if $0 == __FILE__
	require "logger"; $log = Logger.new(STDERR)
	
	N::Cluster.new.exec()
end