module SBDB

# See http://eigenclass.org/hiki/deferred-finalizers-in-Ruby
# Not threadsafe.

class WeakHash
	attr_reader :cache
	def initialize cache = ::Hash.new
		@cache = cache
		@key_map = {}
		@rev_cache = ::Hash.new{|h,k| h[k] = {}}
		@reclaim_value = lambda do |value_id| 
			if @rev_cache.has_key? value_id
				@rev_cache[value_id].each_key{|key| @cache.delete key}
				@rev_cache.delete value_id
			end
		end
		@reclaim_key = lambda do |key_id|
			@cache.delete @key_map.delete(key_id)  if @key_map.has_key? key_id
		end
	end

	def []= key, value
		case key
		when Fixnum, Symbol, true, false
			key2 = key
		else
			key2 = key.dup
		end
		@rev_cache[value.object_id][key2] = true
		@cache[key2] = value.object_id
		@key_map[key.object_id] = key2

		ObjectSpace.define_finalizer(value, @reclaim_value)
		ObjectSpace.define_finalizer(key, @reclaim_key)
		value
	end

	def [] key
		value_id = @cache[key]
		return ObjectSpace._id2ref( value_id)  unless value_id.nil?
		nil
	rescue RangeError
		nil
	end

	def each &e
		@cache.each do |k, vid|
			unless vid.nil?
				obj = begin
						ObjectSpace._id2ref vid
					rescue RangeError
						next
					end
				yield k, obj
			end
		end
	end
end

end