module Iowa

	# Simple LRU cache for caching pages.

	class LRUCache

		# Initialize the empty LRU cache, and set the maximum number of elements
		# that it will contain or the max time to live (in seconds) of a cache item.
		# If both a max and a maxttl are set, the max is a hard maximum that will
		# not be exceeded.
		def initialize(max=20, maxttl=nil)
			@cache = {}
			@queue = []
			@ttl_cache = {}
			@max = max
			@maxttl = maxttl
			@finalizers = []
		end

		# Check to see if the cache contains the given key.

		def include?(key)
			@cache.include?(key)
		end

		# Return the element identified by the given key.

		def [](key)
			r = nil
			if @cache.has_key? key
				r = @cache[key]
				@queue.push @queue.delete(key)
				@ttl_cache[key] = Time.now.to_i
			end
			r
		end

		# Set the element of the cache identified by the given key.  

		def []=(key, val)
			if @queue.length == @max
				d = @queue.shift
				@cache.delete d
			end
			if @queue.first and @maxttl
				now = Time.now.to_i
				while ((@ttl_cache[@queue.first] + @maxttl) < now)
					d = @queue.shift
					do_finalization(d,@cache[d])
					@cache.delete d
				end
			end
			@cache[key] = val
			@ttl_cache[key] = Time.now.to_i
			@queue.push key
		end

		# Allows one to set the maximum size of the cache queue.  If the queue
		# is currently larger than the size that it is being set to, elements
		# will be expired until the queue is at the maximum size.

		def size=(max)
			@max = max
			while @queue.length > @max
				d = @queue.shift
				do_finalization(d,@cache[d])
				@cache.delete d
			end
			@max
		end
		alias maxsize= size=

		# Return the maximum size of the cache.
		def maxsize
			@max
		end

		# Return the current size of the cache.
		def size
			@queue.length
		end

		# Return a copy of current set of keys to cache elements.
		def queue
			@queue.dup
		end
		
		def add_finalizer(*args,&block)
			@finalizers.push [block,args]
		end
		
		def do_finalization(key,obj)
			begin
			@finalizers.each do |f|
				f[0].call(key,obj,*f[1])
			end
			rescue Exception => e
				puts e, e.backtrace
				raise e
			end
		end
	end
end