module Plezi

	# File and Object Caching for Plezi
	module_function
	# contains the cached data, in the format: CACHE_STORE["filename"] = CacheObject
	CACHE_STORE = {}
	LOCK = Mutex.new
	CACHABLE = %w{cache object slim haml css map js html scss sass coffee txt xml json yaml rb}

	@cache_to_disk = true

	# this class holds cached objects (data and modification times)
	class CacheObject
		# Cached attributes
		attr_accessor :data, :mtime

		# initialize a Cached object
		def initialize d = nil, t = Time.now
			@data, @mtime = d, t
		end
	end

	# load the file from the cache (if exists) or the file system (if it doesn't)
	def load_file filename
		cached?(filename) ? get_cached(filename) : reload_file(filename)
	end
	# review a file's modification time
	def file_mtime filename
		return CACHE_STORE[filename].mtime if cached?(filename)
		File.mtime(filename)
	end

	# force a file onto the cache (only if it is cachable - otherwise will load the file but will not cache it).
	def reload_file filename
		if CACHABLE.include? filename.match(/\.([^\.]+)$/)[1]
			return cache_data filename, IO.read(filename), File.mtime(filename)
		else
			return IO.read(filename)
		end
	end
	# places data into the cache, and attempts to save the data to a file name.
	def save_file filename, data, save_to_disk = false
		cache_data filename, data if CACHABLE.include? filename.match(/\.([^\.]+)$/)[1]
		begin
			IO.write filename, data if save_to_disk
		rescue Exception => e
			Plezi.warn("File couldn't be written (#{filename}) - file system error?")
		end
		data
	end
	# places data into the cache, under an identifier ( file name ).
	def cache_data filename, data, mtime = Time.now
		LOCK.synchronize { CACHE_STORE[filename] = CacheObject.new( data, mtime )  }
		data
	end
	# Get data from the cache. will throw an exception if there is no data in the cache.
	def get_cached filename
		CACHE_STORE[filename].data # if CACHE_STORE[filename]
	end

	# returns true if the filename is cached.
	def cached? filename
		!CACHE_STORE[filename].nil?
	end

	# returns true if the file exists on disk or in the cache.
	def file_exists? filename
		(CACHE_STORE[filename] || File.exists?(filename)) ? true : false
	end

	# returns true if the file has been update since data was last cached.
	def cache_needs_update? filename
		return true if CACHE_STORE[filename].nil? || CACHE_STORE[filename].mtime < File.mtime(filename)
		false
	end
end