# code: 
# * George Moschovitis  <gm@navel.gr>
#
# (c) 2004 Navel, all rights reserved.
# $Id: filters.rb 184 2004-12-07 14:42:22Z gmosx $

module N

# = Filtering
#
# Filtering functionality for renders/services. The design 
# and implementation is HEAVILY influenced by Rails.
#
# Examples:
#
# Filter as class:
#
# class TouchFilter
#	end
#
# Filter
# 	before
#		filter
#		after
#
# TODO: 
# implement inheritable filters.
#
module Filtering

	# Ruby is sometimes VERY surprising, the following trick is needed
	# to include singleton methods in other classes.
	#
	def self.append_features(base)
		super; base.extend(ClassMethods)
	end

	module ClassMethods
		# the filters to be evaluated before the method
		@@before_filters = []
		
		# the filters to be evaluated after the method
		@@after_filters = []
		
		#
		#
		def before_filters 
			@@before_filters
		end
		
		#
		#
		def after_filters
			@@after_filters
		end
		
		#
		#
		def prepend_before_filter(*filters, &block)
			filters << block if block_given?
			@@before_filters = filters + @@before_filters
		end
		
		#
		#
		def append_before_filter(*filters, &block)
			filters << block if block_given?
			@@before_filters = @@before_filters + filters
		end
		
		# Alias for the most common case.
		alias :before_filter :prepend_before_filter

		#
		#
		def prepend_after_filter(*filters, &block)
			filters << block if block_given?
			@@after_filters = filters + @@after_filters
		end
		
		#
		#
		def append_after_filter(*filters, &block)
			filters << block if block_given?
			@@after_filters = @@after_filters + filters
		end
		
		# Alias for the most common case.
		alias :after_filter :append_after_filter		
	
		# Install an arround Filter. A filter is a class that responds
		# to the before and after methods. Both methods are prepended to
		# the respective lists.
		#
		def prepend_arround_filter(*filters)
			filters = [filters].flatten
			
			for filter in filters
				if filter.respond_to?(:before)
					prepend_before_filter { |c| filter.before(c) }
				elsif filter.respond_to?(:filter)
					# consider 'filter' as synonym of before.
					prepend_before_filter { |c| filter.filter(c) }
				end
				prepend_after_filter { |c| filter.after(c) } if filter.respond_to?(:after)
			end
		end
		
		# Install an arround Filter. A filter is a class that responds
		# to the before and after methods. Both methods are appended to
		# the respective lists.
		#
		def append_arround_filter(*filters)
			filters = [filters].flatten
			
			for filter in filters
				if filter.respond_to?(:before)
					append_before_filter { |c| filter.before(c) }
				elsif filter.respond_to?(:filter)
					# consider 'filter' as synonym of before.
					append_before_filter { |c| filter.filter(c) }
				end
				append_after_filter { |c| filter.after(c) } if filter.respond_to?(:after)
			end
		end
		
		# Alias for the most common case.
		alias :filter :append_arround_filter
		
		#
		#
		def gen_filters_call_code(filters)
			code = ""
		
			filters.each do |filter| 
				if Symbol === filter
					code << "if #{filter} == false then return false end;"
				elsif filter.respond_to?('call') && (filter.arity == 1 || filter.arity == -1)
					code << 'if filter.call(self) == false then return false end;'
				elsif filter.is_a?(Module) and filter.instance_methods.size > 0
					class_eval "include #{filter};"
					meth = filter.instance_methods[0]
					code << "if #{meth} == false then return false end;"
				elsif filter.respond_to?('filter')
					code << "if #{filter}.filter(self) == false then return false end"
				else
					raise 'Valid filters are either a symbol or a proc/method.'
				end
			end
			
			return code
		end	
	end
	
end

end # module