module REXML
	# If you add a method, keep in mind two things:
	# (1) the first argument will always be a list of nodes from which to
	# filter.  In the case of context methods (such as position), the function
	# should return an array with a value for each child in the array.
	# (2) all method calls from XML will have "-" replaced with "_".
	# Therefore, in XML, "local-name()" is identical (and actually becomes)
	# "local_name()"
	module Functions
		@@node = nil
		@@pair = []
		@@variable = {}
		@@namespace_context = {}

		def Functions::node=(value); @@node = value; end
		def Functions::pair=(value); @@pair = value; end
		def Functions::variable=(value); @@variable = value; end
		def Functions::namespace_context=(value)
			@@namespace_context = value
		end
		def Functions::node; @@node; end
		def Functions::pair; @@pair; end
		def Functions::variable; @@variable; end
		def Functions::namespace_context; @@namespace_context; end

		def Functions::text( )
			return true if @@node.kind_of? Text
		end

		def Functions::last( )
			@@pair[1]
		end

		def Functions::position( )
			@@pair[0]
		end

		def Functions::count( node_set )
			node_set.size
		end

		# Since REXML is non-validating, this method is not implemented as it
		# requires a DTD
		def Functions::id( object )
		end

		# UNTESTED
		def Functions::local_name( node_set=nil )
			get_namespace( node_set ) do |node|
				return node.local_name 
			end
		end

		def Functions::namespace_uri( node_set=nil )
			get_namespace( node_set ) {|node| node.namespace}
		end

		def Functions::name( node_set=nil )
			get_namespace( node_set ) do |node| 
				node.expanded_name
			end
		end

		# Helper method.
		def Functions::get_namespace( node_set = nil )
			if node_set == nil
				yield @@node if @@node.kind_of? Namespace
			else	
				if node_set.kind_of? Namespace
					yield node_set
				else
					return unless node_set.kind_of? Enumerable
					node_set.each { |node| yield node if node.kind_of? Namespace }
				end
			end
		end

		# A node-set is converted to a string by returning the string-value of the
		# node in the node-set that is first in document order. If the node-set is
		# empty, an empty string is returned.
		#
		# A number is converted to a string as follows
		#
		# NaN is converted to the string NaN 
		#
		# positive zero is converted to the string 0 
		#
		# negative zero is converted to the string 0 
		#
		# positive infinity is converted to the string Infinity 
		#
		# negative infinity is converted to the string -Infinity 
		#
		# if the number is an integer, the number is represented in decimal form
		# as a Number with no decimal point and no leading zeros, preceded by a
		# minus sign (-) if the number is negative
		#
		# otherwise, the number is represented in decimal form as a Number
		# including a decimal point with at least one digit before the decimal
		# point and at least one digit after the decimal point, preceded by a
		# minus sign (-) if the number is negative; there must be no leading zeros
		# before the decimal point apart possibly from the one required digit
		# immediately before the decimal point; beyond the one required digit
		# after the decimal point there must be as many, but only as many, more
		# digits as are needed to uniquely distinguish the number from all other
		# IEEE 754 numeric values.
		#
		# The boolean false value is converted to the string false. The boolean
		# true value is converted to the string true.
		#
		# An object of a type other than the four basic types is converted to a
		# string in a way that is dependent on that type.
		def Functions::string( object=nil )
			#object = @context unless object
			if object.kind_of? Array
				string( object[0] )
			elsif object.kind_of? Text
				object.to_s
			elsif object.kind_of? Element
				object.name
			else
				object.to_s
			end
		end

		# UNTESTED
		def Functions::concat( *objects )
			objects.join
		end

		# Fixed by Mike Stok
		def Functions::starts_with( string, test )
			string(string).index(string(test)) == 0
		end

		# Fixed by Mike Stok
		def Functions::contains( string, test )
			string(string).include? string(test)
		end

		# UNTESTED
		def Functions::substring_before( string, test )
			string[ 0...string.index(test) ]
		end

		# UNTESTED
		def Functions::substring_after( string, test )
			string[ string.index(test)+1..-1 ]
		end

		# Take equal portions of Mike Stok and Sean Russell; mix vigorously, and
		# pour into a tall, chilled glass.  Serves 10,000.
		def Functions::substring( string, start, length=0 )
			ruby_string = string(string)
			ruby_length = if length.nil? 
											string.length
										else
											number(length)
										end
			ruby_start = number(start)

			# Handle the special cases
			return '' if (
				ruby_length.nan? or 
				ruby_start.nan? or
				ruby_start.infinite?
			)

			infinite_length = ruby_length.infinite? == 1
			ruby_length = ruby_string.length if infinite_length
				
			# Now, get the bounds.  The XPath bounds are 1..length; the ruby bounds 
			# are 0..length.  Therefore, we have to offset the bounds by one.
			ruby_start = ruby_start.round - 1
			ruby_length = ruby_length.round

			if ruby_start < 0
			 ruby_length += ruby_start unless infinite_length
			 ruby_start = 0
			end
			return '' if ruby_length <= 0
			ruby_string[ruby_start,ruby_length]
		end

		# UNTESTED
		def Functions::string_length( string )
			string(string).length
		end

		# UNTESTED
		def Functions::normalize_space( string=nil )
			string = string(@@node) if string.nil?
			if string.kind_of? Array
				string.collect{|x| string.to_s.strip.gsub(/\s+/um, ' ') if string}
			else
				string.to_s.strip.gsub(/\s+/um, ' ')
			end
		end

		# This is entirely Mike Stok's beast
		def Functions::translate( string, tr1, tr2 )
			from = string(tr1)
			to = string(tr2)

			# the map is our translation table.
			#
			# if a character occurs more than once in the
			# from string then we ignore the second &
			# subsequent mappings
			#
			# if a charactcer maps to nil then we delete it
			# in the output.  This happens if the from
			# string is longer than the to string
			#
			# there's nothing about - or ^ being special in
			# http://www.w3.org/TR/xpath#function-translate
			# so we don't build ranges or negated classes

			map = Hash.new
			0.upto(from.length - 1) { |pos|
				from_char = from[pos]
				unless map.has_key? from_char
					map[from_char] = 
					if pos < to.length
						to[pos]
					else
						nil
					end
				end
			}

			string(string).unpack('U*').collect { |c|
				if map.has_key? c then map[c] else c end
			}.compact.pack('U*')
		end

		# UNTESTED
		def Functions::boolean( object=nil )
			if object.kind_of? String
				if object =~ /\d+/u
					return object.to_f != 0
				else
					return object.size > 0
				end
			elsif object.kind_of? Array
				object = object.find{|x| x and true}
			end
			return object ? true : false
		end

		# UNTESTED
		def Functions::not( object )
			not boolean( object )
		end

		# UNTESTED
		def Functions::true( )
			true
		end

		# UNTESTED
		def Functions::false(  )
			false
		end

		# UNTESTED
		def Functions::lang( language )
			@@node.collect do |node|
				if node.kind_of? Element
					lang = false
					until node.nil? or lang
						lang = compare_language node.attributes["xml:lang"], language
						node = node.parent
					end
				end
			end
		end

		def Functions::compare_language lang1, lang2
			lang2.downcase.index(lang1.downcase) == 0
		end

		# a string that consists of optional whitespace followed by an optional
		# minus sign followed by a Number followed by whitespace is converted to
		# the IEEE 754 number that is nearest (according to the IEEE 754
		# round-to-nearest rule) to the mathematical value represented by the
		# string; any other string is converted to NaN
		#
		# boolean true is converted to 1; boolean false is converted to 0
		#
		# a node-set is first converted to a string as if by a call to the string
		# function and then converted in the same way as a string argument
		#
		# an object of a type other than the four basic types is converted to a
		# number in a way that is dependent on that type
		def Functions::number( object=nil )
			object = @@node unless object
			if object == true
				Float(1)
			elsif object == false
				Float(0)
			elsif object.kind_of? Array
				string( object ).to_f
			elsif object.kind_of? Float
				object
			else
				object.to_s.to_f
			end
		end

		def Functions::sum( nodes )
		end
		
		def Functions::floor( nodes, number )
			number = number.to_f if number.kind_of? String
			number.floor
		end

		def Functions::ceiling( nodes, number )
			number = number.to_f if number.kind_of? String
			number.ceil
		end

		def Functions::round( nodes, number )
			number = number.to_f if number.kind_of? String
			number.round
		end

		def Functions::method_missing( id )
			puts "METHOD MISSING #{id.id2name}"
			XPath.match( @@node, id.id2name )
		end
	end
end
