require "forwardable"

require "rss/rss"

module RSS

	class NotWellFormedError < Error
		attr_reader :line, :element
		def initialize(line=nil, element=nil)
			message = "This is not well formed XML"
			if element or line
				message << "\nerror occurred"
				message << " in #{element}" if element
				message << " at about #{line} line" if line
			end
			message << "\n#{yield}" if block_given?
			super(message)
		end
	end

	class XMLParserNotFound < Error
		def initialize
			super("available XML parser does not found in " <<
						"#{AVAILABLE_PARSER_LIBRARIES.inspect}.")
		end
	end

	class NotValidXMLParser < Error
		def initialize(parser)
			super("#{parser} is not available XML parser. " <<
						"available XML parser is " <<
						"#{AVAILABLE_PARSERS.inspect}.")
		end
	end

	class NSError < InvalidRSSError
		attr_reader :tag, :prefix, :uri
		def initialize(tag, prefix, require_uri)
			@tag, @prefix, @uri = tag, prefix, require_uri
			super("prefix <#{prefix}> doesn't associate uri " <<
						"<#{require_uri}> in tag <#{tag}>")
		end
	end

	class Parser

		extend Forwardable

		class << self

			@@default_parser = nil

			def default_parser
				@@default_parser || AVAILABLE_PARSERS.first
			end

			def default_parser=(new_value)
				if AVAILABLE_PARSERS.include?(new_value)
					@@default_parser = new_value
				else
					raise NotValidXMLParser.new(new_value)
				end
			end

			def parse(rss, do_validate=true, ignore_unknown_element=true, parser_class=default_parser)
				parser = new(rss, parser_class)
				parser.do_validate = do_validate
				parser.ignore_unknown_element = ignore_unknown_element
				parser.parse
			end

		end

		def_delegators(:@parser, :parse, :rss,
									 :ignore_unknown_element,
									 :ignore_unknown_element=, :do_validate,
									 :do_validate=)

		def initialize(rss, parser_class=self.class.default_parser)
			@parser = parser_class.new(rss)
		end
	end

	class BaseParser

		def initialize(rss)
			@listener = listener.new
			@rss = rss
		end

		def rss
			@listener.rss
		end

		def ignore_unknown_element
			@listener.ignore_unknown_element
		end

		def ignore_unknown_element=(new_value)
			@listener.ignore_unknown_element = new_value
		end

		def do_validate
			@listener.do_validate
		end

		def do_validate=(new_value)
			@listener.do_validate = new_value
		end

		def parse
			if @listener.rss.nil?
				_parse
			end
			@listener.rss
		end

	end

	class BaseListener

		extend Utils

		class << self

			@@setter = {}
			def install_setter(uri, tag_name, setter)
				@@setter[uri] = {}  unless @@setter.has_key?(uri)
				@@setter[uri][tag_name] = setter
			end

			def setter(uri, tag_name)
				begin
					@@setter[uri][tag_name]
				rescue NameError
					nil
				end
			end

			def available_tags(uri)
				begin
					@@setter[uri].keys
				rescue NameError
					[]
				end
			end
					
			def install_get_text_element(name, uri, setter)
				install_setter(uri, name, setter)
				def_get_text_element(name, *get_file_and_line_from_caller(1))
			end
			
			private

			def def_get_text_element(name, file, line)
				unless private_instance_methods(false).include?("start_#{name}")
					module_eval(<<-EOT, file, line)
					def start_#{name}(name, prefix, attrs, ns)
						uri = ns[prefix]
						if @do_validate
							tags = self.class.available_tags(uri)
							unless tags.include?(name)
								raise UnknownTagError.new(name, uri)
							end
						end
						start_get_text_element(name, prefix, ns, uri)
					end
					EOT
				end
				send("private", "start_#{name}")
			end

		end

	end

	module ListenerMixin

		attr_reader :rss

		attr_accessor :ignore_unknown_element
		attr_accessor :do_validate

		def initialize
			@rss = nil
			@ignore_unknown_element = true
			@do_validate = true
			@ns_stack = [{}]
			@tag_stack = [[]]
			@text_stack = ['']
			@proc_stack = []
			@last_element = nil
			@version = @encoding = @standalone = nil
		end
		
		def xmldecl(version, encoding, standalone)
			@version, @encoding, @standalone = version, encoding, standalone
		end

		def tag_start(name, attributes)
			@text_stack.push('')

			ns = @ns_stack.last.dup
			attrs = {}
			attributes.each do |n, v|
				if n =~ /\Axmlns:?/
					ns[$'] = v # $' is post match 
				else
					attrs[n] = v
				end
			end
			@ns_stack.push(ns)

			prefix, local = split_name(name)
			@tag_stack.last.push([ns[prefix], local])
			@tag_stack.push([])
			if respond_to?("start_#{local}", true)
				send("start_#{local}", local, prefix, attrs, ns.dup)
			else
				start_else_element(local, prefix, attrs, ns.dup)
			end
		end

		def tag_end(name)
			if DEBUG
				p "end tag #{name}"
				p @tag_stack
			end
			text = @text_stack.pop
			tags = @tag_stack.pop
			pr = @proc_stack.pop
			pr.call(text, tags) unless pr.nil?
		end

		def text(data)
			@text_stack.last << data
		end

		private

		def start_RDF(tag_name, prefix, attrs, ns)
			check_ns(tag_name, prefix, ns, RDF::URI)

			@rss = RDF.new(@version, @encoding, @standalone)
			@rss.do_validate = @do_validate
			@last_element = @rss
			@proc_stack.push Proc.new { |text, tags|
				@rss.validate_for_stream(tags) if @do_validate
			}
		end

		def start_else_element(local, prefix, attrs, ns)
			class_name = local[0,1].upcase << local[1..-1]
			current_class = @last_element.class
			begin
#			if current_class.const_defined?(class_name)
				next_class = current_class.const_get(class_name)
				start_have_something_element(local, prefix, attrs, ns, next_class)
			rescue NameError
#			else
				if @ignore_unknown_element
					@proc_stack.push(nil)
				else
					parent = "ROOT ELEMENT???"
					begin
						parent = current_class::TAG_NAME
					rescue NameError
					end
					raise NotExceptedTagError.new(local, parent)
				end
			end
		end

		NAMESPLIT = /^(?:([\w:][-\w\d.]*):)?([\w:][-\w\d.]*)/
		def split_name(name)
			name =~ NAMESPLIT
			[$1 || '', $2]
		end

		def check_ns(tag_name, prefix, ns, require_uri)
			if @do_validate
				if ns[prefix] == require_uri
					#ns.delete(prefix)
				else
					raise NSError.new(tag_name, prefix, require_uri)
				end
			end
		end

		def start_get_text_element(tag_name, prefix, ns, required_uri)
			@proc_stack.push Proc.new {|text, tags|
				setter = self.class.setter(required_uri, tag_name)
				setter ||= "#{tag_name}="
				if @last_element.respond_to?(setter)
					@last_element.send(setter, text.to_s)
				else
					if @do_validate and not @ignore_unknown_element
						raise NotExceptedTagError.new(tag_name, @last_element.tag_name)
					end
				end
			}
		end

		def start_have_something_element(tag_name, prefix, attrs, ns, klass)

			check_ns(tag_name, prefix, ns, klass.required_uri)

			args = []
			
			klass.get_attributes.each do |a_name, a_uri, required|

				if a_uri
					for prefix, uri in ns
						if uri == a_uri
							val = attrs["#{prefix}:#{a_name}"]
							break if val
						end
					end
				else
					val = attrs[a_name]
				end

				if @do_validate and required and val.nil?
					raise MissingAttributeError.new(tag_name, a_name)
				end

				args << val
			end

			previous = @last_element
			next_element = klass.send(:new, *args)
			next_element.do_validate = @do_validate
			setter = ""
			setter << "#{klass.required_prefix}_" if klass.required_prefix
			setter << "#{tag_name}="
			@last_element.send(setter, next_element)
			@last_element = next_element
			@proc_stack.push Proc.new { |text, tags|
				p(@last_element.class) if DEBUG
				@last_element.content = text if klass.have_content?
				@last_element.validate_for_stream(tags) if @do_validate
				@last_element = previous
			}
		end

	end

	unless const_defined? :AVAILABLE_PARSER_LIBRARIES
		AVAILABLE_PARSER_LIBRARIES = [
			["rss/xmlparser", :XMLParserParser],
			["rss/xmlscanner", :XMLScanParser],
			["rss/rexmlparser", :REXMLParser],
		]
	end

	AVAILABLE_PARSERS = []

	AVAILABLE_PARSER_LIBRARIES.each do |lib, parser|
		begin
			require lib
			AVAILABLE_PARSERS.push(const_get(parser))
		rescue LoadError
		end
	end

	if AVAILABLE_PARSERS.empty?
		raise XMLParserNotFound
	end
end