require "parsedate.rb"
module Eeml
  #a parser for xml eeml v051, implemented with LibXML
  class LibXMLEemlParserV051 # :nodoc:
    include LibXML
    include Exceptions

    @@eeml_version = Constants::EEML['0.5.1']
    #main method
    
    #take an xml string, and create an Environment from it. 
    #If an optional environment is given, that will be populated (overwritten) instead of a new environment.
    def make_environment_from_xml(xml_str, given_environment = nil)
      doc = parse_xml(xml_str)
      raise MissingNamespace if doc.root.namespaces.namespace.blank?
      env = given_environment || Environment.new
      #TODO: what has to be reset in a given environment before passing it for re-population?
      return extract_environment_from_doc(doc, env)
    end

    #take an xml string containing zero or more environment nodes, and create an array of Environment objects from it. 
    def make_environments_from_xml(xml_str)
      doc = parse_xml(xml_str)
      raise MissingNamespace if doc.root.namespaces.namespace.blank?
      return extract_environments_from_doc(doc)
    end

    protected

    def parse_xml(xml_str)
      errors = []
      #http://libxml.rubyforge.org/rdoc/classes/LibXML/XML/Error.html
      #TODO: is the error handler set up per thread? (XML::Error.set_handler)
      XML::Error.set_handler { |error| errors << error } 
  
      #TODO: performance - is this expensive?
      #TODO: are these configurations per-thread?  If they're global (e.g. class variables) then we shouldn't be setting them here.
      XML.default_line_numbers=true
      
      parser = XML::Parser.string(strip_content(xml_str))
      begin
        doc = parser.parse
      rescue XML::Error => e
        #note: errors var available here, too.        
        raise BadXML, "Malformed xml: #{e.class}: #{e}", e.backtrace
      end
      #validation?
      # seems we have to recreate our XML::Schema object on each invocation
      # else libxml segfaults very quickly
      return doc
    end


    #multiple (zero or more)
    def extract_environments_from_doc(doc)
      env_nodes = doc.find('x:environment', "x:#{@@eeml_version[:href]}")
      return env_nodes.map{|env_node| new_env = Environment.new; extract_environment_from_node(env_node, new_env)}
    end

    #single, mandatory
    def extract_environment_from_doc(doc, env_to_populate)
      env_node = find_first_node_or_fail(doc, 'x:environment', 'environment', "x:#{@@eeml_version[:href]}")
      return extract_environment_from_node(env_node, env_to_populate)
    end

    #single, from node (everyone uses this to get the work done)
    def extract_environment_from_node(env_node, env_to_populate)
      env = env_to_populate
      env.identifier = env_node['id']
      env.updated = Time.parse(env_node['updated']) if !env_node['updated'].nil?
      
      env.creator = env_node['creator']

      env.title       = optional_content(env_node, 'x:title', 'title', "x:#{@@eeml_version[:href]}")
      env.feed_url    = optional_content(env_node, 'x:feed', 'feed', "x:#{@@eeml_version[:href]}")
      env.description = optional_content(env_node, 'x:description', 'description', "x:#{@@eeml_version[:href]}")
      env.website     = optional_content(env_node, 'x:website', 'website', "x:#{@@eeml_version[:href]}")
      env.status      = optional_content(env_node, 'x:status', 'status', "x:#{@@eeml_version[:href]}")
      env.email       = optional_content(env_node, 'x:email', 'email', "x:#{@@eeml_version[:href]}")
      env.icon        = optional_content(env_node, 'x:icon', 'icon', "x:#{@@eeml_version[:href]}")
      env.private     = (optional_content(env_node, 'x:private', 'private', "x:#{@@eeml_version[:href]}") == "true")

      #find_first_node_or_fail(env_node, 'x:location', 'location')
      loc_node = env_node.find_first('x:location', "x:#{@@eeml_version[:href]}")
      env.location    = extractLocation(loc_node) if loc_node

      env_node.find('x:tag', "x:#{@@eeml_version[:href]}").each do |tag_node|
        env.tags << tag_node.content.strip
      end
      env.has_tag_element = true

      datastream_nodes = env_node.find('x:data', "x:#{@@eeml_version[:href]}")
      # raise NoDataStreams.new, "no datastreams found"  if datastream_nodes.empty?
      env.add_datastreams(extractDataStreams(datastream_nodes)) unless datastream_nodes.empty?

      return env
    end

    def extractLocation(node)
      #<location domain="physical" exposure="outdoor" disposition="mobile">
      #  <lat>50.1</lat>
      #  <lon>48.7</lon>
      #  <ele>1.34</ele>
      #</location>
      raise "given nil node" if node.nil?
      loc = Location.new
      loc.domain = node['domain']
      loc.disposition = node['disposition']
      loc.exposure = node['exposure']
      loc.name = optional_content(node, 'x:name', 'name', "x:#{@@eeml_version[:href]}")
      loc.latitude = optional_content(node, 'x:lat', 'lat', "x:#{@@eeml_version[:href]}")
      loc.longitude = optional_content(node, 'x:lon', 'lon', "x:#{@@eeml_version[:href]}")
      loc.elevation = optional_content(node, 'x:ele', 'ele', "x:#{@@eeml_version[:href]}")
      return loc
    end

    #return an array (TODO: or a hash?) of DataStream objects from the given list of data nodes
    def extractDataStreams(nodes)
      #<data id="blah1">...</data><data id="blah2">...</data>
      dataStreams = []
      nodes.each do |node|        
        dataStreams << extractDataStream(node)
      end
      return dataStreams
    end

    #builds and returns a detailed exception of the given class, for problems concerning the given node (or its missing children)
    #details include node's name and line number (zero if not available)
    def exception_for_node(node, exception_class, message)
      ex = exception_class.new(message)
      ex.line_num = node.line_num
      ex.node_name = node_name_or_root(node)
      return ex
    end


    def extractDataStream(node)
      #<data id="0">
      #<tag>some_tag</tag>
      #<tag>another_tag</tag>
      #<current_value>0</current_value>
      #<min_value>0.0</min_value>
      #<max_value>1022.0</max_value>
      #<unit symbol="C" type="basicSI">Celsius</unit>
      #</data>
      data = DataStream.new
      raise MissingAttribute.new(node.name, 'id') if node['id'].nil?
      data.identifier = node['id']
      node.find('x:tag', "x:#{@@eeml_version[:href]}").each do |tag_node|
        data.tags << tag_node.content.strip
      end
      data.has_tag_element = true

      value_nodes = node.find('x:current_value', "x:#{@@eeml_version[:href]}")
      # raise exception_for_node(node, DataMissingValue, "Data node is missing current_value node.") if value_nodes.empty?
      raise exception_for_node(node, DataHasMultipleValues, "Data node has multiple 'value' nodes.") if value_nodes.size > 1

      value_node = value_nodes.first

      max_value_node = node.find_first('x:max_value', "x:#{@@eeml_version[:href]}")
      min_value_node = node.find_first('x:min_value', "x:#{@@eeml_version[:href]}")

      value = Value.new
      value.min_value = min_value_node.content if min_value_node
      value.max_value = max_value_node.content if max_value_node
      if value_node
        value.value = value_node.content.strip 
        value.recorded_at = value_node['at'] unless value_node['at'].blank?
      end

      data.add_value(value)

      unit_nodes = node.find('x:unit', "x:#{@@eeml_version[:href]}")
      raise exception_for_node(node, DataHasMultipleUnits, "Data node has multiple 'unit' nodes.") if unit_nodes.size > 1

      unit_node = unit_nodes.first
      unless unit_node.nil?
        data.unit_symbol = unit_node['symbol']
        data.unit_type = unit_node['type']
        data.unit_value = unit_node.content.strip
      end

      return data
    end

    #Helpers ------------------------------------------------------------------
    #Consider mixing these in to the libxml parser for more readable code
    
    #raises MissingNode if the node isn't there
    def mandatory_content(base_node, xpath, description, nslist = nil)
      node = base_node.find_first(xpath, nslist)
      raise(MissingNode.new(node_name_or_root(base_node), description, xpath)) if node.nil?
      return node.content
    end

    #returns the node's content, or the given default if the node isn't there (default itself defaults to nil)
    #description isn't used, but keeps our signature same as mandatory_content(), up to that point.
    def optional_content(base_node, xpath, description, nslist = nil, default = nil)
      node = base_node.find_first(xpath, nslist)
      return node.nil? ? default : node.content
    end


    #get the name of the given node if it is a node, or 'root' if it is a doc.
    #for use only for error messages
    def node_name_or_root(node)
      node.respond_to?(:name) ? node.name : 'root'
    end

    def find_first_node_or_fail(base_node, xpath, description, nslist = nil)
      node = base_node.find_first(xpath, nslist)
      raise(MissingNode.new(node_name_or_root(base_node), description, xpath)) if node.nil?
      return node
    end

  end

end