module X12

  # Main class for creating X12 parsers and factories.
  class Parser

    # These constitute prohibited file names under Microsoft
    MS_DEVICES = [
      'CON',
      'PRN',
      'AUX',
      'CLOCK$',
      'NUL',
      'COM1',
      'LPT1',
      'LPT2',
      'LPT3',
      'COM2',
      'COM3',
      'COM4',
    ].freeze

    # Creates a parser out of a definition.
    #
    # @param file_name [String]
    # @param custom_file [Boolean] (false) Load a custom X12 definition.
    # @return [void]
    def initialize(file_name, custom_file: false)
      save_definition = @x12_definition if defined? @x12_definition

      if custom_file
        str = File.open(file_name, 'r').read
      else
        # Deal with Microsoft devices
        # get the current working directory
        base_name = File.basename(file_name, '.xml')
        if MS_DEVICES.find { |i| i == base_name }
          file_name = File.join(File.dirname, "#{base_name}_.xml")
        end
        file_location = File.join(File.dirname(__FILE__), '../../misc', file_name)

        # Read and parse the definition
        str = File.open(file_location, 'r').read
      end
      # @dir_name = File.dirname(File.expand_path(file_name)) # to look up other files if needed
      @x12_definition = X12::XMLDefinitions.new(str)

      # Populate fields in all segments found in all the loops
      @x12_definition[X12::Loop].each_pair{ |k, v|
        # puts "Populating definitions for loop #{k}"
        process_loop(v)
      } if @x12_definition[X12::Loop]

      # Merge the newly parsed definition into a saved one, if any.
      if save_definition
        @x12_definition.keys.each { |t|
          save_definition[t] ||= {}
          @x12_definition[t].keys.each { |u|
            save_definition[t][u] = @x12_definition[t][u]
          }
          @x12_definition = save_definition
        }
      end

      # puts PP.pp(self, '')
    end

    # Parse a loop of a given name out of a string.
    # Throws an exception if the loop name is not defined.
    def parse(loop_name, str)
      loop = @x12_definition[X12::Loop][loop_name]
      # puts "Loops to parse #{@x12_definition[X12::Loop].keys}"
      throw Exception.new("Cannot find a definition for loop #{loop_name}") unless loop
      loop = loop.dup
      loop.parse(str)
      return loop
    end

    # Make an empty loop to be filled out with information.
    def factory(loop_name)
      loop = @x12_definition[X12::Loop][loop_name]
      throw Exception.new("Cannot find a definition for loop #{loop_name}") unless loop
      loop = loop.dup
      return loop
    end

    private

    # Recursively scan the loop and instantiate fields' definitions for all its segments.
    def process_loop(loop)
      loop.nodes.each do |i|
        case i
          when X12::Loop then process_loop(i)
          when X12::Segment then process_segment(i) unless i.nodes.size > 0
          else return
        end
      end
    end

    # Instantiate segment's fields as previously defined
    def process_segment(segment)
      # puts "Trying to process segment #{segment.inspect}"
      unless @x12_definition[X12::Segment] && @x12_definition[X12::Segment][segment.name]
        # Try to find it in a separate file if missing from the @x12_definition structure
        initialize(segment.name+'.xml')
        segment_definition = @x12_definition[X12::Segment][segment.name]
        throw Exception.new("Cannot find a definition for segment #{segment.name}") unless segment_definition
      else
        segment_definition = @x12_definition[X12::Segment][segment.name]
      end
      segment_definition.nodes.each_index { |i|
        segment.nodes[i] = segment_definition.nodes[i]
        # Make sure we have the validation table if any for this field. Try to read one in if missing.
        table = segment.nodes[i].validation
        if table
          unless @x12_definition[X12::Table] && @x12_definition[X12::Table][table]
            initialize(table + '.xml')
            throw Exception.new("Cannot find a definition for table #{table}") unless @x12_definition[X12::Table] && @x12_definition[X12::Table][table]
          end
        end
      }
    end

  end

end