class RGL::EdgePropertiesMap

def check_properties
  @edge_properties_map.each { |(u, v), property| validate_property(property, u, v) } if @edge_properties_map.respond_to?(:each)
end

def edge_property(u, v)
  if @directed
    property = @edge_properties_map[[u, v]]
  else
    property = @edge_properties_map[[u, v]] || @edge_properties_map[[v, u]]
  end
  validate_property(property, u, v)
  property
end

def initialize(edge_properties_map, directed)
  @edge_properties_map = edge_properties_map
  @directed = directed
  check_properties
end

def report_missing_property(property, u, v)
  raise ArgumentError.new("property of edge (#{u}, #{v}) is not defined") unless property
end

def validate_property(property, u, v)
  report_missing_property(property, u, v)
end