Distance graph builder

distance.ex

defmodule Distance do
  @moduledoc """
  Ensure that you have the following in your mix.exs
  file:
  
      def deps do
        {:libgraph, "~> 0.13"}
      end
      
  """
  @string "Sun 57909227 Mercury
     Earth 384400 Moon
     Sun 149598262 Earth
     Sun Moon
     Deimos Moon
     Deimos
     Deimos Phobos
     Moon
     LROrbiter"

  @doc """
  Parse a string into a list of tuples
  where each tuple is of the form
  {from, to, weight: distance}

  """
  def parse(string \\ @string) when is_binary(string) do
    string
    |> String.split("\n")
    |> Enum.map(&String.trim/1)
    |> Enum.map(&String.split/1)
    |> Enum.map(&do_parse/1)
  end

  @doc """
  Return only those tuples that
  have a distance

  """
  def with_distance(distances) do
    Enum.filter(distances, &has_distance?/1)
  end

  @doc """
  Return only those tuples that
  have no distance

  """
  def with_no_distance(distances) do
    Enum.reject(distances, &has_distance?/1)
  end

  @doc """
  Build a graph of the distances using
  the [libgraph](https://hex.pm/packages/libgraph) library.

  """
  def build_graph(distances) do
    graph = Graph.new()
    edges = with_distance(distances)
    Graph.add_edges(graph, edges)
  end

  @doc """
  Return the distance from one body
  to all its connected bodies.

  """
  def distances_from(graph, body) do
    Graph.out_edges(graph, body)
  end

  defp do_parse([from, distance, to]) do
    {from, to, weight: String.to_integer(distance)}
  end

  defp do_parse([from, to]) do
    {from, to, weight: nil}
  end

  defp do_parse([from]) do
    {from, nil, weight: nil}
  end

  defp has_distance?({_from, _to, weight: weight}) do
    !is_nil(weight)
  end

 end
 

Note that this module requires the libgraph library to be configured in your mix.exs.