defmodule Liaison.NodeHelper do
  @moduledoc """
  NodeHelper aims to make converting between node representations
    into FQDN nodenames

  ### Auto Localhost Calculation
  Ever tried to connect to another local node but your machine name
    is not fun to enter? Now all you need to do is enter a name for the
    node and the localhost is automatically appended


  ### Node Formats
  The following is a list of valid node formats and how they are
  expanded
    * `name` -> `:name@localhost`
    * `name@host` -> `:name@host`
    * `name@a.b.c.d` -> `:"name@a.b.c.d"`
    * `%{name: name}` -> `:name@localhost`
    * `%{name: :random}` -> random 6 digit name, eg: `:atj2ld@localhost`
    * `%{name: [random: 3]}` -> random 3 digit name, eg:`:d5h@localhost`
    * `%{name: name, host: host}` -> `:name@host`
    * `%{name: name, host: :shortname}` -> `:name@localhost`
    * `%{name: name, host: :longname}` -> `:name@localhost_ip`
  """
  alias Liaison.IP

  @type nodename :: atom()
  @type node_format :: String.t() | atom() | map()

  @doc """
  Expands a node format into a fully qualified nodename
  """
  @spec to_nodename(node_format) :: nodename
  def to_nodename(format) when is_binary(format) do
    case String.split(format, "@") do
      [name] -> "#{name}@#{get_localhost()}"
      [name, host] -> "#{name}@#{host}"
    end
    |> String.to_atom()
  end

  def to_nodename(format) when is_atom(format) do
    Atom.to_string(format)
    |> to_nodename()
  end

  def to_nodename(%{name: :random}) do
    random_name()
    |> to_nodename()
  end

  def to_nodename(%{name: [random: n]}) do
    random_name(n)
    |> to_nodename()
  end

  def to_nodename(%{name: name, host: host}) do
    cond do
      host == :shortname -> "#{name}"
      host == :longname -> "#{name}@#{get_localhost_ip()}"
      true -> "#{name}@#{host}"
    end
    |> to_nodename()
  end

  def to_nodename(%{name: name}) do
    to_nodename(name)
  end

  @doc """
  Returns the localhost name of the machine
  """
  @spec get_localhost() :: charlist()
  def get_localhost() do
    elem(:inet.gethostname(), 1)
  end

  @doc """
  Returns the first ip4 address for the machine
  """
  @spec get_localhost_ip() :: String.t()
  def get_localhost_ip() do
    IP.as_string(IP.get_ipv4_addr())
  end

  @doc """
  Returns a random alphanumeric localhost name of length `len`
  """
  @spec random_name(integer) :: String.t()
  def random_name(len \\ 6) do
    opts =
      Enum.to_list(?a..?z) ++
        Enum.to_list(?A..?Z) ++
        Enum.to_list(?1..?9)

    Enum.map(1..len, fn _ -> Enum.random(opts) end)
    |> List.to_string()
  end
end