defmodule Fountainedge.Edge do
  @moduledoc """
  A graph edge directionally links two nodes together.

  Edges are fundamental to the concept of transitioning between
  nodes.

  [Graphviz](https://graphviz.org/)
  is used for presentation and ranking of graph nodes.
  See `Graphvix.Graph.add_edge/4`.
  """

  alias __MODULE__

  @enforce_keys [:id, :next]

  defstruct id: nil,
    next: nil,
    attributes: []

  @typedoc """
  Edge structure.
  * `:id` - Identifier of the `Fountainedge.Node` where the edge is leaving (out from.)
  * `:next` - Identifier of the `Fountainedge.Node` where the edge is pointing (in to.)
  * `:attributes` Optional list of [edge attributes](https://graphviz.org/docs/edges/)
    passed to `Graphvix.Graph.add_edge/4`.
  """

  @type t :: %__MODULE__{
    id: integer,
    next: integer,
    attributes: list()
  }

  @doc """
  Find a matching edge in a list (used internally.)
  """
  @spec find(list(Fountainedge.Edge.t()), Fountainedge.Edge.t()) :: Fountainedge.Edge.t() | nil
  def find(edges, %Edge{} = edge) do
    Enum.find(edges, fn e -> e.id == edge.id && e.next == edge.next end)
  end
end