Community Garden - Elixir - Exercism

community_garden.ex

defmodule Plot do
  @enforce_keys [:plot_id, :registered_to]
  defstruct [:plot_id, :registered_to]
end

defmodule CommunityGarden do
  @spec start(Keyword.t()) :: tuple()
  def start(opts \\ []) do
    Agent.start(fn -> [] end, opts)
  end

  @spec list_registrations(pid()) :: list(Plot)
  def list_registrations(pid) do
    Agent.get(pid, fn state -> state end)
  end

  @spec register(pid(), String.t()) :: Plot
  def register(pid, register_to) do
    Agent.update(pid, fn state ->
      [%Plot{plot_id: get_next_id(state), registered_to: register_to} | state]
    end)

    Agent.get(pid, fn state ->
      [head | _tail] = state
      head
    end)
  end

  defp get_next_id([]), do: 1
  defp get_next_id(plots), do: Enum.sort_by(plots, & &1.plot_id)

  @spec release(pid(), integer()) :: :ok
  def release(pid, plot_id) do
    Agent.update(pid, fn state ->
      Enum.filter(state, fn plot -> plot.plot_id != plot_id end)
    end)
  end

  @spec get_registration(pid(), integer()) :: tuple() | Plot
  def get_registration(pid, plot_id) do
    plot =
      Agent.get(pid, fn state ->
        Enum.find(state, nil, fn plot -> plot.plot_id == plot_id end)
      end)

    cond do
      plot == nil -> {:not_found, "plot is unregistered"}
      true -> plot
    end
  end
end