perspective

defmodule Perspective.EventChain do
  use Agent

  def apply_event(event) do
    Agent.update(__MODULE__, fn events -> [event | events] end)

    %Perspective.EventChain.NewEvent{event: event}
    |> Perspective.Notifications.emit()
  end

  def last() do
    Agent.get(__MODULE__, fn [latest | _rest] -> latest end)
  end

  def since(id) do
    Agent.get(__MODULE__, fn events ->
      Enum.reduce_while(events, [], fn event, since ->
        if event.id == id, do: {:halt, since}, else: {:cont, [event | since]}
      end)
    end)
  end

  def list() do
    Agent.get(__MODULE__, fn events -> events end)
  end

  def load(data) when is_list(data) do
    unless Mix.env() == :test do
      raise "Woah, definitely do NOT run this in production"
    end

    Agent.update(__MODULE__, fn _ -> data end)
  end

  def start_link(_) do
    Agent.start_link(fn -> file_data() end, name: __MODULE__)
  end

  def file_data do
    Perspective.EventChainStorage.read()
  end
end