defmodule GoogleSheets.Supervisor do
  @moduledoc """
  Supervisor for the application. Creates ETS table for storage and launches a process for each spreadsheet configured for polling.
  """

  use Supervisor
  require Keyword
  require Logger

  @doc false
  def start_link do
    Supervisor.start_link(__MODULE__, [], name: __MODULE__)
  end

  @doc false
  def init([]) do
    # ETS table is created here, so that if the updater process dies, the table is not lost.
    # Must set the permission to public, so that the GoogleSheets.Updater can write
    # to the table, even if it's not the owning process.
    :google_sheets =
      :ets.new(:google_sheets, [:set, :named_table, :public, {:read_concurrency, true}])

    spreadsheets = Application.get_env(:google_sheets, :spreadsheets, [])
    supervise(create_children(spreadsheets, []), strategy: :one_for_one)
  end

  # Create a children for each configured spreadsheet
  defp create_children([], children), do: children

  defp create_children([{id, config} | rest], children) do
    Logger.debug("#{id} : #{inspect(config)}")

    create_children(rest, [
      worker(GoogleSheets.Updater, [id, config], id: id, restart: :permanent) | children
    ])
  end
end