defmodule DaProductApp.GlobalSettings do
  @moduledoc """
  GenServer that caches global settings from `global_table` in ShukriaMms database.

  - Loads settings at startup
  - Periodically refreshes (default 10 minutes)
  - Exposes `get_all/0`, `get/1` and `refresh/0` API
  """

  use GenServer
  require Logger
  alias DaProductApp.Repos.ShukriaMmsRepo
  import Ecto.Query

  @name __MODULE__
  @refresh_ms Application.get_env(:da_product_app, :global_settings_refresh_ms, :timer.minutes(10))

  # Public API
  def start_link(_opts) do
    GenServer.start_link(__MODULE__, %{}, name: @name)
  end

  def get_all do
    GenServer.call(@name, :get_all)
  end

  def get(key) do
    Map.get(get_all(), to_string(key))
  end

  def refresh do
    GenServer.cast(@name, :refresh)
  end

  # Callbacks
  @impl true
  def init(_args) do
    state = load_once(%{})
    if is_integer(@refresh_ms) and @refresh_ms > 0 do
      :timer.send_interval(@refresh_ms, :refresh)
    end
    {:ok, state}
  end

  @impl true
  def handle_call(:get_all, _from, state) do
    {:reply, state, state}
  end

  @impl true
  def handle_cast(:refresh, state) do
    {:noreply, load_once(state)}
  end

  @impl true
  def handle_info(:refresh, state) do
    {:noreply, load_once(state)}
  end

  defp load_once(current_state) do
    query = from(g in "global_table", select: {g.config_key, g.config_value})

    case ShukriaMmsRepo.all(query) do
      rows when is_list(rows) ->
        rows
        |> Enum.into(%{}, fn {k, v} -> {to_string(k), v} end)

      _ ->
        Logger.error("GlobalSettings: unexpected response loading settings, keeping last-known state")
        current_state
    end
  rescue
    e ->
      Logger.error("GlobalSettings load error: #{inspect(e)} - keeping last-known state")
      current_state
  end
end