defmodule HAHandler.PGSQL do
  @supervisor HAHandler.PGSQL.Supervisor
  @version_query "SELECT version();"
  @is_in_recovery_query "SELECT pg_is_in_recovery();"

  def get_instances() do
    watchers = Supervisor.which_children(@supervisor)

    for {hostname, pid, _type, _modules} <- watchers do
      {hostname, pid}
    end
  end

  def get_version({hostname, pid}) do
    case GenServer.call(pid, {:execute, @version_query, []}) do
      {:ok, %Postgrex.Result{rows: [[raw_version_string]]}} ->
        version =
          case Regex.run(~r/^PostgreSQL (\d+\.\d+)/, raw_version_string) do
            [_, version_number] -> version_number
            _ -> "unknown"
          end

        %{hostname: hostname, version: version, status: "up"}

      {:error, %DBConnection.ConnectionError{message: _msg, reason: err}} ->
        %{hostname: hostname, version: "unknown", status: err}

      _ ->
        %{hostname: hostname, version: "unknown", status: :unknown}
    end
  end

  def get_operation_mode({_hostname, pid}) do
    case GenServer.call(pid, {:execute, @is_in_recovery_query, []}) do
      {:ok, %Postgrex.Result{rows: [[false]]}} ->
        :primary

      {:ok, %Postgrex.Result{rows: [[true]]}} ->
        :secondary

      _ ->
        :unknown
    end
  end

  def get_stats() do
    get_instances()
    |> Enum.map(fn instance ->
      get_version(instance) |> Map.put(:mode, get_operation_mode(instance))
    end)
  end
end