defmodule Glific.Flows.Periodic do
  @moduledoc """
  A central place to define and execute all periodic flows. The current periodic flows in
  priority order are:

  Monthly, Weekly, Daily
  A specific weekday (i.e - Monday, Tuesday, ..)
  OutOfOffice

  All these flows are shortcode driven for now.

  At some point, we will make this flexible and let the NGO define the periodic interval
  """
  use Publicist

  alias Glific.{
    Flows,
    Flows.FlowContext,
    Messages.Message
  }

  @periodic_flows [
    "monthly",
    "weekly",
    "monday",
    "tuesday",
    "wednesday",
    "thursday",
    "friday",
    "saturday",
    "sunday",
    "daily",
    "outofoffice"
  ]

  # Fill the state flow values with a shortcode -> id map, so we can proceed
  # through our periodic jobs quickly.
  @spec map_flow_ids(map()) :: map()
  defp map_flow_ids(state),
    do: Map.put(state, :flows, Flows.flow_keywords_map(state.organization_id))

  # Compute the offset for the time, so we can check if there is a flow running
  # for that specific periodic event already
  @spec compute_time(DateTime.t(), String.t()) :: DateTime.t()
  defp compute_time(now, "monthly"), do: Timex.beginning_of_month(now)
  defp compute_time(now, "weekly"), do: Timex.beginning_of_week(now, :mon)
  defp compute_time(now, "outofoffice"), do: Glific.go_back_time(24, now, :hour)

  defp compute_time(now, period)
       when period in [
              "monday",
              "tuesday",
              "wednesday",
              "thursday",
              "friday",
              "saturday",
              "sunday",
              "daily"
            ],
       do: Timex.beginning_of_day(now)

  @doc """
  Run all the periodic flows in priority order. Stop when we find the first one that we can execute
  """
  @spec run_flows(map(), Message.t()) :: map()
  def run_flows(state, message) do
    now = DateTime.utc_now()

    state =
      state
      |> Map.merge(%{organization_id: message.organization_id})
      |> map_flow_ids()

    Enum.reduce_while(
      @periodic_flows,
      state,
      fn period, state ->
        since = compute_time(now, period)
        {state, result} = periodic_flow(state, period, message, since)

        if result,
          do: {:halt, state},
          else: {:cont, state}
      end
    )
  end

  @final_phrase "published"

  @spec common_flow(map(), String.t(), Message.t(), DateTime.t()) :: {map(), boolean}
  defp common_flow(state, flow_name, message, since) do
    flow_id = get_in(state, [:flows, "published", flow_name])
    org = Glific.Partners.organization(state[:organization_id])
    flow_config = org.out_of_office

    cond do
      is_nil(flow_id) ->
        {state, false}

      not is_nil(flow_config) && flow_config.run_each_time == true ->
        init_common_flow(state, flow_id, message)

      !Flows.flow_activated(flow_id, message.contact_id, since) ->
        init_common_flow(state, flow_id, message)

      true ->
        {state, false}
    end
  end

  # Run a specific flow and do flow specific checks in the local files, before we invoke the
  # common function to process all periodic flows
  @spec periodic_flow(map(), String.t(), Message.t(), DateTime.t()) :: {map(), boolean}
  defp periodic_flow(state, period, message, since)
       when period in [
              "monday",
              "tuesday",
              "wednesday",
              "thursday",
              "friday",
              "saturday",
              "sunday"
            ] do
    if Date.day_of_week(since) == Timex.day_to_num(period),
      do: common_flow(state, period, message, since),
      else: {state, false}
  end

  defp periodic_flow(state, "outofoffice" = period, message, since) do
    # lets  check if we should initiate the out of office flow
    # lets do this only if we've not sent them the out of office flow
    # in the past 24 hours
    if FunWithFlags.enabled?(
         :out_of_office_active,
         for: %{organization_id: message.organization_id}
       ),
       do: common_flow(state, period, message, since),
       else: common_flow(state, "defaultflow", message, since)
  end

  defp periodic_flow(state, period, message, since),
    do: common_flow(state, period, message, since)

  defp init_common_flow(state, flow_id, message) do
    {:ok, flow} =
      Flows.get_cached_flow(message.organization_id, {:flow_id, flow_id, @final_phrase})

    opts = Keyword.put(Keyword.new(), :flow_keyword, message.body)
    FlowContext.init_context(flow, message.contact, @final_phrase, opts)
    {state, true}
  end
end