defmodule MvWeb.MemberLive.Index.PaymentAging do
  @moduledoc """
  Period-scoped payment aging for the member overview.

  The overview presents payment as an accounts-receivable aging count: per
  member, the number of that member's cycles with `status == :unpaid` whose
  denormalized `cycle_end` falls inside an active period. The period is a view
  dimension that scopes the column and the payment filter together; its default
  is **all outstanding** (both bounds nil → all time). Suspended cycles are
  excluded from the count but surfaced separately in the badge tooltip.

  This module owns:

    * the period value shape and its default,
    * URL param encode/decode for the period,
    * the badge descriptor derived from a count,
    * the open-cycles list (unpaid + suspended, member-relative) that backs the
      badge tooltip.

  The count itself is computed DB-side by the `unpaid_cycle_count` calculation
  on `Mv.Membership.Member`; `open_cycles/2` works over already-loaded cycles.
  """

  use Gettext, backend: MvWeb.Gettext

  alias Mv.Constants
  alias MvWeb.Helpers.MembershipFeeHelpers

  @type period :: %{from: Date.t() | nil, to: Date.t() | nil}

  @payment_period_from_param Constants.payment_period_from_param()
  @payment_period_to_param Constants.payment_period_to_param()

  @doc """
  The default period: all outstanding cycles, all time (both bounds nil).
  """
  @spec default_period() :: period()
  def default_period, do: %{from: nil, to: nil}

  @doc """
  Decodes URL params into a period. Absent or malformed ISO-8601 bounds fall
  back to nil, so no params yields the all-outstanding default.
  """
  @spec parse_period(map()) :: period()
  def parse_period(params) when is_map(params) do
    %{
      from: parse_date(Map.get(params, @payment_period_from_param)),
      to: parse_date(Map.get(params, @payment_period_to_param))
    }
  end

  @doc """
  Encodes a period into URL params. A nil bound is omitted; the default period
  encodes to the empty map (a fresh URL is the canonical default).
  """
  @spec to_params(period()) :: %{optional(String.t()) => String.t()}
  def to_params(%{from: from, to: to}) do
    %{}
    |> maybe_put_date(@payment_period_from_param, from)
    |> maybe_put_date(@payment_period_to_param, to)
  end

  def to_params(_), do: %{}

  @doc """
  Badge descriptor for an unpaid-cycle count. A count of 0 reads "Paid"
  (success); a positive count reads "N unpaid" (error).
  """
  @spec badge(non_neg_integer()) :: %{
          variant: atom(),
          label: String.t(),
          count: non_neg_integer()
        }
  def badge(0), do: %{variant: :success, label: gettext("Paid"), count: 0}

  def badge(count) when is_integer(count) and count > 0 do
    %{
      variant: MembershipFeeHelpers.status_variant(:unpaid),
      label: gettext("%{count} unpaid", count: count),
      count: count
    }
  end

  @doc """
  Splits a member's loaded cycles into the open (unpaid) and suspended cycles
  whose `cycle_end` falls inside `period`, both sorted by `cycle_end`. Paid
  cycles and cycles outside the period are dropped. Used to render the badge
  tooltip. Expects `membership_fee_cycles` to be loaded on the member.
  """
  @spec open_cycles(map(), period()) :: %{unpaid: [map()], suspended: [map()]}
  def open_cycles(member, %{from: from, to: to}) do
    cycles = in_period_cycles(member, from, to)

    %{
      unpaid: cycles |> Enum.filter(&(&1.status == :unpaid)) |> sort_by_end(),
      suspended: cycles |> Enum.filter(&(&1.status == :suspended)) |> sort_by_end()
    }
  end

  defp in_period_cycles(member, from, to) do
    case Map.get(member, :membership_fee_cycles) do
      cycles when is_list(cycles) -> Enum.filter(cycles, &in_period?(&1.cycle_end, from, to))
      _ -> []
    end
  end

  defp in_period?(%Date{} = cycle_end, from, to) do
    (is_nil(from) or Date.compare(cycle_end, from) != :lt) and
      (is_nil(to) or Date.compare(cycle_end, to) != :gt)
  end

  defp in_period?(_, _, _), do: false

  defp sort_by_end(cycles), do: Enum.sort_by(cycles, & &1.cycle_end, Date)

  defp maybe_put_date(params, _key, nil), do: params

  defp maybe_put_date(params, key, %Date{} = date),
    do: Map.put(params, key, Date.to_iso8601(date))

  defp parse_date(nil), do: nil

  defp parse_date(value) when is_binary(value) do
    case Date.from_iso8601(String.trim(value)) do
      {:ok, date} -> date
      _ -> nil
    end
  end

  defp parse_date(_), do: nil
end