defmodule MvWeb.MemberLive.Index.OverviewQuery do
  @moduledoc """
  Builds the Ash query for the member overview from the LiveView's filter/sort
  state, so every filter and sort resolves in PostgreSQL via the `:overview`
  keyset-paginated read action.

  All previously in-memory passes (cycle status, boolean/date custom fields,
  group sort) are expressed here as DB filters/sorts. A unique `id` tie-breaker
  is always appended to the sort so keyset pages never skip or duplicate rows.

  `build/1` returns an unread `Ash.Query`; the caller supplies `page:`/`actor:`
  options to `Ash.read/2`.
  """

  import Ash.Expr

  alias Mv.Membership.Member
  alias MvWeb.MemberLive.Index.DateFilter

  require Ash.Query

  @type opts :: %{optional(atom()) => term()}

  @doc """
  Builds the `:overview` query from the given filter/sort options.

  Recognised keys (all optional):

    * `:search` — full-text search string
    * `:group_filters` / `:groups` — `%{group_id => :in | :not_in}` and the valid groups
    * `:fee_type_filters` / `:fee_types` — `%{fee_type_id => :in | :not_in}` and valid fee types
    * `:date_filters` — built-in join/exit date filter map (see `DateFilter`)
    * `:sort_field` / `:sort_order` — sort key and direction
    * `:today` — reference date for cycle math (defaults to `Date.utc_today/0`)
  """
  @spec build(opts()) :: Ash.Query.t()
  def build(opts \\ %{}) do
    Member
    |> Ash.Query.for_read(:overview)
    |> apply_search(opts[:search])
    |> apply_group_filters(opts[:group_filters], opts[:groups])
    |> apply_fee_type_filters(opts[:fee_type_filters], opts[:fee_types])
    |> apply_date_filters(opts[:date_filters])
    |> apply_cycle_status_filter(
      opts[:cycle_status_filter],
      opts[:show_current_cycle],
      today(opts)
    )
    |> apply_sort(opts[:sort_field], opts[:sort_order])
  end

  defp today(opts), do: opts[:today] || Date.utc_today()

  # ---------------------------------------------------------------------------
  # Search
  # ---------------------------------------------------------------------------

  defp apply_search(query, search) when is_binary(search),
    do: Member.apply_overview_search(query, search)

  defp apply_search(query, _), do: query

  # ---------------------------------------------------------------------------
  # Group filters (AND across selected groups)
  # ---------------------------------------------------------------------------

  defp apply_group_filters(query, group_filters, _groups)
       when group_filters in [nil, %{}],
       do: query

  defp apply_group_filters(query, group_filters, groups) do
    valid_ids = valid_id_set(groups)

    Enum.reduce(group_filters, query, fn {group_id_str, value}, q ->
      if MapSet.member?(valid_ids, group_id_str) do
        apply_one_group_filter(q, group_id_str, value)
      else
        q
      end
    end)
  end

  defp apply_one_group_filter(query, group_id_str, :in) do
    case Ecto.UUID.cast(group_id_str) do
      {:ok, uuid} -> Ash.Query.filter(query, expr(exists(member_groups, group_id == ^uuid)))
      _ -> query
    end
  end

  defp apply_one_group_filter(query, group_id_str, :not_in) do
    case Ecto.UUID.cast(group_id_str) do
      {:ok, uuid} -> Ash.Query.filter(query, expr(not exists(member_groups, group_id == ^uuid)))
      _ -> query
    end
  end

  defp apply_one_group_filter(query, _id, _value), do: query

  # ---------------------------------------------------------------------------
  # Fee-type filters (:in OR; :not_in AND)
  # ---------------------------------------------------------------------------

  defp apply_fee_type_filters(query, fee_type_filters, _fee_types)
       when fee_type_filters in [nil, %{}],
       do: query

  defp apply_fee_type_filters(query, fee_type_filters, fee_types) do
    valid_ids = valid_id_set(fee_types)

    {in_filters, not_in_filters} =
      fee_type_filters
      |> Enum.filter(fn {id_str, _} -> MapSet.member?(valid_ids, id_str) end)
      |> Enum.split_with(fn {_, value} -> value == :in end)

    in_uuids = cast_uuids(Enum.map(in_filters, fn {id_str, _} -> id_str end))

    query =
      if in_uuids == [] do
        query
      else
        Ash.Query.filter(query, expr(membership_fee_type_id in ^in_uuids))
      end

    Enum.reduce(not_in_filters, query, fn {id_str, _}, q ->
      case Ecto.UUID.cast(id_str) do
        {:ok, uuid} ->
          Ash.Query.filter(
            q,
            expr(membership_fee_type_id != ^uuid or is_nil(membership_fee_type_id))
          )

        _ ->
          q
      end
    end)
  end

  # ---------------------------------------------------------------------------
  # Cycle-status filter (paid/unpaid, current or last-completed cycle)
  #
  # Backed by the DB cycle-status aggregates (denormalized `cycle_end`). A member
  # matches only when its selected-cycle status equals the requested status;
  # members with no matching cycle (nil aggregate) are excluded — exactly as the
  # previous in-memory classifier behaved.
  # ---------------------------------------------------------------------------

  defp apply_cycle_status_filter(query, status, _show_current, _today)
       when status not in [:paid, :unpaid],
       do: query

  defp apply_cycle_status_filter(query, status, true = _show_current, today) do
    # Current cycle: contains today; when several would, the one with the latest
    # cycle_start wins. Keep members whose winning current cycle has `status`.
    Ash.Query.filter(
      query,
      expr(
        exists(
          membership_fee_cycles,
          cycle_start <= ^today and cycle_end >= ^today and status == ^status and
            not exists(
              member.membership_fee_cycles,
              cycle_start <= ^today and cycle_end >= ^today and
                cycle_start > parent(cycle_start)
            )
        )
      )
    )
  end

  defp apply_cycle_status_filter(query, status, _show_current, today) do
    # Last completed cycle: most recent cycle that has ended (cycle_end < today).
    Ash.Query.filter(
      query,
      expr(
        exists(
          membership_fee_cycles,
          cycle_end < ^today and status == ^status and
            not exists(
              member.membership_fee_cycles,
              cycle_end < ^today and cycle_start > parent(cycle_start)
            )
        )
      )
    )
  end

  # ---------------------------------------------------------------------------
  # Built-in date filters (join/exit)
  # ---------------------------------------------------------------------------

  defp apply_date_filters(query, nil), do: query

  defp apply_date_filters(query, filters) when is_map(filters),
    do: DateFilter.apply_ash_filter(query, filters)

  # ---------------------------------------------------------------------------
  # Sort (always append the unique id tie-breaker for keyset stability)
  # ---------------------------------------------------------------------------

  defp apply_sort(query, nil, _order), do: Ash.Query.sort(query, id: :asc)
  defp apply_sort(query, _field, nil), do: Ash.Query.sort(query, id: :asc)

  defp apply_sort(query, field, order) do
    case sort_key(field) do
      nil -> Ash.Query.sort(query, id: :asc)
      key -> Ash.Query.sort(query, [{key, order}, {:id, :asc}])
    end
  end

  # Resolves a sort field (atom or string) to a DB sort key, or nil if it is a
  # computed field handled elsewhere / not sortable.
  defp sort_key(field) when field in [:membership_fee_type, "membership_fee_type"],
    do: "membership_fee_type.name"

  defp sort_key(field) when field in [:groups, "groups"], do: :first_group_name

  defp sort_key(field) when is_atom(field) do
    if field in member_sort_fields(), do: field, else: nil
  end

  defp sort_key(field) when is_binary(field) do
    allowed = MapSet.new(member_sort_fields(), &Atom.to_string/1)
    if MapSet.member?(allowed, field), do: String.to_existing_atom(field), else: nil
  end

  defp sort_key(_), do: nil

  defp member_sort_fields do
    Mv.Constants.member_fields() -- [:notes]
  end

  # ---------------------------------------------------------------------------
  # Helpers
  # ---------------------------------------------------------------------------

  defp valid_id_set(records) when is_list(records) do
    records
    |> Enum.map(&to_string(&1.id))
    |> Enum.map(&normalize_uuid/1)
    |> Enum.reject(&is_nil/1)
    |> MapSet.new()
  end

  defp valid_id_set(_), do: MapSet.new()

  defp normalize_uuid(raw) when is_binary(raw) do
    case Ecto.UUID.cast(String.trim(raw)) do
      {:ok, uuid} -> to_string(uuid)
      _ -> nil
    end
  end

  defp normalize_uuid(_), do: nil

  defp cast_uuids(id_strs) do
    id_strs
    |> Enum.map(&Ecto.UUID.cast/1)
    |> Enum.filter(&match?({:ok, _}, &1))
    |> Enum.map(fn {:ok, uuid} -> uuid end)
  end
end