// Pure selection, filtering and grouping rules for the building structure
// view (Gebäude → Etagen → Räume) and grouped floor selects.
import type { BuildingDto, FloorDto, RoomDto } from "../types";

/** Selection key for "Alle" in the building and floor columns. */
export const ALL_SELECTION = "__all__";
/** Selection key for "Ohne Gebäude" / "Ohne Etage". */
export const UNASSIGNED_SELECTION = "__unassigned__";

/** ALL_SELECTION, UNASSIGNED_SELECTION or a building/floor id. */
export type StructureSelection = string;

export const UNASSIGNED_BUILDING_LABEL = "Ohne Gebäude";
export const UNASSIGNED_FLOOR_LABEL = "Ohne Etage";

type BuildingLike = Pick<BuildingDto, "id" | "name">;
type FloorLike = Pick<FloorDto, "id" | "name"> & {
  buildingId?: string | null;
};
type RoomLike = Pick<RoomDto, "floorId">;
type RoomAreaLike = Pick<RoomDto, "floorId" | "areaM2">;

export interface RoomAreaSummary {
  areaM2: number;
  roomCount: number;
  missingAreaCount: number;
}

export interface StructureAreaSummaries {
  total: RoomAreaSummary;
  byBuilding: Map<string | null, RoomAreaSummary>;
  byFloor: Map<string | null, RoomAreaSummary>;
}

export interface FloorGroup<TFloor extends FloorLike = FloorLike> {
  /** null for floors without (known) building. */
  buildingId: string | null;
  label: string;
  floors: TFloor[];
}

/**
 * The building a floor belongs to, or null when it has none or references a
 * building that is not (or no longer) loaded.
 */
export function resolveFloorBuildingId(
  floor: FloorLike,
  buildingIds: ReadonlySet<string>
): string | null {
  const buildingId = floor.buildingId ?? null;
  return buildingId !== null && buildingIds.has(buildingId)
    ? buildingId
    : null;
}

function toIdSet(entries: ReadonlyArray<{ id: string }>) {
  return new Set(entries.map((entry) => entry.id));
}

export function hasFloorsWithoutBuilding(
  floors: ReadonlyArray<FloorLike>,
  buildings: ReadonlyArray<BuildingLike>
): boolean {
  const buildingIds = toIdSet(buildings);
  return floors.some(
    (floor) => resolveFloorBuildingId(floor, buildingIds) === null
  );
}

export function hasRoomsWithoutFloor(
  rooms: ReadonlyArray<RoomLike>,
  floors: ReadonlyArray<FloorLike>
): boolean {
  const floorIds = toIdSet(floors);
  return rooms.some(
    (room) => room.floorId === null || !floorIds.has(room.floorId)
  );
}

/**
 * Groups floors by building in building order; floors without a known
 * building come last under "Ohne Gebäude". Empty groups are omitted and the
 * floor order inside a group is preserved.
 */
export function groupFloorsByBuilding<TFloor extends FloorLike>(
  floors: ReadonlyArray<TFloor>,
  buildings: ReadonlyArray<BuildingLike>
): FloorGroup<TFloor>[] {
  const buildingIds = toIdSet(buildings);
  const floorsByBuilding = new Map<string | null, TFloor[]>();
  for (const floor of floors) {
    const buildingId = resolveFloorBuildingId(floor, buildingIds);
    const group = floorsByBuilding.get(buildingId) ?? [];
    group.push(floor);
    floorsByBuilding.set(buildingId, group);
  }
  const groups: FloorGroup<TFloor>[] = [];
  for (const building of buildings) {
    const groupFloors = floorsByBuilding.get(building.id);
    if (groupFloors?.length) {
      groups.push({
        buildingId: building.id,
        label: building.name,
        floors: groupFloors,
      });
    }
  }
  const unassigned = floorsByBuilding.get(null);
  if (unassigned?.length) {
    groups.push({
      buildingId: null,
      label: UNASSIGNED_BUILDING_LABEL,
      floors: unassigned,
    });
  }
  return groups;
}

/** Floors shown in the floor column for a building selection. */
export function filterFloorsByBuilding<TFloor extends FloorLike>(
  floors: ReadonlyArray<TFloor>,
  buildings: ReadonlyArray<BuildingLike>,
  buildingSelection: StructureSelection
): TFloor[] {
  if (buildingSelection === ALL_SELECTION) {
    return [...floors];
  }
  const buildingIds = toIdSet(buildings);
  const targetBuildingId =
    buildingSelection === UNASSIGNED_SELECTION ? null : buildingSelection;
  return floors.filter(
    (floor) => resolveFloorBuildingId(floor, buildingIds) === targetBuildingId
  );
}

/**
 * "Ohne Etage" is offered only when rooms without floor exist and the
 * building selection can contain them ("Alle" or "Ohne Gebäude"), because a
 * room without floor has no building either.
 */
export function showsRoomsWithoutFloorEntry(
  rooms: ReadonlyArray<RoomLike>,
  floors: ReadonlyArray<FloorLike>,
  buildingSelection: StructureSelection
): boolean {
  return (
    (buildingSelection === ALL_SELECTION ||
      buildingSelection === UNASSIGNED_SELECTION) &&
    hasRoomsWithoutFloor(rooms, floors)
  );
}

/** Rooms shown in the room column for the current selections. */
export function filterRooms<TRoom extends RoomLike>(
  rooms: ReadonlyArray<TRoom>,
  floors: ReadonlyArray<FloorLike>,
  buildings: ReadonlyArray<BuildingLike>,
  buildingSelection: StructureSelection,
  floorSelection: StructureSelection
): TRoom[] {
  const floorIds = toIdSet(floors);
  const isWithoutFloor = (room: RoomLike) =>
    room.floorId === null || !floorIds.has(room.floorId);

  if (floorSelection === UNASSIGNED_SELECTION) {
    return showsRoomsWithoutFloorEntry(rooms, floors, buildingSelection)
      ? rooms.filter(isWithoutFloor)
      : [];
  }
  if (floorSelection !== ALL_SELECTION) {
    return rooms.filter((room) => room.floorId === floorSelection);
  }
  if (buildingSelection === ALL_SELECTION) {
    return [...rooms];
  }
  const visibleFloorIds = toIdSet(
    filterFloorsByBuilding(floors, buildings, buildingSelection)
  );
  return rooms.filter(
    (room) =>
      (room.floorId !== null && visibleFloorIds.has(room.floorId)) ||
      (buildingSelection === UNASSIGNED_SELECTION && isWithoutFloor(room))
  );
}

/** Falls back to "Alle" when a selected building vanished. */
export function normalizeBuildingSelection(
  selection: StructureSelection,
  floors: ReadonlyArray<FloorLike>,
  buildings: ReadonlyArray<BuildingLike>
): StructureSelection {
  if (selection === ALL_SELECTION) {
    return selection;
  }
  if (selection === UNASSIGNED_SELECTION) {
    return hasFloorsWithoutBuilding(floors, buildings)
      ? selection
      : ALL_SELECTION;
  }
  return buildings.some((building) => building.id === selection)
    ? selection
    : ALL_SELECTION;
}

/** Falls back to "Alle" when a selected floor is no longer visible. */
export function normalizeFloorSelection(
  selection: StructureSelection,
  rooms: ReadonlyArray<RoomLike>,
  floors: ReadonlyArray<FloorLike>,
  buildings: ReadonlyArray<BuildingLike>,
  buildingSelection: StructureSelection
): StructureSelection {
  if (selection === ALL_SELECTION) {
    return selection;
  }
  if (selection === UNASSIGNED_SELECTION) {
    return showsRoomsWithoutFloorEntry(rooms, floors, buildingSelection)
      ? selection
      : ALL_SELECTION;
  }
  return filterFloorsByBuilding(floors, buildings, buildingSelection).some(
    (floor) => floor.id === selection
  )
    ? selection
    : ALL_SELECTION;
}

/** Building preselected in the floor dialog ("" = Ohne Gebäude). */
export function defaultBuildingIdForNewFloor(
  buildingSelection: StructureSelection
): string {
  return buildingSelection === ALL_SELECTION ||
    buildingSelection === UNASSIGNED_SELECTION
    ? ""
    : buildingSelection;
}

/** Floor preselected in the room dialog ("" = Ohne Etage). */
export function defaultFloorIdForNewRoom(
  floorSelection: StructureSelection
): string {
  return floorSelection === ALL_SELECTION ||
    floorSelection === UNASSIGNED_SELECTION
    ? ""
    : floorSelection;
}

export function countFloorsByBuilding(
  floors: ReadonlyArray<FloorLike>,
  buildings: ReadonlyArray<BuildingLike>
): Map<string | null, number> {
  const buildingIds = toIdSet(buildings);
  const counts = new Map<string | null, number>();
  for (const floor of floors) {
    const buildingId = resolveFloorBuildingId(floor, buildingIds);
    counts.set(buildingId, (counts.get(buildingId) ?? 0) + 1);
  }
  return counts;
}

/** Room counts per floor id; rooms without known floor count under null. */
export function countRoomsByFloor(
  rooms: ReadonlyArray<RoomLike>,
  floors: ReadonlyArray<FloorLike>
): Map<string | null, number> {
  const floorIds = toIdSet(floors);
  const counts = new Map<string | null, number>();
  for (const room of rooms) {
    const floorId =
      room.floorId !== null && floorIds.has(room.floorId)
        ? room.floorId
        : null;
    counts.set(floorId, (counts.get(floorId) ?? 0) + 1);
  }
  return counts;
}

/**
 * Sums only known room areas and counts missing values separately. Rooms with
 * no known floor/building are grouped under null for the corresponding UI
 * entries "Ohne Etage" and "Ohne Gebäude".
 */
export function summarizeRoomAreas(
  rooms: ReadonlyArray<RoomAreaLike>,
  floors: ReadonlyArray<FloorLike>,
  buildings: ReadonlyArray<BuildingLike>
): StructureAreaSummaries {
  const buildingIds = toIdSet(buildings);
  const floorsById = new Map(floors.map((floor) => [floor.id, floor]));
  const byBuilding = new Map<string | null, RoomAreaSummary>();
  const byFloor = new Map<string | null, RoomAreaSummary>();
  const total = emptyAreaSummary();

  for (const room of rooms) {
    const floor = room.floorId === null ? undefined : floorsById.get(room.floorId);
    const floorId = floor?.id ?? null;
    const buildingId = floor
      ? resolveFloorBuildingId(floor, buildingIds)
      : null;
    addRoomArea(total, room.areaM2);
    addRoomArea(summaryFor(byFloor, floorId), room.areaM2);
    addRoomArea(summaryFor(byBuilding, buildingId), room.areaM2);
  }
  return { total, byBuilding, byFloor };
}

function emptyAreaSummary(): RoomAreaSummary {
  return { areaM2: 0, roomCount: 0, missingAreaCount: 0 };
}

function summaryFor(
  summaries: Map<string | null, RoomAreaSummary>,
  key: string | null
) {
  const existing = summaries.get(key);
  if (existing) return existing;
  const created = emptyAreaSummary();
  summaries.set(key, created);
  return created;
}

function addRoomArea(summary: RoomAreaSummary, areaM2: number | null) {
  summary.roomCount += 1;
  if (areaM2 === null) {
    summary.missingAreaCount += 1;
  } else {
    summary.areaM2 += areaM2;
  }
}

/** "EG · Haus A", "EG" (floor without building) or "Ohne Etage". */
export function describeRoomLocation(
  room: RoomLike,
  floors: ReadonlyArray<FloorLike>,
  buildings: ReadonlyArray<BuildingLike>
): string {
  const floor =
    room.floorId === null
      ? undefined
      : floors.find((entry) => entry.id === room.floorId);
  if (!floor) {
    return UNASSIGNED_FLOOR_LABEL;
  }
  const buildingId = resolveFloorBuildingId(floor, toIdSet(buildings));
  const building =
    buildingId === null
      ? undefined
      : buildings.find((entry) => entry.id === buildingId);
  return building ? `${floor.name} · ${building.name}` : floor.name;
}