import {
  buildPaginatedResult,
  DEFAULT_PAGE_SIZE,
  err,
  ok,
  type PaginationInput,
  type ReadonlyDB,
} from "@tailor-platform/erp-kit/core";
import type { DB } from "../generated/kysely-tailordb";
import { ShiftNotFoundError } from "../lib/errors.generated";

type ShiftPlacementOrderByField = "assignedAt";

export interface ListShiftPlacementsByShiftInput extends PaginationInput<ShiftPlacementOrderByField> {
  shiftId: string;
  /** Include SUPERSEDED / CANCELLED placements (the swap history). Defaults to false. */
  includeInactive?: boolean;
}

/**
 * Function: listShiftPlacementsByShift
 * Description: Returns who is placed on a given Shift, paginated — answers
 * "who is staffing this slot" for team shifts (which may carry more than one
 * placement), open-shift fills, and 応援/multi-site coverage.
 */
export async function run(db: ReadonlyDB<DB>, input: ListShiftPlacementsByShiftInput) {
  const shift = await db
    .selectFrom("Shift")
    .selectAll()
    .where("id", "=", input.shiftId)
    .executeTakeFirst();

  if (!shift) {
    return err(new ShiftNotFoundError(input.shiftId));
  }

  const limit = input.limit ?? DEFAULT_PAGE_SIZE;
  const offset = input.offset ?? 0;
  const orderBy = input.orderBy ?? "assignedAt";
  const orderDirection = input.orderDirection ?? "asc";

  // ACTIVE only by default. Callers that forget this filter double-count a swapped slot —
  // predicted-vs-actual would report the outgoing worker as a no-show and the incoming one twice
  // — so the safe reading is the default and history is opt-in.
  //
  // Unlike the by-assignment queries this does *not* also exclude withdrawn slots: the caller
  // named one shift, and the detail view of a withdrawn slot still has to show who had been on
  // it. "Is this person placed anywhere" is the question that must exclude them.
  let placements = db.selectFrom("ShiftPlacement").selectAll().where("shiftId", "=", input.shiftId);

  if (input.includeInactive !== true) {
    placements = placements.where("status", "=", "ACTIVE");
  }

  const shiftPlacements = await placements
    .orderBy(orderBy, orderDirection)
    // Total order: assignedAt is not unique when a batch places several people at once.
    .orderBy("id", "asc")
    .limit(limit + 1)
    .offset(offset)
    .execute();

  return ok(buildPaginatedResult(shiftPlacements, limit));
}