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

export interface ListVacantPositionsInput extends PaginationInput {}

/**
 * Function: listVacantPositions
 * Returns the paginated list of Positions with no current open primary
 * Assignment (vacancy/TBH), i.e. the count of current open primary Assignments
 * for the Position is less than its headcount. Only current (today-
 * effective) Position generations are considered.
 */
export async function run(db: ReadonlyDB<DB>, input: ListVacantPositionsInput) {
  const limit = input.limit ?? DEFAULT_PAGE_SIZE;
  const offset = input.offset ?? 0;
  const orderBy = input.orderBy ?? "id";
  const orderDirection = input.orderDirection ?? "asc";

  const now = new Date();
  const positions = await db
    .selectFrom("Position")
    .selectAll()
    // Today-effective Position and today-effective occupying Assignments: use window membership, not
    // "effectiveEnd IS NULL", so a scheduled future change neither hides the position in force today
    // nor lets a future occupant/vacancy be counted early (M02).
    .where("effectiveStart", "<=", now)
    .where((eb) => eb.or([eb("effectiveEnd", "is", null), eb("effectiveEnd", ">=", now)]))
    .where((eb) =>
      eb(
        eb
          .selectFrom("Assignment")
          .select((eb2) => eb2.fn.countAll().as("count"))
          .whereRef("Assignment.positionId", "=", "Position.id")
          .where("Assignment.isPrimary", "=", true)
          .where("Assignment.effectiveStart", "<=", now)
          .where((eb2) =>
            eb2.or([
              eb2("Assignment.effectiveEnd", "is", null),
              eb2("Assignment.effectiveEnd", ">=", now),
            ]),
          ),
        "<",
        eb.ref("Position.headcount"),
      ),
    )
    .orderBy(orderBy, orderDirection)
    .limit(limit + 1)
    .offset(offset)
    .execute();

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