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

export interface GetShiftPlacementInput {
  shiftPlacementId: string;
}

/**
 * Function: getShiftPlacement
 * Description: Retrieves a single placement (ShiftPlacement) by id — the
 * lookup behind shift-schedule-detail views and variance calculation, which need to
 * resolve exactly which Assignment is staffing a slot. Returns the placement
 * regardless of the parent Shift's current status.
 */
export async function run(db: ReadonlyDB<DB>, input: GetShiftPlacementInput) {
  const shiftPlacement = await db
    .selectFrom("ShiftPlacement")
    .selectAll()
    .where("id", "=", input.shiftPlacementId)
    .executeTakeFirst();

  if (!shiftPlacement) {
    return err(new ShiftPlacementNotFoundError(input.shiftPlacementId));
  }

  return ok({ shiftPlacement });
}