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

export interface GetEligibilityRuleInput {
  id: string;
}

/**
 * Function: getEligibilityRule
 * Description: Resolves a single EligibilityRule generation by its surrogate id. Because
 * eligibility is effective-dated (ADR-013), an id identifies exactly one generation, not the
 * whole history for its `versionOf`.
 */
export async function run(db: ReadonlyDB<DB>, input: GetEligibilityRuleInput) {
  const eligibilityRule = await db
    .selectFrom("EligibilityRule")
    .selectAll()
    .where("id", "=", input.id)
    .executeTakeFirst();

  if (!eligibilityRule) {
    return err(new EligibilityRuleNotFoundError(input.id));
  }

  return ok({ eligibilityRule });
}