import type { TFunction } from "i18next";
import { REASON_CODES, type LedgerEvent } from "@parking/shared";

// Localize a signed event's reason. The ledger signs a STABLE `reasonCode` (+ params)
// plus an English `reason` fallback (see @parking/shared REASON_CODES). We translate
// the code via the `reason.<code>` catalog so an Albanian operator reads Albanian and
// an English operator reads English — from the SAME immutable event. Legacy events
// (signed before reason codes existed) carry only `reason`, so we show that verbatim.

const CODE_SET = new Set<string>(REASON_CODES);

/** The localized reason sentence for an event, or null if it has no reason at all. */
export function renderReason(payload: LedgerEvent["payload"], t: TFunction): string | null {
  if (!payload) return null;
  const code = typeof payload.reasonCode === "string" ? payload.reasonCode : null;
  if (code && CODE_SET.has(code)) {
    // i18next fills {{param}} from reasonParams; an absent key renders the raw token.
    return t(`reason.${code}`, (payload.reasonParams ?? {}) as Record<string, unknown>);
  }
  // No code (legacy) or an unknown code (forward-compat) → the signed English fallback.
  return typeof payload.reason === "string" ? payload.reason : null;
}