import { DomainError } from "@tailor-platform/erp-kit/app";

/**
 * Validate that `raw` is one of `allowed`, narrowing the return type to the
 * matching literal. Throws a descriptive DomainError listing every accepted
 * value otherwise.
 *
 * Why this exists: erp-kit 0.26.0 moved several enum-typed command inputs
 * (partner type / role / identification type / costing method, etc.) from
 * runtime error codes to compile-time unions. Our GraphQL inputs remain
 * `t.string()`, so each resolver needs a small guard between the loose
 * string input and the typed command call. This helper standardises that
 * pattern.
 *
 * Usage:
 *   const ROLES = ["CUSTOMER", "SUPPLIER"] as const;
 *   const role = assertEnum(context.input.role ?? "SUPPLIER", ROLES, "role");
 *   // role is narrowed to "CUSTOMER" | "SUPPLIER"
 *
 * Implementation note: iterating returns the matching element directly so
 * TypeScript narrows it to `T[number]` without an explicit `as` cast (which
 * `@typescript-eslint/no-unnecessary-type-assertion` would reject — the
 * generic constraint is too loose for the linter to see the cast as load-
 * bearing). O(n) lookup is fine for the 2-6 element tuples we use this for.
 */
export function assertEnum<T extends readonly string[]>(
  raw: string,
  allowed: T,
  fieldName: string,
): T[number] {
  for (const value of allowed) {
    if (value === raw) return value;
  }
  throw new DomainError(`Invalid ${fieldName}: ${raw}. Must be one of ${allowed.join(", ")}.`);
}