/**
 * Formatter contract
 *
 * Deterministic, reusable, UI-only formatting/mapping logic.
 *
 * Based on FORMATTERS.md:
 * - Stateless (Formatters) or Immutable (Display Objects)
 * - Deterministic
 * - Side-effect free
 * - No business rules
 *
 * Uncle Bob says: "Data structures should not have behavior."
 * Formatters ensure ViewData remains a dumb container of primitives.
 */

export interface Formatter {
  /**
   * Format or map the input to a primitive value
   *
   * @returns Primitive values only (strings, numbers, booleans, null)
   */
  format(): string | number | boolean | null;
}

/**
 * Rich Display Object contract (Client-only)
 *
 * Used by ViewModels to provide a rich API to the UI.
 */
export interface DisplayObject {
  /**
   * Primary primitive output
   */
  format(): string | number | boolean | null;
  
  /**
   * Multiple primitive variants
   */
  variants?(): Record<string, string | number | boolean | null>;
}