import { isEqual } from 'lodash';

/**
 * Helper function to check if a value has changed compared to the old value.
 * Uses deep equality comparison for arrays and objects.
 *
 * Key behaviors:
 * - `undefined` = field not provided (returns false)
 * - `null` = explicit value (returns true if different from oldVal)
 * - Empty values (`[]`, `{}`, `''`) are valid changes if oldVal differs
 *
 * @param newVal - The new value to check
 * @param oldVal - The old value to compare against
 * @returns true if the value has changed, false otherwise
 */
export default function hasChanged(newVal: any, oldVal: any): boolean {
  // undefined means the field was not provided in the update request
  // This is distinct from null, which is an explicit value
  if (newVal === undefined) return false;

  // Early return for strict equality (handles primitives and same references)
  // This handles: null === null, 0 === 0, false === false, etc.
  if (newVal === oldVal) return false;

  // null is an explicit value - if we get here, newVal is null but oldVal is not
  // (or vice versa), which means the value has changed
  if (newVal === null || oldVal === null) return true;

  // Use lodash isEqual for deep equality comparison
  // This handles arrays, objects, and nested structures correctly
  if (
    Array.isArray(newVal) ||
    (typeof newVal === 'object' && newVal !== null)
  ) {
    return !isEqual(newVal, oldVal);
  }

  // All other cases: primitive values that are different
  return true;
}