import {
  arrayOf,
  optional,
  optionalKey,
  struct,
  isString,
  isNumber,
} from 'is-kit';

const isUser = struct({
  id: isNumber,
  name: isString,
  nickname: optionalKey(isString),
  displayName: optionalKey(optional(isString)),
});
// isUser: Guard<{
//   id: number;
//   name: string;
//   nickname?: string;
//   displayName?: string | undefined;
// }>

const input: unknown = {
  id: 42,
  name: 'Neko',
  nickname: 'nya',
};

if (isUser(input)) {
  input.nickname?.toUpperCase(); // input narrowed to User shape
}

const isExactUser = struct(
  { id: isNumber, name: isString },
  { exact: true }
);
isExactUser({ id: 1, name: 'A' }); // true
isExactUser({ id: 1, name: 'A', extra: 1 }); // false (extra keys rejected)

const isTeam = struct({
  name: isString,
  members: arrayOf(isUser),
});
// Nested structs compose cleanly; members inherits the User guard.

isTeam({
  name: 'core',
  members: [{ id: 1, name: 'Neko' }],
}); // true
isTeam({
  name: 'core',
  members: [{ id: 1, name: 'Neko', nickname: 123 }],
}); // false (nickname is not a string)

// Use optionalKey(...) when the property may be omitted.
// Use optional(...) when the property exists but its value may be undefined.