// @flow

// see https://gist.github.com/thecotne/6e5969f4aaf8f253985ed36b30ac9fe0
type $FlowGen$If<X: boolean, Then, Else = empty> = $Call<
  ((true, Then, Else) => Then) & ((false, Then, Else) => Else),
  X,
  Then,
  Else
>;

type $FlowGen$Assignable<A, B> = $Call<
  ((...r: [B]) => true) & ((...r: [A]) => false),
  A
>;

export type Array<T> = $FlowGen$If<
  $FlowGen$Assignable<Belt.UseMutableArrays, 1>,
  T[],
  $ReadOnlyArray<T>
>;
export type Mutable<T> = $ObjMapi<T, <P>(P) => $ElementType<T, P>>;
export type EmptyObject = { [key: string]: any, ... };
export type ExtractValue<T> = Exclude<T, null | void>;
export type ExtractNested<T> = $FlowGen$If<
  $FlowGen$Assignable<T, Array<K>>,
  ExtractNested<K>,
  T
>;
export type GuardArray<T: mixed> = $FlowGen$If<
  $FlowGen$Assignable<Extract<T, Array<any>>, empty>,
  Array<mixed>,
  Extract<T, Array<any>>
>;
export type GuardPromise<T: mixed> = $FlowGen$If<
  $FlowGen$Assignable<Extract<T, Promise<any>>, empty>,
  Promise<mixed>,
  Extract<T, Promise<any>>
>;
export type GuardObject<T: mixed> = $FlowGen$If<
  $FlowGen$Assignable<
    Exclude<Extract<T, { [key: string]: any }>, Function | Array<any>>,
    empty
  >,
  {
    [k: string]: mixed,
    ...
  },
  Exclude<Extract<T, { [key: string]: any }>, Function | Array<any>>
>;
export type GuardValue<T, V> = $FlowGen$If<
  $FlowGen$Assignable<Extract<T, V>, empty>,
  V,
  $FlowGen$If<$FlowGen$Assignable<Extract<T, V>, any>, V, Extract<T, V>>
>;