yay-machine/src/MachineState.ts

A modern, simple, lightweight, zero-dependency, TypeScript state-machine library

/**
 * The base type for all machine events.
 * User-defined events do not need to extend this interface, just conform to its shape,
 * and can also have their own arbitrary properties.
 */
export interface MachineState<Name extends string = string> {
  /**
   * The unique name (or names if a string-union) of the event.
   */
  readonly name: Name;
}

export type ExtractState<
  StateType extends MachineState,
  Name extends StateType["name"],
> =
  Extract<StateType, { name: Name }> extends never
    ? ExtractComplexState<StateType, Name>
    : Extract<StateType, { name: Name }>;

type ExtractComplexState<
  StateType extends MachineState,
  Name extends StateType["name"],
> = StateType extends {
  name: infer N;
}
  ? Name extends N
    ? StateType /* & { name: Name } */
    : never
  : never;

export type StateData<
  StateType extends MachineState,
  Name extends StateType["name"],
> = keyof Omit<ExtractState<StateType, Name>, "name"> extends never
  ? never
  : Omit<ExtractState<StateType, Name>, "name">;

type ExpandStateDataTypes<StateType extends MachineState> = {
  [Name in StateType["name"]]: StateData<StateType, Name>;
};

type Values<T> = T[keyof T];

type AllValuesCompatible<T> =
  Values<T> extends infer V
    ? { [K in keyof T]: V extends T[K] ? true : false }[keyof T] extends true
      ? true
      : false
    : false;

export type IsStateDataHomogenous<StateType extends MachineState> =
  AllValuesCompatible<ExpandStateDataTypes<StateType>>;