// reactivity/src/system.ts

export const enum ReactiveFlags {
  None = 0, 
  Mutable = 1 << 0,
  Watching = 1 << 1,
  RecursedCheck = 1 << 2,
  Recursed = 1 << 3,
  Dirty = 1 << 4,
  Pending = 1 << 5,
}

export function propagate(link: Link): void {
  ...
  if (
    !(
      flags &
      (ReactiveFlags.RecursedCheck |
        ReactiveFlags.Recursed |
        ReactiveFlags.Dirty |
        ReactiveFlags.Pending)
    )
  ) {
    sub.flags = flags | ReactiveFlags.Pending
  } else if (
    !(flags & (ReactiveFlags.RecursedCheck | ReactiveFlags.Recursed))
  ) {
    flags = ReactiveFlags.None
  } else if (!(flags & ReactiveFlags.RecursedCheck)) {
    sub.flags = (flags & ~ReactiveFlags.Recursed) | ReactiveFlags.Pending
  } else if (
    !(flags & (ReactiveFlags.Dirty | ReactiveFlags.Pending)) &&
    isValidLink(link, sub)
  ) {
    sub.flags = flags | ReactiveFlags.Recursed | ReactiveFlags.Pending
    flags &= ReactiveFlags.Mutable
  } else {
    flags = ReactiveFlags.None
  }
  ...
}

class StatusMachine {
  constructor(flags = ReactiveFlags.None) {
    this.flags = flags;
  }

  mutable() {
    this.flags |= ReactiveFlags.Mutable;
    return this;
  }

  unmutable() {
    this.flags &= ~ReactiveFlags.Mutable;
    return this;
  }

  watching() {
    this.flags |= ReactiveFlags.Watching;
    return this;
  }

  unwatching() {
    this.flags &= ~ReactiveFlags.Watching;
    return this;
  }

  // ...

  get value() {
    return this.flags;
  }

  has(flag) {
    return (this.flags & flag) !== 0;
  }
}

const flags = new StatusMachine();
console.log(flags.mutable().watching().unmutable().value);