import { OnAnimationFrame } from "../../../animation/OnAnimationFrame";
import { OnChange, OnHashChange, OnVisibilityChange } from "../../EventListeners";

export class HashScroll
{
  static _hasScrolled = false;
  static _hasListener = false;
  
  static applyOnDocument( onAnimationFrame:OnAnimationFrame )
  {
    HashScroll._hasScrolled = false;
    HashScroll.scroll();


    if ( this._hasListener )
    {
      return;
    } 

    OnVisibilityChange.add( document, HashScroll._visibilityHandler );

    HashScroll._hasListener = true;

    OnHashChange.add( window, ()=> HashScroll.scroll() );
      
    
    
  }

  static scroll()
  {
    console.log( "Scrolling:", document.hidden );
    let hash = location.hash;

    if ( hash )
    {
      let el = document.querySelector( hash );

      if ( el )
      {
        el.scrollIntoView( { behavior: "smooth", block: "start" } );
      }
    }

  }

  static _doScrollOnce()
  {
    if ( this._hasScrolled )
    {
      return;
    }

    HashScroll.scroll();

    HashScroll._hasScrolled = true;
    document.removeEventListener( "visibilitychange", HashScroll._visibilityHandler );
  }

  static _visibilityHandler = () =>
  {
    if ( ! document.hidden )
    {
      HashScroll._doScrollOnce();
    }
  }
}