import type {ExternalSource} from './selectors.ts';
/** Presentation invalidations only. Commands, history and network work never wait here. */
export type FrameClock={request(callback:()=>void):unknown;cancel(handle:unknown):void};
export function createFrameQueue<K>(clock:FrameClock,publish:(dirty:ReadonlySet<K>)=>void){
 let dirty=new Set<K>(),scheduled:{handle?:unknown}|undefined,disposed=false;
 function flush(){if(disposed)return;const pending=scheduled;scheduled=undefined;if(pending)clock.cancel(pending.handle);if(!dirty.size)return;const batch=dirty;dirty=new Set();publish(batch);}
 return Object.freeze({
  invalidate(keys:Iterable<K>){if(disposed)return;for(const key of keys)dirty.add(key);if(!dirty.size||scheduled)return;const pending: {handle?:unknown}={};scheduled=pending;try{pending.handle=clock.request(()=>{if(scheduled!==pending)return;scheduled=undefined;flush();});}catch(error){scheduled=undefined;throw error;}},
  flush,
  dispose(){if(disposed)return;disposed=true;if(scheduled)clock.cancel(scheduled.handle);scheduled=undefined;dirty.clear();},
 });
}

/** Coalesce presentation notifications; immediate invalidations flush pending work synchronously. */
export function createFrameSource<S>(source:{getSnapshot():S;subscribe(notify:(immediate?:boolean)=>void):()=>void},clock:FrameClock):ExternalSource<S>{
 return Object.freeze({getSnapshot:()=>source.getSnapshot(),subscribe(notify:()=>void){
  const queue=createFrameQueue<number>(clock,()=>notify());
  let stop:()=>void;
  try{stop=source.subscribe(immediate=>{queue.invalidate([0]);if(immediate)queue.flush();});}catch(error){queue.dispose();throw error;}
  return()=>{try{stop();}finally{queue.dispose();}};
 }});
}