import { LinkedList } from "./LinkedList";

export class Scheduler {
   running = false;

   array = new LinkedList<() => void>();

   isRunning(): boolean {
      return this.running;
   }

   setImmediate(thunk: () => void) {
      const handle = setImmediate(() => this.dispatch(thunk));
      return () => {
         clearImmediate(handle);
      };
   }

   setImmediatePromise(thunk: () => void) {
      let cancelled = false;
      Promise.resolve(thunk).then((t) => {
         if (!cancelled) {
            this.dispatch(t);
         }
      });
      return () => {
         cancelled = true;
      };
   }

   dispatchFn =
      typeof setImmediate === "function"
         ? (thunk: () => void) => this.setImmediate(thunk)
         : (thunk: () => void) => this.setImmediatePromise(thunk);

   run(): void {
      this.running = true;
      let next = this.array.deleteHead()?.value;

      while (next) {
         next();
         next = this.array.deleteHead()?.value;
      }
      this.running = false;
   }

   dispatch(thunk: () => void): void {
      this.array.append(thunk);

      if (!this.running) {
         this.run();
      }
   }

   dispatchLater(thunk: () => void): () => void {
      return this.dispatchFn(thunk);
   }
}

export const defaultScheduler: Scheduler = (() => new Scheduler())();