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import {
  type Computation,
  effect,
  type ReactiveValue,
  signal,
} from "./signals.js";

export interface Pending {
  isSettled: false;
  isRejected: false;
  isResolved: false;
}

const pending: Pending = {
  isRejected: false,
  isResolved: false,
  isSettled: false,
};

export interface Resolved<T> {
  isSettled: true;
  isRejected: false;
  isResolved: true;
  data: T;
}

export interface Rejected<E> {
  isSettled: true;
  isRejected: true;
  isResolved: false;
  error: E;
}

export type PromiseSnapshot<T, E> = Pending | Resolved<T> | Rejected<E>;

export function asyncDerived<T, E = unknown>(
  f: (ctx: Computation, abort: AbortSignal) => Promise<T>,
): ReactiveValue<PromiseSnapshot<T, E>> {
  const $s = signal<PromiseSnapshot<T, E>>(pending);

  effect((ctx) => {
    const abortController = new AbortController();

    $s.set(pending);

    f(ctx, abortController.signal)
      .then((data) => {
        if (abortController.signal.aborted) {
          return;
        }

        $s.set({
          isRejected: false,
          isResolved: true,
          isSettled: true,
          data,
        });
      })
      .catch((error) => {
        if (abortController.signal.aborted) {
          return;
        }

        $s.set({
          isRejected: true,
          isResolved: false,
          isSettled: true,
          error,
        });
      });

    return () => {
      abortController.abort();
    };
  });

  return $s;
}