"use client";

import { useEffect, useRef, useState } from "react";
import { useCreateFlow } from "../context/CreateFlowContext";
import { flushPendingCommunityAvatar } from "../../../../lib/create/flushPendingCommunityAvatar";

/** Background tries after a transient upload failure. The file stays staged. */
const MAX_FLUSH_ATTEMPTS = 4;

/**
 * After sign-in, uploads a community avatar staged in IndexedDB (anonymous pick)
 * and writes `communityAvatarUrl` on success. A transient failure retries with
 * backoff while this layout stays mounted.
 */
export function CreateFlowPendingAvatarFlush({
  sessionUser,
  sessionResolved,
}: {
  sessionUser: { id: string; email: string } | null | undefined;
  sessionResolved: boolean;
}) {
  const { state, updateState } = useCreateFlow();
  const [attempt, setAttempt] = useState(0);
  /** One successful flush per signed-in user id (survives the effect re-running). */
  const lastFlushedUserIdRef = useRef<string | null>(null);
  const hasServerAvatar =
    typeof state.communityAvatarUrl === "string" &&
    state.communityAvatarUrl.trim().length > 0;

  useEffect(() => {
    if (!sessionResolved || !sessionUser) return;
    if (lastFlushedUserIdRef.current === sessionUser.id) return;
    if (hasServerAvatar) return;
    if (attempt >= MAX_FLUSH_ATTEMPTS) return;
    let cancelled = false;
    let timer: ReturnType<typeof setTimeout> | undefined;

    void (async () => {
      const result = await flushPendingCommunityAvatar();
      if (cancelled) return;
      if (result.status === "uploaded") {
        updateState({ communityAvatarUrl: result.url });
        lastFlushedUserIdRef.current = sessionUser.id;
        return;
      }
      if (result.status !== "failed") return;
      if (attempt + 1 >= MAX_FLUSH_ATTEMPTS) return;
      const delay = Math.min(20_000, 5_000 * 2 ** attempt);
      timer = setTimeout(() => {
        if (!cancelled) setAttempt((current) => current + 1);
      }, delay);
    })();

    return () => {
      cancelled = true;
      if (timer) clearTimeout(timer);
    };
  }, [attempt, hasServerAvatar, sessionResolved, sessionUser, updateState]);

  return null;
}