"use client";

import { useEffect } from "react";
import { useParams, useRouter } from "next/navigation";
import { useQuery } from "@tanstack/react-query";
import { workspaceApi } from "@/lib/api";
import { sortByPosition } from "@/lib/utils";

/**
 * Workspace landing: redirect to the first top-level page (by fractional
 * position), or create a "Home" page when the workspace is empty.
 *
 * The param may be the magic value `default` (the root page + the middleware
 * redirect both target /w/default) — no workspace has that id/slug, so it is
 * resolved to the user's first workspace from GET /workspaces.
 */
export default function WorkspaceIndexPage() {
  const params = useParams<{ workspace: string }>();
  const slugOrId = params?.workspace ?? "default";
  const router = useRouter();
  const isDefault = slugOrId === "default";

  // `default` → the user's first workspace (id order; the personal
  // workspace is created first at registration).
  const workspaces = useQuery({
    queryKey: ["workspaces"],
    queryFn: () => workspaceApi.list(),
    enabled: isDefault,
    retry: false
  });
  useEffect(() => {
    const first = workspaces.data?.[0];
    if (isDefault && first) {
      router.replace(`/w/${first.id}`, { scroll: false });
    }
  }, [isDefault, workspaces.data, router]);

  const workspace = useQuery({
    queryKey: ["workspaces", slugOrId],
    queryFn: () => workspaceApi.get(slugOrId),
    // Skip the (always-404) lookup while resolving the `default` alias.
    enabled: slugOrId.length > 0 && !isDefault,
    retry: false
  });

  const pages = useQuery({
    queryKey: ["workspaces", slugOrId, "pages", "index"],
    queryFn: () => workspaceApi.pages(slugOrId, { parent: null, limit: 100 }),
    enabled: Boolean(workspace.data?.id),
    retry: false
  });

  useEffect(() => {
    if (!workspace.data?.id) return;
    const wsId = workspace.data.id;
    const list = pages.data ? sortByPosition(pages.data) : [];
    if (list.length > 0) {
      router.replace(`/w/${slugOrId}/page/${list[0]?.id}`);
      return;
    }
    // Empty workspace → create the "Home" page (idempotent: we redirect
    // before the second call could create a duplicate because the query
    // revalidates with the new page on the next visit).
    let cancelled = false;
    workspaceApi
      .pages(wsId, { parent: null, limit: 5 })
      .then(async (existing) => {
        if (existing.length > 0) {
          if (!cancelled) router.replace(`/w/${slugOrId}/page/${existing[0]?.id}`);
          return;
        }
        const home = await createHome(wsId);
        if (!cancelled && home) router.replace(`/w/${slugOrId}/page/${home.id}`);
      })
      .catch(() => {
        /* login-expired or transient — middleware/refresh handles it */
      });
    return () => {
      cancelled = true;
    };
    // eslint-disable-next-line react-hooks/exhaustive-deps
  }, [workspace.data?.id, pages.data, slugOrId, router]);

  return (
    <div className="flex h-full items-center justify-center text-sm text-muted-foreground" role="status">
      Opening your workspace…
    </div>
  );
}

async function createHome(workspaceId: string) {
  const { pageApi } = await import("@/lib/api");
  return pageApi.create({ workspaceId, parentId: null, title: "Home" });
}