import { useEffect, useRef, useState } from "react";

type ExchangeState = "working" | "failed" | "missing";

const MagicLink = function () {
  const started = useRef(false);
  const [state, setState] = useState<ExchangeState>("working");

  useEffect(() => {
    // React Strict Mode runs effects twice in development. Never redeem twice.
    if (started.current) return;
    started.current = true;

    const params = new URLSearchParams(window.location.search);
    const token = params.get("token");
    if (!token) {
      setState("missing");
      return;
    }

    // Keep the credential out of browser history and subsequent Referer headers.
    window.history.replaceState({}, "", window.location.pathname);

    void fetch("/auth/magic-link/exchange", {
      method: "POST",
      credentials: "include",
      headers: { "Content-Type": "application/json" },
      body: JSON.stringify({ token: token }),
    })
      .then((response) => {
        if (!response.ok) throw new Error("Magic-link exchange failed");
        window.location.replace("/");
      })
      .catch(() => setState("failed"));
  }, []);

  if (state === "missing") {
    return <p>This login link is missing its token.</p>;
  }
  if (state === "failed") {
    return <p>This login link is invalid or has expired.</p>;
  }
  return <p>Signing you in…</p>;
};

export default MagicLink;