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;