import { getSession } from "next-auth/react";
import { useAuthStore } from "@/store/authStore";

const decodeJwtPayload = (token: string) => {
  const parts = token.split(".");
  if (parts.length < 2) {
    console.warn("Invalid JWT format.");
    return null;
  }
  const base64 = parts[1].replace(/-/g, "+").replace(/_/g, "/");
  const padded = base64.padEnd(Math.ceil(base64.length / 4) * 4, "=");
  try {
    const json =
      typeof window !== "undefined"
        ? window.atob(padded)
        : Buffer.from(padded, "base64").toString("utf-8");
    return JSON.parse(json);
  } catch (error) {
    console.warn("Failed to decode JWT payload.", error);
    return null;
  }
};

const isTokenExpired = (token: string) => {
  const payload = decodeJwtPayload(token);
  if (!payload) {
    return true;
  }
  if (typeof payload.exp !== "number") {
    return false;
  }
  const now = Date.now();
  return now >= payload.exp * 1000 - 30_000;
};

export const getAccessToken = async () => {
  const { accessToken, setAccessToken } = useAuthStore.getState();
  if (accessToken && !isTokenExpired(accessToken)) {
    return accessToken;
  }
  if (accessToken) {
    setAccessToken(null);
  }
  const session = await getSession();
  if (session?.error) {
    return null;
  }
  const token = typeof session?.accessToken === "string" ? session.accessToken : null;
  if (token && !isTokenExpired(token)) {
    setAccessToken(token);
    return token;
  }
  return null;
};