// src/session.ts
import { createCookieSessionStorage } from "astro-session";

// your session data type which define the shape of your session data
export type SessionData = {
  count: number;
  user: User | null;
};

export const { getSession, commitSession } =
  createCookieSessionStorage<SessionData>(
    { count: 0, user: null }, // the default value on new session created, this must match your SessionData

    {
      cookie: {
        // all of these are optional
        name: "__session-id",
        path: "/",
        secret: "not-secret", // even if optional, this is mandatory when passing your app in production
      },
    }
  );

---
// src/pages/index.astro
import { getSession, commitSession } from "../session"

// get the session
const session = await getSession(Astro.request);

// update specific value in the session
session.set('count', session.get('count') + 1);
// or
// session.set('count', (value) => value + 1);

// get specific value in the session
const count = session.get('count');

// save the session in the cookie (mandatory to persist data from one request to another)
Astro.response.headers.set("set-cookie", await commitSession(session));
---

<p>You visited this page: {{ count }}</p>

// src/routes/api/login.ts
import type { APIContext } from "astro";
import { commitSession, getSession } from "../../utils/session";

export async function post({ request }: APIContext) {
  const session = await getSession(request);
  const formData = await request.formData();

  const email = formData.get("email");
  const password = formData.get("password");

  // checks for email + password combinaison
  const user = await validateCredentials(email, password);

  if (!user) {
    // if email or password incorrect, flash a message to show the user what is the error
    session.flash("error", "Invalid email/password");

    return new Response(null, {
      status: 302,
      headers: {
        location: "/login",
        // commit the session to persist it
        "set-cookie": await commitSession(session),
      },
    });
  }

  // if the credentials are valid, save the user in session
  session.set("user", user);

  // redirect to the dashboard
  return new Response(null, {
    status: 302,
    headers: {
      location: "/dashboard",
      // commit the session to persist it
      "set-cookie": await commitSession(session),
    },
  });
}

---
// src/routes/login.astro
import { getSession, commitSession } from "astro-session";

const session = await getSession(Astro.request);

// if the user is already authenticated, redirect to the dashboard
if (!session.get('user')) {
  return Astro.redirect('/dashboard')
}

// get the error message if there is any and delete it after accessing it
// flash data are accessible only once and get deleted after
const error = session.flash('error');

// persist the session data
Astro.response.headers.set("set-cookie", await commitSession(session));
---

<!-- display error if there is any in the session -->
{!!error && <p>{error}</p>}

<form method="post" action="/api/login">
  <input name="email" type="email" placeholder="Email" />

  <input name="password" type="password" placeholder="Password" />

  <button type="submit">Login</button>
</form>