/* Brain of Reese — admin sign-in (phase 16, A10 revised).
 *
 * One admin, one password. On submit → POST /api/login: 204 sets the
 * signed session cookie and we redirect to `?next` (same-origin relative
 * URLs only — "/…" but never "//host" or an absolute URL; default
 * /sources.html). A 401 keeps the form and announces through the
 * role=alert error region. On load, /api/whoami already says admin →
 * straight to `next`, no form.
 *
 * No CDN, no state in this file: the signed cookie is the whole session.
 * All DOM ids match frontend/login.html.
 */

const form = document.querySelector("#login-form");
const passwordInput = document.querySelector("#login-password");
const submitBtn = document.querySelector("#login-submit");
const errorEl = document.querySelector("#login-error");

const DEFAULT_NEXT = "/sources.html";

/* Same-origin relative URLs only: honor `?next=/…`, reject anything that
   would leave the origin (protocol-relative "//…" or absolute). */
function safeNext() {
  const next = new URLSearchParams(window.location.search).get("next") || DEFAULT_NEXT;
  return next.startsWith("/") && !next.startsWith("//") ? next : DEFAULT_NEXT;
}

function showError(message) {
  errorEl.textContent = message;
  errorEl.hidden = false;
  submitBtn.disabled = false;
  passwordInput.focus();
  passwordInput.select();
}

async function alreadySignedIn() {
  try {
    const r = await fetch("/api/whoami");
    if (!r.ok) return false;
    return (await r.json()).authenticated === true;
  } catch {
    return false; // API unreachable: stay on the form — submit will explain
  }
}

form.addEventListener("submit", async (e) => {
  e.preventDefault();
  errorEl.hidden = true;
  errorEl.textContent = "";
  submitBtn.disabled = true;
  try {
    const r = await fetch("/api/login", {
      method: "POST",
      headers: { "Content-Type": "application/json" },
      body: JSON.stringify({ password: passwordInput.value }),
    });
    if (r.status === 204) {
      // Session cookie set — off to the requested page.
      window.location.replace(safeNext());
      return;
    }
    // One generic failure (401); anything else is a server-side surprise.
    const detail =
      r.status === 401
        ? "Invalid password — try again."
        : `Sign-in failed (HTTP ${r.status}) — try again.`;
    showError(detail);
  } catch {
    showError("Could not reach the server — try again.");
  }
});

/* Already the admin? Skip the form and go straight to the target. */
(async () => {
  if (await alreadySignedIn()) {
    window.location.replace(safeNext());
    return;
  }
  passwordInput.focus();
})();