<?php
/**
 * login_confirm.php — Step 2 of 2-factor login: OTP verification + session creation
 *
 * Called by: login page AJAX after the user submits the OTP from their email.
 * Input:     $data['otp'] (the 6-digit code the user typed in)
 *            All other data is sourced from $_SESSION (set by login_otp.php).
 *
 * This is the second and final step of the login flow. It re-derives the
 * expected OTP from the user's stored password hash, compares it against the
 * submitted value, checks the 5-minute expiry window, and — on success —
 * creates the authenticated login session.
 *
 * Full flow:
 *   1. Load credentials and user_id from session (written by login_otp.php).
 *   2. Fetch the user's full row by user_id to get the current password hash.
 *   3. Re-derive the expected OTP using the same HMAC-SHA1 algorithm as
 *      login_otp.php (same secret key = password hash, same time_step = 180s).
 *      Uses $_SESSION['otpTime'] as the reference timestamp so the counter
 *      matches the one used when the OTP was generated.
 *   4. Check both conditions that must be true for the OTP to be valid:
 *        a. The submitted OTP matches the re-derived expected value.
 *        b. The elapsed time since otpTime is ≤ 5 minutes.
 *      Fail either → return "Wrong OTP! Please try again."
 *   5. On success:
 *        a. Force-replace session_token in DB — writing a new token invalidates
 *           any prior session (old device gets kicked out by db_auth.php on its
 *           next request). No block: password + OTP is full 2FA proof of identity.
 *        b. session_regenerate_id(true) — prevents session fixation attack by
 *           issuing a new session ID and deleting the old one.
 *        c. Generate a fresh CSRF token and store in session.
 *        d. Write the authenticated login session keys:
 *             login_status=1, login_username, login_name, login_surname,
 *             login_company_id (from user's default_company).
 *   6. Return { success: 1, message: "Login Complete!" }.
 *
 * Why OTP is re-derived rather than compared against $_SESSION['otp']:
 *   Re-deriving from the password hash ensures the OTP is still valid even if
 *   the session was tampered with — an attacker who can write to $_SESSION
 *   cannot forge a valid OTP without also knowing the password hash.
 *
 * Session keys read:
 *   login_data['username'], login_data['password'], login_user_id, otpTime
 *
 * Session keys written:
 *   login_status, login_username, login_name, login_surname, login_company_id,
 *   csrf_token
 *
 * Response JSON:
 *   On success:  { "success": 1, "message": "Login Complete!" }
 *   On failure:  { "message": "Wrong OTP! Please try again. (Our OTP is valid for 5 minute)" }
 */

require_once '../../../session.php';
require_once '../../../config.php';
require_once '../../../preset.php';
define('UNAUTHENTICATED_ROUTE', true);
require_once '../../../assets/utils/db_auth.php';

// ── Step 1: Load session state written by login_otp.php ───────────────────────
$data["username"] = $_SESSION["login_data"]['username'];
$data["password"] = $_SESSION["login_data"]['password'];
$user_id          = $_SESSION["login_user_id"];

// ── Step 2: Fetch user record — need password hash to re-derive the OTP ───────
$sth = $pdo1->prepare("select * from user where user_id = :user_id limit 1;");
$sth->execute([":user_id" => $user_id]);
$temp = $sth->fetch(PDO::FETCH_ASSOC);

// ── Step 3: Re-derive expected OTP ────────────────────────────────────────────
// Uses $_SESSION['otpTime'] (set when the OTP was generated) as the TOTP
// counter base. This is the same algorithm used in login_otp.php and
// request_new_otp.php — any change to one must be reflected in all three.
function generateOTP($sercet_key, $time_step = 180, $length = 6) {
    $counter = floor($_SESSION["otpTime"] / $time_step);
    $data    = pack("NN", 0, $counter);
    $hash    = hash_hmac('sha1', $data, $sercet_key, true);
    $offset  = ord(substr($hash, -1)) & 0x0F;
    $value   = unpack("N", substr($hash, $offset, 4));
    $otp     = ($value[1] & 0x7FFFFFFF) % pow(10, $length);

    return str_pad(strval($otp), $length, '0', STR_PAD_LEFT);
}

$otp = generateOTP($temp["password"]);

// ── Step 3b: Calculate elapsed time since OTP was issued ──────────────────────
// otpTime is the Unix timestamp stored by login_otp.php when the OTP was sent.
// The diff is computed in minutes for the 5-minute validity window check.
$otp_time         = isset($_SESSION['otpTime']) ? (int)$_SESSION['otpTime'] : 0;
$now              = time();
$otp_diff_seconds = max(0, $now - $otp_time);
$otp_diff_minutes = $otp_diff_seconds / 60.0;

// Store for debug convenience — visible in $_SESSION on the session inspect page
$_SESSION["now"]  = $now;
$_SESSION["diff"] = $otp_diff_minutes;

// ── Step 4: Validate OTP value and expiry ─────────────────────────────────────
// Skipped for staff/viewer roles — login_otp.php sets skip_otp=true in session
// so they never receive or enter an OTP. Admin/owner always go through this check.
if (empty($_SESSION['skip_otp'])) {
    if ($data["otp"] != $otp || $otp_diff_minutes > 5) {
        $answer["message"] = "Wrong OTP! Please try again. (Our OTP is valid for 5 minute)";
        exit(json_encode($answer));
    }
}

// ── Step 4b: Claim session — always replace existing token ────────────────────
// Password + OTP is full 2FA proof of identity, so we always grant the login.
// Writing a new token here also invalidates any prior session: db_auth.php
// compares session_token in the DB to the one stored in the PHP session, so the
// old device is kicked out on its next request. This also fixes the case where
// a PHP session expired without clearing the DB token, which would otherwise
// permanently block re-login.
$session_token = bin2hex(random_bytes(32));
$sth_claim = $pdo1->prepare(
    "UPDATE user
     SET session_token     = :token,
         session_token_at  = NOW(),
         session_last_seen = NOW()
     WHERE user_id = :uid"
);
$sth_claim->execute([
    ':token' => $session_token,
    ':uid'   => $user_id,
]);

if ($sth_claim->rowCount() !== 1) {
    $answer["message"] = "Login failed: user record not found.";
    exit(json_encode($answer));
}

// ── Step 5a: Regenerate session ID ────────────────────────────────────────────
// session_regenerate_id(true) issues a brand-new session ID and deletes the old
// session file, preventing session fixation attacks where an attacker pre-sets
// a session ID before the user logs in.
session_regenerate_id(true);

// ── Step 5b: Issue CSRF token ─────────────────────────────────────────────────
// A fresh 256-bit token is generated here and stored in session. All subsequent
// POST requests from the authenticated app must include this token in the
// X-CSRF-Token header (validated by individual engine endpoints).
$_SESSION['csrf_token'] = bin2hex(random_bytes(32));

// ── Step 5c: Write authenticated login session ────────────────────────────────
// These keys are read by db_auth.php on every subsequent request to gate access.
// login_company_id is the user's default_company — used to scope all DB queries.
$_SESSION["login_status"]         = 1;
$_SESSION['session_token']        = $session_token;
$_SESSION["login_user_id"]        = (int)$temp["user_id"];
$_SESSION["login_username"]       = $temp["username"];
$_SESSION["login_name"]           = $temp["name"];
$_SESSION["login_surname"]        = $temp["surname"];
$_SESSION["login_company_id"]     = $temp["default_company"];
$_SESSION["login_profile_picture"] = $temp["profile_picture"] ?? '';
$_SESSION["login_license"]         = $temp["license"] ?? 'user';
// Required by db_auth.php's per-request OTP integrity check. For skip_otp users
// (staff/viewer) this was never written by login_otp.php, so we set it here.
$_SESSION["otp"]                  = $otp;
// license='owner' means the user holds their own subscription — use user.app_access.
// license='user' means they were invited — use company_map_user.app_access instead.
$_SESSION["login_app_access"] = $temp["app_access"] ?? 'wms';

$role_sth = $pdo1->prepare(
    "SELECT role, app_access FROM company_map_user
     WHERE company_id = :company_id AND user_id = :user_id
     LIMIT 1"
);
$role_sth->execute([
    ':company_id' => $_SESSION["login_company_id"],
    ':user_id'    => $_SESSION["login_user_id"],
]);
$map_row = $role_sth->fetch(PDO::FETCH_ASSOC);
$_SESSION["login_role"] = $map_row['role'] ?? 'viewer';

if (($temp['license'] ?? 'owner') !== 'owner') {
    $_SESSION["login_app_access"] = $map_row['app_access'] ?? 'wms';
}

// ── Step 6: Respond ───────────────────────────────────────────────────────────
$answer["success"] = 1;
$answer["message"] = "Login Complete!";
exit(json_encode($answer));