Add open student registration with email confirmation and approval

Students could previously join by invite only. Add an optional
self-approval mode, toggled from Studio Settings → Registration: anyone
may sign up on the existing [us_student_register] page, confirm their
email via a tokenised link, and then be approved by a studio admin
before the account is usable.

- Enabling the toggle mirrors WordPress's own membership settings
  (users_can_register + default_role = us_student) and snapshots their
  previous values so disabling restores them.
- WordPress's native registration form is blocked while open
  registration is on (login_init redirect + registration_errors
  fail-safe + register_url) so it cannot bypass signup policy acceptance.
- Pending accounts: unconfirmed email cannot log in; confirmed but
  unapproved can log in but the booking capability is withheld and the
  booking page shows an "awaiting approval" screen.
- Approve/reject from Students → Pending Students; reject hard-deletes
  the account so the email is freed to re-apply.
- Invite registration is unchanged; both modes coexist.

Account lifecycle lives in user meta (RegistrationStatus); no new tables.

Closes #63

Co-Authored-By: Claude Opus 4.8 <[email protected]>

src/Payment/StudioSettings.php

@@ -16,6 +16,18 @@ class StudioSettings {
 	public const OPT_ETRANSFER_EMAIL = 'us_etransfer_email';
 	public const OPT_HST_RATE        = 'us_hst_rate';
 
+	public const OPT_REGISTRATION_MODE = 'us_registration_mode';
+	public const MODE_INVITE           = 'invite';
+	public const MODE_SELF_APPROVAL    = 'self_approval';
+
+	/**
+	 * Snapshots of the two core WordPress options this feature takes over while
+	 * open registration is enabled, so disabling restores them exactly rather
+	 * than clobbering a site that set them for its own reasons.
+	 */
+	public const OPT_PREV_USERS_CAN_REGISTER = 'us_registration_prev_can_register';
+	public const OPT_PREV_DEFAULT_ROLE       = 'us_registration_prev_default_role';
+
 	public function publishableKey(): string {
 		return Val::string( get_option( self::OPT_PUBLISHABLE, '' ) );
 	}
@@ -65,6 +77,24 @@ class StudioSettings {
 		return '' !== $this->publishableKey() && '' !== $this->secretKey();
 	}
 
+	/**
+	 * Which student registration mode is active: `invite` (default) — only a
+	 * valid invite token grants the registration form — or `self_approval` —
+	 * anyone may sign up, confirm their email, and await studio approval.
+	 */
+	public function registrationMode(): string {
+		return self::MODE_SELF_APPROVAL === get_option( self::OPT_REGISTRATION_MODE, self::MODE_INVITE )
+			? self::MODE_SELF_APPROVAL
+			: self::MODE_INVITE;
+	}
+
+	/**
+	 * Whether anyone may self-register (the `self_approval` mode).
+	 */
+	public function openRegistrationEnabled(): bool {
+		return self::MODE_SELF_APPROVAL === $this->registrationMode();
+	}
+
 	public function renderPage(): void {
 		if ( ! current_user_can( RoleManager::CAP_MANAGE_BILLING ) ) {
 			wp_die( esc_html__( 'You do not have permission to manage billing settings.', 'unsupervised-schedular' ) );
@@ -86,6 +116,7 @@ class StudioSettings {
 		$etransferEmail   = $this->etransferEmail();
 		$hstRate          = $this->hstRate();
 		$stripeConfigured = $this->isStripeConfigured();
+		$openRegistration = $this->openRegistrationEnabled();
 
 		include USC_PLUGIN_DIR . 'templates/admin/settings.php';
 	}
@@ -111,6 +142,43 @@ class StudioSettings {
 		// phpcs:ignore WordPress.Security.ValidatedSanitizedInput.MissingUnslash, WordPress.Security.ValidatedSanitizedInput.InputNotSanitized -- Val::float() coerces to float; slashes cannot survive numeric coercion.
 		$hstRate = isset( $_POST['hst_rate'] ) ? Val::float( $_POST['hst_rate'] ) : 0.0;
 		update_option( self::OPT_HST_RATE, max( 0.0, $hstRate ) );
+
+		$this->applyRegistrationMode( isset( $_POST['open_registration'] ) );
 		// phpcs:enable WordPress.Security.NonceVerification.Missing
 	}
+
+	/**
+	 * Enable or disable open (self-approval) registration, mirroring the change
+	 * into the two core WordPress options it depends on.
+	 *
+	 * Enabling snapshots the current `users_can_register` and `default_role`,
+	 * then turns registration on and makes Student the default new-user role.
+	 * Disabling restores that snapshot, so this toggle never permanently
+	 * overwrites a site's own membership settings. Only transitions act, so
+	 * saving unrelated settings leaves the core options untouched.
+	 */
+	private function applyRegistrationMode( bool $enable ): void {
+		$currentlyOpen = $this->openRegistrationEnabled();
+
+		if ( $enable && ! $currentlyOpen ) {
+			update_option( self::OPT_PREV_USERS_CAN_REGISTER, get_option( 'users_can_register' ) ? '1' : '0' );
+			update_option( self::OPT_PREV_DEFAULT_ROLE, Val::string( get_option( 'default_role', 'subscriber' ) ) );
+
+			update_option( 'users_can_register', '1' );
+			update_option( 'default_role', RoleManager::STUDENT );
+			update_option( self::OPT_REGISTRATION_MODE, self::MODE_SELF_APPROVAL );
+			return;
+		}
+
+		if ( ! $enable && $currentlyOpen ) {
+			$prevCanRegister = '1' === Val::string( get_option( self::OPT_PREV_USERS_CAN_REGISTER, '0' ) );
+			$prevRole        = Val::string( get_option( self::OPT_PREV_DEFAULT_ROLE, 'subscriber' ) );
+
+			update_option( 'users_can_register', $prevCanRegister ? '1' : '0' );
+			update_option( 'default_role', '' !== $prevRole ? $prevRole : 'subscriber' );
+			delete_option( self::OPT_PREV_USERS_CAN_REGISTER );
+			delete_option( self::OPT_PREV_DEFAULT_ROLE );
+			update_option( self::OPT_REGISTRATION_MODE, self::MODE_INVITE );
+		}
+	}
 }