Add invite-only group classes

Group classes can now be marked invite-only (us_offerings.access_mode).
Invite-only classes are hidden from the public catalog and reachable only
when the instructor lets someone in via one of three paths, managed from
My Lessons -> My Group Classes:

- Add students directly: enrols them now with a pending payment.
- Make available: grants registered students access to self-enrol through
  the normal paid flow (multi-select, emailed a notice).
- Invite by email: tokenised registration invite tied to the class for a
  non-account address; after they register the class becomes enrollable.
  Reuses an existing pending invite instead of sending a second link.

New us_group_access table records grants; GET /offerings merges granted
invite-only classes for the caller; enrolment requires a grant
(403 invite_required) and flips it to enrolled on success.

composer test (487), composer lint, composer cs all pass.

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

src/GroupClass/GroupAccessRepository.php

@@ -0,0 +1,132 @@
+<?php
+declare(strict_types=1);
+
+namespace Unsupervised\Schedular\GroupClass;
+
+class GroupAccessRepository {
+
+	private string $table;
+
+	public function __construct( private \wpdb $db ) {
+		$this->table = $db->prefix . 'us_group_access';
+	}
+
+	public function insert( GroupAccess $access ): int {
+		$this->db->insert(
+			$this->table,
+			[
+				'offering_id' => $access->offeringId,
+				'student_id'  => $access->studentId,
+				'email'       => $access->email,
+				'invite_id'   => $access->inviteId,
+				'status'      => $access->status,
+				'invited_by'  => $access->invitedBy,
+				'created_at'  => current_time( 'mysql' ),
+			],
+			[ '%d', '%d', '%s', '%d', '%s', '%d', '%s' ]
+		);
+
+		return $this->db->insert_id;
+	}
+
+	/**
+	 * Whether a student holds a live (invited or enrolled) grant for an offering.
+	 */
+	public function hasGrant( int $offeringId, int $studentId ): bool {
+		$count = (int) $this->db->get_var(
+			$this->db->prepare(
+				'SELECT COUNT(*) FROM %i WHERE offering_id = %d AND student_id = %d AND status IN ( %s, %s )',
+				$this->table,
+				$offeringId,
+				$studentId,
+				GroupAccess::STATUS_INVITED,
+				GroupAccess::STATUS_ENROLLED
+			)
+		);
+
+		return $count > 0;
+	}
+
+	/**
+	 * The offering ids a student holds a live grant for — the invite-only classes
+	 * to fold into their catalogue view.
+	 *
+	 * @return list<int>
+	 */
+	public function findGrantedOfferingIds( int $studentId ): array {
+		$rows = $this->db->get_col(
+			$this->db->prepare(
+				'SELECT DISTINCT offering_id FROM %i WHERE student_id = %d AND status IN ( %s, %s )',
+				$this->table,
+				$studentId,
+				GroupAccess::STATUS_INVITED,
+				GroupAccess::STATUS_ENROLLED
+			)
+		);
+
+		return array_values( array_map( \Unsupervised\Schedular\Val::int( ... ), $rows ) );
+	}
+
+	/**
+	 * All grants for an offering, newest first.
+	 *
+	 * @return list<GroupAccess>
+	 */
+	public function findByOffering( int $offeringId ): array {
+		$rows = $this->db->get_results(
+			$this->db->prepare(
+				'SELECT * FROM %i WHERE offering_id = %d ORDER BY id DESC',
+				$this->table,
+				$offeringId
+			)
+		);
+
+		return array_map( GroupAccess::fromRow( ... ), $rows ?? [] );
+	}
+
+	/**
+	 * Point email-invite grants for an address at the account created when the
+	 * invitation was accepted, so the granted class unlocks for the new student.
+	 * Only grants still awaiting an account (`student_id` NULL) are linked.
+	 */
+	public function linkStudentByEmail( string $email, int $studentId ): bool {
+		if ( '' === $email ) {
+			return false;
+		}
+
+		$sql = $this->db->prepare(
+			'UPDATE %i SET student_id = %d WHERE email = %s AND student_id IS NULL',
+			$this->table,
+			$studentId,
+			$email
+		);
+
+		return null !== $sql && false !== $this->db->query( $sql );
+	}
+
+	/**
+	 * Flip a student's live grant for an offering to enrolled.
+	 */
+	public function markEnrolled( int $offeringId, int $studentId ): bool {
+		return false !== $this->db->update(
+			$this->table,
+			[ 'status' => GroupAccess::STATUS_ENROLLED ],
+			[
+				'offering_id' => $offeringId,
+				'student_id'  => $studentId,
+			],
+			[ '%s' ],
+			[ '%d', '%d' ]
+		);
+	}
+
+	public function revoke( int $id ): bool {
+		return false !== $this->db->update(
+			$this->table,
+			[ 'status' => GroupAccess::STATUS_REVOKED ],
+			[ 'id' => $id ],
+			[ '%s' ],
+			[ '%d' ]
+		);
+	}
+}