Add Class.addUser and scaffolding for Class.removeUser

lib/Class.js

@@ -206,12 +206,40 @@ class Class {
 		}).length;
 	}
 
-	addTeacher() {
+	async addUser(u) {
+		const validTypes = [ 'account', 'student' ];
 
+		if (!validTypes.includes(u.type))
+			throw new Error('Invalid user type');
+
+		const sql = `
+			insert into ${u.type}ClassLink(
+				${u.type}Id,
+				classId)
+			values
+				(?, ?);
+		`;
+
+		try {
+			await this.#conn.runQuery(sql, [
+				u.id,
+				this.id
+			]);
+		} catch (e) {
+			console.error(e);
+			throw new Error('Could not add user to class');
+		}
 	}
 
-	removeTeacher() {
-
+	removeUser(u) {
+		switch (u.type) {
+			case 'account':
+				break;
+			case 'student':
+				break;
+			default:
+				throw new Error('Invalid user type');
+		}
 	}
 
 	calculateAverageMovement() {