Implement simple user creation system

Assets/Common/Scripts/UserCreationScreen.cs

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+using System;
+using System.Collections;
+using System.Collections.Generic;
+using System.Text.RegularExpressions;
+using TMPro;
+using UnityEngine;
+using UnityEngine.Events;
+using UnityEngine.SceneManagement;
+using UnityEngine.UI;
+
+public class UserCreationScreen : MonoBehaviour
+{
+    // Max length of a username
+    private const int MAX_USERNAME_LENGTH = 12;
+
+    [Header("UI References")]
+    // Reference to the input text field for username
+    public TMP_InputField inputName;
+    // Reference to the avatar-list container
+    public Transform avatarsContainer;
+
+    [Header("Prefab")]
+    // Avatar prefab
+    public GameObject avatarPrefab;
+    // List of all sprites that are supported as avatars
+    public List<Sprite> sprites = new List<Sprite>();
+
+    [Header("Users List")]
+    // Reference to the UserList ScriptableObject
+    public UserList users;
+
+    [SerializeField]
+    // Current selected avatar
+    private int selectedAvatar = 0;
+    // List of references to avatar background sprites (so we can color them nicely)
+    private List<Image> avatars = new List<Image>();
+
+
+    void Start()
+    {
+        for (int i = 0; i < sprites.Count; i++)
+        {
+            // Create instance of prefab
+            GameObject instance = GameObject.Instantiate(avatarPrefab, avatarsContainer);
+
+            // Store value of i so we can use it the callback (else it would get the value of sprites.Count)
+            int x = i;
+            // Add onClick callback
+            instance.GetComponent<Button>().onClick.AddListener(() => UpdateAvatar(x));
+
+            // Store reference to image for fancy coloring
+            Image background = instance.GetComponent<Image>();
+            avatars.Add(background);
+            // Set background color
+            background.color = selectedAvatar == i ? Color.blue : Color.gray;
+            // Find correct component for setting the sprite
+            foreach (Image img in background.GetComponentsInChildren<Image>())
+                if (img != background)
+                {
+                    img.sprite = sprites[i];
+                    break;
+                }
+        }
+    }
+
+    // Update the current selected avatar
+    private void UpdateAvatar(int newAvatar)
+    {
+        avatars[selectedAvatar].color = Color.gray;
+        selectedAvatar = newAvatar;
+        avatars[selectedAvatar].color = Color.blue;
+    }
+
+    // Check if a given string is a correct username (using Regex)
+    static public bool IsValidUsername(string username)
+    {
+        return new Regex($@"^[abcdefghijklmnopqrstuvwxyz]{{1,{MAX_USERNAME_LENGTH}}}$").IsMatch(username);
+    }
+
+    // Create a new user (will be called by button)
+    public void CreateUser()
+    {
+        string username = inputName.text;
+        if (IsValidUsername(username))
+        {
+            if (!users.GetUserByUsername(username))
+            {
+                // Create a new entry in the UserList ScriptableObject
+                users.CreateAndAddNewUser(username, sprites[selectedAvatar]);
+                // TODO: change scene, for now just change to StartScreen
+                SceneManager.LoadScene("Common/Scenes/StartScreen");
+            }
+            // TODO: give more feedback to user
+            // Warn user that username already exists
+            else Debug.LogWarning($"Username '{username}' already exists!");
+        }
+        // TODO: give more feedback to user
+        // Warn user that username is invalid
+        else Debug.LogWarning($"Invalid username '{username}'!");
+    }
+}