Create UserNameColorGenerator used to generate a user name color from user id

Riot/Utils/UserNameColorGenerator.swift

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+/*
+ Copyright 2019 New Vector Ltd
+ 
+ Licensed under the Apache License, Version 2.0 (the "License");
+ you may not use this file except in compliance with the License.
+ You may obtain a copy of the License at
+ 
+ http://www.apache.org/licenses/LICENSE-2.0
+ 
+ Unless required by applicable law or agreed to in writing, software
+ distributed under the License is distributed on an "AS IS" BASIS,
+ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ See the License for the specific language governing permissions and
+ limitations under the License.
+ */
+
+import Foundation
+import UIKit
+
+/// Generate a user name color from user id
+@objcMembers
+final class UserNameColorGenerator: NSObject {
+    
+    // MARK: - Properties
+    
+    /// User name colors.
+    var userNameColors: [UIColor] = []
+    
+    /// Fallback color when `userNameColors` is empty.
+    var defaultColor: UIColor = .black
+    
+    // MARK: - Public
+    
+    /// Generate a user name color from the user ID.
+    ///
+    /// - Parameter userId: The user ID of the user.
+    /// - Returns: A color associated to the user ID.
+    func color(from userId: String) -> UIColor {
+        guard self.userNameColors.isEmpty == false else {
+            return self.defaultColor
+        }
+        
+        guard userId.isEmpty == false else {
+            return self.userNameColors[0]
+        }
+        
+        let senderNameColorIndex = Int(userId.vc_hashCode % Int32(self.userNameColors.count))
+        return self.userNameColors[senderNameColorIndex]
+    }
+}