first commit

Nitrox.Launcher/Models/Validators/BackupAttribute.cs

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+using System;
+using System.ComponentModel.DataAnnotations;
+using System.IO;
+using Nitrox.Launcher.Models.Design;
+
+namespace Nitrox.Launcher.Models.Validators;
+
+/// <summary>
+///     Checks that value is a usable <see cref="BackupItem" />.
+/// </summary>
+public sealed class BackupAttribute : TypedValidationAttribute<BackupItem>
+{
+    protected override ValidationResult IsValid(BackupItem value, ValidationContext context)
+    {
+        if (value == null)
+        {
+            return new ValidationResult($"{context.DisplayName} must not be null.");
+        }
+        if (value.BackupFileName == null || value.BackupFileName.AsSpan().Trim().IsEmpty)
+        {
+            return new ValidationResult($"{context.DisplayName} must have a backup path assigned");
+        }
+        if (!File.Exists(value.BackupFileName))
+        {
+            return new ValidationResult($"{context.DisplayName} must point to a valid file.");
+        }
+        return ValidationResult.Success;
+    }
+}