feat: 初始功能

Services/Printing/PrintFileGuards.cs

@@ -0,0 +1,22 @@
+using CloudPrint.Client.Models;
+using System.IO;
+
+namespace CloudPrint.Client.Services.Printing;
+
+internal static class PrintFileGuards
+{
+    public static void EnsurePrintableFile(PrintJob job)
+    {
+        ArgumentNullException.ThrowIfNull(job);
+
+        if (string.IsNullOrWhiteSpace(job.PrinterName))
+        {
+            throw new InvalidOperationException("打印机名称不能为空");
+        }
+
+        if (string.IsNullOrWhiteSpace(job.FilePath) || !File.Exists(job.FilePath))
+        {
+            throw new FileNotFoundException("待打印文件不存在", job.FilePath);
+        }
+    }
+}