Add invoice model

Distribution/Models/Invoice.cs

@@ -0,0 +1,30 @@
+using System.ComponentModel.DataAnnotations.Schema;
+
+namespace Distribution.Models
+{
+    public class Invoice : Template
+    {
+        public Guid FK_OrderId { get; set; }
+        [ForeignKey("FK_OrderId")]
+        public Order Order { get; set; }
+
+        public InvoiceStatus Status { get; set; } = InvoiceStatus.Draft;
+
+        public Guid CreatedByUserId { get; set; }
+        [ForeignKey("CreatedByUserId")]
+        public User CreatedByUser { get; set; }
+
+        public DateTime? PrintedAt { get; set; }
+        public Guid? PrintedByUserId { get; set; }
+        [ForeignKey("PrintedByUserId")]
+        public User? PrintedByUser { get; set; }
+
+        public DateTime? FinalizedAt { get; set; }
+        public Guid? FinalizedByUserId { get; set; }
+        [ForeignKey("FinalizedByUserId")]
+        public User? FinalizedByUser { get; set; }
+
+        /// <summary>Reflects current PO line items through Draft/Printed; locked at Finalized.</summary>
+        public decimal TotalAmount { get; set; }
+    }
+}