feat: add invoice versioning models and enums

Distribution/Models/Enums.cs

@@ -18,6 +18,7 @@ namespace Distribution.Models
     public enum ShopPOStatus { Pending, PartiallyFulfilled, Fulfilled, Cancelled }
 
     public enum InvoiceStatus { Draft, Printed, Finalized }
+    public enum InvoiceVersionStage { Created, DraftEdited, Printed, Finalized }
 
     public enum PaymentStatus { Pending, PartiallyPaid, Paid }
 

Distribution/Models/Invoice.cs

@@ -21,6 +21,7 @@ namespace Distribution.Models
 
         public decimal TotalAmount { get; set; }
 
+        public ICollection<InvoiceItem> Items { get; set; } = new List<InvoiceItem>();
         public ICollection<Payment> Payments { get; set; } = new List<Payment>();
     }
 }

Distribution/Models/InvoiceItem.cs

@@ -0,0 +1,23 @@
+using System.ComponentModel.DataAnnotations.Schema;
+
+namespace Distribution.Models
+{
+    public class InvoiceItem : Template
+    {
+        public Guid FK_InvoiceId { get; set; }
+        [ForeignKey("FK_InvoiceId")]
+        public Invoice Invoice { get; set; }
+
+        public Guid? FK_ShopPOItemId { get; set; }
+        [ForeignKey("FK_ShopPOItemId")]
+        public ShopPOItem? ShopPOItem { get; set; }
+
+        public Guid FK_ItemId { get; set; }
+        [ForeignKey("FK_ItemId")]
+        public Item Item { get; set; }
+
+        public int Quantity { get; set; }
+        public decimal UnitPrice { get; set; }
+        public bool IsRemoved { get; set; }
+    }
+}

Distribution/Models/InvoiceVersion.cs

@@ -0,0 +1,19 @@
+using System.ComponentModel.DataAnnotations.Schema;
+
+namespace Distribution.Models
+{
+    // Immutable snapshot of an invoice's lines at a point in its lifecycle.
+    public class InvoiceVersion : Template
+    {
+        public Guid FK_InvoiceId { get; set; }
+        [ForeignKey("FK_InvoiceId")]
+        public Invoice Invoice { get; set; }
+
+        public int VersionNumber { get; set; }
+        public InvoiceVersionStage Stage { get; set; }
+        public decimal TotalAmount { get; set; }
+        public Guid CreatedBy { get; set; }
+
+        public ICollection<InvoiceVersionItem> Items { get; set; } = new List<InvoiceVersionItem>();
+    }
+}

Distribution/Models/InvoiceVersionItem.cs

@@ -0,0 +1,23 @@
+using System.ComponentModel.DataAnnotations.Schema;
+
+namespace Distribution.Models
+{
+    public class InvoiceVersionItem : Template
+    {
+        public Guid FK_InvoiceVersionId { get; set; }
+        [ForeignKey("FK_InvoiceVersionId")]
+        public InvoiceVersion InvoiceVersion { get; set; }
+
+        public Guid? FK_ShopPOItemId { get; set; }
+        [ForeignKey("FK_ShopPOItemId")]
+        public ShopPOItem? ShopPOItem { get; set; }
+
+        public Guid FK_ItemId { get; set; }
+        [ForeignKey("FK_ItemId")]
+        public Item Item { get; set; }
+
+        public int Quantity { get; set; }
+        public decimal UnitPrice { get; set; }
+        public bool IsRemoved { get; set; }
+    }
+}