From 689e7ffd96d9ca377760f862d105fb2eaebb1278 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Dawid=20P=C4=85gowski?= <dawidpag@protonmail.com>
Date: Wed, 23 Aug 2023 00:53:29 +0200
Subject: [PATCH] Increase the maximum date

The spec goes up to a full 2168 year, but the PLC date type goes up to 2169 June 06 which is represented by 65535 (max ushort value).
---
 S7.Net/Types/Date.cs | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/S7.Net/Types/Date.cs b/S7.Net/Types/Date.cs
index 980742e..ef6cc79 100644
--- a/S7.Net/Types/Date.cs
+++ b/S7.Net/Types/Date.cs
@@ -15,8 +15,14 @@ namespace S7.Net.Types
         
         /// <summary>
         /// Maximum allowed date for the IEC date type
+        /// <remarks>
+        /// Although the spec allows only a max date of 31-12-2168, the PLC IEC date goes up to 06-06-2169 (which is the actual
+        /// WORD max value - 65535) 
+        /// </remarks>
         /// </summary>
-        public static readonly System.DateTime IecMaxDate = new(year: 2168, month: 12, day: 31);
+        public static readonly System.DateTime IecMaxDate = new(year: 2169, month: 06, day: 06);
+        
+        private static readonly ushort MaxNumberOfDays = (ushort)(IecMaxDate - IecMinDate).TotalDays;
         
         /// <summary>
         /// Converts a word (2 bytes) to IEC date (<see cref="System.DateTime"/>)
@@ -29,6 +35,12 @@ namespace S7.Net.Types
             }
 
             var daysSinceDateStart = Word.FromByteArray(bytes);
+            if (daysSinceDateStart > MaxNumberOfDays)
+            {
+                throw new ArgumentException($"Read number exceeded the number of maximum days in the IEC date (read: {daysSinceDateStart}, max: {MaxNumberOfDays})", 
+                    nameof(bytes));
+            }
+            
             return IecMinDate.AddDays(daysSinceDateStart);
         }