From 647ff9fd0b6a908e123d41620aa72ddf406275a2 Mon Sep 17 00:00:00 2001
From: Joachim Spange <joachim.spange@kd.kongsberg.com>
Date: Wed, 29 Jan 2025 13:59:40 +0100
Subject: [PATCH] =?UTF-8?q?=E2=9C=A8=20Parse=20date=20and=20time=20(mmddyy?=
 =?UTF-8?q?=20and=20hhmmss.sss)=20format=20to=20UTC=20DateTime(fullYear,?=
 =?UTF-8?q?=20month,=20day,=20hours,=20minutes,=20seconds,=20milliseconds,?=
 =?UTF-8?q?=20DateTimeKind.Utc)?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 src/NmeaParser/Nmea/NmeaMessage.cs | 62 ++++++++++++++++++++++++++++++
 1 file changed, 62 insertions(+)

diff --git a/src/NmeaParser/Nmea/NmeaMessage.cs b/src/NmeaParser/Nmea/NmeaMessage.cs
index 6566bca..a1cd9f2 100644
--- a/src/NmeaParser/Nmea/NmeaMessage.cs
+++ b/src/NmeaParser/Nmea/NmeaMessage.cs
@@ -309,6 +309,68 @@ namespace NmeaParser.Messages
             return TimeSpan.Zero;
         }
 
+        /// <summary>
+        /// Parse from mmddyy + hhmmss.ss to DateTime (used in e.g. Ggk)
+        /// https://receiverhelp.trimble.com/alloy-gnss/en-us/NMEA-0183messages_PTNL_GGK.html
+        /// </summary>
+        internal static DateTime? StringsToUtcDateTime(string dateField, string timeField)
+        {
+            if (string.IsNullOrWhiteSpace(dateField) || string.IsNullOrWhiteSpace(timeField))
+                return null;
+
+            // 2. Parse date (mmddyy)
+            //    - Typically the year is 2 digits; you must decide how to handle the century.
+            //    - For example, if year < 80 => 20xx; else => 19xx
+            if (dateField.Length < 6) return null;
+            if (!int.TryParse(dateField.Substring(0, 2), out int month)) return null;     // mm
+            if (!int.TryParse(dateField.Substring(2, 2), out int day)) return null;       // dd
+            if (!int.TryParse(dateField.Substring(4, 2), out int year)) return null;      // yy
+
+            int fullYear = (year < 80) ? (2000 + year) : (1900 + year);
+
+            // 3. Parse time (hhmmss.ss)
+            //    - The fractional seconds might be optional or might have variable length.
+            //    - Parse hours, minutes, and then the part after the decimal.
+            //    - Time can be "hhmmss", or "hhmmss.sss", etc.
+            // Example: "102939.00" => hh=10, mm=29, ss=39, fraction=0
+            if (timeField.Length < 6) return null;
+            if (!int.TryParse(timeField.Substring(0, 2), out int hours)) return null;     // hh
+            if (!int.TryParse(timeField.Substring(2, 2), out int minutes)) return null;   // mm
+
+            // The seconds part can have a decimal fraction
+            // So we split around the decimal point:
+            double secondsDouble;
+            if (timeField.Length > 4)
+            {
+                string secString = timeField.Substring(4);  // "39.00 in example above"
+                if (!double.TryParse(secString,
+                                     System.Globalization.NumberStyles.Float,
+                                     System.Globalization.CultureInfo.InvariantCulture,
+                                     out secondsDouble))
+                {
+                    return null;
+                }
+            }
+            else
+            {
+                secondsDouble = 0.0;
+            }
+            int seconds = (int)secondsDouble;
+            int milliseconds = (int)((secondsDouble - seconds) * 1000.0);
+
+            // 4. Construct the UTC DateTime
+            try
+            {
+                var result = new DateTime(fullYear, month, day, hours, minutes, seconds, milliseconds, DateTimeKind.Utc);
+                return result;
+            }
+            catch
+            {
+                // If the date/time is invalid (e.g. month=13, day=32), we return null or handle differently
+                return null;
+            }
+        }
+
         /// <summary>
         /// Indicates whether the current object is equal to another object of the same type.
         /// </summary>