Include getlatest endpoint in yaml and call before shipcall sync in reg update

misc/BreCalApi.yaml

@@ -457,8 +457,43 @@ paths:
           $ref: '#/components/responses/500'
         '503':
           $ref: '#/components/responses/503'
+  /getlatest:
+    get:
+      description: 'Returns timestamps for latest data changes'
+      summary: Get latest timestamps of changes
+      tags:
+        - shipcall
+      operationId: getLatest      
+      responses:
+        '200':
+          description: ship call list
+          content:
+            application/json:
+              schema:
+                $ref: '#/components/schemas/latest'        
+        '401':
+          $ref: '#/components/responses/401'
+        '500':
+          $ref: '#/components/responses/500'
+        '503':
+          $ref: '#/components/responses/503'
 components:
   schemas:
+    latest:
+      type: object
+      properties:
+        shipcalls:
+          type: string
+          format: date-time
+          nullable: true
+        times:
+          type: string
+          format: date-time
+          nullable: true
+        ship:
+          type: string
+          format: date-time
+          nullable: true
     credentials:
       type: object
       properties:

src/BreCalClient/MainWindow.xaml.cs

@@ -39,7 +39,7 @@ namespace BreCalClient
         #region Fields
 
         //private static int _uiUpdateRunning = 0;
-        private static SemaphoreSlim uiLock = new SemaphoreSlim(1);
+        private static readonly SemaphoreSlim uiLock = new SemaphoreSlim(1);
 
         private Credentials? _credentials;
 
@@ -65,6 +65,10 @@ namespace BreCalClient
         // private bool _sequenceChanged = false;
         private HistoryDialog? _historyDialog;
 
+        // Fields to store the latest check flags
+        private DateTime? _latestShipcall;
+        private DateTime? _latestShip;
+
         #endregion
 
         #region Enums
@@ -443,7 +447,47 @@ namespace BreCalClient
                 }
 
                 List<Shipcall>? shipcalls = null;
+                bool skipShipLoad, skipShipcallLoad;
+                skipShipLoad = false;
+                skipShipcallLoad = false;
+
                 try
+                {
+                    // this only works with API v1.3 onwards
+                    Latest latest = await _shipcallApi.GetLatestAsync();
+                    
+                    if (latest != null)
+                    {
+                        // compare timestamps to decide whether an update is required
+                        if ((_latestShip != null) && ((latest.Ship.HasValue &&
+                                                      (latest.Ship.Value <= _latestShip.Value)) ||
+                                                      !_latestShip.HasValue)
+                                                      )
+                        {
+                            skipShipLoad = true;
+                        }
+
+                        if(!skipShipLoad)
+                        {
+                            _latestShip = latest.Ship ?? DateTime.Now;
+                        }
+
+
+                        if ((_latestShipcall != null) && ((latest.Shipcalls.HasValue &&
+                                                         (latest.Shipcalls.Value <= _latestShipcall.Value)) ||
+                                                         !_latestShipcall.HasValue)
+                                                      )
+                        {
+                            skipShipcallLoad = true;
+                        }
+
+                        if(!skipShipcallLoad)
+                        {
+                            _latestShipcall = latest.Shipcalls ?? DateTime.Now;
+                        }
+                    }
+
+                    if (!skipShipcallLoad)
                     {
                         if (this.searchPastDays != 0)
                             shipcalls = await _shipcallApi.ShipcallsGetAsync(this.searchPastDays);
@@ -458,6 +502,7 @@ namespace BreCalClient
                             generalProgressStatus.Value = 0;
                         }));
                     }
+                }
                 catch (Exception ex)
                 {
                     this.Dispatcher.Invoke(new Action(() =>