Add provider-aware activity filter API

Legacy/F4SDM42WebApi/ActivityFilterService.cs

@@ -0,0 +1,63 @@
+using System.Collections.Generic;
+using System;
+using System.Threading;
+using System.Threading.Tasks;
+
+using C4IT.FASD.Base;
+using C4IT.Logging;
+
+using static C4IT.Logging.cLogManager;
+
+namespace C4IT.F4SD
+{
+    public partial class F4SDHelperService
+    {
+        private static readonly AsyncLocal<cActivityFilterPolicy> currentActivityFilters =
+            new AsyncLocal<cActivityFilterPolicy>();
+
+        private sealed class ActivityFilterScope : IDisposable
+        {
+            private readonly cActivityFilterPolicy previous;
+
+            public ActivityFilterScope(cActivityFilterPolicy filters)
+            {
+                previous = currentActivityFilters.Value;
+                currentActivityFilters.Value = filters;
+            }
+
+            public void Dispose()
+            {
+                currentActivityFilters.Value = previous;
+            }
+        }
+
+        internal IDisposable BeginActivityFilterScope(cActivityFilterPolicy filters)
+        {
+            return new ActivityFilterScope(filters);
+        }
+
+        internal async Task<string> ApplyActivityFiltersAsync(string baseFilter, cActivityFilterPolicy policy)
+        {
+            var result = await ActivityFilterCompiler.CompileAsync(policy ?? currentActivityFilters.Value, null);
+            if (!result.Success)
+            {
+                LogEntry($"Activity filter rejected (fail closed): {result.Error}", LogLevels.Error);
+                return null;
+            }
+
+            return string.IsNullOrWhiteSpace(result.Clause)
+                ? baseFilter
+                : $"({baseFilter}) AND ({result.Clause})";
+        }
+
+        internal cTicketActivityFilterCapabilities GetActivityFilterCapabilities()
+        {
+            return new cTicketActivityFilterCapabilities
+            {
+                Provider = ActivityFilterCompiler.ProviderName,
+                CommonFields = new List<string> { ActivityFilterCompiler.AssignmentGroupField },
+                ProviderFields = new List<string> { ActivityFilterCompiler.QueueField }
+            };
+        }
+    }
+}