Forms version follows coalition forms

api/src/Feature.Forms/FetchAll/Endpoint.cs

@@ -1,6 +1,5 @@
 using Feature.Forms.Models;
 using Microsoft.EntityFrameworkCore;
-using Vote.Monitor.Core.Helpers;
 using Vote.Monitor.Domain;
 using Vote.Monitor.Domain.Entities.FormAggregate;
 using Vote.Monitor.Domain.Entities.FormBase;
@@ -80,7 +79,9 @@ public override async Task<Results<Ok<NgoFormsResponseModel>, NotFound>> Execute
         return TypedResults.Ok(new NgoFormsResponseModel
         {
             ElectionRoundId = monitoringNgo.ElectionRoundId,
-            Version = DeterministicGuid.Create(resultForms.Select(x => x.Id)).ToString(),
+            // The same key as forms:version, so it changes when a form's content changes, not only the set of forms.
+            Version = await ObserverFormsVersion.GetAsync(context, req.ElectionRoundId, monitoringNgo.MonitoringNgoId,
+                monitoringNgo.FormsVersion, ct),
             Forms = resultForms.OrderBy(x => x.DisplayOrder).ThenBy(x => x.Code).ToList()
         });
     }

api/src/Feature.Forms/GetFormsVersion/Endpoint.cs

@@ -15,7 +15,7 @@ public override void Configure()
         Summary(s =>
         {
             s.Summary = "Gets current version of forms for users monitoring ngo";
-            s.Description = "Cache key changes every time any form changes";
+            s.Description = "Cache key changes every time any form the observer receives changes, coalition forms included";
         });
     }
 
@@ -28,7 +28,7 @@ public override async Task<Results<Ok<FormVersionResponseModel>, NotFound>> Exec
             .Where(x => x.ElectionRoundId == req.ElectionRoundId)
             .Where(x => x.Status == MonitoringObserverStatus.Active)
             .Where(x => x.MonitoringNgo.ElectionRoundId == req.ElectionRoundId)
-            .Select(x => new { x.MonitoringNgo.FormsVersion, x.MonitoringNgo.ElectionRoundId })
+            .Select(x => new { x.MonitoringNgoId, x.MonitoringNgo.FormsVersion, x.MonitoringNgo.ElectionRoundId })
             .FirstOrDefaultAsync(ct);
 
         if (monitoringNgo is null)
@@ -38,7 +38,9 @@ public override async Task<Results<Ok<FormVersionResponseModel>, NotFound>> Exec
 
         return TypedResults.Ok(new FormVersionResponseModel
         {
-            ElectionRoundId = monitoringNgo.ElectionRoundId, CacheKey = monitoringNgo.FormsVersion.ToString()
+            ElectionRoundId = monitoringNgo.ElectionRoundId,
+            CacheKey = await ObserverFormsVersion.GetAsync(context, req.ElectionRoundId, monitoringNgo.MonitoringNgoId,
+                monitoringNgo.FormsVersion, ct)
         });
     }
 }

api/src/Feature.Forms/ObserverFormsVersion.cs

@@ -0,0 +1,43 @@
+using Microsoft.EntityFrameworkCore;
+using Vote.Monitor.Core.Helpers;
+using Vote.Monitor.Domain;
+using Vote.Monitor.Domain.Entities.FormBase;
+
+namespace Feature.Forms;
+
+/// <summary>
+/// The cache key of the forms an observer's monitoring NGO hands out (<c>forms:version</c> and <c>forms:fetchAll</c>).
+/// An NGO's own <c>FormsVersion</c> changes whenever one of its forms changes, but in a coalition its observers also
+/// receive forms owned by other NGOs (<see cref="Vote.Monitor.Domain.Entities.CoalitionAggregate.CoalitionFormAccess"/>):
+/// the key therefore also follows those owners' versions and which forms are shared, so editing a published shared
+/// form or granting access to one gives every receiving NGO a new key.
+/// </summary>
+public static class ObserverFormsVersion
+{
+    public static async Task<string> GetAsync(VoteMonitorContext context, Guid electionRoundId, Guid monitoringNgoId,
+        Guid ownFormsVersion, CancellationToken ct)
+    {
+        var shared = await context.CoalitionFormAccess
+            .Where(x => x.MonitoringNgoId == monitoringNgoId && x.Coalition.ElectionRoundId == electionRoundId)
+            .Where(x => x.Form.FormType != FormType.CitizenReporting)
+            .Select(x => new { x.FormId, x.Form.MonitoringNgo.FormsVersion })
+            .AsNoTracking()
+            .ToListAsync(ct);
+
+        // Outside a coalition the key stays the NGO's own version, as before.
+        if (shared.Count == 0)
+        {
+            return ownFormsVersion.ToString();
+        }
+
+        var parts = shared
+            .Select(x => x.FormsVersion)
+            .Distinct()
+            .Order()
+            .Select(version => $"owner:{version}")
+            .Concat(shared.Select(x => x.FormId).Distinct().Order().Select(id => $"form:{id}"))
+            .Prepend($"own:{ownFormsVersion}");
+
+        return DeterministicGuid.Create(string.Join('|', parts)).ToString();
+    }
+}