remove the total history tracking and the priority queue for just tracking the variables.

dotnet/SafelyYou/Devices.cs

@@ -1,6 +1,4 @@
 using System.Collections.Concurrent;
-using System.Runtime.InteropServices;
-using SafelyYou.Config;
 
 namespace SafelyYou;
 
@@ -16,82 +14,68 @@ public sealed class KnownDevices
     public bool Contains(DeviceId deviceId) => _knownDevices.Contains(deviceId);
 }
 
-public readonly record struct HeartBeatRange(DateTimeOffset Start, DateTimeOffset? End);
-
 public sealed class DeviceHeartBeatHistory
 {
-    private readonly HeartBeatHistoryConfig _config;
-
     public enum AddResult { Added, OutOfSequence }
 
-    public DeviceHeartBeatHistory(HeartBeatHistoryConfig config) => _config = config;
+    public long NumberOfHeartBeats { get; private set; }
+    public DateTimeOffset? FirstHeartBeat { get; private set; }
+    public DateTimeOffset? LastHeartBeat { get; private set; }
 
-    private readonly PriorityQueue<HeartBeatRange, DateTimeOffset> _histories = 
-        // lowest priority is first, but this allows the highest date to be dequeued first
-        new PriorityQueue<HeartBeatRange, DateTimeOffset>(new InverseDateTimeComparer());
-
-    private sealed class InverseDateTimeComparer : IComparer<DateTimeOffset>
-    {
-        public int Compare(DateTimeOffset x, DateTimeOffset y) => -(x.CompareTo(y));
-    }
-
-    /// <summary>Returns Added, needed to be used as an expression</summary>
-    private static AddResult Replace(PriorityQueue<HeartBeatRange, DateTimeOffset> histories, HeartBeatRange updated)
-    {
-        histories.DequeueEnqueue(updated, updated.Start);
-        return AddResult.Added;
-    }
-
-    /// <summary>Returns Added, needed to be used as an expression</summary>
-    private static AddResult EnqueueNew(PriorityQueue<HeartBeatRange, DateTimeOffset> histories, DateTimeOffset sentAt)
-    {
-        histories.Enqueue(new HeartBeatRange(sentAt, null), sentAt);
-        return AddResult.Added;
-    }
-    
     public AddResult Add(DateTimeOffset sentAt)
     {
-        // check the latest first, assuming things are in order
+        // Reject heartbeats that arrive before the latest registered time.
-        // if it's "in the past" and doesn't make sense, return an error
+        // Gaps are fine: uptime can be derived from first, last, and count.
-        
+        if (LastHeartBeat is null)
-        // histories that are adjacent are combined, if there's more than a one minute gap (what about a margin of error?)
-        // then create a new entry. The margin is coming from the config. I've set it to 1 second.
-        
-        if (!_histories.TryPeek(out var last, out _))
-            return EnqueueNew(_histories, sentAt);
-
-        // last registered heartbeat is End if set, otherwise Start
-        return (sentAt, last.Start, last.End) switch
         {
-            var (sent, start, _) when sent < start => AddResult.OutOfSequence,
+            FirstHeartBeat = sentAt;
-            (var sent, _, { } end) when sent < end => AddResult.OutOfSequence,
+            LastHeartBeat = sentAt;
-            // no End yet: extend if within Window of Start
+            NumberOfHeartBeats = 1;
-            (var sent, var start, null) when sent <= start + _config.Window => Replace(_histories, last with { End = sentAt }),
+            return AddResult.Added;
-            // End set: extend if within Window of End
+        }
-            (var sent, _, { } end) when sent <= end + _config.Window => Replace(_histories, last with { End = sentAt }),
+
-            // gap larger than Window: start a new range
+        if (sentAt < LastHeartBeat)
-            _ => EnqueueNew(_histories, sentAt),
+            return AddResult.OutOfSequence;
-        };
+
+        // note: does not account for rejecting heartbeats that come between the one minute window.
+        LastHeartBeat = sentAt;
+        NumberOfHeartBeats++;
+        return AddResult.Added;
     }
 }
 
 public sealed class HeartBeatHistories
 {
-    private readonly HeartBeatHistoryConfig _config;
     private readonly ConcurrentDictionary<DeviceId, DeviceHeartBeatHistory> _histories = new();
 
-    public HeartBeatHistories(HeartBeatHistoryConfig config) => _config = config;
-
     public DeviceHeartBeatHistory.AddResult Add(DeviceId deviceId, DateTimeOffset sentAt)
     {
         if (!_histories.TryGetValue(deviceId, out var history))
         {
-            history = new(_config);
+            history = new();
             _histories[deviceId] = history;
         }
 
         return history.Add(sentAt);
     }
+
+    public double Uptime(DeviceId deviceId)
+    {
+        if (!_histories.TryGetValue(deviceId, out var history)) return 0;
+        
+        var heartBeatMinutes = 
+            (history.FirstHeartBeat, history.LastHeartBeat) switch
+            {
+                ({} first, {} second ) => (second - first).TotalMinutes,
+                (not null, null) => 1,
+                (null, _) => 0
+            };
+
+        if (heartBeatMinutes == 0) return 0L;
+
+        var uptime = (history.NumberOfHeartBeats / heartBeatMinutes) * 100L;
+        return uptime;
+    }
 }