Adding player sensing

microservices/CharacterApi/Services/CharacterStore.cs

@@ -17,6 +17,8 @@ public class CharacterStore
 
         var ownerIndex = Builders<Character>.IndexKeys.Ascending(c => c.OwnerUserId);
         _col.Indexes.CreateOne(new CreateIndexModel<Character>(ownerIndex));
+        var coordIndex = Builders<Character>.IndexKeys.Ascending("Coord.X").Ascending("Coord.Y");
+        _col.Indexes.CreateOne(new CreateIndexModel<Character>(coordIndex));
     }
 
     public Task CreateAsync(Character character) => _col.InsertOneAsync(character);
@@ -30,11 +32,38 @@ public class CharacterStore
     public async Task<bool> UpdateCoordAsync(string id, Coord coord)
     {
         var filter = Builders<Character>.Filter.Eq(c => c.Id, id);
-        var update = Builders<Character>.Update.Set(c => c.Coord, coord);
+        var update = Builders<Character>.Update
+            .Set(c => c.Coord, coord)
+            .Set(c => c.LastSeenUtc, DateTime.UtcNow);
         var result = await _col.UpdateOneAsync(filter, update);
         return result.ModifiedCount > 0 || result.MatchedCount > 0;
     }
 
+    public async Task<bool> TouchAsync(string id)
+    {
+        var filter = Builders<Character>.Filter.Eq(c => c.Id, id);
+        var update = Builders<Character>.Update.Set(c => c.LastSeenUtc, DateTime.UtcNow);
+        var result = await _col.UpdateOneAsync(filter, update);
+        return result.ModifiedCount > 0 || result.MatchedCount > 0;
+    }
+
+    public Task<List<VisibleCharacter>> GetVisibleOthersAsync(string characterId, int x, int y, int radius, DateTime onlineSinceUtc) =>
+        _col.Find(c =>
+                c.Id != characterId &&
+                c.Coord.X >= x - radius &&
+                c.Coord.X <= x + radius &&
+                c.Coord.Y >= y - radius &&
+                c.Coord.Y <= y + radius &&
+                c.LastSeenUtc >= onlineSinceUtc)
+            .Project(c => new VisibleCharacter
+            {
+                Id = c.Id ?? string.Empty,
+                Name = c.Name,
+                Coord = c.Coord,
+                LastSeenUtc = c.LastSeenUtc
+            })
+            .ToListAsync();
+
     public async Task<bool> DeleteForOwnerAsync(string id, string ownerUserId, bool allowAnyOwner)
     {
         var filter = Builders<Character>.Filter.Eq(c => c.Id, id);