Adding player sensing

microservices/CharacterApi/Controllers/CharactersController.cs

@@ -13,6 +13,7 @@ namespace CharacterApi.Controllers;
 [Route("api/[controller]")]
 public class CharactersController : ControllerBase
 {
+    private static readonly TimeSpan PresenceTimeout = TimeSpan.FromSeconds(45);
     private readonly CharacterStore _characters;
     private readonly IHttpClientFactory _httpClientFactory;
     private readonly IConfiguration _configuration;
@@ -43,6 +44,7 @@ public class CharactersController : ControllerBase
             Name = req.Name.Trim(),
             Coord = new Coord { X = 0, Y = 0 },
             VisionRadius = 3,
+            LastSeenUtc = DateTime.UtcNow,
             CreatedUtc = DateTime.UtcNow
         };
 
@@ -89,6 +91,8 @@ public class CharactersController : ControllerBase
             return Forbid();
         }
 
+        await _characters.TouchAsync(id);
+
         _logger.LogInformation(
             "Visible locations requested for character {CharacterId} at ({X},{Y}) radius {VisionRadius} by user {UserId}",
             character.Id,
@@ -164,6 +168,53 @@ public class CharactersController : ControllerBase
         }
     }
 
+    [HttpGet("{id}/visible-characters")]
+    [Authorize(Roles = "USER,SUPER")]
+    public async Task<IActionResult> VisibleCharacters(string id)
+    {
+        var userId = User.FindFirstValue(ClaimTypes.NameIdentifier);
+        if (string.IsNullOrWhiteSpace(userId))
+            return Unauthorized();
+
+        var allowAnyOwner = User.IsInRole("SUPER");
+        var character = await _characters.GetByIdAsync(id);
+        if (character is null)
+            return NotFound();
+        if (!allowAnyOwner && character.OwnerUserId != userId)
+            return Forbid();
+
+        await _characters.TouchAsync(id);
+
+        var onlineSinceUtc = DateTime.UtcNow.Subtract(PresenceTimeout);
+        var visibleCharacters = await _characters.GetVisibleOthersAsync(
+            id,
+            character.Coord.X,
+            character.Coord.Y,
+            character.VisionRadius > 0 ? character.VisionRadius : 3,
+            onlineSinceUtc);
+
+        return Ok(visibleCharacters);
+    }
+
+    [HttpPost("{id}/heartbeat")]
+    [Authorize(Roles = "USER,SUPER")]
+    public async Task<IActionResult> Heartbeat(string id)
+    {
+        var userId = User.FindFirstValue(ClaimTypes.NameIdentifier);
+        if (string.IsNullOrWhiteSpace(userId))
+            return Unauthorized();
+
+        var allowAnyOwner = User.IsInRole("SUPER");
+        var character = await _characters.GetByIdAsync(id);
+        if (character is null)
+            return NotFound();
+        if (!allowAnyOwner && character.OwnerUserId != userId)
+            return Forbid();
+
+        await _characters.TouchAsync(id);
+        return Ok(new { lastSeenUtc = DateTime.UtcNow });
+    }
+
     [HttpPut("{id}/coord")]
     [Authorize(Roles = "USER,SUPER")]
     public async Task<IActionResult> UpdateCoord(string id, [FromBody] UpdateCharacterCoordRequest req)

microservices/CharacterApi/Models/Character.cs

@@ -17,5 +17,7 @@ public class Character
 
     public int VisionRadius { get; set; } = 3;
 
+    public DateTime LastSeenUtc { get; set; } = DateTime.UtcNow;
+
     public DateTime CreatedUtc { get; set; } = DateTime.UtcNow;
 }

microservices/CharacterApi/Models/VisibleCharacter.cs

@@ -0,0 +1,12 @@
+namespace CharacterApi.Models;
+
+public class VisibleCharacter
+{
+    public string Id { get; set; } = string.Empty;
+
+    public string Name { get; set; } = string.Empty;
+
+    public Coord Coord { get; set; } = new();
+
+    public DateTime LastSeenUtc { get; set; }
+}

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);