Refactor backend into domain-first slices

apps/backend/Universe/Api/StreamWorldHandler.cs

@@ -0,0 +1,53 @@
+using System.Text.Json;
+using FastEndpoints;
+
+namespace SpaceGame.Api.Universe.Api;
+
+public sealed class StreamWorldHandler(WorldService worldService) : EndpointWithoutRequest
+{
+  private static readonly JsonSerializerOptions SseJsonOptions = new(JsonSerializerDefaults.Web);
+
+  public override void Configure()
+  {
+    Get("/api/world/stream");
+    AllowAnonymous();
+  }
+
+  public override async Task HandleAsync(CancellationToken cancellationToken)
+  {
+    HttpContext.Response.Headers.Append("Cache-Control", "no-cache");
+    HttpContext.Response.Headers.Append("Content-Type", "text/event-stream");
+
+    var afterSequenceRaw = HttpContext.Request.Query["afterSequence"].ToString();
+    _ = long.TryParse(afterSequenceRaw, out var afterSequence);
+
+    var scopeKind = HttpContext.Request.Query["scopeKind"].ToString();
+    if (string.IsNullOrWhiteSpace(scopeKind))
+    {
+      scopeKind = HttpContext.Request.Query["scope"].ToString();
+    }
+
+    if (string.IsNullOrWhiteSpace(scopeKind))
+    {
+      scopeKind = "universe";
+    }
+
+    var systemId = HttpContext.Request.Query["systemId"].ToString();
+    var bubbleId = HttpContext.Request.Query["bubbleId"].ToString();
+    var scope = new ObserverScope(
+      scopeKind,
+      string.IsNullOrWhiteSpace(systemId) ? null : systemId,
+      string.IsNullOrWhiteSpace(bubbleId) ? null : bubbleId);
+    var stream = worldService.Subscribe(scope, afterSequence, cancellationToken);
+
+    await HttpContext.Response.WriteAsync(": connected\n\n", cancellationToken);
+    await HttpContext.Response.Body.FlushAsync(cancellationToken);
+
+    await foreach (var delta in stream.ReadAllAsync(cancellationToken))
+    {
+      var payload = JsonSerializer.Serialize(delta, SseJsonOptions);
+      await HttpContext.Response.WriteAsync($"event: world-delta\ndata: {payload}\n\n", cancellationToken);
+      await HttpContext.Response.Body.FlushAsync(cancellationToken);
+    }
+  }
+}