Respect shard concurrency limit

Myriad/Gateway/Cluster.cs

@@ -2,6 +2,7 @@
 using System.Collections.Concurrent;
 using System.Collections.Generic;
 using System.Linq;
+using System.Threading;
 using System.Threading.Tasks;
 
 using Myriad.Types;
@@ -46,33 +47,55 @@ namespace Myriad.Gateway
         public async Task Start(GatewayInfo.Bot info, ClusterSessionState? lastState = null)
         {
             if (lastState != null && lastState.Shards.Count == info.Shards)
-                await Resume(info.Url, lastState);
+                await Resume(info.Url, lastState, info.SessionStartLimit.MaxConcurrency);
             else
-                await Start(info.Url, info.Shards);
+                await Start(info.Url, info.Shards, info.SessionStartLimit.MaxConcurrency);
         }
 
-        public async Task Resume(string url, ClusterSessionState sessionState)
+        public async Task Resume(string url, ClusterSessionState sessionState, int concurrency)
         {
             _logger.Information("Resuming session with {ShardCount} shards at {Url}", sessionState.Shards.Count, url);
             foreach (var shardState in sessionState.Shards)
                 CreateAndAddShard(url, shardState.Shard, shardState.Session);
 
-            await StartShards();
+            await StartShards(concurrency);
         }
 
-        public async Task Start(string url, int shardCount)
+        public async Task Start(string url, int shardCount, int concurrency)
         {
             _logger.Information("Starting {ShardCount} shards at {Url}", shardCount, url);
             for (var i = 0; i < shardCount; i++)
                 CreateAndAddShard(url, new ShardInfo(i, shardCount), null);
 
-            await StartShards();
+            await StartShards(concurrency);
         }
 
-        private async Task StartShards()
+        private async Task StartShards(int concurrency)
         {
+            var lastTime = DateTimeOffset.UtcNow;
+            var identifyCalls = 0;
+            
             _logger.Information("Connecting shards...");
-            await Task.WhenAll(_shards.Values.Select(s => s.Start()));
+            foreach (var shard in _shards.Values)
+            {
+                if (identifyCalls >= concurrency)
+                {
+                    var timeout = lastTime + TimeSpan.FromSeconds(5.5);
+                    var delay = timeout - DateTimeOffset.UtcNow;
+
+                    if (delay > TimeSpan.Zero)
+                    {
+                        _logger.Information("Hit shard concurrency limit, waiting {Delay}", delay);
+                        await Task.Delay(delay);
+                    }
+
+                    identifyCalls = 0;
+                    lastTime = DateTimeOffset.UtcNow;
+                }
+
+                await shard.Start();
+                identifyCalls++;
+            }
         }
 
         private void CreateAndAddShard(string url, ShardInfo shardInfo, ShardSessionInfo? session)

Myriad/Types/Gateway/SessionStartLimit.cs

@@ -5,5 +5,6 @@
         public int Total { get; init; }
         public int Remaining { get; init; }
         public int ResetAfter { get; init; }
+        public int MaxConcurrency { get; init; }
     }
 }