Merge pull request #127 from dangershony/segwit-wait-chain

Segwit check, wait for chain header to download

Breeze/src/Breeze.Wallet/LightWalletFeature.cs

-using Stratis.Bitcoin.Builder.Feature;
+using System;
+using System.Threading;
+using System.Threading.Tasks;
+using Stratis.Bitcoin.Builder.Feature;
 using Microsoft.Extensions.DependencyInjection;
 using NBitcoin;
 using NBitcoin.Protocol;
+using Stratis.Bitcoin;
 using Stratis.Bitcoin.Builder;
 using Stratis.Bitcoin.Connection;
 using Stratis.Bitcoin.Consensus;
 using Stratis.Bitcoin.Consensus.Deployments;
+using Stratis.Bitcoin.Utilities;
 using Stratis.Bitcoin.Wallet;
 using Stratis.Bitcoin.Wallet.Controllers;
 
@@ -18,15 +23,19 @@ namespace Breeze.Wallet
         private readonly IConnectionManager connectionManager;
         private readonly ConcurrentChain chain;
         private readonly NodeDeployments nodeDeployments;
+        private readonly IAsyncLoopFactory asyncLoopFactory;
+        private readonly FullNode.CancellationProvider cancellationProvider;
 
         public LightWalletFeature(IWalletSyncManager walletSyncManager, IWalletManager walletManager, IConnectionManager connectionManager, 
-            ConcurrentChain chain, NodeDeployments nodeDeployments)
+            ConcurrentChain chain, NodeDeployments nodeDeployments, IAsyncLoopFactory asyncLoopFactory, FullNode.CancellationProvider cancellationProvider)
         {
             this.walletSyncManager = walletSyncManager;
             this.walletManager = walletManager;
             this.connectionManager = connectionManager;
             this.chain = chain;
             this.nodeDeployments = nodeDeployments;
+            this.asyncLoopFactory = asyncLoopFactory;
+            this.cancellationProvider = cancellationProvider;
         }
 
         public override void Start()
@@ -36,9 +45,32 @@ namespace Breeze.Wallet
             this.walletManager.Initialize();
             this.walletSyncManager.Initialize();
 
+            this.StartDeploymentsChecksLoop();
+        }
+
+        public void StartDeploymentsChecksLoop()
+        {
+            var loopToken = CancellationTokenSource.CreateLinkedTokenSource(this.cancellationProvider.Cancellation.Token);
+            this.asyncLoopFactory.Run("LightWalletFeature.CheckDeployments", token =>
+                {
+                    if(!this.chain.IsDownloaded())
+                        return Task.CompletedTask;
+
+                    // check segwit activation on the chain of headers
+                    // if segwit is active signal to only connect to 
+                    // nodes that also signal they are segwit nodes
                     var flags = this.nodeDeployments.GetFlags(this.walletSyncManager.WalletTip);
                     if (flags.ScriptFlags.HasFlag(ScriptVerify.Witness))
                         this.connectionManager.AddDiscoveredNodesRequirement(NodeServices.NODE_WITNESS);
+
+                    // done checking
+                    loopToken.Cancel();
+                    
+                    return Task.CompletedTask;
+                },
+                loopToken.Token,
+                repeatEvery: TimeSpans.TenSeconds,
+                startAfter: TimeSpans.TenSeconds);
         }
 
         public override void Stop()