From f9f34c6067a1e260ac8cd761c1f98bf2d6836b02 Mon Sep 17 00:00:00 2001
From: Maciej Hirsz <1096222+maciejhirsz@users.noreply.github.com>
Date: Thu, 21 Feb 2019 16:20:52 +0100
Subject: [PATCH] Downgrade block on disconnect (#114)

---
 packages/backend/src/Chain.ts | 39 ++++++++++++++++++++++++++++-------
 1 file changed, 31 insertions(+), 8 deletions(-)

diff --git a/packages/backend/src/Chain.ts b/packages/backend/src/Chain.ts
index d46c0d3..1701868 100644
--- a/packages/backend/src/Chain.ts
+++ b/packages/backend/src/Chain.ts
@@ -35,14 +35,7 @@ export default class Chain {
     this.nodes.add(node);
     this.feeds.broadcast(Feed.addedNode(node));
 
-    node.events.once('disconnect', () => {
-      node.events.removeAllListeners();
-
-      this.nodes.delete(node);
-      this.feeds.broadcast(Feed.removedNode(node));
-
-      this.events.emit('disconnect', this.nodeCount);
-    });
+    node.events.once('disconnect', () => this.removeNode(node));
 
     node.events.on('block', () => this.updateBlock(node));
     node.events.on('finalized', () => this.updateFinalized(node));
@@ -54,6 +47,19 @@ export default class Chain {
     this.updateFinalized(node);
   }
 
+  public removeNode(node: Node) {
+    node.events.removeAllListeners();
+
+    this.nodes.delete(node);
+    this.feeds.broadcast(Feed.removedNode(node));
+
+    this.events.emit('disconnect', this.nodeCount);
+
+    if (this.height === node.best.number) {
+      this.downgradeBlock();
+    }
+  }
+
   public addFeed(feed: Feed) {
     this.feeds.add(feed);
 
@@ -118,6 +124,23 @@ export default class Chain {
     console.log(`[${this.label}] ${node.name} imported ${height}, block time: ${node.blockTime / 1000}s, average: ${node.average / 1000}s | latency ${node.latency}`);
   }
 
+  private downgradeBlock() {
+    let height = 0 as Types.BlockNumber;
+
+    for (const node of this.nodes) {
+      if (this.height === node.best.number) {
+        return;
+      }
+
+      if (node.best.number > height) {
+        height = node.best.number;
+      }
+    }
+
+    this.height = height;
+    this.feeds.broadcast(Feed.bestBlock(this.height, this.blockTimestamp, this.averageBlockTime));
+  }
+
   private updateFinalized(node: Node) {
     if (node.finalized.gt(this.finalized)) {
       this.finalized = node.finalized;