From bb5239ad5178e91df814ecd4682b20420ca06d0d Mon Sep 17 00:00:00 2001
From: Roman Rodionov <roman_rodionov@epam.com>
Date: Mon, 13 May 2024 11:11:41 +0200
Subject: [PATCH] #4548 - Cyclic chains disappear from canvas when try to Edit
 in the sequence mode (#4609)

- used lastNonEmptyNode instead of lastNode for cyclic chain end bond render

Co-authored-by: Dmitry Baranov <baranov.d.v.1988@gmail.com>
---
 .../renderers/sequence/SequenceRenderer.ts    |  2 +-
 .../domain/entities/monomer-chains/Chain.ts   | 19 +++++++++++++++++++
 2 files changed, 20 insertions(+), 1 deletion(-)

diff --git a/packages/ketcher-core/src/application/render/renderers/sequence/SequenceRenderer.ts b/packages/ketcher-core/src/application/render/renderers/sequence/SequenceRenderer.ts
index 58c0ef56a7..e8d3fbadb9 100644
--- a/packages/ketcher-core/src/application/render/renderers/sequence/SequenceRenderer.ts
+++ b/packages/ketcher-core/src/application/render/renderers/sequence/SequenceRenderer.ts
@@ -218,7 +218,7 @@ export class SequenceRenderer {
         const bondRenderer = new PolymerBondSequenceRenderer(
           polymerBond,
           chain.firstNode,
-          chain.lastNode,
+          chain.lastNonEmptyNode,
         );
         bondRenderer.show();
         polymerBond.setRenderer(bondRenderer);
diff --git a/packages/ketcher-core/src/domain/entities/monomer-chains/Chain.ts b/packages/ketcher-core/src/domain/entities/monomer-chains/Chain.ts
index 143490ba5a..8058ccae23 100644
--- a/packages/ketcher-core/src/domain/entities/monomer-chains/Chain.ts
+++ b/packages/ketcher-core/src/domain/entities/monomer-chains/Chain.ts
@@ -95,10 +95,29 @@ export class Chain {
     return this.subChains[this.subChains.length - 1];
   }
 
+  public get nodes() {
+    const nodes: SubChainNode[] = [];
+    this.subChains.forEach((subChain) => {
+      nodes.push(...subChain.nodes);
+    });
+
+    return nodes;
+  }
+
   public get lastNode() {
     return this.lastSubChain?.lastNode;
   }
 
+  public get lastNonEmptyNode() {
+    if (this.lastNode instanceof EmptySequenceNode) {
+      const nodes = this.nodes;
+
+      return nodes[nodes.length - 2];
+    } else {
+      return this.lastNode;
+    }
+  }
+
   public get firstSubChain() {
     return this.subChains[0];
   }