#4548 - Cyclic chains disappear from canvas when try to Edit in the s…

…equence mode (#4609)

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

Co-authored-by: Dmitry Baranov <baranov.d.v.1988@gmail.com>

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);

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];
   }