#5740 - Establishing connection between ambiguous phosphate and sugar works wrong

packages/ketcher-core/src/domain/entities/AmbiguousMonomer.ts

@@ -135,15 +135,38 @@ export class AmbiguousMonomer extends BaseMonomer implements IVariantMonomer {
   }
 
   public getValidSourcePoint(_secondMonomer?: BaseMonomer) {
-    return MONOMER_CLASS_TO_CONSTRUCTOR[
-      this.monomerClass
-    ].prototype.getValidSourcePoint.call(this, _secondMonomer);
+    const proto = MONOMER_CLASS_TO_CONSTRUCTOR[this.monomerClass].prototype;
+    return proto.getValidSourcePoint.call(
+      this._createContextProxy(proto),
+      _secondMonomer,
+    );
   }
 
   public getValidTargetPoint(_firstMonomer: BaseMonomer) {
-    return MONOMER_CLASS_TO_CONSTRUCTOR[
-      this.monomerClass
-    ].prototype.getValidTargetPoint.call(this, _firstMonomer);
+    const proto = MONOMER_CLASS_TO_CONSTRUCTOR[this.monomerClass].prototype;
+    return proto.getValidTargetPoint.call(
+      this._createContextProxy(proto),
+      _firstMonomer,
+    );
+  }
+
+  private _createContextProxy(proto: Record<string, unknown>) {
+    return new Proxy(this, {
+      get(target, prop, receiver) {
+        if (
+          typeof prop === 'string' &&
+          !(prop in AmbiguousMonomer.prototype) &&
+          prop in proto
+        ) {
+          const value = proto[prop];
+          if (typeof value === 'function') {
+            return (...args: unknown[]) => value.call(receiver, ...args);
+          }
+          return value;
+        }
+        return Reflect.get(target, prop, receiver);
+      },
+    });
   }
 
   public get SubChainConstructor() {

packages/ketcher-core/src/domain/entities/Phosphate.ts

@@ -1,10 +1,10 @@
 import { BaseMonomer } from './BaseMonomer';
 import { AttachmentPointName, MonomerItemType } from 'domain/types';
 import { Vec2 } from './vec2';
-import { Sugar } from './Sugar';
 import { PhosphateSubChain } from 'domain/entities/monomer-chains/PhosphateSubChain';
 import { SubChainNode } from 'domain/entities/monomer-chains/types';
 import { RnaSubChain } from 'domain/entities/monomer-chains/RnaSubChain';
+import { isSugarOrAmbiguousSugar } from 'domain/helpers/monomers';
 
 export class Phosphate extends BaseMonomer {
   constructor(monomerItem: MonomerItemType, _position?: Vec2) {
@@ -54,7 +54,7 @@ export class Phosphate extends BaseMonomer {
     }
 
     // If other monomer is not a Sugar, we want to open modal
-    if (!(otherMonomer instanceof Sugar)) {
+    if (!isSugarOrAmbiguousSugar(otherMonomer)) {
       return;
     }
     // If we chose a specific AP on other monomer, we want to determine the correct AP on this one

packages/ketcher-core/src/domain/entities/Sugar.ts

@@ -1,11 +1,13 @@
 import { BaseMonomer } from './BaseMonomer';
 import { RNABase } from './RNABase';
-import { Phosphate } from './Phosphate';
 import { AttachmentPointName } from 'domain/types';
 import { RnaSubChain } from 'domain/entities/monomer-chains/RnaSubChain';
 import { SubChainNode } from 'domain/entities/monomer-chains/types';
 import { PhosphateSubChain } from 'domain/entities/monomer-chains/PhosphateSubChain';
-import { isRnaBaseOrAmbiguousRnaBase } from 'domain/helpers/monomers';
+import {
+  isPhosphateOrAmbiguousPhosphate,
+  isRnaBaseOrAmbiguousRnaBase,
+} from 'domain/helpers/monomers';
 import { IVariantMonomer } from 'domain/entities/types';
 import { PolymerBond } from 'domain/entities/PolymerBond';
 
@@ -52,7 +54,7 @@ export class Sugar extends BaseMonomer {
 
     // If other monomer is neither a Phosphate nor RNABase, open modal
     if (
-      !(otherMonomer instanceof Phosphate) &&
+      !isPhosphateOrAmbiguousPhosphate(otherMonomer) &&
       !isRnaBaseOrAmbiguousRnaBase(otherMonomer)
     ) {
       return;

packages/ketcher-core/src/domain/helpers/monomers.ts

@@ -322,6 +322,26 @@ export function isRnaBaseOrAmbiguousRnaBase(
   );
 }
 
+export function isPhosphateOrAmbiguousPhosphate(
+  monomer?: BaseMonomer,
+): monomer is Phosphate | AmbiguousMonomer {
+  return (
+    monomer instanceof Phosphate ||
+    (monomer instanceof AmbiguousMonomer &&
+      monomer.monomerClass === KetMonomerClass.Phosphate)
+  );
+}
+
+export function isSugarOrAmbiguousSugar(
+  monomer?: BaseMonomer,
+): monomer is Sugar | AmbiguousMonomer {
+  return (
+    monomer instanceof Sugar ||
+    (monomer instanceof AmbiguousMonomer &&
+      monomer.monomerClass === KetMonomerClass.Sugar)
+  );
+}
+
 export function isRnaBaseApplicableForAntisense(monomer?: BaseMonomer) {
   return (
     monomer instanceof UnsplitNucleotide ||