#4724 After clicking the "Clear Canvas" button multiple times, a user has to click the "Undo" button multiple times to return the structure

[Copilot]

How did you fix the issue?

In Macromolecules mode, clicking "Clear Canvas" on an empty canvas created undo history entries, requiring multiple undo operations to restore a structure. Micro mode had no such issue due to a guard in the action handler.

Root cause: ClearTool unconditionally updated history regardless of canvas state. Macromolecules mode invokes ClearTool directly, bypassing the isBlank() check present in the ketcher-react action handler.

Fix: Added early return in ClearTool constructor when canvas is empty:

constructor(private readonly editor: CoreEditor) {
  this.editor = editor;

  // Only update history if there are entities to delete
  if (!this.editor.drawingEntitiesManager.hasDrawingEntities) {
    return;
  }

  this.history = new EditorHistory(editor);
  // ... rest of clear logic
}

This prevents history updates and object creation when clearing an already-empty canvas, making behavior consistent across both modes.

Check list

• unit-tests written
• e2e-tests written
• documentation updated
• PR name follows the pattern #1234 – issue name
• branch name doesn't contain '#'
• PR is linked with the issue
• base branch (master or release/xx) is correct
• task status changed to "Code review"
• reviewers are notified about the pull request

Original prompt

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This section details on the original issue you should resolve

<issue_title>After clicking the "Clear Canvas" button multiple times, a user has to click the "Undo" button multiple times to return the structure </issue_title>
<issue_description>Steps to Reproduce

1. Select Macromolecules mode:

2. Draw any structure on the canvas (for example click any structure in macromolecules library):

3. Click on the "Clear Canvas" button 5 times:

4. Click on the "Undo" button:

Actual behavior
The structure does not return to the canvas. To make it appear again, "Undo" button needs to be clicked same number of times as "Clear Canvas" button, inconsistently with the Micro mode, where the structure returns after 1 click no matter how many times "Clear Canvas" was clicked. Note: issue is reproduced in all layout modes (sequence, snake, flex).

Expected behavior
The structure returns to the canvas after 1 click

Screenshots

2024-05-31_19h47_00.mp4

Related to #4543

Desktop (please complete the following information):

• OS: Windows 10 Pro (version 22H2) x64
• Browser: Сhrome
• Version: (125.0.6422.113) x64

Ketcher version 2.21.0-rc.2, Build at 2024-05-31; 07:23:21</issue_description>

Comments on the Issue (you are @copilot in this section)

@d-mrzv Reproduced by agent - https://chatgpt.com/share/691608c7-6230-8002-bc7d-7a532a801346

• Fixes After clicking the "Clear Canvas" button multiple times, a user has to click the "Undo" button multiple times to return the structure  #4724

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