Xtext - AutoEdits with backspace

Question

Assume following situation: We have a document, which contains spaces
( for example denoted as _ ) And we have caret behind those (4)spaces

_ _ _ _|

I want editor to delete all 4 spaces instead of one when user presses backspace.

I am extending DefaultIndentLineAutoEditStrategy where I override following method

public void customizeDocumentCommand(IDocument d, DocumentCommand c)

I am facing two problems:

1. How to detect backspace have been used from DocumentCommand? If you use newline c.text contains "\n" or "\r\n" but if you use backspace it equals to "".
2. How do I insert 3 more backspaces? Appending "\b" to c.text does not work.

Answer 1

Ok I managed to implement it.

1. if (c.text.equals("") && c.length == 1) condition detects usage of backspace/delete
2. Deleting 3 more characters can be done as following:
   c.offset-=3; c.length=4;

whole implementation can look like this:

private void handleBackspace(IDocument d, DocumentCommand c) {
        if (c.offset == -1 || d.getLength() == 0)
            return;
        int p = (c.offset == d.getLength() ? c.offset - 1 : c.offset);
        IRegion info;
        try {
            info = d.getLineInformationOfOffset(p);
            String line = d.get(info.getOffset(), info.getLength());
            int lineoffset = info.getOffset();
            /*Make sure unindent is made only if user is indented and has caret in correct position */
            if ((p-lineoffset+1)%4==0&&((line.startsWith("    ") && !line.startsWith("     ")) || (line.startsWith("        ") && !line.startsWith("         ")))){ //1 or 2 level fixed indent
                c.offset-=3;
                c.length=4;
            }

        }catch (org.eclipse.jface.text.BadLocationException e) {
            e.printStackTrace();
        }
    }