!7

!include #1006440 // Concepts

sclass EditRecorder {
  Session session;
  
  // editor state
  S text = "";
  int caret;
  
  bool verbose = true;
  
  // update the text
  void update(S newText) {
    S a = text, b = newText;
    int i = lCommonPrefix(a, b);
    a = substring(a, i);
    b = substring(b, i);
    int j = lCommonSuffix(a, b);
    a = substring(a, 0, l(a)-j);
    b = substring(b, 0, l(b)-j);
    
    // Now differing part remains in a and b;
    // i and j give length of unchanged beginning+end
    
    if (empty(a) && empty(b)) {
      if (verbose) print("no change");
      ret;
    }
    
    EChange change = cnew(EChange, +session,
      startIndex := i, endIndex := i+l(a), text := b);
    if (verbose) print("change: " + renderConcept(change));
    
    // Verify the change we made
    assertEquals(newText, replayEdit(change, text));
    text = newText;
  }
  
  void updateCaret(int pos) {
    if (pos != caret) {
      cnew(ECaret, +session, +pos);
      caret = pos;
    }
  }
}

static Session session;
static JTextArea ta;
static EditRecorder er;

p-substance {
  db(); // persistence
  session = new Session;
  print("Session: " + session.id);
  ta = showText("");
  er = nu(EditRecorder, +session);
  onUpdate(ta, r { er.update(ta.getText()) });
  onCaret(ta, r { er.updateCaret(ta.getCaretPosition()) });
}

Began life as a copy of #1006437