sclass HCRUD_Data {
  new Map<S, Renderer> renderers;
  new SS fieldHelp;
  
  abstract sclass Renderer {
    swappable O preprocessValue(O value) { ret value; }
  }
  
  srecord TextArea(int cols, int rows) extends Renderer {
    // star constructor syntax not working here (transpiler bug)
    TextArea(int cols, int rows, IF1 preprocessValue) {
      this.cols = cols;
      this.rows = rows;
      this.preprocessValue = preprocessValue;
    }
  }
  
  srecord TextField(int cols) extends Renderer {}
  srecord ComboBox(LS entries) extends Renderer {
    // help find item to select
    swappable S valueToEntry(O value) { ret strOrNull(value); }
    
    ComboBox(S... entries) { this(asList(entries)); }
    
    // star constructor syntax not working here (transpiler bug)
    ComboBox(LS entries, IF1<O, S> valueToEntry) {
      this.entries = entries;
      this.valueToEntry = valueToEntry;
    }
  }
  srecord CheckBox() extends Renderer {}
  
  srecord FlexibleLengthList(Renderer itemRenderer) extends Renderer {}

  S itemName() { ret "object"; }
  S itemNamePlural() { ret plural(itemName()); }
  
  //LS fields() { null; }
  
  L<MapSO> list() { null; }
  L<MapSO> list(IntRange range) { ret subListOrFull(list(), range); }
  
  S idField() { ret "id"; }
  Map<S, O> emptyObject() { null; }
  Map<S, O> getObject(O id) { null; }
  
  // return ID
  O createObject(SS map) { throw unimplemented(); }
  
  // return text msg
  S deleteObject(O id) { throw unimplemented(); }
  
  bool objectCanBeDeleted(O id) { true; }
  
  // return text msg
  S updateObject(O id, SS map) { throw unimplemented(); }
  
  // return null for standard input field
  Renderer getRenderer(S field) { ret renderers.get(field); }
  
  // returns HTML
  S fieldHelp(S field) { ret fieldHelp.get(field); }
  
  returnSelf addRenderer(S field, Renderer renderer) { renderers.put(field, renderer); }
  
  returnSelf fieldHelp(S field, S help, S... more) {
    fieldHelp.put(field, help);
    for (int i = 0; i+1 < l(more); i += 2)
      fieldHelp.put(more[i], more[i+1]);
  }
  
  S fieldNameToHTML(S name) {
    S help = fieldHelp.get(name);
    ret spanTitle(help, htmlencode2(humanizeLabel(name)));
  }
}