const KEYCODE_A = 0;
const KEYCODE_HOME = 115;
const KEYCODE_DEL = 117;
const KEYCODE_END = 119;
const KEYCODE_LEFT = 123;
const KEYCODE_RIGHT = 124;

class TextEditingRawKeyboardListener extends StatelessWidget {
  final Widget child;
  final FocusNode focusNode;
  final TextEditingController controller;

  TextEditingRawKeyboardListener({Key key, this.child, this.focusNode, this.controller}): super(key: key);

  @override
  Widget build(BuildContext context) => RawKeyboardListener(
    child: child,
    focusNode: focusNode,
    onKey: onKeyEvent
  );

  void onKeyEvent(RawKeyEvent e) {
    if (e.runtimeType != RawKeyDownEvent || e.data.runtimeType != RawKeyEventDataAndroid)
      return;
    final keyEvent = e.data as RawKeyEventDataAndroid;
    if (keyEvent.isModifierPressed(ModifierKey.metaModifier)) {
      if (keyEvent.keyCode == KEYCODE_A)
        controller.selection = TextSelection(baseOffset: 0, extentOffset: controller.text.length);
    }
    else if (keyEvent.isModifierPressed(ModifierKey.shiftModifier)) {
      if (keyEvent.keyCode == KEYCODE_LEFT)
        controller.selection = controller.selection.copyWith(extentOffset: max(controller.selection.extentOffset - 1, 0));
      else if (keyEvent.keyCode == KEYCODE_RIGHT)
        controller.selection = controller.selection.copyWith(extentOffset: min(controller.selection.extentOffset + 1, controller.text.length));
      else if (keyEvent.keyCode == KEYCODE_HOME)
        controller.selection = controller.selection.copyWith(extentOffset: 0);
      else if (keyEvent.keyCode == KEYCODE_END)
        controller.selection = controller.selection.copyWith(extentOffset: controller.text.length);
    }
    else if (keyEvent.keyCode == KEYCODE_HOME)
      controller.selection = TextSelection.collapsed(offset: 0);
    else if (keyEvent.keyCode == KEYCODE_END)
      controller.selection = TextSelection.collapsed(offset: controller.text.length);
    else if (keyEvent.keyCode == KEYCODE_DEL) {
      final start = min(controller.selection.baseOffset, controller.selection.extentOffset);
      var end = max(controller.selection.baseOffset, controller.selection.extentOffset);
      if (start == end && end < controller.text.length) {
        // If nothing is selected, behave as if the character after the cursor was selected (only for DEL).
        end += 1;
      }
      controller.text = controller.text.substring(0, start)
                      + controller.text.substring(end);
      controller.selection = TextSelection.collapsed(offset: start);
    }
  }
}