initial attempt at undo redo state

use_undo_redo.dart

import 'dart:math' as math;

import 'package:flutter/material.dart';
import 'package:flutter_hooks/flutter_hooks.dart';
import 'package:tuple/tuple.dart';

@immutable
class UndoRedoHandler {
  const UndoRedoHandler({
    required this.resetState,
    required this.index,
    required this.lastIndex,
    required this.goBack,
    required this.goForward,
  });

  final void Function() resetState;

  final int index;

  final int lastIndex;

  /// Allows you to go back (undo) N steps.
  /// Tries to go back in the history, returns true if it was possible.
  final bool Function(int) goBack;

  /// Allows you to go forward (redo) N steps.
  /// Tries to go forward in the history, returns true if it was possible.
  final bool Function(int) goForward;
}

Tuple2<ValueNotifier<T>, UndoRedoHandler> useUndoRedoState<T>(
  T initialData, {
  int maxHistory = 10,
  bool Function(T a, T b)? equals,
}) {
  final index = useState<int>(0);
  final history = useValueNotifier([initialData]);

  bool pushValue(T value) {
    final current = history.value[index.value];

    if (equals != null) {
      if (equals(current, value)) return false;
    } else {
      if (value == current) return false;
    }

    // Remove all values after the current index
    final copy = history.value.sublist(0, index.value + 1);

    // Trim the copy so it is only maxHistory long
    if (copy.length > maxHistory) {
      copy.removeRange(0, copy.length - maxHistory);
    }

    // Add the new value
    copy.add(value);

    // Update the state
    history.value = copy;
    index.value = copy.length - 1;

    return true;
  }

  // Clear all state history
  void resetState() {
    index.value = 0;
    history.value = [initialData];
  }

  bool goBack(int steps) {
    final newIndex = math.max(0, index.value - steps);
    if (newIndex == index.value) {
      return false;
    }

    index.value = newIndex;
    return true;
  }

  bool goForward(int steps) {
    final newIndex = math.min(history.value.length - 1, index.value + steps);
    if (newIndex == index.value) {
      return false;
    }

    index.value = newIndex;
    return true;
  }

  return Tuple2(
    current,
    UndoRedoHandler(
      resetState: resetState,
      index: index.value,
      lastIndex: history.value.length - 1,
      goBack: goBack,
      goForward: goForward,
    ),
  );
}