Implement "move" to troubleshooter to simulate movement

lib/mod_list_troubleshooter.dart

@@ -12,6 +12,13 @@ import 'package:rimworld_modman/mod_list.dart';
 ///
 /// These approaches help RimWorld mod users identify which mods are causing problems
 /// when many mods are installed.
+class Move {
+  final int startIndex;
+  final int endIndex;
+
+  Move({required this.startIndex, required this.endIndex});
+}
+
 class ModListTroubleshooter {
   final ModList originalModList;
   ModList currentModList;
@@ -25,78 +32,108 @@ class ModListTroubleshooter {
       _startIndex = 0,
       _endIndex = modList.activeMods.length;
 
-  ModList binaryForward() {
+  Move binaryForwardMove() {
     final midIndex = (_startIndex + _endIndex) ~/ 2;
+    return Move(startIndex: midIndex, endIndex: _endIndex);
+  }
+
+  Move binaryBackwardMove() {
+    final midIndex = ((_startIndex + _endIndex) / 2).ceil();
+    return Move(startIndex: _startIndex, endIndex: midIndex);
+  }
+
+  ModList binaryForward() {
+    final move = binaryForwardMove();
     final subset = originalModList.activeMods.keys.toList().sublist(
-      midIndex,
+      move.startIndex,
-      _endIndex,
+      move.endIndex,
     );
     currentModList.disableAll();
     currentModList.enableMods(subset);
-    _startIndex = midIndex;
+    _startIndex = move.startIndex;
+    _endIndex = move.endIndex;
     return currentModList;
   }
 
   ModList binaryBackward() {
-    final midIndex = ((_startIndex + _endIndex) / 2).ceil();
+    final move = binaryBackwardMove();
     final subset = originalModList.activeMods.keys.toList().sublist(
-      _startIndex,
+      move.startIndex,
-      midIndex,
+      move.endIndex,
     );
     currentModList.disableAll();
     currentModList.enableMods(subset);
-    _endIndex = midIndex;
+    _startIndex = move.startIndex;
+    _endIndex = move.endIndex;
     return currentModList;
   }
 
   // If the current selection is not equal to our proposed step size
   // We do not MOVE but instead just return the correct amount of mods from the start
-  ModList linearForward({int stepSize = 20}) {
+  Move linearForwardMove({int stepSize = 20}) {
+    var start = _startIndex;
+    var end = _endIndex;
     // If we are not "in step"
-    if (_endIndex - _startIndex == stepSize) {
+    if (end - start == stepSize) {
       // Move the indices forward by the step size, step forward
-      _startIndex += stepSize;
+      start += stepSize;
-      _endIndex += stepSize;
+      end += stepSize;
     } else {
-      // Correct the end index to be in step
+      end = start + stepSize;
-      _endIndex = _startIndex + stepSize;
-    }
-    if (_endIndex > originalModList.activeMods.length) {
-      // If we are at the end of the list, move the start index such that we return
-      // At most the step size amount of mods
-      _endIndex = originalModList.activeMods.length;
-      _startIndex = (_endIndex - stepSize).clamp(0, _endIndex);
     }
 
+    if (end > originalModList.activeMods.length) {
+      // If we are at the end of the list, move the start index such that we return
+      // At most the step size amount of mods
+      end = originalModList.activeMods.length;
+      start = (end - stepSize).clamp(0, end);
+    }
+
+    return Move(startIndex: start, endIndex: end);
+  }
+
+  Move linearBackwardMove({int stepSize = 20}) {
+    var start = _startIndex;
+    var end = _endIndex;
+    if (end - start == stepSize) {
+      start -= stepSize;
+      end -= stepSize;
+    } else {
+      start = end - stepSize;
+    }
+
+    if (start < 0) {
+      start = 0;
+      end = stepSize.clamp(0, originalModList.activeMods.length);
+    }
+    return Move(startIndex: start, endIndex: end);
+  }
+
+  ModList linearForward({int stepSize = 20}) {
+    final move = linearForwardMove(stepSize: stepSize);
     final subset = originalModList.activeMods.keys.toList().sublist(
-      _startIndex,
+      move.startIndex,
-      _endIndex,
+      move.endIndex,
     );
 
     currentModList.disableAll();
     currentModList.enableMods(subset);
+    _startIndex = move.startIndex;
+    _endIndex = move.endIndex;
     return currentModList;
   }
 
   ModList linearBackward({int stepSize = 20}) {
-    if (_endIndex - _startIndex == stepSize) {
+    final move = linearBackwardMove(stepSize: stepSize);
-      _startIndex -= stepSize;
-      _endIndex -= stepSize;
-    } else {
-      _startIndex = _endIndex - stepSize;
-    }
-    if (_startIndex < 0) {
-      _startIndex = 0;
-      _endIndex = stepSize.clamp(0, originalModList.activeMods.length);
-    }
-
     final subset = originalModList.activeMods.keys.toList().sublist(
-      _startIndex,
+      move.startIndex,
-      _endIndex,
+      move.endIndex,
     );
 
     currentModList.disableAll();
     currentModList.enableMods(subset);
+    _startIndex = move.startIndex;
+    _endIndex = move.endIndex;
     return currentModList;
   }