fix: improves cursor left word delete (#88)

* refactor: add position_extension file

* feat: move word/sentence del to new file

* test: cursor left word delete

* test: for cursor left sentence delete

* chore: formatting arrow keys test

* refactor: consolidate goLeft and goRight into one

lib/src/extensions/extensions.dart

@@ -7,3 +7,4 @@ export 'text_node_extensions.dart';
 
 export 'text_style_extension.dart';
 export 'url_launcher_extension.dart';
+export 'position_extension.dart';

lib/src/extensions/position_extension.dart

@@ -0,0 +1,94 @@
+import 'package:appflowy_editor/appflowy_editor.dart';
+import 'package:flutter/material.dart';
+
+enum SelectionRange {
+  character,
+  word,
+}
+
+extension PositionExtension on Position {
+  Position? moveHorizontal(
+    EditorState editorState, {
+    bool moveLeft = true,
+    SelectionRange selectionRange = SelectionRange.character,
+  }) {
+    final node = editorState.document.nodeAtPath(path);
+    if (node == null) {
+      return null;
+    }
+
+    if (moveLeft && offset == 0) {
+      final previousEnd = node.previous?.selectable?.end();
+      if (previousEnd != null) {
+        return previousEnd;
+      }
+      return null;
+    } else if (!moveLeft) {
+      final end = node.selectable?.end();
+      if (end != null && offset >= end.offset) {
+        return node.next?.selectable?.start();
+      }
+    }
+
+    switch (selectionRange) {
+      case SelectionRange.character:
+        if (node is TextNode) {
+          return Position(
+            path: path,
+            offset: moveLeft
+                ? node.delta.prevRunePosition(offset)
+                : node.delta.nextRunePosition(offset),
+          );
+        }
+
+        return Position(path: path, offset: offset);
+      case SelectionRange.word:
+        if (node is TextNode) {
+          final result = moveLeft
+              ? node.selectable?.getWordBoundaryInPosition(
+                  Position(
+                    path: path,
+                    offset: node.delta.prevRunePosition(offset),
+                  ),
+                )
+              : node.selectable?.getWordBoundaryInPosition(this);
+          if (result != null) {
+            return moveLeft ? result.start : result.end;
+          }
+        }
+
+        return Position(path: path, offset: offset);
+    }
+  }
+
+  Position? moveVertical(
+    EditorState editorState, {
+    bool upwards = true,
+  }) {
+    final selection =
+        editorState.service.selectionService.currentSelection.value;
+    final rects = editorState.service.selectionService.selectionRects;
+    if (rects.isEmpty || selection == null) {
+      return null;
+    }
+
+    Offset offset;
+    if (selection.isBackward) {
+      final rect = rects.reduce(
+        (current, next) => current.bottom >= next.bottom ? current : next,
+      );
+      offset = upwards
+          ? rect.topRight.translate(0, -rect.height)
+          : rect.bottomRight.translate(0, rect.height);
+    } else {
+      final rect = rects.reduce(
+        (current, next) => current.top <= next.top ? current : next,
+      );
+      offset = upwards
+          ? rect.topLeft.translate(0, -rect.height)
+          : rect.bottomLeft.translate(0, rect.height);
+    }
+
+    return editorState.service.selectionService.getPositionInOffset(offset);
+  }
+}