feat: implement handler - press the enter key in the edge of text node

frontend/app_flowy/packages/flowy_editor/lib/document/node.dart

@@ -1,6 +1,7 @@
 import 'dart:collection';
 import 'package:flowy_editor/document/path.dart';
 import 'package:flowy_editor/document/text_delta.dart';
+import 'package:flowy_editor/operation/operation.dart';
 import 'package:flutter/material.dart';
 import './attributes.dart';
 
@@ -172,6 +173,14 @@ class TextNode extends Node {
     required Delta delta,
   }) : _delta = delta;
 
+  TextNode.empty()
+      : _delta = Delta([TextInsert('')]),
+        super(
+          type: 'text',
+          children: LinkedList(),
+          attributes: {},
+        );
+
   Delta get delta {
     return _delta;
   }

frontend/app_flowy/packages/flowy_editor/lib/extensions/node_extensions.dart

@@ -1,5 +1,3 @@
-import 'dart:math';
-
 import 'package:flowy_editor/document/node.dart';
 import 'package:flowy_editor/document/selection.dart';
 import 'package:flowy_editor/extensions/object_extensions.dart';

frontend/app_flowy/packages/flowy_editor/lib/extensions/path_extensions.dart

@@ -22,4 +22,15 @@ extension PathExtensions on Path {
     }
     return true;
   }
+
+  Path get next {
+    Path nextPath = Path.from(this, growable: true);
+    if (isEmpty) {
+      return nextPath;
+    }
+    final last = nextPath.last;
+    return nextPath
+      ..removeLast()
+      ..add(last + 1);
+  }
 }

frontend/app_flowy/packages/flowy_editor/lib/render/node_widget_builder.dart

@@ -31,7 +31,7 @@ class NodeWidgetBuilder<T extends Node> {
       throw UnimplementedError();
 
   /// TODO: refactore this part.
-  /// return widget embeded with ChangeNotifier and widget itself.
+  /// return widget embedded with ChangeNotifier and widget itself.
   Widget call(
     BuildContext buildContext,
   ) {

frontend/app_flowy/packages/flowy_editor/lib/service/editor_service.dart

@@ -1,5 +1,6 @@
 import 'package:flowy_editor/render/selection/floating_shortcut_widget.dart';
 import 'package:flowy_editor/service/input_service.dart';
+import 'package:flowy_editor/service/internal_key_event_handlers/enter_in_edge_of_text_node_handler.dart';
 import 'package:flowy_editor/service/shortcut_service.dart';
 import 'package:flowy_editor/service/internal_key_event_handlers/arrow_keys_handler.dart';
 import 'package:flowy_editor/service/internal_key_event_handlers/delete_nodes_handler.dart';
@@ -47,6 +48,7 @@ class _FlowyEditorState extends State<FlowyEditor> {
             flowyDeleteNodesHandler,
             deleteSingleTextNodeHandler,
             arrowKeysHandler,
+            enterInEdgeOfTextNodeHandler,
             ...widget.keyEventHandlers,
           ],
           editorState: editorState,

frontend/app_flowy/packages/flowy_editor/lib/service/input_service.dart

@@ -1,5 +1,8 @@
+import 'package:flowy_editor/document/position.dart';
+import 'package:flowy_editor/document/selection.dart';
 import 'package:flowy_editor/editor_state.dart';
 import 'package:flowy_editor/document/node.dart';
+import 'package:flowy_editor/operation/transaction_builder.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter/services.dart';
 
@@ -86,7 +89,18 @@ class _FlowyInputState extends State<FlowyInput>
   }
 
   @override
-  void apply(List<TextEditingDelta> deltas) {}
+  void apply(List<TextEditingDelta> deltas) {
+// TODO: implement the detail
+    for (final delta in deltas) {
+      if (delta is TextEditingDeltaInsertion) {
+      } else if (delta is TextEditingDeltaDeletion) {
+      } else if (delta is TextEditingDeltaReplacement) {
+      } else if (delta is TextEditingDeltaNonTextUpdate) {
+        // We don't need to care the [TextEditingDeltaNonTextUpdate].
+        // Do nothing.
+      }
+    }
+  }
 
   @override
   void close() {

frontend/app_flowy/packages/flowy_editor/lib/service/internal_key_event_handlers/enter_in_edge_of_text_node_handler.dart

@@ -0,0 +1,46 @@
+import 'package:flowy_editor/document/node.dart';
+import 'package:flowy_editor/document/position.dart';
+import 'package:flowy_editor/document/selection.dart';
+import 'package:flowy_editor/operation/transaction_builder.dart';
+import 'package:flowy_editor/service/keyboard_service.dart';
+import 'package:flowy_editor/extensions/path_extensions.dart';
+import 'package:flowy_editor/extensions/node_extensions.dart';
+import 'package:flutter/material.dart';
+import 'package:flutter/services.dart';
+
+FlowyKeyEventHandler enterInEdgeOfTextNodeHandler = (editorState, event) {
+  if (event.logicalKey != LogicalKeyboardKey.enter) {
+    return KeyEventResult.ignored;
+  }
+
+  final nodes = editorState.service.selectionService.currentSelectedNodes.value;
+  final selection = editorState.service.selectionService.currentSelection;
+  if (selection == null ||
+      nodes.length != 1 ||
+      nodes.first is! TextNode ||
+      !selection.isCollapsed) {
+    return KeyEventResult.ignored;
+  }
+
+  final textNode = nodes.first as TextNode;
+
+  if (textNode.selectable!.end() == selection.end) {
+    TransactionBuilder(editorState)
+      ..insertNode(
+        textNode.path.next,
+        TextNode.empty(),
+      )
+      ..commit();
+    return KeyEventResult.handled;
+  } else if (textNode.selectable!.start() == selection.start) {
+    TransactionBuilder(editorState)
+      ..insertNode(
+        textNode.path,
+        TextNode.empty(),
+      )
+      ..commit();
+    return KeyEventResult.handled;
+  }
+
+  return KeyEventResult.ignored;
+};