Userクラス削除しUserAccountクラスとBotAccoutクラス、これらの基底クラスを追加。DirectMessageクラスを追加。

lib/models/account.dart

@@ -0,0 +1,71 @@
+import 'package:mikata/models/direct_message.dart';
+import 'package:uuid/uuid.dart';
+import 'dart:math';
+
+String createUserID({int length = 8}) {
+    const String charset = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";
+    final Random random = Random.secure();
+    final String randomStr =  List.generate(length, (_) => charset[random.nextInt(charset.length)]).join();
+    return randomStr;
+}
+
+class Account {
+// protected member
+    String _userName;
+    String _userID;
+    final String _userUUID;
+
+// public method
+    Account({
+        required String userName,
+        String? userID,
+        String? userUUID
+    }) : _userName = userName,
+        _userID    = userID ?? createUserID(),
+        _userUUID  = userUUID ?? Uuid().v4();
+
+    String get userName => _userName;
+    set userName(String name) {
+        if (name.isNotEmpty) _userName = name;
+    }
+
+    String get userID => _userID;
+    set userID(String id) {
+        if (id.isNotEmpty) _userID = id;
+    }
+
+    String get userUUID => _userUUID;
+}
+
+class UserAccount extends Account {
+// public member
+    final Set<String> follow = {}; // userUUID
+    final Set<String> follower = {}; // userUUID
+
+// public method
+    UserAccount({
+        required super.userName,
+        super.userID,
+        super.userUUID
+    });
+}
+
+class BotAccount extends Account {
+// private member
+    final List<DirectMessage> _dmLists = [];
+
+// public method
+    BotAccount({
+        required super.userName,
+        super.userID,
+        super.userUUID
+    });
+
+    void addDM(DirectMessage dm) {
+        _dmLists.add(dm);
+    }
+
+    void removeDM(DirectMessage dm) {
+        _dmLists.remove(dm);
+    }
+}

lib/models/direct_message.dart

@@ -0,0 +1,52 @@
+class DirectMessage {
+// private member
+    String _userName;
+    String _userID;
+    final String _userUUID;
+    final DateTime _dateTime;
+    final String _content;
+
+// public method
+    DirectMessage({
+        required String userName,
+        required String userID,
+        required String userUUID,
+        DateTime? dateTime,
+        required String content
+    }) : _userName = userName,
+        _userID    = userID,
+        _userUUID  = userUUID,
+        _dateTime  = dateTime ?? DateTime.now(),
+        _content   = content;
+
+    DirectMessage.fromJson(Map<String, dynamic> json) :
+        _userName = json["userName"],
+        _userID   = json["userID"],
+        _userUUID = json["userUUID"],
+        _dateTime = json["dateTime"],
+        _content  = json["content"];
+
+    Map<String, dynamic> toJson() => {
+        "userName" : userName,
+        "userID"   : userID,
+        "userUUID" : userUUID,
+        "dateTime" : dateTime,
+        "content"  : content,
+    };
+
+    String get userName => _userName;
+    set userName(String name) {
+        if (name.isNotEmpty) _userName = name;
+    }
+
+    String get userID => _userID;
+    set userID(String id) {
+        if (id.isNotEmpty) _userID = id;   
+    }
+
+    String get userUUID => _userUUID;
+
+    DateTime get dateTime => _dateTime;
+
+    String get content => _content;
+}

lib/models/post.dart

@@ -4,9 +4,6 @@ import 'package:flutter/foundation.dart';
 // Package imports:
 import 'package:uuid/uuid.dart';
 
-// Project imports:
-import 'package:mikata/models/user.dart';
-
 class Post {
 // punlic member
 
@@ -158,8 +155,4 @@ class Post {
   		 	_relativeTime = '${(difference.inDays / 365).floor()}年前';
   		}
 	}
-}
-
-Post makePost(User user, String content) {
-    return Post(authorName: user.userName, authorUuid: user.userUuid, content: content);
-}
+}

lib/providers/posts_provider.dart

@@ -6,7 +6,7 @@ import 'package:hooks_riverpod/hooks_riverpod.dart';
 
 // Project imports:
 import 'package:mikata/models/post.dart';
-import 'package:mikata/models/user.dart';
+import 'package:mikata/models/account.dart';
 
 class PostNotifier extends AsyncNotifier<List<Post>> {
   @override
@@ -29,13 +29,13 @@ class PostNotifier extends AsyncNotifier<List<Post>> {
   }
 
   List<Post> _dummyPosts() {
-    final users = <User>[
-      User(userName: 'Alice'),
-      User(userName: 'Bob'),
-      User(userName: 'Carol'),
-      User(userName: 'Dave'),
-      User(userName: 'Eve'),
-      User(userName: 'Frank'),
+    final users = <BotAccount>[
+      BotAccount(userName: 'Alice'),
+      BotAccount(userName: 'Bob'),
+      BotAccount(userName: 'Carol'),
+      BotAccount(userName: 'Dave'),
+      BotAccount(userName: 'Eve'),
+      BotAccount(userName: 'Frank'),
     ];
 
     final now = DateTime.now();
@@ -69,7 +69,7 @@ class PostNotifier extends AsyncNotifier<List<Post>> {
 
       return Post(
         authorName: user.userName,
-        authorUuid: user.userUuid,
+        authorUuid: user.userUUID,
         content: bodies[index],
         replyCount: index % 4,
         likeCount: (index * 3) % 50,

test/account_test.dart

@@ -0,0 +1,10 @@
+import 'package:flutter_test/flutter_test.dart';
+import 'package:mikata/models/account.dart';
+
+void main() {
+    test("UserIDを生成する", () {
+        final String id = createUserID();
+        print(id);
+        expect(id.length, 8);
+    });
+}