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lib/core/utils/date_utils.dart

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+import 'package:intl/intl.dart';
+
+abstract final class AppDateUtils {
+  static final _dateFormat = DateFormat('yyyy-MM-dd');
+  static final _dateTimeFormat = DateFormat('yyyy-MM-dd HH:mm:ss');
+  static final _timeFormat = DateFormat('HH:mm');
+  static final _koreanDateFormat = DateFormat('yyyy년 MM월 dd일');
+
+  static String formatDate(DateTime date) => _dateFormat.format(date);
+
+  static String formatDateTime(DateTime date) => _dateTimeFormat.format(date);
+
+  static String formatTime(DateTime date) => _timeFormat.format(date);
+
+  static String formatKoreanDate(DateTime date) => _koreanDateFormat.format(date);
+
+  static DateTime? tryParse(String? dateString) {
+    if (dateString == null) return null;
+    try {
+      return DateTime.parse(dateString);
+    } catch (_) {
+      return null;
+    }
+  }
+
+  static String timeAgo(DateTime date) {
+    final now = DateTime.now();
+    final diff = now.difference(date);
+
+    if (diff.inDays > 365) {
+      return '${diff.inDays ~/ 365}년 전';
+    } else if (diff.inDays > 30) {
+      return '${diff.inDays ~/ 30}개월 전';
+    } else if (diff.inDays > 0) {
+      return '${diff.inDays}일 전';
+    } else if (diff.inHours > 0) {
+      return '${diff.inHours}시간 전';
+    } else if (diff.inMinutes > 0) {
+      return '${diff.inMinutes}분 전';
+    } else {
+      return '방금 전';
+    }
+  }
+}

lib/core/utils/extensions.dart

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+import 'package:flutter/material.dart';
+
+extension BuildContextExtension on BuildContext {
+  ThemeData get theme => Theme.of(this);
+  TextTheme get textTheme => Theme.of(this).textTheme;
+  ColorScheme get colorScheme => Theme.of(this).colorScheme;
+  MediaQueryData get mediaQuery => MediaQuery.of(this);
+  Size get screenSize => MediaQuery.sizeOf(this);
+  double get screenWidth => screenSize.width;
+  double get screenHeight => screenSize.height;
+  bool get isMobile => screenWidth < 600;
+  bool get isTablet => screenWidth >= 600 && screenWidth < 1200;
+  bool get isDesktop => screenWidth >= 1200;
+
+  void showSnackBar(String message, {bool isError = false}) {
+    ScaffoldMessenger.of(this).showSnackBar(
+      SnackBar(
+        content: Text(message),
+        backgroundColor: isError ? colorScheme.error : null,
+        behavior: SnackBarBehavior.floating,
+      ),
+    );
+  }
+}
+
+extension StringExtension on String {
+  String get capitalize =>
+      isEmpty ? this : '${this[0].toUpperCase()}${substring(1)}';
+
+  bool get isValidEmail => RegExp(
+        r'^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$',
+      ).hasMatch(this);
+
+  bool get isValidPassword => length >= 8;
+}
+
+extension DateTimeExtension on DateTime {
+  String get toFormattedString => '$year-${month.toString().padLeft(2, '0')}-${day.toString().padLeft(2, '0')}';
+
+  String get toFormattedDateTime =>
+      '$toFormattedString ${hour.toString().padLeft(2, '0')}:${minute.toString().padLeft(2, '0')}';
+}

lib/core/utils/validators.dart

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+abstract final class Validators {
+  static String? email(String? value) {
+    if (value == null || value.isEmpty) {
+      return '이메일을 입력해주세요';
+    }
+    final emailRegex = RegExp(
+      r'^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$',
+    );
+    if (!emailRegex.hasMatch(value)) {
+      return '올바른 이메일 형식이 아닙니다';
+    }
+    return null;
+  }
+
+  static String? password(String? value) {
+    if (value == null || value.isEmpty) {
+      return '비밀번호를 입력해주세요';
+    }
+    if (value.length < 8) {
+      return '비밀번호는 8자 이상이어야 합니다';
+    }
+    return null;
+  }
+
+  static String? required(String? value, [String? fieldName]) {
+    if (value == null || value.trim().isEmpty) {
+      return '${fieldName ?? '이 필드'}를 입력해주세요';
+    }
+    return null;
+  }
+
+  static String? minLength(String? value, int min, [String? fieldName]) {
+    if (value == null || value.length < min) {
+      return '${fieldName ?? '이 필드'}는 $min자 이상이어야 합니다';
+    }
+    return null;
+  }
+
+  static String? maxLength(String? value, int max, [String? fieldName]) {
+    if (value != null && value.length > max) {
+      return '${fieldName ?? '이 필드'}는 $max자 이하여야 합니다';
+    }
+    return null;
+  }
+}