feat: add invitations constants and service to frontend

frontend/lib/constants/api_constants.dart

@@ -1,10 +1,13 @@
 class ApiConstants {
   static const String baseUrl = 'http://localhost:8080';
-  
+
   // Auth endpoints
   static const String loginEndpoint = '/login';
-  
+
   // User endpoints
   static const String getUserEndpoint = '/getUser';
   static const String updateUserEndpoint = '/updateUser';
-}
+
+  // Invitation endpoints
+  static const String getAllInvitationsEndpoint = '/invitations/all';
+}

frontend/lib/models/invitation_models.dart

@@ -0,0 +1,131 @@
+class InvitationTag {
+  final int id;
+  final String name;
+  final String colorHex;
+  final String iconName;
+
+  InvitationTag({
+    required this.id,
+    required this.name,
+    required this.colorHex,
+    required this.iconName,
+  });
+
+  factory InvitationTag.fromJson(Map<String, dynamic> json) {
+    return InvitationTag(
+      id: json['id'],
+      name: json['name'],
+      colorHex: json['colorHex'],
+      iconName: json['iconName'],
+    );
+  }
+}
+
+class InvitationCreator {
+  final int id;
+  final String displayName;
+  final String? avatar;
+
+  InvitationCreator({
+    required this.id,
+    required this.displayName,
+    this.avatar,
+  });
+
+  factory InvitationCreator.fromJson(Map<String, dynamic> json) {
+    return InvitationCreator(
+      id: json['id'],
+      displayName: json['displayName'],
+      avatar: json['avatar'],
+    );
+  }
+}
+
+class Invitation {
+  final int id;
+  final String title;
+  final String? description;
+  final DateTime? dateTime;
+  final String? location;
+  final int maxParticipants;
+  final int currentAttendees;
+  final InvitationTag tag;
+  final InvitationCreator creator;
+  final DateTime createdAt;
+
+  Invitation({
+    required this.id,
+    required this.title,
+    this.description,
+    this.dateTime,
+    this.location,
+    required this.maxParticipants,
+    required this.currentAttendees,
+    required this.tag,
+    required this.creator,
+    required this.createdAt,
+  });
+
+  factory Invitation.fromJson(Map<String, dynamic> json) {
+    return Invitation(
+      id: json['id'],
+      title: json['title'],
+      description: json['description'],
+      dateTime: json['dateTime'] != null ? DateTime.parse(json['dateTime']) : null,
+      location: json['location'],
+      maxParticipants: json['maxParticipants'],
+      currentAttendees: json['currentAttendees'],
+      tag: InvitationTag.fromJson(json['tag']),
+      creator: InvitationCreator.fromJson(json['creator']),
+      createdAt: DateTime.parse(json['createdAt']),
+    );
+  }
+}
+
+class InvitationsResponse {
+  final bool status;
+  final String? message;
+  final InvitationsData? data;
+
+  InvitationsResponse({
+    required this.status,
+    this.message,
+    this.data,
+  });
+
+  factory InvitationsResponse.fromJson(Map<String, dynamic> json) {
+    return InvitationsResponse(
+      status: json['status'],
+      message: json['message'],
+      data: json['data'] != null ? InvitationsData.fromJson(json['data']) : null,
+    );
+  }
+}
+
+class InvitationsData {
+  final List<Invitation> created;
+  final List<Invitation> accepted;
+  final List<Invitation> available;
+
+  InvitationsData({
+    required this.created,
+    required this.accepted,
+    required this.available,
+  });
+
+  factory InvitationsData.fromJson(Map<String, dynamic> json) {
+    return InvitationsData(
+      created: (json['created'] as List)
+          .map((item) => Invitation.fromJson(item))
+          .toList(),
+      accepted: (json['accepted'] as List)
+          .map((item) => Invitation.fromJson(item))
+          .toList(),
+      available: (json['available'] as List)
+          .map((item) => Invitation.fromJson(item))
+          .toList(),
+    );
+  }
+  
+  bool get isEmpty => created.isEmpty && accepted.isEmpty && available.isEmpty;
+}

frontend/lib/utils/invitation_utils.dart

@@ -0,0 +1,115 @@
+import 'package:flutter/material.dart';
+
+class InvitationUtils {
+  static IconData getIconFromName(String iconName) {
+    switch (iconName) {
+      case 'sports_soccer':
+        return Icons.sports_soccer;
+      case 'restaurant':
+        return Icons.restaurant;
+      case 'games':
+        return Icons.games;
+      case 'menu_book':
+        return Icons.menu_book;
+      case 'group':
+        return Icons.group;
+      case 'flight':
+        return Icons.flight;
+      case 'music_note':
+        return Icons.music_note;
+      case 'movie':
+        return Icons.movie;
+      case 'coffee':
+        return Icons.coffee;
+      case 'local_dining':
+        return Icons.local_dining;
+      case 'sports':
+        return Icons.sports;
+      case 'school':
+        return Icons.school;
+      default:
+        return Icons.category;
+    }
+  }
+
+  static Color getColorFromHex(String hexColor) {
+    String cleanHex = hexColor.replaceAll('#', '');
+    if (cleanHex.length == 6) {
+      cleanHex = 'FF' + cleanHex;
+    }
+    return Color(int.parse(cleanHex, radix: 16));
+  }
+
+  static String getRelativeTime(DateTime dateTime) {
+    final now = DateTime.now();
+    final difference = now.difference(dateTime);
+
+    if (difference.inMinutes < 1) {
+      return 'just now';
+    } else if (difference.inMinutes < 60) {
+      return '${difference.inMinutes}m ago';
+    } else if (difference.inHours < 24) {
+      return '${difference.inHours}h ago';
+    } else if (difference.inDays == 1) {
+      return 'yesterday';
+    } else if (difference.inDays < 7) {
+      return '${difference.inDays}d ago';
+    } else {
+      return '${dateTime.day}/${dateTime.month}/${dateTime.year}';
+    }
+  }
+
+  static String getRelativeDateTime(DateTime dateTime) {
+    final now = DateTime.now();
+    final today = DateTime(now.year, now.month, now.day);
+    final tomorrow = today.add(Duration(days: 1));
+    final eventDate = DateTime(dateTime.year, dateTime.month, dateTime.day);
+
+    String timeString = _formatTime(dateTime);
+
+    if (eventDate == today) {
+      return 'today at $timeString';
+    } else if (eventDate == tomorrow) {
+      return 'tomorrow at $timeString';
+    } else if (eventDate.isAfter(today) && eventDate.isBefore(today.add(Duration(days: 7)))) {
+      List<String> weekdays = ['Mon', 'Tue', 'Wed', 'Thu', 'Fri', 'Sat', 'Sun'];
+      return '${weekdays[eventDate.weekday - 1]} at $timeString';
+    } else {
+      return '${eventDate.day}/${eventDate.month} at $timeString';
+    }
+  }
+
+  static String _formatTime(DateTime dateTime) {
+    int hour = dateTime.hour;
+    String period = hour >= 12 ? 'PM' : 'AM';
+    hour = hour > 12 ? hour - 12 : (hour == 0 ? 12 : hour);
+    String minute = dateTime.minute.toString().padLeft(2, '0');
+    return '$hour:$minute $period';
+  }
+
+  static String truncateDescription(String? description, {int maxLength = 80}) {
+    if (description == null || description.isEmpty) return '';
+    if (description.length <= maxLength) return description;
+    return '${description.substring(0, maxLength)}...';
+  }
+
+  static String getParticipantsStatus(int current, int max) {
+    int needed = max - current;
+    if (needed <= 2 && needed > 0) {
+      return '$needed more person${needed == 1 ? '' : 's'} needed';
+    } else {
+      return '$current/$max';
+    }
+  }
+
+  static Color getParticipantsStatusColor(int current, int max) {
+    int needed = max - current;
+    if (needed <= 2 && needed > 0) {
+      return Colors.orange;
+    } else if (current == max) {
+      return Colors.green;
+    } else {
+      return Colors.blue;
+    }
+  }
+}