frontend/src/navigation/SimpleMobileTabNavigator.tsx

/**
 * 简单的移动端 Tab Navigator
 * 
 * 不使用 React Navigation 的 Tab Navigator，而是使用一个简单的自定义实现
 * 这样可以完全避免 React Navigation 状态恢复的问题
 */

import React, { useEffect, useState, useCallback } from 'react';
import {
  View,
  StyleSheet,
  TouchableOpacity,
  Text,
  Dimensions,
} from 'react-native';
import { useSafeAreaInsets } from 'react-native-safe-area-context';
import { MaterialCommunityIcons } from '@expo/vector-icons';

import { colors, shadows } from '../theme';
import { useTotalUnreadCount } from '../stores';
import { messageManager } from '../stores';

// ==================== 导入屏幕组件 ====================
import { HomeScreen, SearchScreen } from '../screens/home';
import { ScheduleScreen, CourseDetailScreen } from '../screens/schedule';
import {
  MessageListScreen,
  NotificationsScreen,
  PrivateChatInfoScreen,
} from '../screens/message';
import { ProfileScreen, SettingsScreen, EditProfileScreen, NotificationSettingsScreen, BlockedUsersScreen, AccountSecurityScreen } from '../screens/profile';

// ==================== 类型定义 ====================
type TabName = 'HomeTab' | 'MessageTab' | 'ScheduleTab' | 'ProfileTab';

// ==================== 常量 ====================
const TAB_BAR_HEIGHT = 64;
const TAB_BAR_MARGIN = 14;
const TAB_BAR_FLOATING_MARGIN = 12;

// ==================== 组件 ====================

/**
 * 简化的 Stack Navigator 包装
 */
function SimpleStackNavigator({ 
  children, 
  screenName 
}: { 
  children: React.ReactNode; 
  screenName: string;
}) {
  return (
    <View style={styles.stackContainer}>
      {children}
    </View>
  );
}

/**
 * 主组件：SimpleMobileTabNavigator
 */
export function SimpleMobileTabNavigator() {
  const insets = useSafeAreaInsets();
  const messageUnreadCount = useTotalUnreadCount();
  const [activeTab, setActiveTab] = useState<TabName>('HomeTab');

  // 初始化 MessageManager
  useEffect(() => {
    messageManager.initialize();
  }, []);

  // 处理 Tab 切换
  const handleTabPress = useCallback((tabName: TabName) => {
    setActiveTab(tabName);
  }, []);

  // 渲染当前 Tab 的内容
  const renderTabContent = () => {
    switch (activeTab) {
      case 'HomeTab':
        return <HomeScreen />;
      case 'MessageTab':
        return <MessageListScreen />;
      case 'ScheduleTab':
        return <ScheduleScreen />;
      case 'ProfileTab':
        return <ProfileScreen />;
      default:
        return <HomeScreen />;
    }
  };

  // 渲染 Tab Bar 图标
  const renderTabIcon = (tabName: TabName, isActive: boolean) => {
    const iconColor = isActive ? colors.primary.main : colors.text.secondary;
    const iconSize = isActive ? 26 : 24;

    switch (tabName) {
      case 'HomeTab':
        return (
          <MaterialCommunityIcons
            name={isActive ? 'home' : 'home-outline'}
            size={iconSize}
            color={iconColor}
          />
        );
      case 'MessageTab':
        return (
          <MaterialCommunityIcons
            name={isActive ? 'message-text' : 'message-text-outline'}
            size={iconSize}
            color={iconColor}
          />
        );
      case 'ScheduleTab':
        return (
          <MaterialCommunityIcons
            name={isActive ? 'calendar-today' : 'calendar-today'}
            size={iconSize}
            color={iconColor}
          />
        );
      case 'ProfileTab':
        return (
          <MaterialCommunityIcons
            name={isActive ? 'account' : 'account-outline'}
            size={iconSize}
            color={iconColor}
          />
        );
      default:
        return null;
    }
  };

  // 渲染 Tab Bar 标签
  const renderTabLabel = (tabName: TabName, isActive: boolean) => {
    const labels: Record<TabName, string> = {
      HomeTab: '首页',
      MessageTab: '消息',
      ScheduleTab: '课表',
      ProfileTab: '我的',
    };

    return (
      <Text
        style={[
          styles.tabLabel,
          isActive && styles.tabLabelActive,
        ]}
      >
        {labels[tabName]}
      </Text>
    );
  };

  return (
    <View style={styles.container}>
      {/* 内容区域 */}
      <View style={styles.content}>
        {renderTabContent()}
      </View>

      {/* Tab Bar */}
      <View
        style={[
          styles.tabBar,
          {
            bottom: TAB_BAR_FLOATING_MARGIN + insets.bottom,
          },
        ]}
      >
        {(['HomeTab', 'MessageTab', 'ScheduleTab', 'ProfileTab'] as TabName[]).map(
          (tabName) => {
            const isActive = activeTab === tabName;
            const showBadge = tabName === 'MessageTab' && messageUnreadCount > 0;

            return (
              <TouchableOpacity
                key={tabName}
                style={[
                  styles.tabItem,
                  isActive && styles.tabItemActive,
                ]}
                onPress={() => handleTabPress(tabName)}
                activeOpacity={0.7}
              >
                <View style={styles.tabIconContainer}>
                  {renderTabIcon(tabName, isActive)}
                  {showBadge && (
                    <View style={styles.badge}>
                      <Text style={styles.badgeText}>
                        {messageUnreadCount > 99 ? '99+' : messageUnreadCount}
                      </Text>
                    </View>
                  )}
                </View>
                {renderTabLabel(tabName, isActive)}
              </TouchableOpacity>
            );
          }
        )}
      </View>
    </View>
  );
}

// ==================== 样式 ====================
const styles = StyleSheet.create({
  container: {
    flex: 1,
    backgroundColor: colors.background.default,
  },
  stackContainer: {
    flex: 1,
  },
  content: {
    flex: 1,
    marginBottom: TAB_BAR_HEIGHT + TAB_BAR_FLOATING_MARGIN * 2,
  },
  tabBar: {
    position: 'absolute',
    left: TAB_BAR_MARGIN,
    right: TAB_BAR_MARGIN,
    height: TAB_BAR_HEIGHT,
    backgroundColor: colors.background.paper,
    borderRadius: 24,
    borderTopWidth: 1,
    borderTopColor: `${colors.divider}88`,
    flexDirection: 'row',
    alignItems: 'center',
    justifyContent: 'space-around',
    paddingHorizontal: 8,
    ...shadows.lg,
  },
  tabItem: {
    flex: 1,
    alignItems: 'center',
    justifyContent: 'center',
    paddingVertical: 6,
    borderRadius: 18,
  },
  tabItemActive: {
    backgroundColor: `${colors.primary.main}15`,
  },
  tabIconContainer: {
    position: 'relative',
    width: 38,
    height: 30,
    alignItems: 'center',
    justifyContent: 'center',
    borderRadius: 15,
  },
  tabLabel: {
    fontSize: 12,
    fontWeight: '600',
    marginTop: -2,
    letterSpacing: 0.2,
    color: colors.text.secondary,
  },
  tabLabelActive: {
    color: colors.primary.main,
  },
  badge: {
    position: 'absolute',
    top: -2,
    right: -2,
    backgroundColor: colors.error.main,
    borderRadius: 10,
    minWidth: 18,
    height: 18,
    alignItems: 'center',
    justifyContent: 'center',
    paddingHorizontal: 4,
  },
  badgeText: {
    color: colors.primary.contrast,
    fontSize: 10,
    fontWeight: '600',
  },
});