frontend/src/utils/conversationStorage.js

/**
 * Conversation Storage Utility
 * Handles conversation persistence with localStorage
 */

const STORAGE_KEY = 'ca_study_conversations';
const MAX_CONVERSATIONS = 50; // Limit to prevent localStorage overflow

export class ConversationStorage {
  
  /**
   * Load all conversations from localStorage
   */
  static loadConversations() {
    try {
      const stored = localStorage.getItem(STORAGE_KEY);
      if (!stored) return [];
      
      const conversations = JSON.parse(stored);
      
      // Convert date strings back to Date objects
      return conversations.map(conv => ({
        ...conv,
        createdAt: new Date(conv.createdAt),
        messages: conv.messages.map(msg => ({
          ...msg,
          timestamp: new Date(msg.timestamp)
        }))
      }));
    } catch (error) {
      console.error('Error loading conversations:', error);
      return [];
    }
  }

  /**
   * Save conversations to localStorage
   */
  static saveConversations(conversations) {
    try {
      // Limit the number of conversations to prevent localStorage overflow
      const limitedConversations = conversations.slice(0, MAX_CONVERSATIONS);
      localStorage.setItem(STORAGE_KEY, JSON.stringify(limitedConversations));
      return true;
    } catch (error) {
      console.error('Error saving conversations:', error);
      // Handle localStorage quota exceeded
      if (error.name === 'QuotaExceededError') {
        // Try to save with fewer conversations
        const reducedConversations = conversations.slice(0, 25);
        try {
          localStorage.setItem(STORAGE_KEY, JSON.stringify(reducedConversations));
          return true;
        } catch (retryError) {
          console.error('Error saving reduced conversations:', retryError);
        }
      }
      return false;
    }
  }

  /**
   * Add a new conversation
   */
  static addConversation(conversation) {
    const conversations = this.loadConversations();
    const newConversations = [conversation, ...conversations];
    return this.saveConversations(newConversations);
  }

  /**
   * Update an existing conversation
   */
  static updateConversation(conversationId, updates) {
    const conversations = this.loadConversations();
    const updatedConversations = conversations.map(conv => 
      conv.id === conversationId ? { ...conv, ...updates } : conv
    );
    return this.saveConversations(updatedConversations);
  }

  /**
   * Delete a conversation
   */
  static deleteConversation(conversationId) {
    const conversations = this.loadConversations();
    const filteredConversations = conversations.filter(conv => conv.id !== conversationId);
    return this.saveConversations(filteredConversations);
  }

  /**
   * Add a message to a conversation
   */
  static addMessage(conversationId, message) {
    const conversations = this.loadConversations();
    const updatedConversations = conversations.map(conv => {
      if (conv.id === conversationId) {
        return {
          ...conv,
          messages: [...conv.messages, message],
          updatedAt: new Date()
        };
      }
      return conv;
    });
    return this.saveConversations(updatedConversations);
  }

  /**
   * Search conversations by title or content
   */
  static searchConversations(query) {
    const conversations = this.loadConversations();
    const lowercaseQuery = query.toLowerCase();
    
    return conversations.filter(conv => 
      conv.title.toLowerCase().includes(lowercaseQuery) ||
      conv.messages.some(msg => 
        msg.content.toLowerCase().includes(lowercaseQuery)
      )
    );
  }

  /**
   * Get conversation statistics
   */
  static getStatistics() {
    const conversations = this.loadConversations();
    const totalMessages = conversations.reduce((sum, conv) => sum + conv.messages.length, 0);
    
    return {
      totalConversations: conversations.length,
      totalMessages,
      storageSize: this.getStorageSize(),
      oldestConversation: conversations.length > 0 ? 
        conversations[conversations.length - 1].createdAt : null,
      newestConversation: conversations.length > 0 ? 
        conversations[0].createdAt : null
    };
  }

  /**
   * Get storage size in KB
   */
  static getStorageSize() {
    try {
      const stored = localStorage.getItem(STORAGE_KEY);
      return stored ? Math.round(new Blob([stored]).size / 1024) : 0;
    } catch (error) {
      return 0;
    }
  }

  /**
   * Export conversations as JSON
   */
  static exportConversations() {
    const conversations = this.loadConversations();
    const exportData = {
      exportDate: new Date().toISOString(),
      version: '1.0',
      conversations
    };
    
    const blob = new Blob([JSON.stringify(exportData, null, 2)], { 
      type: 'application/json' 
    });
    
    const url = URL.createObjectURL(blob);
    const a = document.createElement('a');
    a.href = url;
    a.download = `ca_study_conversations_${new Date().toISOString().split('T')[0]}.json`;
    document.body.appendChild(a);
    a.click();
    document.body.removeChild(a);
    URL.revokeObjectURL(url);
  }

  /**
   * Import conversations from JSON file
   */
  static importConversations(file) {
    return new Promise((resolve, reject) => {
      const reader = new FileReader();
      reader.onload = (e) => {
        try {
          const importData = JSON.parse(e.target.result);
          
          if (!importData.conversations || !Array.isArray(importData.conversations)) {
            reject(new Error('Invalid conversation file format'));
            return;
          }
          
          const existingConversations = this.loadConversations();
          const mergedConversations = [...importData.conversations, ...existingConversations];
          
          // Remove duplicates based on ID
          const uniqueConversations = mergedConversations.filter((conv, index, self) =>
            index === self.findIndex(c => c.id === conv.id)
          );
          
          const success = this.saveConversations(uniqueConversations);
          resolve({ success, count: importData.conversations.length });
        } catch (error) {
          reject(error);
        }
      };
      reader.onerror = () => reject(new Error('Error reading file'));
      reader.readAsText(file);
    });
  }

  /**
   * Clear all conversations
   */
  static clearAllConversations() {
    try {
      localStorage.removeItem(STORAGE_KEY);
      return true;
    } catch (error) {
      console.error('Error clearing conversations:', error);
      return false;
    }
  }
}

export default ConversationStorage;