import time
from collections import defaultdict

class HistoryManager:
    _instance = None

    @classmethod
    def get_instance(cls):
        """Get the singleton instance of HistoryManager."""
        if cls._instance is None:
            cls._instance = cls()
        return cls._instance

    def __init__(self):
        if self._instance is not None:
            raise Exception("This class is a singleton!")
        self.user_histories = defaultdict(list) 
        self.expiration_time = 1800 

    def add_history(self, user_id, query, response):
        """Add a user query and AI response to the history."""
        timestamp = time.time()
        print(f"adding history {user_id} {query} {response}")
        
        self.user_histories[user_id].append({'timestamp': timestamp, 'query': query, 'response': response})
        
        

    def get_history(self, user_id, limit=10, offset=0):
        """Retrieve a limited number of history entries for a given user ID with offset."""
        if user_id not in self.user_histories.keys():

            return []  

        histories = self.user_histories[user_id]
        return histories[-(offset + limit):-offset] if offset else histories[-limit:]  # Get entries based on limit and offset

    def cleanup_histories(self):
        """Remove histories older than the expiration time."""
        print("Cleaning")
        current_time = time.time()
        expired_keys = [user_id for user_id, histories in self.user_histories.items() 
                        if all((current_time - entry['timestamp']) > self.expiration_time for entry in histories)]
        print("Start Cleaning")
        for user_id in expired_keys:
            del self.user_histories[user_id]
            print(f"Removed history for user ID: {user_id}")  # Debugging line