# cache_implementation.py
import time
from typing import Optional

class SessionCache:
    def __init__(self):
        self.memory_cache = {}
        self.hits = 0
        self.misses = 0
        
    def get(self, session_id: str) -> Optional[dict]:
        if session_id in self.memory_cache:
            self.hits += 1
            return self.memory_cache[session_id]
        self.misses += 1
        return None
        
    def set(self, session_id: str, data: dict, ttl: int = 3600):
        # Size-based eviction
        if self._get_total_size() > 100 * 1024 * 1024:  # 100MB limit
            self._evict_oldest()
            
        compressed_data = self._compress_data(data)
        self.memory_cache[session_id] = {
            'data': compressed_data,
            'timestamp': time.time(),
            'ttl': ttl
        }
    
    def delete(self, session_id: str):
        """
        Remove session from cache
        """
        if session_id in self.memory_cache:
            del self.memory_cache[session_id]
    
    def clear(self):
        """
        Clear all cached sessions
        """
        self.memory_cache.clear()
        self.hits = 0
        self.misses = 0
    
    def get_hit_rate(self) -> float:
        """
        Calculate cache hit rate
        """
        total = self.hits + self.misses
        return self.hits / total if total > 0 else 0.0
    
    def _get_total_size(self) -> int:
        """
        Calculate total size of cached data
        """
        # TODO: Implement actual size calculation
        return len(str(self.memory_cache))
    
    def _evict_oldest(self):
        """
        Evict oldest session based on timestamp
        """
        if not self.memory_cache:
            return
        
        oldest_session = min(
            self.memory_cache.items(),
            key=lambda x: x[1].get('timestamp', 0)
        )
        del self.memory_cache[oldest_session[0]]
    
    def _compress_data(self, data: dict) -> dict:
        """
        Compress data using specified compression algorithm
        """
        # TODO: Implement actual gzip compression if needed
        # For now, return as-is
        return data