import time
import psutil
import threading

class PerformanceMonitor:
    def __init__(self):
        self._start_time = None
        self._last_frame_time = 0.0
        self._fps = 0.0
        self._frame_count = 0
        self._fps_last_time = time.time()
        self._process = psutil.Process()
        self._cpu_usage = 0.0
        self._cpu_lock = threading.Lock()
        
        # Input lag tracking
        self._last_input_time = None
        self._input_lag_ms = 0.0
        
        # Start CPU usage monitoring thread
        self._stop_event = threading.Event()
        self._cpu_thread = threading.Thread(target=self._monitor_cpu, daemon=True)
        self._cpu_thread.start()

    def _monitor_cpu(self):
        while not self._stop_event.is_set():
            # psutil.cpu_percent is better than process.cpu_percent for real-time
            usage = self._process.cpu_percent(interval=1.0)
            with self._cpu_lock:
                self._cpu_usage = usage
            time.sleep(0.1)

    def start_frame(self):
        self._start_time = time.time()

    def record_input_event(self):
        self._last_input_time = time.time()

    def end_frame(self):
        if self._start_time is None:
            return
        
        end_time = time.time()
        self._last_frame_time = (end_time - self._start_time) * 1000.0
        self._frame_count += 1
        
        # Calculate input lag if an input occurred during this frame
        if self._last_input_time is not None:
            self._input_lag_ms = (end_time - self._last_input_time) * 1000.0
            self._last_input_time = None
        
        elapsed_since_fps = end_time - self._fps_last_time
        if elapsed_since_fps >= 1.0:
            self._fps = self._frame_count / elapsed_since_fps
            self._frame_count = 0
            self._fps_last_time = end_time

    def get_metrics(self):
        with self._cpu_lock:
            cpu_usage = self._cpu_usage
            
        return {
            'last_frame_time_ms': self._last_frame_time,
            'fps': self._fps,
            'cpu_percent': cpu_usage,
            'input_lag_ms': self._input_lag_ms
        }

    def stop(self):
        self._stop_event.set()
        self._cpu_thread.join(timeout=2.0)