"""
Frame timing utilities — FPS control and precise timing.
"""

import time


class FrameTimer:
    """Frame timer for consistent render loop timing."""

    def __init__(self, target_frame_dt: float = 0.05):
        self.target_frame_dt = target_frame_dt
        self._frame_count = 0
        self._start_time = time.monotonic()
        self._last_frame_time = self._start_time

    @property
    def fps(self) -> float:
        """Current FPS based on elapsed frames."""
        elapsed = time.monotonic() - self._start_time
        if elapsed > 0:
            return self._frame_count / elapsed
        return 0.0

    def sleep_until_next_frame(self) -> float:
        """Sleep to maintain target frame rate. Returns actual elapsed time."""
        now = time.monotonic()
        elapsed = now - self._last_frame_time
        self._last_frame_time = now
        self._frame_count += 1

        sleep_time = max(0, self.target_frame_dt - elapsed)
        if sleep_time > 0:
            time.sleep(sleep_time)
        return elapsed

    def reset(self) -> None:
        """Reset frame counter and start time."""
        self._frame_count = 0
        self._start_time = time.monotonic()
        self._last_frame_time = self._start_time


def calculate_scroll_step(
    scroll_dur: float, view_height: int, padding: int = 15
) -> float:
    """Calculate scroll step interval for smooth scrolling.

    Args:
        scroll_dur: Duration in seconds for one headline to scroll through view
        view_height: Terminal height in rows
        padding: Extra rows for off-screen content

    Returns:
        Time in seconds between scroll steps
    """
    return scroll_dur / (view_height + padding) * 2