"""Annotated video writer — wraps OpenCV VideoWriter for output."""

from __future__ import annotations

from pathlib import Path

import cv2
import numpy as np


class AnnotatedVideoWriter:
    """Writes annotated frames to an MP4 file.

    Args:
        output_path: Destination .mp4 file path.
        fps: Frames per second for the output video.
        frame_size: (width, height) tuple.
        codec: FourCC codec string (default "mp4v").
    """

    def __init__(
        self,
        output_path: str,
        fps: float,
        frame_size: tuple[int, int],
        codec: str = "mp4v",
    ) -> None:
        if fps <= 0:
            raise ValueError(f"fps must be > 0, got {fps}")
        self._path = Path(output_path)
        self._path.parent.mkdir(parents=True, exist_ok=True)

        w, h = frame_size
        fourcc = cv2.VideoWriter_fourcc(*codec)
        self._writer = cv2.VideoWriter(str(self._path), fourcc, fps, (w, h))
        self._frame_count = 0

        if not self._writer.isOpened():
            raise RuntimeError(f"Failed to open VideoWriter for {self._path}")

    def write_frame(self, frame: np.ndarray) -> None:
        """Write one frame. Frame size must match constructor frame_size."""
        self._writer.write(frame)
        self._frame_count += 1

    def finish(self) -> None:
        """Release the writer. Idempotent — safe to call multiple times."""
        if self._writer is not None and self._writer.isOpened():
            self._writer.release()

    @property
    def frame_count(self) -> int:
        return self._frame_count