"""Video processing utilities for the DRS application.

This module provides helper functions to save uploaded videos to the
filesystem and to trim the last N seconds from a video.  Using
OpenCV's ``VideoCapture`` and ``VideoWriter`` avoids external
dependencies like ffmpeg or moviepy, which may not be installed in
all execution environments.
"""

from __future__ import annotations

import os
import shutil
from pathlib import Path
from typing import Union

import cv2


def save_uploaded_video(name: str, file_obj: Union[bytes, str, Path]) -> str:
    """Persist an uploaded video to a predictable location on disk.

    When a user records or uploads a video in the Gradio interface, it
    arrives as a temporary file object.  To analyse the video later we
    copy it into the working directory using its original filename.

    Parameters
    ----------
    name: str
        The original filename from the upload widget.
    file_obj: Union[bytes, str, Path]
        The file-like object representing the uploaded video.  Gradio
        passes the file as a ``gradio.Files`` object whose `.name`
        property holds the temporary path.  This function accepts
        either the temporary path or an open file handle.

    Returns
    -------
    str
        The absolute path where the video has been saved.
    """
    # Determine a safe output directory.  Use the current working
    # directory so that Gradio can later access the file by path.
    output_dir = Path(os.getcwd()) / "user_videos"
    output_dir.mkdir(exist_ok=True)

    # Compose an output filename; avoid overwriting by prefixing with an
    # incrementing integer if necessary.
    base_name = Path(name).stem
    ext = Path(name).suffix or ".mp4"
    counter = 0
    dest = output_dir / f"{base_name}{ext}"
    while dest.exists():
        counter += 1
        dest = output_dir / f"{base_name}_{counter}{ext}"

    # If file_obj is a path, simply copy it; otherwise, read and write
    if isinstance(file_obj, (str, Path)):
        shutil.copy(str(file_obj), dest)
    else:
        # Gradio passes a file-like object with a `.read()` method
        with open(dest, "wb") as f_out:
            f_out.write(file_obj.read())
    return str(dest)


def trim_last_seconds(input_path: str, output_path: str, seconds: int) -> None:
    """Save the last ``seconds`` of a video to ``output_path``.

    This function reads the entire video file, calculates the starting
    frame corresponding to ``seconds`` before the end, and writes the
    remaining frames to a new video using OpenCV.  If the video is
    shorter than the requested duration, the whole video is copied.

    Parameters
    ----------
    input_path: str
        Path to the source video file.
    output_path: str
        Path where the trimmed video will be saved.
    seconds: int
        The duration from the end of the video to retain.
    """
    cap = cv2.VideoCapture(input_path)
    if not cap.isOpened():
        raise RuntimeError(f"Unable to open video: {input_path}")

    fps = cap.get(cv2.CAP_PROP_FPS)
    total_frames = int(cap.get(cv2.CAP_PROP_FRAME_COUNT))
    if fps <= 0:
        fps = 30.0  # default fallback
    frames_to_keep = int(seconds * fps)
    start_frame = max(total_frames - frames_to_keep, 0)

    # Prepare writer with the same properties as the input
    width = int(cap.get(cv2.CAP_PROP_FRAME_WIDTH))
    height = int(cap.get(cv2.CAP_PROP_FRAME_HEIGHT))
    fourcc = cv2.VideoWriter_fourcc(*"mp4v")
    out = cv2.VideoWriter(output_path, fourcc, fps, (width, height))

    # Skip frames until start_frame
    current = 0
    while current < start_frame:
        ret, _ = cap.read()
        if not ret:
            break
        current += 1

    # Write remaining frames
    while True:
        ret, frame = cap.read()
        if not ret:
            break
        out.write(frame)

    cap.release()
    out.release()