#!/usr/bin/env python3
import subprocess
import json
import os
import sys
import argparse

def get_best_hwaccel():
    """
    Checks for available FFmpeg hardware acceleration methods and returns the best one.
    Priority is defined as: cuda > qsv > dxva2.
    Returns the name of the best available method, or None if none are found.
    """
    priority = ['cuda', 'qsv', 'dxva2']
    print("Checking for available hardware acceleration...")
    try:
        # Run ffmpeg to list available hardware acceleration methods
        result = subprocess.run(
            ['ffmpeg', '-hide_banner', '-hwaccels'],
            capture_output=True, text=True, encoding='utf-8', check=False
        )
        
        if result.returncode != 0:
            print("Warning: Could not query FFmpeg for hardware acceleration. Using software decoding.")
            return None

        # Parse the output to get a list of available methods
        available_methods = result.stdout.strip().split('\n')
        if len(available_methods) > 1:
            available_methods = available_methods[1:]

        # Check for our preferred methods in order of priority
        for method in priority:
            if method in available_methods:
                print(f"Found best available hardware acceleration: {method}")
                return method
        
        print("No high-priority hardware acceleration (cuda, qsv, dxva2) found. Using software decoding.")
        return None

    except FileNotFoundError:
        # This will be handled by the main ffmpeg call later, so we just return None.
        return None
    except Exception as e:
        print(f"Warning: An error occurred while checking for hwaccel: {e}. Using software decoding.")
        return None

def detect_scenes(video_path, hwaccel=None, threshold=0.4):
    """
    Uses FFmpeg to detect scene changes in a video and saves the timestamps to a JSON file.
    """
    print(f"Starting scene detection for: {os.path.basename(video_path)}")
    
    # Define the output JSON file path based on the input video name
    base_name = os.path.splitext(video_path)[0]
    json_output_path = f"{base_name}.scenes.json"

    # Base FFmpeg command
    command = ['ffmpeg', '-hide_banner']

    # If hardware acceleration is specified, add the relevant flags
    if hwaccel:
        print(f"Attempting to use hardware acceleration: {hwaccel}")
        command.extend(['-hwaccel', hwaccel])

    # Add the rest of the command arguments
    # The filter string is now built dynamically with the specified threshold
    filter_string = f"select='gt(scene,{threshold})',showinfo"
    command.extend([
        '-i', video_path,
        '-vf', filter_string,
        '-f', 'null',
        '-'
    ])

    # Execute the FFmpeg command
    try:
        # Use Popen to start the process and read its output in real-time
        process = subprocess.Popen(command, stderr=subprocess.PIPE, text=True, encoding='utf-8')

        scene_timestamps = []
        
        # Read stderr line by line as it's produced
        for line in iter(process.stderr.readline, ''):
            # Check for scene detection output (which contains pts_time)
            if 'pts_time:' in line:
                timestamp_str = line.split('pts_time:')[1].split()[0]
                scene_timestamps.append(float(timestamp_str))
            # Check for ffmpeg's progress line (which starts with 'frame=')
            # and print it to the actual stderr to show progress
            elif line.strip().startswith('frame='):
                # Use sys.stderr to avoid interfering with stdout prints
                # Use '\r' to have the line overwrite itself, mimicking ffmpeg's behavior
                sys.stderr.write(f'\r{line.strip()}')
                sys.stderr.flush()

        # Wait for the process to finish and get the return code
        process.wait()
        
        # Print a newline to move past the progress bar
        sys.stderr.write('\n')
        sys.stderr.flush()

        if process.returncode != 0:
            print(f"\nWarning: FFmpeg may have encountered an error (exit code: {process.returncode}).")

        if not scene_timestamps:
            print("Warning: No scenes were detected. The output file will be empty.")

        # Save the detected scenes to a JSON file
        with open(json_output_path, 'w') as json_file:
            json.dump(scene_timestamps, json_file, indent=4)

        print(f"Scene detection completed. {len(scene_timestamps)} scenes found.")
        print(f"Results saved to: {json_output_path}")

    except FileNotFoundError:
        print("Error: 'ffmpeg' command not found. Is it installed and in your system's PATH?")
    except Exception as e:
        print(f"An error occurred: {e}")

def main():
    """
    Main function to handle command-line arguments.
    """
    parser = argparse.ArgumentParser(description="Detect scene changes in a video using FFmpeg.")
    parser.add_argument("video_path", help="Path to the video file.")
    parser.add_argument(
        "-t", "--threshold",
        type=float,
        default=0.4,
        help="Set the scene detection threshold (0.0 to 1.0). Lower is more sensitive. Default: 0.4"
    )
    
    args = parser.parse_args()

    if not os.path.isfile(args.video_path):
        print(f"Error: Input file not found: '{args.video_path}'")
        sys.exit(1)
        
    # Automatically determine the best hardware acceleration method
    hwaccel_method = get_best_hwaccel()
    
    detect_scenes(args.video_path, hwaccel_method, args.threshold)

if __name__ == "__main__":
    main()