import yt_dlp
import os
import time

def download_audio(url, output_folder, max_length_seconds=600):
    """
    Downloads audio from a YouTube URL.
    Returns the path to the downloaded file or raises an Exception.
    Enforces max_length_seconds (default 10 mins).
    """
    
    timestamp = int(time.time())
    output_template = os.path.join(output_folder, f'yt_{timestamp}_%(id)s.%(ext)s')

    ydl_opts = {
        'format': 'bestaudio/best',
        'outtmpl': output_template,
        'postprocessors': [{
            'key': 'FFmpegExtractAudio',
            'preferredcodec': 'mp3',
            'preferredquality': '192',
        }],
        'quiet': True,
        'no_warnings': True,
        'noplaylist': True,
        'match_filter': yt_dlp.utils.match_filter_func("duration <= " + str(max_length_seconds))
    }

    try:
        with yt_dlp.YoutubeDL(ydl_opts) as ydl:
            info = ydl.extract_info(url, download=True)
            # The file path might differ slightly because of the postprocessor (mp3 conversion)
            # yt-dlp usually returns the final filename in 'requested_downloads' or similar, 
            # but constructing it from info is safer if we know the template.
            # However, extract_info returns the info dict. 
            
            # Since we force mp3, the file will end in .mp3
            # We used %(id)s in template, so we can reconstruct or find it.
            
            # Let's find the file in the folder that matches the timestamp prefix
            # This is safer than guessing what yt-dlp named it exactly
            
            valid_files = [f for f in os.listdir(output_folder) if f.startswith(f'yt_{timestamp}_') and f.endswith('.mp3')]
            if not valid_files:
                 raise Exception("Download failed: Audio file not found after processing.")
            
            return os.path.join(output_folder, valid_files[0])

    except yt_dlp.utils.DownloadError as e:
        if "video is too long" in str(e).lower() or "duration" in str(e).lower():
             raise Exception(f"Video is too long. Maximum allowed duration is {max_length_seconds} seconds.")
        raise Exception(f"Failed to download video: {str(e)}")