main.py

"""
main.py
Developed by Alperen Sümeroğlu - YouTube Audio Converter API
Clean, modular Flask-based backend for downloading and serving YouTube audio tracks.
Utilizes yt-dlp and FFmpeg for conversion and token-based access management.
"""

import secrets
import threading
from flask import Flask, request, jsonify, send_from_directory
from uuid import uuid4
from pathlib import Path
import yt_dlp
import access_manager
from constants import *

# Initialize the Flask application
app = Flask(__name__)


@app.route("/", methods=["GET"])
def handle_audio_request():
    """
    Main endpoint to receive a YouTube video URL, download the audio in MP3 format,
    and return a unique token for accessing the file later.

    Query Parameters:
        - url (str): Full YouTube video URL.

    Returns:
        - JSON: {"token": <download_token>}
    """
    video_url = request.args.get("url")
    if not video_url:
        return jsonify(error="Missing 'url' parameter in request."), BAD_REQUEST

    filename = f"{uuid4()}.mp3"
    output_path = Path(ABS_DOWNLOADS_PATH) / filename

    # yt-dlp configuration for downloading best audio and converting to mp3
    ydl_opts = {
        'format': 'bestaudio/best',
        'outtmpl': str(output_path),
        'postprocessors': [{
            'key': 'FFmpegExtractAudio',
            'preferredcodec': 'mp3',
            'preferredquality': '192'
        }],
        'quiet': True
    }

    try:
        with yt_dlp.YoutubeDL(ydl_opts) as ydl:
            ydl.download([video_url])
    except Exception as e:
        return jsonify(error="Failed to download or convert audio.", detail=str(e)), INTERNAL_SERVER_ERROR

    return _generate_token_response(filename)


@app.route("/download", methods=["GET"])
def download_audio():
    """
    Endpoint to serve an audio file associated with a given token.
    If token is valid and not expired, returns the associated MP3 file.

    Query Parameters:
        - token (str): Unique access token

    Returns:
        - MP3 audio file as attachment or error JSON
    """
    token = request.args.get("token")
    if not token:
        return jsonify(error="Missing 'token' parameter in request."), BAD_REQUEST

    if not access_manager.has_access(token):
        return jsonify(error="Token is invalid or unknown."), UNAUTHORIZED

    if not access_manager.is_valid(token):
        return jsonify(error="Token has expired."), REQUEST_TIMEOUT

    try:
        filename = access_manager.get_audio_file(token)
        return send_from_directory(ABS_DOWNLOADS_PATH, filename=filename, as_attachment=True)
    except FileNotFoundError:
        return jsonify(error="Requested file could not be found on the server."), NOT_FOUND


def _generate_token_response(filename: str):
    """
    Generates a secure download token for a given filename,
    registers it in the access manager, and returns the token as JSON.

    Args:
        filename (str): The name of the downloaded MP3 file

    Returns:
        JSON: {"token": <generated_token>}
    """
    token = secrets.token_urlsafe(TOKEN_LENGTH)
    access_manager.add_token(token, filename)
    return jsonify(token=token)


def main():
    """
    Starts the background thread for automatic token cleanup
    and launches the Flask development server.
    """
    token_cleaner_thread = threading.Thread(
        target=access_manager.manage_tokens,
        daemon=True
    )
    token_cleaner_thread.start()
    app.run(debug=True)


if __name__ == "__main__":
    main()