from flask import Flask, request, jsonify, Response
import random
import string
import threading
import time
from datetime import datetime, timedelta

app = Flask(__name__)

transfers = {}
transfer_data = {}
transfer_lock = threading.Lock()

# Настройки
KEEP_ALIVE_INTERVAL = 10  # Отправлять keep-alive каждые 25 секунд
TRANSFER_TIMEOUT = 3600   # 1 час таймаута передачи

def generate_short_id(length=8):
    while True:
        token = ''.join(random.choices(string.ascii_letters + string.digits, k=length))
        if token not in transfers:
            return token

@app.route('/download/<transfer_id>', methods=['GET'])
def download_file(transfer_id):
    def generate():
        last_activity = time.time()
        index = 0
        
        while True:
            with transfer_lock:
                # Проверка таймаута
                if time.time() - last_activity > TRANSFER_TIMEOUT:
                    break
                
                transfer = transfers.get(transfer_id)
                if not transfer:
                    break
                
                chunks = transfer_data.get(transfer_id, [])
                
                # Отправка доступных чанков
                while index < len(chunks):
                    yield chunks[index]
                    last_activity = time.time()
                    index += 1
                
                if transfer['completed']:
                    break

            # Отправка keep-alive
            if time.time() - last_activity > KEEP_ALIVE_INTERVAL:
                yield b'\0'  # Пустой чанк для поддержания соединения
                last_activity = time.time()
            
            time.sleep(0.5)

    return Response(
        generate(),
        mimetype='application/octet-stream',
        headers={
            'Content-Disposition': f'attachment; filename="{transfers[transfer_id]["filename"]}"',
            'Cache-Control': 'no-store'
        }
    )