from django.http import StreamingHttpResponse, HttpResponse
from django.views.decorators.csrf import csrf_exempt
from django.views.decorators.http import require_http_methods
from rest_framework.decorators import api_view, permission_classes
from rest_framework.permissions import AllowAny
from rest_framework.response import Response
from rest_framework import status
from . import services
import queue
import json


@csrf_exempt
@require_http_methods(["GET", "OPTIONS"])
def create_sse_event(request):
    """
    创建一个 SSE 事件流响应。
    客户端连接到此端点后会保持长连接，等待服务器推送事件。
    
    使用方法：
    - GET /sse/
    - 保持连接打开以接收实时事件
    
    注意：
    - 使用纯 Django 视图，不使用 DRF，避免内容协商导致的 406 错误
    - SSE 需要特殊的 CORS 配置
    """
    # 处理 OPTIONS 预检请求
    if request.method == 'OPTIONS':
        response = HttpResponse()
        origin = request.META.get('HTTP_ORIGIN')
        if origin:
            response['Access-Control-Allow-Origin'] = origin
            response['Access-Control-Allow-Methods'] = 'GET, OPTIONS'
            response['Access-Control-Allow-Headers'] = 'authorization, content-type, cache-control, accept'
            response['Access-Control-Allow-Credentials'] = 'true'
            response['Access-Control-Max-Age'] = '86400'  # 24小时
        return response
    
    def event_stream():
        # 创建一个同步队列用于接收消息
        conn_queue = queue.Queue(maxsize=100)
        services.push_connection(conn_queue)
        
        try:
            # 发送初始连接成功消息
            yield f"data: {json.dumps({'type': 'connected', 'message': 'SSE connection established'})}\n\n"
            
            # 持续从队列中获取消息并发送给客户端
            while True:
                try:
                    # 使用同步方式等待新消息，带超时（30秒）以便发送心跳
                    message = conn_queue.get(timeout=30.0)
                    yield f"data: {json.dumps(message)}\n\n"
                except queue.Empty:
                    # 30秒超时，发送心跳保持连接活跃
                    yield f": heartbeat\n\n"
                except Exception as e:
                    print(f"Error in SSE stream: {e}")
                    break
        finally:
            # 清理：从连接集合中移除此队列
            services.remove_connection(conn_queue)
    
    response = StreamingHttpResponse(
        event_stream(),
        content_type='text/event-stream',
    )
    
    # SSE 必需的响应头
    response['Cache-Control'] = 'no-cache'
    response['X-Accel-Buffering'] = 'no'  # 禁用 nginx 缓冲
    
    # CORS 响应头（django-cors-headers 中间件会自动添加，但我们显式设置以确保）
    # 如果请求带有 Origin 头，手动添加 CORS 响应头
    origin = request.META.get('HTTP_ORIGIN')
    if origin:
        response['Access-Control-Allow-Origin'] = origin
        response['Access-Control-Allow-Credentials'] = 'true'
    
    return response


@api_view(['POST'])
@permission_classes([AllowAny])
def push_test_event(request):
    """
    向所有连接的客户端广播一个 SSE 测试事件。
    """
    services.push_simple_message_with_object_id('order_paid', '订单已支付', 12345)
    return Response({
        'status': 'ok',
        'message': 'Test event broadcasted',
        'clients': len(services.get_active_connections())
    })


@api_view(['GET'])
@permission_classes([AllowAny])
def get_sse_status(request):
    """
    获取 SSE 连接状态信息。
    
    返回：
    - clients: 当前连接的客户端数量
    - status: 服务状态
    """
    active_connections = services.get_active_connections()
    return Response({
        'status': 'running',
        'clients': len(active_connections),
        'message': f'SSE server is running with {len(active_connections)} active connection(s)',
    })


@api_view(['POST'])
@permission_classes([AllowAny])
def shutdown_sse(request):
    """
    优雅关闭所有SSE连接的端点
    """
    services.push_sse_event_to_all({
        'type': 'server_shutdown',
        'message': 'Server is shutting down, please reconnect later'
    })
    
    return Response({
        'status': 'ok',
        'message': 'Shutdown signal sent to all SSE connections',
        'clients': len(services.get_active_connections())
    })