"""
可选：慢请求追踪（默认关闭，不影响现网）。
启用: 在 gunicorn systemd 的 Environment 加 SLOW_REQUEST_TRACE=1 后 restart。
日志: /tmp/slow-request-trace.log
"""
import logging
import os
import time

logger = logging.getLogger('slow_request')

_ENABLED = os.environ.get('SLOW_REQUEST_TRACE', '').strip() in ('1', 'true', 'yes')
_THRESHOLD_MS = float(os.environ.get('SLOW_REQUEST_THRESHOLD_MS', '300'))
_LOG_PATH = os.environ.get('SLOW_REQUEST_LOG', '/tmp/slow-request-trace.log')


class SlowRequestTraceMiddleware:
    def __init__(self, get_response):
        self.get_response = get_response

    def __call__(self, request):
        if not _ENABLED:
            return self.get_response(request)

        t0 = time.perf_counter()
        from django.db import connection, reset_queries
        reset_queries()
        response = self.get_response(request)
        elapsed_ms = (time.perf_counter() - t0) * 1000

        if elapsed_ms >= _THRESHOLD_MS:
            n_sql = len(connection.queries)
            sql_ms = sum(float(q.get('time', 0)) for q in connection.queries) * 1000
            line = (
                f"{elapsed_ms:.0f}ms total | sql={n_sql}条/{sql_ms:.0f}ms | "
                f"{request.method} {request.path} | status={response.status_code}\n"
            )
            try:
                with open(_LOG_PATH, 'a', encoding='utf-8') as f:
                    f.write(line)
                    if n_sql <= 30:
                        for q in sorted(connection.queries, key=lambda x: -float(x.get('time', 0)))[:5]:
                            sql = q['sql'][:200].replace('\n', ' ')
                            f.write(f"  {float(q['time'])*1000:.0f}ms {sql}\n")
            except OSError:
                logger.warning('slow request trace write failed')
        return response