"""
HTTP server that implements the Python WSGI protocol (PEP 333, rev 1.21).

Based on wsgiref.simple_server which is part of the standard library since 2.5.

This is a simple server for use in testing or debugging Django apps. It hasn't
been reviewed for security issues. DON'T USE IT FOR PRODUCTION USE!
"""

import logging
import socket
import socketserver
import sys
from wsgiref import simple_server

from django.core.exceptions import ImproperlyConfigured
from django.core.handlers.wsgi import LimitedStream
from django.core.wsgi import get_wsgi_application
from django.db import connections
from django.utils.module_loading import import_string

__all__ = ('WSGIServer', 'WSGIRequestHandler')

logger = logging.getLogger('django.server')


def get_internal_wsgi_application():
    """
    Load and return the WSGI application as configured by the user in
    ``settings.WSGI_APPLICATION``. With the default ``startproject`` layout,
    this will be the ``application`` object in ``projectname/wsgi.py``.

    This function, and the ``WSGI_APPLICATION`` setting itself, are only useful
    for Django's internal server (runserver); external WSGI servers should just
    be configured to point to the correct application object directly.

    If settings.WSGI_APPLICATION is not set (is ``None``), return
    whatever ``django.core.wsgi.get_wsgi_application`` returns.
    """
    from django.conf import settings
    app_path = getattr(settings, 'WSGI_APPLICATION')
    if app_path is None:
        return get_wsgi_application()

    try:
        return import_string(app_path)
    except ImportError as err:
        raise ImproperlyConfigured(
            "WSGI application '%s' could not be loaded; "
            "Error importing module." % app_path
        ) from err


def is_broken_pipe_error():
    exc_type, _, _ = sys.exc_info()
    return issubclass(exc_type, (
        BrokenPipeError,
        ConnectionAbortedError,
        ConnectionResetError,
    ))


class WSGIServer(simple_server.WSGIServer):
    """BaseHTTPServer that implements the Python WSGI protocol"""

    request_queue_size = 10

    def __init__(self, *args, ipv6=False, allow_reuse_address=True, **kwargs):
        if ipv6:
            self.address_family = socket.AF_INET6
        self.allow_reuse_address = allow_reuse_address
        super().__init__(*args, **kwargs)

    def handle_error(self, request, client_address):
        if is_broken_pipe_error():
            logger.info("- Broken pipe from %s\n", client_address)
        else:
            super().handle_error(request, client_address)


class ThreadedWSGIServer(socketserver.ThreadingMixIn, WSGIServer):
    """A threaded version of the WSGIServer"""
    daemon_threads = True

    def __init__(self, *args, connections_override=None, **kwargs):
        super().__init__(*args, **kwargs)
        self.connections_override = connections_override

    # socketserver.ThreadingMixIn.process_request() passes this method as
    # the target to a new Thread object.
    def process_request_thread(self, request, client_address):
        if self.connections_override:
            # Override this thread's database connections with the ones
            # provided by the parent thread.
            for alias, conn in self.connections_override.items():
                connections[alias] = conn
        super().process_request_thread(request, client_address)

    def _close_connections(self):
        # Used for mocking in tests.
        connections.close_all()

    def close_request(self, request):
        self._close_connections()
        super().close_request(request)


class ServerHandler(simple_server.ServerHandler):
    http_version = '1.1'

    def __init__(self, stdin, stdout, stderr, environ, **kwargs):
        """
        Use a LimitedStream so that unread request data will be ignored at
        the end of the request. WSGIRequest uses a LimitedStream but it
        shouldn't discard the data since the upstream servers usually do this.
        This fix applies only for testserver/runserver.
        """
        try:
            content_length = int(environ.get('CONTENT_LENGTH'))
        except (ValueError, TypeError):
            content_length = 0
        super().__init__(LimitedStream(stdin, content_length), stdout, stderr, environ, **kwargs)

    def cleanup_headers(self):
        super().cleanup_headers()
        # HTTP/1.1 requires support for persistent connections. Send 'close' if
        # the content length is unknown to prevent clients from reusing the
        # connection.
        if 'Content-Length' not in self.headers:
            self.headers['Connection'] = 'close'
        # Persistent connections require threading server.
        elif not isinstance(self.request_handler.server, socketserver.ThreadingMixIn):
            self.headers['Connection'] = 'close'
        # Mark the connection for closing if it's set as such above or if the
        # application sent the header.
        if self.headers.get('Connection') == 'close':
            self.request_handler.close_connection = True

    def close(self):
        self.get_stdin()._read_limited()
        super().close()


class WSGIRequestHandler(simple_server.WSGIRequestHandler):
    protocol_version = 'HTTP/1.1'

    def address_string(self):
        # Short-circuit parent method to not call socket.getfqdn
        return self.client_address[0]

    def log_message(self, format, *args):
        extra = {
            'request': self.request,
            'server_time': self.log_date_time_string(),
        }
        if args[1][0] == '4':
            # 0x16 = Handshake, 0x03 = SSL 3.0 or TLS 1.x
            if args[0].startswith('\x16\x03'):
                extra['status_code'] = 500
                logger.error(
                    "You're accessing the development server over HTTPS, but "
                    "it only supports HTTP.\n", extra=extra,
                )
                return

        if args[1].isdigit() and len(args[1]) == 3:
            status_code = int(args[1])
            extra['status_code'] = status_code

            if status_code >= 500:
                level = logger.error
            elif status_code >= 400:
                level = logger.warning
            else:
                level = logger.info
        else:
            level = logger.info

        level(format, *args, extra=extra)

    def get_environ(self):
        # Strip all headers with underscores in the name before constructing
        # the WSGI environ. This prevents header-spoofing based on ambiguity
        # between underscores and dashes both normalized to underscores in WSGI
        # env vars. Nginx and Apache 2.4+ both do this as well.
        for k in self.headers:
            if '_' in k:
                del self.headers[k]

        return super().get_environ()

    def handle(self):
        self.close_connection = True
        self.handle_one_request()
        while not self.close_connection:
            self.handle_one_request()
        try:
            self.connection.shutdown(socket.SHUT_WR)
        except (AttributeError, OSError):
            pass

    def handle_one_request(self):
        """Copy of WSGIRequestHandler.handle() but with different ServerHandler"""
        self.raw_requestline = self.rfile.readline(65537)
        if len(self.raw_requestline) > 65536:
            self.requestline = ''
            self.request_version = ''
            self.command = ''
            self.send_error(414)
            return

        if not self.parse_request():  # An error code has been sent, just exit
            return

        handler = ServerHandler(
            self.rfile, self.wfile, self.get_stderr(), self.get_environ()
        )
        handler.request_handler = self      # backpointer for logging & connection closing
        handler.run(self.server.get_app())


def run(addr, port, wsgi_handler, ipv6=False, threading=False, server_cls=WSGIServer):
    server_address = (addr, port)
    if threading:
        httpd_cls = type('WSGIServer', (socketserver.ThreadingMixIn, server_cls), {})
    else:
        httpd_cls = server_cls
    httpd = httpd_cls(server_address, WSGIRequestHandler, ipv6=ipv6)
    if threading:
        # ThreadingMixIn.daemon_threads indicates how threads will behave on an
        # abrupt shutdown; like quitting the server by the user or restarting
        # by the auto-reloader. True means the server will not wait for thread
        # termination before it quits. This will make auto-reloader faster
        # and will prevent the need to kill the server manually if a thread
        # isn't terminating correctly.
        httpd.daemon_threads = True
    httpd.set_app(wsgi_handler)
    httpd.serve_forever()
