# This file is part of Radicale Server - Calendar Server
# Copyright © 2008 Nicolas Kandel
# Copyright © 2008 Pascal Halter
# Copyright © 2008-2017 Guillaume Ayoub
# Copyright © 2017-2019 Unrud <unrud@outlook.com>
#
# This library is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This library is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with Radicale.  If not, see <http://www.gnu.org/licenses/>.

"""
Built-in WSGI server.

Uses forking on POSIX to overcome Python's GIL.

"""

import contextlib
import multiprocessing
import os
import select
import socket
import socketserver
import ssl
import sys
import threading
import wsgiref.simple_server
from urllib.parse import unquote

from radicale import Application
from radicale.log import logger

try:
    import systemd.daemon
except ImportError:
    systemd = None

USE_FORKING = hasattr(os, "fork")
try:
    multiprocessing.BoundedSemaphore()
except Exception:
    # HACK: Workaround for Android
    USE_FORKING = False

if USE_FORKING:
    ParallelizationMixIn = socketserver.ForkingMixIn
else:
    ParallelizationMixIn = socketserver.ThreadingMixIn

HAS_IPV6 = socket.has_ipv6
if hasattr(socket, "EAI_NONAME"):
    EAI_NONAME = socket.EAI_NONAME
else:
    HAS_IPV6 = False
if hasattr(socket, "EAI_ADDRFAMILY"):
    EAI_ADDRFAMILY = socket.EAI_ADDRFAMILY
elif os.name == "nt":
    EAI_ADDRFAMILY = None
else:
    HAS_IPV6 = False
if hasattr(socket, "IPPROTO_IPV6"):
    IPPROTO_IPV6 = socket.IPPROTO_IPV6
elif os.name == "nt":
    IPPROTO_IPV6 = 41
else:
    HAS_IPV6 = False
if hasattr(socket, "IPV6_V6ONLY"):
    IPV6_V6ONLY = socket.IPV6_V6ONLY
elif os.name == "nt":
    IPV6_V6ONLY = 27
else:
    HAS_IPV6 = False


class ParallelHTTPServer(ParallelizationMixIn,
                         wsgiref.simple_server.WSGIServer):

    # wait for child processes/threads
    _block_on_close = True

    # These class attributes must be set before creating instance
    client_timeout = None
    max_connections = None

    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        if USE_FORKING:
            sema_class = multiprocessing.BoundedSemaphore
        else:
            sema_class = threading.BoundedSemaphore
        if self.max_connections:
            self.connections_guard = sema_class(self.max_connections)
        else:
            # use dummy context manager
            self.connections_guard = contextlib.ExitStack()

    def server_bind(self):
        if isinstance(self.server_address, socket.socket):
            # Socket activation
            self.socket = self.server_address
            self.server_address = self.socket.getsockname()
            host, port = self.server_address[:2]
            self.server_name = socket.getfqdn(host)
            self.server_port = port
            self.setup_environ()
            return
        try:
            super().server_bind()
        except socket.gaierror as e:
            if (not HAS_IPV6 or self.address_family != socket.AF_INET or
                    e.errno not in (EAI_NONAME, EAI_ADDRFAMILY)):
                raise
            # Try again with IPv6
            self.address_family = socket.AF_INET6
            self.socket = socket.socket(self.address_family, self.socket_type)
            # Only allow IPv6 connections to the IPv6 socket
            self.socket.setsockopt(IPPROTO_IPV6, IPV6_V6ONLY, 1)
            super().server_bind()

    def get_request(self):
        # Set timeout for client
        socket_, address = super().get_request()
        if self.client_timeout:
            socket_.settimeout(self.client_timeout)
        return socket_, address

    def process_request(self, request, client_address):
        try:
            return super().process_request(request, client_address)
        finally:
            # Modify OpenSSL's RNG state, in case process forked
            # See https://docs.python.org/3.7/library/ssl.html#multi-processing
            ssl.RAND_add(os.urandom(8), 0.0)

    def finish_request_locked(self, request, client_address):
        return super().finish_request(request, client_address)

    def finish_request(self, request, client_address):
        """Don't overwrite this! (Modified by tests.)"""
        with self.connections_guard:
            return self.finish_request_locked(request, client_address)

    def handle_error(self, request, client_address):
        if issubclass(sys.exc_info()[0], socket.timeout):
            logger.info("client timed out", exc_info=True)
        else:
            logger.error("An exception occurred during request: %s",
                         sys.exc_info()[1], exc_info=True)


class ParallelHTTPSServer(ParallelHTTPServer):

    # These class attributes must be set before creating instance
    certificate = None
    key = None
    protocol = None
    ciphers = None
    certificate_authority = None

    def server_bind(self):
        """Create server by wrapping HTTP socket in an SSL socket."""
        super().server_bind()
        self.socket = ssl.wrap_socket(
            self.socket, self.key, self.certificate, server_side=True,
            cert_reqs=ssl.CERT_REQUIRED if self.certificate_authority else
            ssl.CERT_NONE,
            ca_certs=self.certificate_authority or None,
            ssl_version=self.protocol, ciphers=self.ciphers,
            do_handshake_on_connect=False)

    def finish_request_locked(self, request, client_address):
        try:
            try:
                request.do_handshake()
            except socket.timeout:
                raise
            except Exception as e:
                raise RuntimeError("SSL handshake failed: %s" % e) from e
        except Exception:
            try:
                self.handle_error(request, client_address)
            finally:
                self.shutdown_request(request)
            return
        return super().finish_request_locked(request, client_address)


class ServerHandler(wsgiref.simple_server.ServerHandler):

    # Don't pollute WSGI environ with OS environment
    os_environ = {}

    def log_exception(self, exc_info):
        logger.error("An exception occurred during request: %s",
                     exc_info[1], exc_info=exc_info)


class RequestHandler(wsgiref.simple_server.WSGIRequestHandler):
    """HTTP requests handler."""

    def log_request(self, code="-", size="-"):
        """Disable request logging."""

    def log_error(self, format_, *args):
        logger.error("An error occurred during request: %s", format_ % args)

    def get_environ(self):
        env = super().get_environ()
        if hasattr(self.connection, "getpeercert"):
            # The certificate can be evaluated by the auth module
            env["REMOTE_CERTIFICATE"] = self.connection.getpeercert()
        # Parent class only tries latin1 encoding
        env["PATH_INFO"] = unquote(self.path.split("?", 1)[0])
        return env

    def handle(self):
        """Copy of WSGIRequestHandler.handle 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():
            return

        handler = ServerHandler(
            self.rfile, self.wfile, self.get_stderr(), self.get_environ()
        )
        handler.request_handler = self
        handler.run(self.server.get_app())


def serve(configuration, shutdown_socket=None):
    """Serve radicale from configuration."""
    logger.info("Starting Radicale")
    # Copy configuration before modifying
    configuration = configuration.copy()
    configuration.update({"internal": {"internal_server": "True"}}, "server",
                         internal=True)

    # Create collection servers
    servers = {}
    if configuration.get("server", "ssl"):
        server_class = ParallelHTTPSServer
    else:
        server_class = ParallelHTTPServer

    class ServerCopy(server_class):
        """Copy, avoids overriding the original class attributes."""
    ServerCopy.client_timeout = configuration.get("server", "timeout")
    ServerCopy.max_connections = configuration.get("server", "max_connections")
    if configuration.get("server", "ssl"):
        ServerCopy.certificate = configuration.get("server", "certificate")
        ServerCopy.key = configuration.get("server", "key")
        ServerCopy.certificate_authority = configuration.get(
            "server", "certificate_authority")
        ServerCopy.ciphers = configuration.get("server", "ciphers")
        ServerCopy.protocol = getattr(
            ssl, configuration.get("server", "protocol"), ssl.PROTOCOL_SSLv23)
        # Test if the SSL files can be read
        for name in ["certificate", "key"] + (
                ["certificate_authority"]
                if ServerCopy.certificate_authority else []):
            filename = getattr(ServerCopy, name)
            try:
                open(filename, "r").close()
            except OSError as e:
                raise RuntimeError("Failed to read SSL %s %r: %s" %
                                   (name, filename, e)) from e

    class RequestHandlerCopy(RequestHandler):
        """Copy, avoids overriding the original class attributes."""
    if not configuration.get("server", "dns_lookup"):
        RequestHandlerCopy.address_string = lambda self: self.client_address[0]

    if systemd:
        listen_fds = systemd.daemon.listen_fds()
    else:
        listen_fds = []

    server_addresses = []
    if listen_fds:
        logger.info("Using socket activation")
        ServerCopy.address_family = socket.AF_UNIX
        for fd in listen_fds:
            server_addresses.append(socket.fromfd(
                fd, ServerCopy.address_family, ServerCopy.socket_type))
    else:
        for address, port in configuration.get("server", "hosts"):
            server_addresses.append((address, port))

    application = Application(configuration)
    for server_address in server_addresses:
        try:
            server = ServerCopy(server_address, RequestHandlerCopy)
            server.set_app(application)
        except OSError as e:
            raise RuntimeError(
                "Failed to start server %r: %s" % (server_address, e)) from e
        servers[server.socket] = server
        logger.info("Listening to %r on port %d%s",
                    server.server_name, server.server_port, " using SSL"
                    if configuration.get("server", "ssl") else "")

    # Main loop: wait for requests on any of the servers or program shutdown
    sockets = list(servers.keys())
    # Use socket pair to get notified of program shutdown
    if shutdown_socket:
        sockets.append(shutdown_socket)
    select_timeout = None
    if os.name == "nt":
        # Fallback to busy waiting. (select.select blocks SIGINT on Windows.)
        select_timeout = 1.0
    logger.info("Radicale server ready")

    with contextlib.ExitStack() as stack:
        for _, server in servers.items():
            stack.callback(server.server_close)
        while True:
            rlist, _, xlist = select.select(
                sockets, [], sockets, select_timeout)
            if xlist:
                raise RuntimeError("unhandled socket error")
            if shutdown_socket in rlist:
                logger.info("Stopping Radicale")
                break
            if rlist:
                server = servers.get(rlist[0])
                if server:
                    server.handle_request()
                    server.service_actions()