#!/usr/bin/env python
#
# Electrum - lightweight Bitcoin client
# Copyright (C) 2011 thomasv@gitorious
#
# Permission is hereby granted, free of charge, to any person
# obtaining a copy of this software and associated documentation files
# (the "Software"), to deal in the Software without restriction,
# including without limitation the rights to use, copy, modify, merge,
# publish, distribute, sublicense, and/or sell copies of the Software,
# and to permit persons to whom the Software is furnished to do so,
# subject to the following conditions:
#
# The above copyright notice and this permission notice shall be
# included in all copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
# EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
# MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
# NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
# BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
# ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
# CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
# SOFTWARE.
import os
import re
import ssl
import sys
import traceback
import asyncio
import socket
from typing import Tuple, Union, List, TYPE_CHECKING, Optional, Set
from collections import defaultdict
from ipaddress import IPv4Network, IPv6Network, ip_address, IPv6Address
import itertools
import logging

import aiorpcx
from aiorpcx import RPCSession, Notification, NetAddress, NewlineFramer
from aiorpcx.curio import timeout_after, TaskTimeout
from aiorpcx.jsonrpc import JSONRPC, CodeMessageError
from aiorpcx.rawsocket import RSClient
import certifi

from .util import ignore_exceptions, log_exceptions, bfh, SilentTaskGroup
from . import util
from . import x509
from . import pem
from . import version
from . import blockchain
from .blockchain import Blockchain
from . import constants
from .i18n import _
from .logging import Logger

if TYPE_CHECKING:
    from .network import Network
    from .simple_config import SimpleConfig


ca_path = certifi.where()

BUCKET_NAME_OF_ONION_SERVERS = 'onion'

MAX_INCOMING_MSG_SIZE = 1_000_000  # in bytes


class NetworkTimeout:
    # seconds
    class Generic:
        NORMAL = 30
        RELAXED = 45
        MOST_RELAXED = 180
    class Urgent(Generic):
        NORMAL = 10
        RELAXED = 20
        MOST_RELAXED = 60

class NotificationSession(RPCSession):

    def __init__(self, *args, **kwargs):
        super(NotificationSession, self).__init__(*args, **kwargs)
        self.subscriptions = defaultdict(list)
        self.cache = {}
        self.default_timeout = NetworkTimeout.Generic.NORMAL
        self._msg_counter = itertools.count(start=1)
        self.interface = None  # type: Optional[Interface]
        self.cost_hard_limit = 0  # disable aiorpcx resource limits

    async def handle_request(self, request):
        self.maybe_log(f"--> {request}")
        try:
            if isinstance(request, Notification):
                params, result = request.args[:-1], request.args[-1]
                key = self.get_hashable_key_for_rpc_call(request.method, params)
                if key in self.subscriptions:
                    self.cache[key] = result
                    for queue in self.subscriptions[key]:
                        await queue.put(request.args)
                else:
                    raise Exception(f'unexpected notification')
            else:
                raise Exception(f'unexpected request. not a notification')
        except Exception as e:
            self.interface.logger.info(f"error handling request {request}. exc: {repr(e)}")
            await self.close()

    async def send_request(self, *args, timeout=None, **kwargs):
        # note: semaphores/timeouts/backpressure etc are handled by
        # aiorpcx. the timeout arg here in most cases should not be set
        msg_id = next(self._msg_counter)
        self.maybe_log(f"<-- {args} {kwargs} (id: {msg_id})")
        try:
            # note: RPCSession.send_request raises TaskTimeout in case of a timeout.
            # TaskTimeout is a subclass of CancelledError, which is *suppressed* in TaskGroups
            response = await asyncio.wait_for(
                super().send_request(*args, **kwargs),
                timeout)
        except (TaskTimeout, asyncio.TimeoutError) as e:
            raise RequestTimedOut(f'request timed out: {args} (id: {msg_id})') from e
        except CodeMessageError as e:
            self.maybe_log(f"--> {repr(e)} (id: {msg_id})")
            raise
        else:
            self.maybe_log(f"--> {response} (id: {msg_id})")
            return response

    def set_default_timeout(self, timeout):
        self.sent_request_timeout = timeout
        self.max_send_delay = timeout

    async def subscribe(self, method: str, params: List, queue: asyncio.Queue):
        # note: until the cache is written for the first time,
        # each 'subscribe' call might make a request on the network.
        key = self.get_hashable_key_for_rpc_call(method, params)
        self.subscriptions[key].append(queue)
        if key in self.cache:
            result = self.cache[key]
        else:
            result = await self.send_request(method, params)
            self.cache[key] = result
        await queue.put(params + [result])

    def unsubscribe(self, queue):
        """Unsubscribe a callback to free object references to enable GC."""
        # note: we can't unsubscribe from the server, so we keep receiving
        # subsequent notifications
        for v in self.subscriptions.values():
            if queue in v:
                v.remove(queue)

    @classmethod
    def get_hashable_key_for_rpc_call(cls, method, params):
        """Hashable index for subscriptions and cache"""
        return str(method) + repr(params)

    def maybe_log(self, msg: str) -> None:
        if not self.interface: return
        if self.interface.debug or self.interface.network.debug:
            self.interface.logger.debug(msg)

    def default_framer(self):
        # overridden so that max_size can be customized
        return NewlineFramer(max_size=MAX_INCOMING_MSG_SIZE)


class NetworkException(Exception): pass


class GracefulDisconnect(NetworkException):
    log_level = logging.INFO

    def __init__(self, *args, log_level=None, **kwargs):
        Exception.__init__(self, *args, **kwargs)
        if log_level is not None:
            self.log_level = log_level


class RequestTimedOut(GracefulDisconnect):
    def __str__(self):
        return _("Network request timed out.")


class RequestCorrupted(GracefulDisconnect): pass

class ErrorParsingSSLCert(Exception): pass
class ErrorGettingSSLCertFromServer(Exception): pass
class ConnectError(NetworkException): pass


class _RSClient(RSClient):
    async def create_connection(self):
        try:
            return await super().create_connection()
        except OSError as e:
            # note: using "from e" here will set __cause__ of ConnectError
            raise ConnectError(e) from e


def deserialize_server(server_str: str) -> Tuple[str, str, str]:
    # host might be IPv6 address, hence do rsplit:
    host, port, protocol = str(server_str).rsplit(':', 2)
    if not host:
        raise ValueError('host must not be empty')
    if host[0] == '[' and host[-1] == ']':  # IPv6
        host = host[1:-1]
    if protocol not in ('s', 't'):
        raise ValueError('invalid network protocol: {}'.format(protocol))
    net_addr = NetAddress(host, port)  # this validates host and port
    host = str(net_addr.host)  # canonical form (if e.g. IPv6 address)
    return host, port, protocol


def serialize_server(host: str, port: Union[str, int], protocol: str) -> str:
    return str(':'.join([host, str(port), protocol]))


def _get_cert_path_for_host(*, config: 'SimpleConfig', host: str) -> str:
    filename = host
    try:
        ip = ip_address(host)
    except ValueError:
        pass
    else:
        if isinstance(ip, IPv6Address):
            filename = f"ipv6_{ip.packed.hex()}"
    return os.path.join(config.path, 'certs', filename)


class Interface(Logger):

    LOGGING_SHORTCUT = 'i'

    def __init__(self, network: 'Network', server: str, proxy: Optional[dict]):
        self.ready = asyncio.Future()
        self.got_disconnected = asyncio.Future()
        self.server = server
        self.host, self.port, self.protocol = deserialize_server(self.server)
        self.port = int(self.port)
        Logger.__init__(self)
        assert network.config.path
        self.cert_path = _get_cert_path_for_host(config=network.config, host=self.host)
        self.blockchain = None  # type: Optional[Blockchain]
        self._requested_chunks = set()  # type: Set[int]
        self.network = network
        self._set_proxy(proxy)
        self.session = None  # type: Optional[NotificationSession]
        self._ipaddr_bucket = None

        self.tip_header = None
        self.tip = 0

        # Dump network messages (only for this interface).  Set at runtime from the console.
        self.debug = False

        asyncio.run_coroutine_threadsafe(
            self.network.main_taskgroup.spawn(self.run()), self.network.asyncio_loop)
        self.group = SilentTaskGroup()

    def diagnostic_name(self):
        return str(NetAddress(self.host, self.port))

    def __str__(self):
        return f"<Interface {self.diagnostic_name()}>"

    def _set_proxy(self, proxy: dict):
        if proxy:
            username, pw = proxy.get('user'), proxy.get('password')
            if not username or not pw:
                auth = None
            else:
                auth = aiorpcx.socks.SOCKSUserAuth(username, pw)
            addr = NetAddress(proxy['host'], proxy['port'])
            if proxy['mode'] == "socks4":
                self.proxy = aiorpcx.socks.SOCKSProxy(addr, aiorpcx.socks.SOCKS4a, auth)
            elif proxy['mode'] == "socks5":
                self.proxy = aiorpcx.socks.SOCKSProxy(addr, aiorpcx.socks.SOCKS5, auth)
            else:
                raise NotImplementedError  # http proxy not available with aiorpcx
        else:
            self.proxy = None

    async def is_server_ca_signed(self, ca_ssl_context):
        """Given a CA enforcing SSL context, returns True if the connection
        can be established. Returns False if the server has a self-signed
        certificate but otherwise is okay. Any other failures raise.
        """
        try:
            await self.open_session(ca_ssl_context, exit_early=True)
        except ConnectError as e:
            cause = e.__cause__
            if isinstance(cause, ssl.SSLError) and cause.reason == 'CERTIFICATE_VERIFY_FAILED':
                # failures due to self-signed certs are normal
                return False
            raise
        return True

    async def _try_saving_ssl_cert_for_first_time(self, ca_ssl_context):
        ca_signed = await self.is_server_ca_signed(ca_ssl_context)
        if ca_signed:
            with open(self.cert_path, 'w') as f:
                # empty file means this is CA signed, not self-signed
                f.write('')
        else:
            await self.save_certificate()

    def _is_saved_ssl_cert_available(self):
        if not os.path.exists(self.cert_path):
            return False
        with open(self.cert_path, 'r') as f:
            contents = f.read()
        if contents == '':  # CA signed
            return True
        # pinned self-signed cert
        try:
            b = pem.dePem(contents, 'CERTIFICATE')
        except SyntaxError as e:
            self.logger.info(f"error parsing already saved cert: {e}")
            raise ErrorParsingSSLCert(e) from e
        try:
            x = x509.X509(b)
        except Exception as e:
            self.logger.info(f"error parsing already saved cert: {e}")
            raise ErrorParsingSSLCert(e) from e
        try:
            x.check_date()
            return True
        except x509.CertificateError as e:
            self.logger.info(f"certificate has expired: {e}")
            os.unlink(self.cert_path)  # delete pinned cert only in this case
            return False

    async def _get_ssl_context(self):
        if self.protocol != 's':
            # using plaintext TCP
            return None

        # see if we already have cert for this server; or get it for the first time
        ca_sslc = ssl.create_default_context(purpose=ssl.Purpose.SERVER_AUTH, cafile=ca_path)
        if not self._is_saved_ssl_cert_available():
            try:
                await self._try_saving_ssl_cert_for_first_time(ca_sslc)
            except (OSError, ConnectError, aiorpcx.socks.SOCKSError) as e:
                raise ErrorGettingSSLCertFromServer(e) from e
        # now we have a file saved in our certificate store
        siz = os.stat(self.cert_path).st_size
        if siz == 0:
            # CA signed cert
            sslc = ca_sslc
        else:
            # pinned self-signed cert
            sslc = ssl.create_default_context(ssl.Purpose.SERVER_AUTH, cafile=self.cert_path)
            sslc.check_hostname = 0
        return sslc

    def handle_disconnect(func):
        async def wrapper_func(self: 'Interface', *args, **kwargs):
            try:
                return await func(self, *args, **kwargs)
            except GracefulDisconnect as e:
                self.logger.log(e.log_level, f"disconnecting due to {repr(e)}")
            except aiorpcx.jsonrpc.RPCError as e:
                self.logger.warning(f"disconnecting due to {repr(e)}")
                self.logger.debug(f"(disconnect) trace for {repr(e)}", exc_info=True)
            finally:
                await self.network.connection_down(self)
                if not self.got_disconnected.done():
                    self.got_disconnected.set_result(1)
                # if was not 'ready' yet, schedule waiting coroutines:
                self.ready.cancel()
        return wrapper_func

    @ignore_exceptions  # do not kill main_taskgroup
    @log_exceptions
    @handle_disconnect
    async def run(self):
        try:
            ssl_context = await self._get_ssl_context()
        except (ErrorParsingSSLCert, ErrorGettingSSLCertFromServer) as e:
            self.logger.info(f'disconnecting due to: {repr(e)}')
            return
        try:
            await self.open_session(ssl_context)
        except (asyncio.CancelledError, ConnectError, aiorpcx.socks.SOCKSError) as e:
            # make SSL errors for main interface more visible (to help servers ops debug cert pinning issues)
            if (isinstance(e, ConnectError) and isinstance(e.__cause__, ssl.SSLError)
                    and self.is_main_server() and not self.network.auto_connect):
                self.logger.warning(f'Cannot connect to main server due to SSL error '
                                    f'(maybe cert changed compared to "{self.cert_path}"). Exc: {repr(e)}')
            else:
                self.logger.info(f'disconnecting due to: {repr(e)}')
            return

    def _mark_ready(self) -> None:
        if self.ready.cancelled():
            raise GracefulDisconnect('conn establishment was too slow; *ready* future was cancelled')
        if self.ready.done():
            return

        assert self.tip_header
        chain = blockchain.check_header(self.tip_header)
        if not chain:
            self.blockchain = blockchain.get_best_chain()
        else:
            self.blockchain = chain
        assert self.blockchain is not None

        self.logger.info(f"set blockchain with height {self.blockchain.height()}")

        self.ready.set_result(1)

    async def save_certificate(self):
        if not os.path.exists(self.cert_path):
            # we may need to retry this a few times, in case the handshake hasn't completed
            for _ in range(10):
                dercert = await self.get_certificate()
                if dercert:
                    self.logger.info("succeeded in getting cert")
                    with open(self.cert_path, 'w') as f:
                        cert = ssl.DER_cert_to_PEM_cert(dercert)
                        # workaround android bug
                        cert = re.sub("([^\n])-----END CERTIFICATE-----","\\1\n-----END CERTIFICATE-----",cert)
                        f.write(cert)
                        # even though close flushes we can't fsync when closed.
                        # and we must flush before fsyncing, cause flush flushes to OS buffer
                        # fsync writes to OS buffer to disk
                        f.flush()
                        os.fsync(f.fileno())
                    break
                await asyncio.sleep(1)
            else:
                raise GracefulDisconnect("could not get certificate after 10 tries")

    async def get_certificate(self):
        sslc = ssl.SSLContext()
        try:
            async with _RSClient(session_factory=RPCSession,
                                 host=self.host, port=self.port,
                                 ssl=sslc, proxy=self.proxy) as session:
                return session.transport._asyncio_transport._ssl_protocol._sslpipe._sslobj.getpeercert(True)
        except ValueError:
            return None

    async def get_block_header(self, height, assert_mode):
        self.logger.info(f'requesting block header {height} in mode {assert_mode}')
        # use lower timeout as we usually have network.bhi_lock here
        timeout = self.network.get_network_timeout_seconds(NetworkTimeout.Urgent)
        res = await self.session.send_request('blockchain.block.headers', [height,1], timeout=timeout)
        return blockchain.deserialize_header(bytes.fromhex(res['hex']), height)

    async def request_chunk(self, height: int, tip=None, *, can_return_early=False):
        index = height // 2016
        if can_return_early and index in self._requested_chunks:
            return
        self.logger.info(f"requesting chunk from height {height}")
        size = 2016
        if tip is not None:
            size = min(size, tip - index * 2016 + 1)
            size = max(size, 0)
        try:
            self._requested_chunks.add(index)
            res = await self.session.send_request('blockchain.block.headers', [index * 2016, size])
        finally:
            self._requested_chunks.discard(index)
        conn = self.blockchain.connect_chunk(index, res['hex'])
        if not conn:
            return conn, 0
        return conn, res['count']

    def is_main_server(self) -> bool:
        return self.network.default_server == self.server

    async def open_session(self, sslc, exit_early=False):
        async with _RSClient(session_factory=NotificationSession,
                             host=self.host, port=self.port,
                             ssl=sslc, proxy=self.proxy) as session:
            self.session = session  # type: NotificationSession
            self.session.interface = self
            self.session.set_default_timeout(self.network.get_network_timeout_seconds(NetworkTimeout.Generic))
            try:
                ver = await session.send_request('server.version', [self.client_name(), version.PROTOCOL_VERSION])
            except aiorpcx.jsonrpc.RPCError as e:
                raise GracefulDisconnect(e)  # probably 'unsupported protocol version'
            if exit_early:
                return
            if not self.network.check_interface_against_healthy_spread_of_connected_servers(self):
                raise GracefulDisconnect(f'too many connected servers already '
                                         f'in bucket {self.bucket_based_on_ipaddress()}')
            self.logger.info(f"connection established. version: {ver}")

            try:
                async with self.group as group:
                    await group.spawn(self.ping)
                    await group.spawn(self.run_fetch_blocks)
                    await group.spawn(self.monitor_connection)
            except aiorpcx.jsonrpc.RPCError as e:
                if e.code in (JSONRPC.EXCESSIVE_RESOURCE_USAGE,
                              JSONRPC.SERVER_BUSY,
                              JSONRPC.METHOD_NOT_FOUND):
                    raise GracefulDisconnect(e, log_level=logging.WARNING) from e
                raise

    async def monitor_connection(self):
        while True:
            await asyncio.sleep(1)
            if not self.session or self.session.is_closing():
                raise GracefulDisconnect('session was closed')

    async def ping(self):
        while True:
            await asyncio.sleep(300)
            await self.session.send_request('server.ping')

    async def close(self):
        if self.session:
            await self.session.close()
        # monitor_connection will cancel tasks

    async def run_fetch_blocks(self):
        header_queue = asyncio.Queue()
        await self.session.subscribe('blockchain.headers.subscribe', [True], header_queue)
        while True:
            item = await header_queue.get()
            print(item)
            raw_header = item[1]
            print(raw_header)
            height = raw_header['height']
            header = blockchain.deserialize_header(bfh(raw_header['hex']), height)
            self.tip_header = header
            self.tip = height
            if self.tip < constants.net.max_checkpoint():
                raise GracefulDisconnect('server tip below max checkpoint')
            self._mark_ready()
            await self._process_header_at_tip()
            self.network.trigger_callback('network_updated')
            await self.network.switch_unwanted_fork_interface()
            await self.network.switch_lagging_interface()

    async def _process_header_at_tip(self):
        height, header = self.tip, self.tip_header
        async with self.network.bhi_lock:
            if self.blockchain.height() >= height and self.blockchain.check_header(header):
                # another interface amended the blockchain
                self.logger.info(f"skipping header {height}")
                return
            _, height = await self.step(height, header)
            # in the simple case, height == self.tip+1
            if height <= self.tip:
                await self.sync_until(height)
        self.network.trigger_callback('blockchain_updated')

    async def sync_until(self, height, next_height=None):
        if next_height is None:
            next_height = self.tip
        last = None
        while last is None or height <= next_height:
            prev_last, prev_height = last, height
            if next_height > height + 10:
                could_connect, num_headers = await self.request_chunk(height, next_height)
                if not could_connect:
                    if height <= constants.net.max_checkpoint():
                        raise GracefulDisconnect('server chain conflicts with checkpoints or genesis')
                    last, height = await self.step(height)
                    continue
                self.network.trigger_callback('network_updated')
                height = (height // 2016 * 2016) + num_headers
                assert height <= next_height+1, (height, self.tip)
                last = 'catchup'
            else:
                last, height = await self.step(height)
            assert (prev_last, prev_height) != (last, height), 'had to prevent infinite loop in interface.sync_until'
        return last, height

    async def step(self, height, header=None):
        assert 0 <= height <= self.tip, (height, self.tip)
        if header is None:
            header = await self.get_block_header(height, 'catchup')

        chain = blockchain.check_header(header) if 'mock' not in header else header['mock']['check'](header)
        if chain:
            self.blockchain = chain if isinstance(chain, Blockchain) else self.blockchain
            # note: there is an edge case here that is not handled.
            # we might know the blockhash (enough for check_header) but
            # not have the header itself. e.g. regtest chain with only genesis.
            # this situation resolves itself on the next block
            return 'catchup', height+1

        can_connect = blockchain.can_connect(header) if 'mock' not in header else header['mock']['connect'](height)
        if not can_connect:
            self.logger.info(f"can't connect {height}")
            height, header, bad, bad_header = await self._search_headers_backwards(height, header)
            chain = blockchain.check_header(header) if 'mock' not in header else header['mock']['check'](header)
            can_connect = blockchain.can_connect(header) if 'mock' not in header else header['mock']['connect'](height)
            assert chain or can_connect
        if can_connect:
            self.logger.info(f"could connect {height}")
            height += 1
            if isinstance(can_connect, Blockchain):  # not when mocking
                self.blockchain = can_connect
                self.blockchain.save_header(header)
            return 'catchup', height

        good, bad, bad_header = await self._search_headers_binary(height, bad, bad_header, chain)
        return await self._resolve_potential_chain_fork_given_forkpoint(good, bad, bad_header)

    async def _search_headers_binary(self, height, bad, bad_header, chain):
        assert bad == bad_header['block_height']
        _assert_header_does_not_check_against_any_chain(bad_header)

        self.blockchain = chain if isinstance(chain, Blockchain) else self.blockchain
        good = height
        while True:
            assert good < bad, (good, bad)
            height = (good + bad) // 2
            self.logger.info(f"binary step. good {good}, bad {bad}, height {height}")
            header = await self.get_block_header(height, 'binary')
            chain = blockchain.check_header(header) if 'mock' not in header else header['mock']['check'](header)
            if chain:
                self.blockchain = chain if isinstance(chain, Blockchain) else self.blockchain
                good = height
            else:
                bad = height
                bad_header = header
            if good + 1 == bad:
                break

        mock = 'mock' in bad_header and bad_header['mock']['connect'](height)
        real = not mock and self.blockchain.can_connect(bad_header, check_height=False)
        if not real and not mock:
            raise Exception('unexpected bad header during binary: {}'.format(bad_header))
        _assert_header_does_not_check_against_any_chain(bad_header)

        self.logger.info(f"binary search exited. good {good}, bad {bad}")
        return good, bad, bad_header

    async def _resolve_potential_chain_fork_given_forkpoint(self, good, bad, bad_header):
        assert good + 1 == bad
        assert bad == bad_header['block_height']
        _assert_header_does_not_check_against_any_chain(bad_header)
        # 'good' is the height of a block 'good_header', somewhere in self.blockchain.
        # bad_header connects to good_header; bad_header itself is NOT in self.blockchain.

        bh = self.blockchain.height()
        assert bh >= good, (bh, good)
        if bh == good:
            height = good + 1
            self.logger.info(f"catching up from {height}")
            return 'no_fork', height

        # this is a new fork we don't yet have
        height = bad + 1
        self.logger.info(f"new fork at bad height {bad}")
        forkfun = self.blockchain.fork if 'mock' not in bad_header else bad_header['mock']['fork']
        b = forkfun(bad_header)  # type: Blockchain
        self.blockchain = b
        assert b.forkpoint == bad
        return 'fork', height

    async def _search_headers_backwards(self, height, header):
        async def iterate():
            nonlocal height, header
            checkp = False
            if height <= constants.net.max_checkpoint():
                height = constants.net.max_checkpoint()
                checkp = True
            header = await self.get_block_header(height, 'backward')
            chain = blockchain.check_header(header) if 'mock' not in header else header['mock']['check'](header)
            can_connect = blockchain.can_connect(header) if 'mock' not in header else header['mock']['connect'](height)
            if chain or can_connect:
                return False
            if checkp:
                raise GracefulDisconnect("server chain conflicts with checkpoints")
            return True

        bad, bad_header = height, header
        _assert_header_does_not_check_against_any_chain(bad_header)
        with blockchain.blockchains_lock: chains = list(blockchain.blockchains.values())
        local_max = max([0] + [x.height() for x in chains]) if 'mock' not in header else float('inf')
        height = min(local_max + 1, height - 1)
        while await iterate():
            bad, bad_header = height, header
            delta = self.tip - height
            height = self.tip - 2 * delta

        _assert_header_does_not_check_against_any_chain(bad_header)
        self.logger.info(f"exiting backward mode at {height}")
        return height, header, bad, bad_header

    @classmethod
    def client_name(cls) -> str:
        return f'electrum/{version.ELECTRUM_VERSION}'

    def is_tor(self):
        return self.host.endswith('.onion')

    def ip_addr(self) -> Optional[str]:
        session = self.session
        if not session: return None
        peer_addr = session.remote_address()
        if not peer_addr: return None
        return str(peer_addr.host)

    def bucket_based_on_ipaddress(self) -> str:
        def do_bucket():
            if self.is_tor():
                return BUCKET_NAME_OF_ONION_SERVERS
            try:
                ip_addr = ip_address(self.ip_addr())
            except ValueError:
                return ''
            if not ip_addr:
                return ''
            if ip_addr.version == 4:
                slash16 = IPv4Network(ip_addr).supernet(prefixlen_diff=32-16)
                return str(slash16)
            elif ip_addr.version == 6:
                slash48 = IPv6Network(ip_addr).supernet(prefixlen_diff=128-48)
                return str(slash48)
            return ''

        if not self._ipaddr_bucket:
            self._ipaddr_bucket = do_bucket()
        return self._ipaddr_bucket


def _assert_header_does_not_check_against_any_chain(header: dict) -> None:
    chain_bad = blockchain.check_header(header) if 'mock' not in header else header['mock']['check'](header)
    if chain_bad:
        raise Exception('bad_header must not check!')


def check_cert(host, cert):
    try:
        b = pem.dePem(cert, 'CERTIFICATE')
        x = x509.X509(b)
    except:
        traceback.print_exc(file=sys.stdout)
        return

    try:
        x.check_date()
        expired = False
    except:
        expired = True

    m = "host: %s\n"%host
    m += "has_expired: %s\n"% expired
    util.print_msg(m)


# Used by tests
def _match_hostname(name, val):
    if val == name:
        return True

    return val.startswith('*.') and name.endswith(val[1:])


def test_certificates():
    from .simple_config import SimpleConfig
    config = SimpleConfig()
    mydir = os.path.join(config.path, "certs")
    certs = os.listdir(mydir)
    for c in certs:
        p = os.path.join(mydir,c)
        with open(p, encoding='utf-8') as f:
            cert = f.read()
        check_cert(c, cert)

if __name__ == "__main__":
    test_certificates()