# -*- coding: utf-8 -*-
# Copyright 2019 New Vector Ltd
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

import email.mime.multipart
import email.utils
import logging
from email.mime.multipart import MIMEMultipart
from email.mime.text import MIMEText
from typing import List

from twisted.internet import defer

from synapse.api.errors import StoreError
from synapse.logging.context import make_deferred_yieldable
from synapse.metrics.background_process_metrics import run_as_background_process
from synapse.types import UserID
from synapse.util import stringutils

try:
    from synapse.push.mailer import load_jinja2_templates
except ImportError:
    load_jinja2_templates = None

logger = logging.getLogger(__name__)


class AccountValidityHandler(object):
    def __init__(self, hs):
        self.hs = hs
        self.config = hs.config
        self.store = self.hs.get_datastore()
        self.sendmail = self.hs.get_sendmail()
        self.clock = self.hs.get_clock()

        self._account_validity = self.hs.config.account_validity
        self._show_users_in_user_directory = self.hs.config.show_users_in_user_directory
        self.profile_handler = self.hs.get_profile_handler()

        if (
            self._account_validity.enabled
            and self._account_validity.renew_by_email_enabled
            and load_jinja2_templates
        ):
            # Don't do email-specific configuration if renewal by email is disabled.
            try:
                app_name = self.hs.config.email_app_name

                self._subject = self._account_validity.renew_email_subject % {
                    "app": app_name
                }

                self._from_string = self.hs.config.email_notif_from % {"app": app_name}
            except Exception:
                # If substitution failed, fall back to the bare strings.
                self._subject = self._account_validity.renew_email_subject
                self._from_string = self.hs.config.email_notif_from

            self._raw_from = email.utils.parseaddr(self._from_string)[1]

            self._template_html, self._template_text = load_jinja2_templates(
                self.config.email_template_dir,
                [
                    self.config.email_expiry_template_html,
                    self.config.email_expiry_template_text,
                ],
                apply_format_ts_filter=True,
                apply_mxc_to_http_filter=True,
                public_baseurl=self.config.public_baseurl,
            )

            # Check the renewal emails to send and send them every 30min.
            def send_emails():
                # run as a background process to make sure that the database transactions
                # have a logcontext to report to
                return run_as_background_process(
                    "send_renewals", self._send_renewal_emails
                )

            self.clock.looping_call(send_emails, 30 * 60 * 1000)

        # If account_validity is enabled,check every hour to remove expired users from
        # the user directory
        if self._account_validity.enabled:
            self.clock.looping_call(
                self._mark_expired_users_as_inactive, 60 * 60 * 1000
            )

    async def _send_renewal_emails(self):
        """Gets the list of users whose account is expiring in the amount of time
        configured in the ``renew_at`` parameter from the ``account_validity``
        configuration, and sends renewal emails to all of these users as long as they
        have an email 3PID attached to their account.
        """
        expiring_users = await self.store.get_users_expiring_soon()

        if expiring_users:
            for user in expiring_users:
                await self._send_renewal_email(
                    user_id=user["user_id"], expiration_ts=user["expiration_ts_ms"]
                )

    async def send_renewal_email_to_user(self, user_id: str):
        expiration_ts = await self.store.get_expiration_ts_for_user(user_id)
        await self._send_renewal_email(user_id, expiration_ts)

    async def _send_renewal_email(self, user_id: str, expiration_ts: int):
        """Sends out a renewal email to every email address attached to the given user
        with a unique link allowing them to renew their account.

        Args:
            user_id: ID of the user to send email(s) to.
            expiration_ts: Timestamp in milliseconds for the expiration date of
                this user's account (used in the email templates).
        """
        addresses = await self._get_email_addresses_for_user(user_id)

        # Stop right here if the user doesn't have at least one email address.
        # In this case, they will have to ask their server admin to renew their
        # account manually.
        # We don't need to do a specific check to make sure the account isn't
        # deactivated, as a deactivated account isn't supposed to have any
        # email address attached to it.
        if not addresses:
            return

        try:
            user_display_name = await self.store.get_profile_displayname(
                UserID.from_string(user_id).localpart
            )
            if user_display_name is None:
                user_display_name = user_id
        except StoreError:
            user_display_name = user_id

        renewal_token = await self._get_renewal_token(user_id)
        url = "%s_matrix/client/unstable/account_validity/renew?token=%s" % (
            self.hs.config.public_baseurl,
            renewal_token,
        )

        template_vars = {
            "display_name": user_display_name,
            "expiration_ts": expiration_ts,
            "url": url,
        }

        html_text = self._template_html.render(**template_vars)
        html_part = MIMEText(html_text, "html", "utf8")

        plain_text = self._template_text.render(**template_vars)
        text_part = MIMEText(plain_text, "plain", "utf8")

        for address in addresses:
            raw_to = email.utils.parseaddr(address)[1]

            multipart_msg = MIMEMultipart("alternative")
            multipart_msg["Subject"] = self._subject
            multipart_msg["From"] = self._from_string
            multipart_msg["To"] = address
            multipart_msg["Date"] = email.utils.formatdate()
            multipart_msg["Message-ID"] = email.utils.make_msgid()
            multipart_msg.attach(text_part)
            multipart_msg.attach(html_part)

            logger.info("Sending renewal email to %s", address)

            await make_deferred_yieldable(
                self.sendmail(
                    self.hs.config.email_smtp_host,
                    self._raw_from,
                    raw_to,
                    multipart_msg.as_string().encode("utf8"),
                    reactor=self.hs.get_reactor(),
                    port=self.hs.config.email_smtp_port,
                    requireAuthentication=self.hs.config.email_smtp_user is not None,
                    username=self.hs.config.email_smtp_user,
                    password=self.hs.config.email_smtp_pass,
                    requireTransportSecurity=self.hs.config.require_transport_security,
                )
            )

        await self.store.set_renewal_mail_status(user_id=user_id, email_sent=True)

    async def _get_email_addresses_for_user(self, user_id: str) -> List[str]:
        """Retrieve the list of email addresses attached to a user's account.

        Args:
            user_id: ID of the user to lookup email addresses for.

        Returns:
            Email addresses for this account.
        """
        threepids = await self.store.user_get_threepids(user_id)

        addresses = []
        for threepid in threepids:
            if threepid["medium"] == "email":
                addresses.append(threepid["address"])

        return addresses

    async def _get_renewal_token(self, user_id: str) -> str:
        """Generates a 32-byte long random string that will be inserted into the
        user's renewal email's unique link, then saves it into the database.

        Args:
            user_id: ID of the user to generate a string for.

        Returns:
            The generated string.

        Raises:
            StoreError(500): Couldn't generate a unique string after 5 attempts.
        """
        attempts = 0
        while attempts < 5:
            try:
                renewal_token = stringutils.random_string(32)
                await self.store.set_renewal_token_for_user(user_id, renewal_token)
                return renewal_token
            except StoreError:
                attempts += 1
        raise StoreError(500, "Couldn't generate a unique string as refresh string.")

    async def renew_account(self, renewal_token: str) -> bool:
        """Renews the account attached to a given renewal token by pushing back the
        expiration date by the current validity period in the server's configuration.

        Args:
            renewal_token: Token sent with the renewal request.
        Returns:
            Whether the provided token is valid.
        """
        try:
            user_id = await self.store.get_user_from_renewal_token(renewal_token)
        except StoreError:
            return False

        logger.debug("Renewing an account for user %s", user_id)
        await self.renew_account_for_user(user_id)

        return True

    async def renew_account_for_user(
        self, user_id: str, expiration_ts: int = None, email_sent: bool = False
    ) -> int:
        """Renews the account attached to a given user by pushing back the
        expiration date by the current validity period in the server's
        configuration.

        Args:
            renewal_token: Token sent with the renewal request.
            expiration_ts: New expiration date. Defaults to now + validity period.
            email_sen: Whether an email has been sent for this validity period.
                Defaults to False.

        Returns:
            New expiration date for this account, as a timestamp in
            milliseconds since epoch.
        """
        if expiration_ts is None:
            expiration_ts = self.clock.time_msec() + self._account_validity.period

        await self.store.set_account_validity_for_user(
            user_id=user_id, expiration_ts=expiration_ts, email_sent=email_sent
        )

        # Check if renewed users should be reintroduced to the user directory
        if self._show_users_in_user_directory:
            # Show the user in the directory again by setting them to active
            await self.profile_handler.set_active(
                [UserID.from_string(user_id)], True, True
            )

        return expiration_ts

    @defer.inlineCallbacks
    def _mark_expired_users_as_inactive(self):
        """Iterate over active, expired users. Mark them as inactive in order to hide them
        from the user directory.

        Returns:
            Deferred
        """
        # Get active, expired users
        active_expired_users = yield self.store.get_expired_users()

        # Mark each as non-active
        yield self.profile_handler.set_active(active_expired_users, False, True)