import datetime
import hashlib
import logging
import os
import smtplib
from contextlib import suppress
from email.headerregistry import Address
from email.parser import Parser
from email.policy import default
from email.utils import formataddr, parseaddr
from typing import Any, Callable, Dict, List, Mapping, Optional, Sequence, Tuple, Union

import backoff
import css_inline
import orjson
from django.conf import settings
from django.core.mail import EmailMultiAlternatives, get_connection
from django.core.mail.backends.base import BaseEmailBackend
from django.core.mail.backends.smtp import EmailBackend
from django.core.mail.message import sanitize_address
from django.core.management import CommandError
from django.db import transaction
from django.db.models import QuerySet
from django.http import HttpRequest
from django.template import loader
from django.utils.timezone import now as timezone_now
from django.utils.translation import gettext as _
from django.utils.translation import override as override_language

from confirmation.models import generate_key
from zerver.lib.logging_util import log_to_file
from zerver.models import EMAIL_TYPES, Realm, ScheduledEmail, UserProfile, get_user_profile_by_id
from zproject.email_backends import EmailLogBackEnd, get_forward_address

MAX_CONNECTION_TRIES = 3

## Logging setup ##

logger = logging.getLogger("zulip.send_email")
log_to_file(logger, settings.EMAIL_LOG_PATH)


def get_inliner_instance() -> css_inline.CSSInliner:
    return css_inline.CSSInliner()


class FromAddress:
    SUPPORT = parseaddr(settings.ZULIP_ADMINISTRATOR)[1]
    NOREPLY = parseaddr(settings.NOREPLY_EMAIL_ADDRESS)[1]

    support_placeholder = "SUPPORT"
    no_reply_placeholder = "NO_REPLY"
    tokenized_no_reply_placeholder = "TOKENIZED_NO_REPLY"

    # Generates an unpredictable noreply address.
    @staticmethod
    def tokenized_no_reply_address() -> str:
        if settings.ADD_TOKENS_TO_NOREPLY_ADDRESS:
            return parseaddr(settings.TOKENIZED_NOREPLY_EMAIL_ADDRESS)[1].format(
                token=generate_key()
            )
        return FromAddress.NOREPLY

    @staticmethod
    def security_email_from_name(
        language: Optional[str] = None, user_profile: Optional[UserProfile] = None
    ) -> str:
        if language is None:
            assert user_profile is not None
            language = user_profile.default_language

        with override_language(language):
            return _("Zulip Account Security")


def build_email(
    template_prefix: str,
    to_user_ids: Optional[List[int]] = None,
    to_emails: Optional[List[str]] = None,
    from_name: Optional[str] = None,
    from_address: Optional[str] = None,
    reply_to_email: Optional[str] = None,
    language: Optional[str] = None,
    context: Mapping[str, Any] = {},
    realm: Optional[Realm] = None,
) -> EmailMultiAlternatives:
    # Callers should pass exactly one of to_user_id and to_email.
    assert (to_user_ids is None) ^ (to_emails is None)
    if to_user_ids is not None:
        to_users = [get_user_profile_by_id(to_user_id) for to_user_id in to_user_ids]
        if realm is None:
            assert len({to_user.realm_id for to_user in to_users}) == 1
            realm = to_users[0].realm
        to_emails = []
        for to_user in to_users:
            stringified = str(
                Address(display_name=to_user.full_name, addr_spec=to_user.delivery_email)
            )
            # Check ASCII encoding length.  Amazon SES rejects emails
            # with From or To values longer than 320 characters (which
            # appears to be a misinterpretation of the RFC); in that
            # case we drop the name part from the address, under the
            # theory that it's better to send the email with a
            # simplified field than not at all.
            if len(sanitize_address(stringified, "utf-8")) > 320:
                stringified = str(Address(addr_spec=to_user.delivery_email))
            to_emails.append(stringified)

    # Attempt to suppress all auto-replies.  This header originally
    # came out of Microsoft Outlook and friends, but seems reasonably
    # commonly-recognized.
    extra_headers = {"X-Auto-Response-Suppress": "All"}

    if realm is not None:
        # formaddr is meant for formatting (display_name, email_address) pair for headers like "To",
        # but we can use its utility for formatting the List-Id header, as it follows the same format,
        # except having just a domain instead of an email address.
        extra_headers["List-Id"] = formataddr((realm.name, realm.host))

    assert settings.STATIC_URL is not None
    context = {
        **context,
        "support_email": FromAddress.SUPPORT,
        # Emails use unhashed image URLs so that those continue to
        # work over time, even if the prod-static directory is cleaned
        # out; as such, they just use a STATIC_URL prefix.
        "email_images_base_url": settings.STATIC_URL + "images/emails",
        "physical_address": settings.PHYSICAL_ADDRESS,
    }

    def get_inlined_template(template: str) -> str:
        inliner = get_inliner_instance()
        return inliner.inline(template)

    def render_templates() -> Tuple[str, str, str]:
        email_subject = (
            loader.render_to_string(
                template_prefix + ".subject.txt", context=context, using="Jinja2_plaintext"
            )
            .strip()
            .replace("\n", "")
        )
        message = loader.render_to_string(
            template_prefix + ".txt", context=context, using="Jinja2_plaintext"
        )

        html_message = loader.render_to_string(template_prefix + ".html", context)
        return (get_inlined_template(html_message), message, email_subject)

    # The i18n story for emails is a bit complicated.  For emails
    # going to a single user, we want to use the language that user
    # has configured for their Zulip account.  For emails going to
    # multiple users or to email addresses without a known Zulip
    # account (E.g. invitations), we want to use the default language
    # configured for the Zulip organization.
    #
    # See our i18n documentation for some high-level details:
    # https://zulip.readthedocs.io/en/latest/translating/internationalization.html

    if not language and to_user_ids is not None:
        language = to_users[0].default_language
    if language:
        with override_language(language):
            # Make sure that we render the email using the target's native language
            (html_message, message, email_subject) = render_templates()
    else:
        (html_message, message, email_subject) = render_templates()
        logger.warning("Missing language for email template '%s'", template_prefix)

    if from_name is None:
        from_name = "Zulip"
    if from_address is None:
        from_address = FromAddress.NOREPLY
    if from_address == FromAddress.tokenized_no_reply_placeholder:
        from_address = FromAddress.tokenized_no_reply_address()
    if from_address == FromAddress.no_reply_placeholder:
        from_address = FromAddress.NOREPLY
    if from_address == FromAddress.support_placeholder:
        from_address = FromAddress.SUPPORT

    # Set the "From" that is displayed separately from the envelope-from.
    extra_headers["From"] = str(Address(display_name=from_name, addr_spec=from_address))
    # As above, with the "To" line, we drop the name part if it would
    # result in an address which is longer than 320 bytes.
    if len(sanitize_address(extra_headers["From"], "utf-8")) > 320:
        extra_headers["From"] = str(Address(addr_spec=from_address))

    # If we have an unsubscribe link for this email, configure it for
    # "Unsubscribe" buttons in email clients via the List-Unsubscribe header.
    #
    # Note that Microsoft ignores URLs in List-Unsubscribe headers, as
    # they only support the alternative `mailto:` format, which we
    # have not implemented.
    if "unsubscribe_link" in context:
        extra_headers["List-Unsubscribe"] = f"<{context['unsubscribe_link']}>"
        extra_headers["List-Unsubscribe-Post"] = "List-Unsubscribe=One-Click"

    reply_to = None
    if reply_to_email is not None:
        reply_to = [reply_to_email]
    # Remove the from_name in the reply-to for noreply emails, so that users
    # see "noreply@..." rather than "Zulip" or whatever the from_name is
    # when they reply in their email client.
    elif from_address == FromAddress.NOREPLY:
        reply_to = [FromAddress.NOREPLY]

    envelope_from = FromAddress.NOREPLY
    mail = EmailMultiAlternatives(
        email_subject, message, envelope_from, to_emails, reply_to=reply_to, headers=extra_headers
    )
    if html_message is not None:
        mail.attach_alternative(html_message, "text/html")
    return mail


class EmailNotDeliveredError(Exception):
    pass


class DoubledEmailArgumentError(CommandError):
    def __init__(self, argument_name: str) -> None:
        msg = (
            f"Argument '{argument_name}' is ambiguously present in both options and email template."
        )
        super().__init__(msg)


class NoEmailArgumentError(CommandError):
    def __init__(self, argument_name: str) -> None:
        msg = f"Argument '{argument_name}' is required in either options or email template."
        super().__init__(msg)


# When changing the arguments to this function, you may need to write a
# migration to change or remove any emails in ScheduledEmail.
def send_email(
    template_prefix: str,
    to_user_ids: Optional[List[int]] = None,
    to_emails: Optional[List[str]] = None,
    from_name: Optional[str] = None,
    from_address: Optional[str] = None,
    reply_to_email: Optional[str] = None,
    language: Optional[str] = None,
    context: Mapping[str, Any] = {},
    realm: Optional[Realm] = None,
    connection: Optional[BaseEmailBackend] = None,
    dry_run: bool = False,
    request: Optional[HttpRequest] = None,
) -> None:
    mail = build_email(
        template_prefix,
        to_user_ids=to_user_ids,
        to_emails=to_emails,
        from_name=from_name,
        from_address=from_address,
        reply_to_email=reply_to_email,
        language=language,
        context=context,
        realm=realm,
    )
    template = template_prefix.split("/")[-1]

    log_email_config_errors()

    if dry_run:
        print(mail.message().get_payload()[0])
        return

    if connection is None:
        connection = get_connection()

    cause = ""
    if request is not None:
        cause = f" (triggered from {request.META['REMOTE_ADDR']})"

    logging_recipient: Union[str, List[str]] = mail.to
    if realm is not None:
        logging_recipient = f"{mail.to} in {realm.string_id}"

    logger.info("Sending %s email to %s%s", template, logging_recipient, cause)

    try:
        # This will call .open() for us, which is a no-op if it's already open;
        # it will only call .close() if it was not open to begin with
        if connection.send_messages([mail]) == 0:
            logger.error("Unknown error sending %s email to %s", template, mail.to)
            raise EmailNotDeliveredError
    except smtplib.SMTPResponseException as e:
        logger.exception(
            "Error sending %s email to %s with error code %s: %s",
            template,
            mail.to,
            e.smtp_code,
            e.smtp_error,
            stack_info=True,
        )
        raise EmailNotDeliveredError
    except smtplib.SMTPException as e:
        logger.exception("Error sending %s email to %s: %s", template, mail.to, e, stack_info=True)
        raise EmailNotDeliveredError


@backoff.on_exception(backoff.expo, OSError, max_tries=MAX_CONNECTION_TRIES, logger=None)
def initialize_connection(connection: Optional[BaseEmailBackend] = None) -> BaseEmailBackend:
    if not connection:
        connection = get_connection()
        assert connection is not None

    if connection.open():
        # If it's a new connection, no need to no-op to check connectivity
        return connection

    if isinstance(connection, EmailLogBackEnd) and not get_forward_address():
        # With the development environment backend and without a
        # configured forwarding address, we don't actually send emails.
        #
        # As a result, the connection cannot be closed by the server
        # (as there is none), and `connection.noop` is not
        # implemented, so we need to return the connection early.
        return connection

    # No-op to ensure that we don't return a connection that has been
    # closed by the mail server.
    if isinstance(connection, EmailBackend):
        try:
            assert connection.connection is not None
            status = connection.connection.noop()[0]
        except Exception:
            status = -1
        if status != 250:
            # Close and connect again.
            connection.close()
            connection.open()

    return connection


def send_future_email(
    template_prefix: str,
    realm: Realm,
    to_user_ids: Optional[List[int]] = None,
    to_emails: Optional[List[str]] = None,
    from_name: Optional[str] = None,
    from_address: Optional[str] = None,
    language: Optional[str] = None,
    context: Mapping[str, Any] = {},
    delay: datetime.timedelta = datetime.timedelta(0),
) -> None:
    template_name = template_prefix.split("/")[-1]
    email_fields = {
        "template_prefix": template_prefix,
        "from_name": from_name,
        "from_address": from_address,
        "language": language,
        "context": context,
    }

    if settings.DEVELOPMENT_LOG_EMAILS:
        send_email(
            template_prefix,
            to_user_ids=to_user_ids,
            to_emails=to_emails,
            from_name=from_name,
            from_address=from_address,
            language=language,
            context=context,
        )
        # For logging the email

    assert (to_user_ids is None) ^ (to_emails is None)
    with transaction.atomic():
        email = ScheduledEmail.objects.create(
            type=EMAIL_TYPES[template_name],
            scheduled_timestamp=timezone_now() + delay,
            realm=realm,
            data=orjson.dumps(email_fields).decode(),
        )

        # We store the recipients in the ScheduledEmail object itself,
        # rather than the JSON data object, so that we can find and clear
        # them using clear_scheduled_emails.
        try:
            if to_user_ids is not None:
                email.users.add(*to_user_ids)
            else:
                assert to_emails is not None
                assert len(to_emails) == 1
                email.address = parseaddr(to_emails[0])[1]
                email.save()
        except Exception as e:
            email.delete()
            raise e


def send_email_to_admins(
    template_prefix: str,
    realm: Realm,
    from_name: Optional[str] = None,
    from_address: Optional[str] = None,
    language: Optional[str] = None,
    context: Mapping[str, Any] = {},
) -> None:
    admins = realm.get_human_admin_users()
    admin_user_ids = [admin.id for admin in admins]
    send_email(
        template_prefix,
        to_user_ids=admin_user_ids,
        from_name=from_name,
        from_address=from_address,
        language=language,
        context=context,
    )


def send_email_to_billing_admins_and_realm_owners(
    template_prefix: str,
    realm: Realm,
    from_name: Optional[str] = None,
    from_address: Optional[str] = None,
    language: Optional[str] = None,
    context: Mapping[str, Any] = {},
) -> None:
    send_email(
        template_prefix,
        to_user_ids=[user.id for user in realm.get_human_billing_admin_and_realm_owner_users()],
        from_name=from_name,
        from_address=from_address,
        language=language,
        context=context,
    )


def clear_scheduled_invitation_emails(email: str) -> None:
    """Unlike most scheduled emails, invitation emails don't have an
    existing user object to key off of, so we filter by address here."""
    items = ScheduledEmail.objects.filter(
        address__iexact=email, type=ScheduledEmail.INVITATION_REMINDER
    )
    items.delete()


@transaction.atomic(savepoint=False)
def clear_scheduled_emails(user_id: int, email_type: Optional[int] = None) -> None:
    # We need to obtain a FOR UPDATE lock on the selected rows to keep a concurrent
    # execution of this function (or something else) from deleting them before we access
    # the .users attribute.
    items = (
        ScheduledEmail.objects.filter(users__in=[user_id])
        .prefetch_related("users")
        .select_for_update()
    )
    if email_type is not None:
        items = items.filter(type=email_type)

    for item in items:
        item.users.remove(user_id)
        if item.users.all().count() == 0:
            # Due to our transaction holding the row lock we have a guarantee
            # that the obtained COUNT is accurate, thus we can reliably use it
            # to decide whether to delete the ScheduledEmail row.
            item.delete()


def handle_send_email_format_changes(job: Dict[str, Any]) -> None:
    # Reformat any jobs that used the old to_email
    # and to_user_ids argument formats.
    if "to_email" in job:
        if job["to_email"] is not None:
            job["to_emails"] = [job["to_email"]]
        del job["to_email"]
    if "to_user_id" in job:
        if job["to_user_id"] is not None:
            job["to_user_ids"] = [job["to_user_id"]]
        del job["to_user_id"]


def deliver_scheduled_emails(email: ScheduledEmail) -> None:
    data = orjson.loads(email.data)
    user_ids = list(email.users.values_list("id", flat=True))
    if not user_ids and not email.address:
        # This state doesn't make sense, so something must have mutated the object
        logger.warning(
            "ScheduledEmail %s at %s had empty users and address attributes: %r",
            email.id,
            email.scheduled_timestamp,
            data,
        )
        email.delete()
        return

    if user_ids:
        data["to_user_ids"] = user_ids
    if email.address is not None:
        data["to_emails"] = [email.address]
    handle_send_email_format_changes(data)
    send_email(**data)
    email.delete()


def get_header(option: Optional[str], header: Optional[str], name: str) -> str:
    if option and header:
        raise DoubledEmailArgumentError(name)
    if not option and not header:
        raise NoEmailArgumentError(name)
    return str(option or header)


def send_custom_email(
    users: QuerySet[UserProfile],
    *,
    target_emails: Sequence[str] = [],
    options: Dict[str, Any],
    add_context: Optional[Callable[[Dict[str, Union[List[str], str]], UserProfile], None]] = None,
) -> None:
    """
    Helper for `manage.py send_custom_email`.

    Can be used directly with from a management shell with
    send_custom_email(user_profile_list, dict(
        markdown_template_path="/path/to/markdown/file.md",
        subject="Email subject",
        from_name="Sender Name")
    )
    """

    with open(options["markdown_template_path"]) as f:
        text = f.read()
        parsed_email_template = Parser(policy=default).parsestr(text)
        email_template_hash = hashlib.sha256(text.encode()).hexdigest()[0:32]

    email_id = f"zerver/emails/custom/custom_email_{email_template_hash}"
    markdown_email_base_template_path = "templates/zerver/emails/custom_email_base.pre.html"
    html_template_path = f"templates/{email_id}.html"
    plain_text_template_path = f"templates/{email_id}.txt"
    subject_path = f"templates/{email_id}.subject.txt"
    os.makedirs(os.path.dirname(html_template_path), exist_ok=True)

    # First, we render the Markdown input file just like our
    # user-facing docs with render_markdown_path.
    with open(plain_text_template_path, "w") as f:
        f.write(parsed_email_template.get_payload())

    from zerver.lib.templates import render_markdown_path

    rendered_input = render_markdown_path(plain_text_template_path.replace("templates/", ""))

    # And then extend it with our standard email headers.
    with open(html_template_path, "w") as f:
        with open(markdown_email_base_template_path) as base_template:
            # We use an ugly string substitution here, because we want to:
            #  1. Only run Jinja once on the supplied content
            #  2. Allow the supplied content to have jinja interpolation in it
            #  3. Have that interpolation happen in the context of
            #     each individual email we send, so the contents can
            #     vary user-to-user
            f.write(base_template.read().replace("{{ rendered_input }}", rendered_input))

    with open(subject_path, "w") as f:
        f.write(get_header(options.get("subject"), parsed_email_template.get("subject"), "subject"))

    # Finally, we send the actual emails.
    for user_profile in users.select_related("realm").order_by("id"):
        if options.get("admins_only") and not user_profile.is_realm_admin:
            continue
        context: Dict[str, Union[List[str], str]] = {
            "realm_uri": user_profile.realm.uri,
            "realm_name": user_profile.realm.name,
        }
        if add_context is not None:
            add_context(context, user_profile)
        with suppress(EmailNotDeliveredError):
            send_email(
                email_id,
                to_user_ids=[user_profile.id],
                from_address=FromAddress.SUPPORT,
                reply_to_email=options.get("reply_to"),
                from_name=get_header(
                    options.get("from_name"), parsed_email_template.get("from"), "from_name"
                ),
                context=context,
                dry_run=options["dry_run"],
            )

        if options["dry_run"]:
            break

    # Now send emails to any recipients without a user account.
    # This code path is intended for rare RemoteZulipServer emails.
    for email_address in target_emails:
        send_email(
            email_id,
            to_emails=[email_address],
            from_address=FromAddress.SUPPORT,
            reply_to_email=options.get("reply_to"),
            from_name=get_header(
                options.get("from_name"), parsed_email_template.get("from"), "from_name"
            ),
            context={"remote_server_email": True},
            dry_run=options["dry_run"],
        )

        if options["dry_run"]:
            break


def log_email_config_errors() -> None:
    """
    The purpose of this function is to log (potential) config errors,
    but without raising an exception.
    """
    if settings.EMAIL_HOST_USER and settings.EMAIL_HOST_PASSWORD is None:
        logger.error(
            "An SMTP username was set (EMAIL_HOST_USER), but password is unset (EMAIL_HOST_PASSWORD).  "
            "To disable SMTP authentication, set EMAIL_HOST_USER to an empty string."
        )
