# Copyright: (c) 2008, Jarek Zgoda <jarek.zgoda@gmail.com>

__revision__ = "$Id: models.py 28 2009-10-22 15:03:02Z jarek.zgoda $"
import datetime
import secrets
from base64 import b32encode
from typing import List, Mapping, Optional, Union
from urllib.parse import urljoin

from django.conf import settings
from django.contrib.contenttypes.fields import GenericForeignKey
from django.contrib.contenttypes.models import ContentType
from django.db import models
from django.db.models import CASCADE
from django.http import HttpRequest, HttpResponse
from django.shortcuts import render
from django.urls import reverse
from django.utils.timezone import now as timezone_now
from typing_extensions import Protocol

from zerver.lib.types import UnspecifiedValue
from zerver.models import EmailChangeStatus, MultiuseInvite, PreregistrationUser, Realm, UserProfile


class HasRealmObject(Protocol):
    realm: Realm


class OptionalHasRealmObject(Protocol):
    realm: Optional[Realm]


class ConfirmationKeyException(Exception):
    WRONG_LENGTH = 1
    EXPIRED = 2
    DOES_NOT_EXIST = 3

    def __init__(self, error_type: int) -> None:
        super().__init__()
        self.error_type = error_type


def render_confirmation_key_error(
    request: HttpRequest, exception: ConfirmationKeyException
) -> HttpResponse:
    if exception.error_type == ConfirmationKeyException.WRONG_LENGTH:
        return render(request, "confirmation/link_malformed.html", status=404)
    if exception.error_type == ConfirmationKeyException.EXPIRED:
        return render(request, "confirmation/link_expired.html", status=404)
    return render(request, "confirmation/link_does_not_exist.html", status=404)


def generate_key() -> str:
    # 24 characters * 5 bits of entropy/character = 120 bits of entropy
    return b32encode(secrets.token_bytes(15)).decode().lower()


ConfirmationObjT = Union[MultiuseInvite, PreregistrationUser, EmailChangeStatus]


def get_object_from_key(
    confirmation_key: str, confirmation_types: List[int], activate_object: bool = True
) -> ConfirmationObjT:
    # Confirmation keys used to be 40 characters
    if len(confirmation_key) not in (24, 40):
        raise ConfirmationKeyException(ConfirmationKeyException.WRONG_LENGTH)
    try:
        confirmation = Confirmation.objects.get(
            confirmation_key=confirmation_key, type__in=confirmation_types
        )
    except Confirmation.DoesNotExist:
        raise ConfirmationKeyException(ConfirmationKeyException.DOES_NOT_EXIST)

    if confirmation.expiry_date is not None and timezone_now() > confirmation.expiry_date:
        raise ConfirmationKeyException(ConfirmationKeyException.EXPIRED)

    obj = confirmation.content_object
    assert obj is not None
    if activate_object and hasattr(obj, "status"):
        obj.status = getattr(settings, "STATUS_ACTIVE", 1)
        obj.save(update_fields=["status"])
    return obj


def create_confirmation_link(
    obj: Union[Realm, HasRealmObject, OptionalHasRealmObject],
    confirmation_type: int,
    *,
    validity_in_days: Union[Optional[int], UnspecifiedValue] = UnspecifiedValue(),
    url_args: Mapping[str, str] = {},
) -> str:
    # validity_in_days is an override for the default values which are
    # determined by the confirmation_type - its main purpose is for use
    # in tests which may want to have control over the exact expiration time.
    key = generate_key()
    realm = None
    if isinstance(obj, Realm):
        realm = obj
    elif hasattr(obj, "realm"):
        realm = obj.realm

    current_time = timezone_now()
    expiry_date = None
    if not isinstance(validity_in_days, UnspecifiedValue):
        if validity_in_days is None:
            expiry_date = None
        else:
            assert validity_in_days is not None
            expiry_date = current_time + datetime.timedelta(days=validity_in_days)
    else:
        expiry_date = current_time + datetime.timedelta(
            days=_properties[confirmation_type].validity_in_days
        )

    Confirmation.objects.create(
        content_object=obj,
        date_sent=current_time,
        confirmation_key=key,
        realm=realm,
        expiry_date=expiry_date,
        type=confirmation_type,
    )
    return confirmation_url(key, realm, confirmation_type, url_args)


def confirmation_url(
    confirmation_key: str,
    realm: Optional[Realm],
    confirmation_type: int,
    url_args: Mapping[str, str] = {},
) -> str:
    url_args = dict(url_args)
    url_args["confirmation_key"] = confirmation_key
    return urljoin(
        settings.ROOT_DOMAIN_URI if realm is None else realm.uri,
        reverse(_properties[confirmation_type].url_name, kwargs=url_args),
    )


class Confirmation(models.Model):
    content_type = models.ForeignKey(ContentType, on_delete=CASCADE)
    object_id: int = models.PositiveIntegerField(db_index=True)
    content_object = GenericForeignKey("content_type", "object_id")
    date_sent: datetime.datetime = models.DateTimeField(db_index=True)
    confirmation_key: str = models.CharField(max_length=40, db_index=True)
    expiry_date: Optional[datetime.datetime] = models.DateTimeField(db_index=True, null=True)
    realm: Optional[Realm] = models.ForeignKey(Realm, null=True, on_delete=CASCADE)

    # The following list is the set of valid types
    USER_REGISTRATION = 1
    INVITATION = 2
    EMAIL_CHANGE = 3
    UNSUBSCRIBE = 4
    SERVER_REGISTRATION = 5
    MULTIUSE_INVITE = 6
    REALM_CREATION = 7
    REALM_REACTIVATION = 8
    type: int = models.PositiveSmallIntegerField()

    def __str__(self) -> str:
        return f"<Confirmation: {self.content_object}>"

    class Meta:
        unique_together = ("type", "confirmation_key")


class ConfirmationType:
    def __init__(
        self,
        url_name: str,
        validity_in_days: int = settings.CONFIRMATION_LINK_DEFAULT_VALIDITY_DAYS,
    ) -> None:
        self.url_name = url_name
        self.validity_in_days = validity_in_days


_properties = {
    Confirmation.USER_REGISTRATION: ConfirmationType("get_prereg_key_and_redirect"),
    Confirmation.INVITATION: ConfirmationType(
        "get_prereg_key_and_redirect", validity_in_days=settings.INVITATION_LINK_VALIDITY_DAYS
    ),
    Confirmation.EMAIL_CHANGE: ConfirmationType("confirm_email_change"),
    Confirmation.UNSUBSCRIBE: ConfirmationType(
        "unsubscribe",
        validity_in_days=1000000,  # should never expire
    ),
    Confirmation.MULTIUSE_INVITE: ConfirmationType(
        "join", validity_in_days=settings.INVITATION_LINK_VALIDITY_DAYS
    ),
    Confirmation.REALM_CREATION: ConfirmationType("get_prereg_key_and_redirect"),
    Confirmation.REALM_REACTIVATION: ConfirmationType("realm_reactivation"),
}


def one_click_unsubscribe_link(user_profile: UserProfile, email_type: str) -> str:
    """
    Generate a unique link that a logged-out user can visit to unsubscribe from
    Zulip e-mails without having to first log in.
    """
    return create_confirmation_link(
        user_profile, Confirmation.UNSUBSCRIBE, url_args={"email_type": email_type}
    )


# Functions related to links generated by the generate_realm_creation_link.py
# management command.
# Note that being validated here will just allow the user to access the create_realm
# form, where they will enter their email and go through the regular
# Confirmation.REALM_CREATION pathway.
# Arguably RealmCreationKey should just be another ConfirmationObjT and we should
# add another Confirmation.type for this; it's this way for historical reasons.


def validate_key(creation_key: Optional[str]) -> Optional["RealmCreationKey"]:
    """Get the record for this key, raising InvalidCreationKey if non-None but invalid."""
    if creation_key is None:
        return None
    try:
        key_record = RealmCreationKey.objects.get(creation_key=creation_key)
    except RealmCreationKey.DoesNotExist:
        raise RealmCreationKey.Invalid()
    time_elapsed = timezone_now() - key_record.date_created
    if time_elapsed.total_seconds() > settings.REALM_CREATION_LINK_VALIDITY_DAYS * 24 * 3600:
        raise RealmCreationKey.Invalid()
    return key_record


def generate_realm_creation_url(by_admin: bool = False) -> str:
    key = generate_key()
    RealmCreationKey.objects.create(
        creation_key=key, date_created=timezone_now(), presume_email_valid=by_admin
    )
    return urljoin(
        settings.ROOT_DOMAIN_URI,
        reverse("create_realm", kwargs={"creation_key": key}),
    )


class RealmCreationKey(models.Model):
    creation_key = models.CharField("activation key", db_index=True, max_length=40)
    date_created = models.DateTimeField("created", default=timezone_now)

    # True just if we should presume the email address the user enters
    # is theirs, and skip sending mail to it to confirm that.
    presume_email_valid: bool = models.BooleanField(default=False)

    class Invalid(Exception):
        pass