# Copyright © 2017 Tom Hacohen
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU Affero General Public License as
# published by the Free Software Foundation, version 3.
#
# 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 this program. If not, see <http://www.gnu.org/licenses/>.

import typing as t
from pathlib import Path

from django.conf import settings
from django.core.validators import RegexValidator
from django.db import models, transaction
from django.db.models import Max, Value as Val
from django.db.models.functions import Coalesce, Greatest
from django.utils.crypto import get_random_string
from django.utils.functional import cached_property

from . import app_settings

UidValidator = RegexValidator(regex=r"^[a-zA-Z0-9\-_]{20,}$", message="Not a valid UID")


def stoken_annotation_builder(stoken_id_fields: t.List[str]):
    aggr_fields = [Coalesce(Max(field), Val(0)) for field in stoken_id_fields]
    return Greatest(*aggr_fields) if len(aggr_fields) > 1 else aggr_fields[0]


class CollectionType(models.Model):
    owner = models.ForeignKey(settings.AUTH_USER_MODEL, on_delete=models.CASCADE)
    uid = models.BinaryField(editable=True, blank=False, null=False, db_index=True, unique=True, max_length=1024)

    objects: models.manager.BaseManager["CollectionType"]


class Collection(models.Model):
    main_item = models.OneToOneField("CollectionItem", related_name="parent", null=True, on_delete=models.SET_NULL)
    # The same as main_item.uid, we just also save it here so we have DB constraints for uniqueness (and efficiency)
    uid = models.CharField(db_index=True, unique=True, blank=False, max_length=43, validators=[UidValidator])
    owner = models.ForeignKey(settings.AUTH_USER_MODEL, on_delete=models.CASCADE)

    stoken_annotation = stoken_annotation_builder(["items__revisions__stoken", "members__stoken"])

    objects: models.manager.BaseManager["Collection"]

    def __str__(self):
        return self.uid

    @property
    def content(self) -> "CollectionItemRevision":
        assert self.main_item is not None
        return self.main_item.content

    @property
    def etag(self) -> str:
        return self.content.uid

    @cached_property
    def stoken(self) -> str:
        stoken_id = (
            self.__class__.objects.filter(main_item=self.main_item, items__revisions__current=True)
            .annotate(max_stoken=self.stoken_annotation)
            .values("max_stoken")
            .first()["max_stoken"]
        )

        if stoken_id == 0:
            raise Exception("stoken is None. Should never happen")

        return Stoken.objects.get(id=stoken_id).uid


class CollectionItem(models.Model):
    uid = models.CharField(db_index=True, blank=False, max_length=43, validators=[UidValidator])
    collection = models.ForeignKey(Collection, related_name="items", on_delete=models.CASCADE)
    version = models.PositiveSmallIntegerField()
    encryptionKey = models.BinaryField(editable=True, blank=False, null=True)

    stoken_annotation = stoken_annotation_builder(["revisions__stoken"])

    objects: models.manager.BaseManager["CollectionItem"]

    class Meta:
        unique_together = ("uid", "collection")

    def __str__(self):
        return "{} {}".format(self.uid, self.collection.uid)

    @cached_property
    def content(self) -> "CollectionItemRevision":
        return self.revisions.filter(current=True)[0]

    @property
    def etag(self) -> str:
        return self.content.uid


def chunk_directory_path(instance: "CollectionItemChunk", filename: str) -> Path:
    custom_func = app_settings.CHUNK_PATH_FUNC
    if custom_func is not None:
        return custom_func(instance, filename)

    col: Collection = instance.collection
    user_id: int = col.owner.id
    uid_prefix: str = instance.uid[:2]
    uid_rest: str = instance.uid[2:]
    return Path("user_{}".format(user_id), col.uid, uid_prefix, uid_rest)


class CollectionItemChunk(models.Model):
    uid = models.CharField(db_index=True, blank=False, null=False, max_length=60, validators=[UidValidator])
    collection = models.ForeignKey(Collection, related_name="chunks", on_delete=models.CASCADE)
    chunkFile = models.FileField(upload_to=chunk_directory_path, max_length=150, unique=True)

    objects: models.manager.BaseManager["CollectionItemChunk"]

    def __str__(self):
        return self.uid

    class Meta:
        unique_together = ("collection", "uid")


def generate_stoken_uid():
    return get_random_string(32, allowed_chars="abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789-_")


class Stoken(models.Model):
    id: int
    uid = models.CharField(
        db_index=True,
        unique=True,
        blank=False,
        null=False,
        default=generate_stoken_uid,
        max_length=43,
        validators=[UidValidator],
    )

    objects: models.manager.BaseManager["Stoken"]


class CollectionItemRevision(models.Model):
    stoken = models.OneToOneField(Stoken, on_delete=models.PROTECT)
    uid = models.CharField(
        db_index=True, unique=True, blank=False, null=False, max_length=43, validators=[UidValidator]
    )
    item = models.ForeignKey(CollectionItem, related_name="revisions", on_delete=models.CASCADE)
    meta = models.BinaryField(editable=True, blank=False, null=False)
    current = models.BooleanField(db_index=True, default=True, null=True)
    deleted = models.BooleanField(default=False)

    objects: models.manager.BaseManager["CollectionItemRevision"]

    class Meta:
        unique_together = ("item", "current")

    def __str__(self):
        return "{} {} current={}".format(self.uid, self.item.uid, self.current)


class RevisionChunkRelation(models.Model):
    chunk = models.ForeignKey(CollectionItemChunk, related_name="revisions_relation", on_delete=models.CASCADE)
    revision = models.ForeignKey(CollectionItemRevision, related_name="chunks_relation", on_delete=models.CASCADE)

    objects: models.manager.BaseManager["RevisionChunkRelation"]

    class Meta:
        ordering = ("id",)


class AccessLevels(models.IntegerChoices):
    READ_ONLY = 0
    ADMIN = 1
    READ_WRITE = 2


class CollectionMember(models.Model):
    stoken = models.OneToOneField(Stoken, on_delete=models.PROTECT, null=True)
    collection = models.ForeignKey(Collection, related_name="members", on_delete=models.CASCADE)
    user = models.ForeignKey(settings.AUTH_USER_MODEL, on_delete=models.CASCADE)
    encryptionKey = models.BinaryField(editable=True, blank=False, null=False)
    collectionType = models.ForeignKey(CollectionType, on_delete=models.PROTECT, null=True)
    accessLevel = models.IntegerField(
        choices=AccessLevels.choices,
        default=AccessLevels.READ_ONLY,
    )

    stoken_annotation = stoken_annotation_builder(["stoken"])

    objects: models.manager.BaseManager["CollectionMember"]

    class Meta:
        unique_together = ("user", "collection")

    def __str__(self):
        return "{} {}".format(self.collection.uid, self.user)

    def revoke(self):
        with transaction.atomic():
            CollectionMemberRemoved.objects.update_or_create(
                collection=self.collection,
                user=self.user,
                defaults={
                    "stoken": Stoken.objects.create(),
                },
            )

            self.delete()


class CollectionMemberRemoved(models.Model):
    stoken = models.OneToOneField(Stoken, on_delete=models.PROTECT, null=True)
    collection = models.ForeignKey(Collection, related_name="removed_members", on_delete=models.CASCADE)
    user = models.ForeignKey(settings.AUTH_USER_MODEL, on_delete=models.CASCADE)

    objects: models.manager.BaseManager["CollectionMemberRemoved"]

    class Meta:
        unique_together = ("user", "collection")

    def __str__(self):
        return "{} {}".format(self.collection.uid, self.user)


class CollectionInvitation(models.Model):
    uid = models.CharField(db_index=True, blank=False, null=False, max_length=43, validators=[UidValidator])
    version = models.PositiveSmallIntegerField(default=1)
    fromMember = models.ForeignKey(CollectionMember, on_delete=models.CASCADE)
    # FIXME: make sure to delete all invitations for the same collection once one is accepted
    # Make sure to not allow invitations if already a member

    user = models.ForeignKey(settings.AUTH_USER_MODEL, related_name="incoming_invitations", on_delete=models.CASCADE)
    signedEncryptionKey = models.BinaryField(editable=False, blank=False, null=False)
    accessLevel = models.IntegerField(
        choices=AccessLevels.choices,
        default=AccessLevels.READ_ONLY,
    )

    objects: models.manager.BaseManager["CollectionInvitation"]

    class Meta:
        unique_together = ("user", "fromMember")

    def __str__(self):
        return "{} {}".format(self.fromMember.collection.uid, self.user)

    @cached_property
    def collection(self) -> Collection:
        return self.fromMember.collection


class UserInfo(models.Model):
    owner = models.OneToOneField(settings.AUTH_USER_MODEL, on_delete=models.CASCADE, primary_key=True)
    version = models.PositiveSmallIntegerField(default=1)
    loginPubkey = models.BinaryField(editable=True, blank=False, null=False)
    pubkey = models.BinaryField(editable=True, blank=False, null=False)
    encryptedContent = models.BinaryField(editable=True, blank=False, null=False)
    salt = models.BinaryField(editable=True, blank=False, null=False)

    objects: models.manager.BaseManager["UserInfo"]

    def __str__(self):
        return "UserInfo<{}>".format(self.owner)