from datetime import datetime, timedelta
from hashlib import sha256

import shortuuid
from django.core.validators import MaxLengthValidator
from django.db import models
from django.urls import reverse
from django.utils import timezone
from django.utils.translation import gettext_lazy as _

from webtools import settings


class PasteQuerySet(models.QuerySet):
    def by_secret(self, secret):
        auth = sha256(secret.encode("UTF-8")).hexdigest()
        return self.filter(auth=auth)


class Paste(models.Model):
    """Paste object."""

    objects = PasteQuerySet.as_manager()
    filename = models.CharField(max_length=255, default="")
    slug = models.SlugField(unique=True, editable=False)
    content = models.TextField(
        validators=[MaxLengthValidator(settings.PASTE["max_characters"])]
    )
    size = models.IntegerField(default=0, editable=False)
    paste_time = models.DateTimeField(auto_now_add=True)
    access_time = models.DateTimeField(auto_now=True)
    viewcount = models.IntegerField(default=0, editable=False)

    # auth stores a sha256 (hexdigest) of the Authentication header.
    auth = models.CharField(max_length=64, default="")

    def set_secret(self, secret=None):
        if not secret:
            return
        self.auth = sha256(secret.encode("UTF-8")).hexdigest()

    def compute_size(self):
        """Computes size."""
        self.size = len(self.content)

    def get_absolute_url(self):
        return reverse("short_paste", kwargs={"slug": self.slug})

    def incr_viewcount(self):
        """Increment view counter."""
        self.viewcount = self.viewcount + 1
        self.save()

    def __str__(self):
        excerpt = repr(self.content.split("\n")[0][:100]) + (
            "..." if len(self.content) > 100 else ""
        )
        return f"{self.slug} - {excerpt}"

    @classmethod
    def choose_prefix(cls, filenames):
        """Find a prefix free for all the given filenames.

        Such as <prefix>/filename is unused.
        """
        while True:
            uuid = shortuuid.uuid()
            for i in range(4, len(uuid) + 1):
                potential_uuid = uuid[:i]
                for filename in filenames:
                    slug = f"{potential_uuid}/{filename}"
                    if not any(cls.objects.filter(slug=slug) for filename in filenames):
                        return potential_uuid

    def choose_slug(self):
        while True:
            uuid = shortuuid.uuid()
            for i in range(4, len(uuid)):
                potential_uuid = uuid[:i]
                if not type(self).objects.filter(slug=potential_uuid):
                    self.slug = potential_uuid
                    return