import uuid

from django.contrib.auth.models import User
from django.db import models
from django.urls import reverse
from django.utils import timezone


def gen_message_id():
    """Generate a time-based identifier for use in "In-Reply-To" header."""
    return f'<{uuid.uuid1()}@sfconservancy.org>'


class Candidate(models.Model):
    """A source/binary release we'd like to verify CCS status of."""

    name = models.CharField('Candidate name', max_length=50)
    slug = models.SlugField(max_length=50, unique=True)
    vendor = models.CharField('Vendor name', max_length=50)
    device = models.CharField('Device name', max_length=50)
    release_date = models.DateField(null=True, blank=True)
    description = models.TextField(blank=True)
    source_url = models.URLField()
    binary_url = models.URLField(blank=True)
    ordering = models.SmallIntegerField(default=0)
    email_message_id = models.CharField(max_length=255, default=gen_message_id)

    class Meta:
        ordering = ['ordering', 'name']

    def __str__(self):
        return self.name

    def get_absolute_url(self):
        return reverse('usethesource:candidate', kwargs={'slug': self.slug})


class Comment(models.Model):
    """A comment about experiences or learnings building the candidate."""

    candidate = models.ForeignKey(Candidate, on_delete=models.CASCADE)
    user = models.ForeignKey(User, on_delete=models.PROTECT)
    time = models.DateTimeField(default=timezone.now)
    message = models.TextField()
    email_message_id = models.CharField(max_length=255, default=gen_message_id)

    def __str__(self):
        return f'{self.id}: {self.candidate.name}, {self.user}, {self.time}'

    def _find_previous_comment(self):
        try:
            return self.__class__.objects.filter(candidate=self.candidate, id__lt=self.id).latest('id')
        except self.__class__.DoesNotExist:
            return None

    def in_reply_to(self):
        """Determine the message_id of the previous comment or the candidate.

        Used for email threading.
        """
        if prev_comment := self._find_previous_comment():
            return prev_comment.email_message_id
        else:
            return self.candidate.email_message_id

    class Meta:
        ordering = ['id']