import re
import secrets
from django.conf import settings
from django.db import models
from django.db.models.signals import post_delete
from django.dispatch import receiver
from django.urls import reverse
from django.utils import timezone
from django.utils.translation import gettext_lazy as _

TAG_RE = re.compile(r'(?<!\w)#([\wäöüÄÖÜß-]+)')
LINK_RE = re.compile(r'\[\[(todo|note|link|journal)?:?(\d+)\]\]', re.I)
FENCE_RE = re.compile(r'^\s*(`{3,}|~{3,})')
INLINE_CODE_RE = re.compile(r'(`+).*?\1', re.S)


def without_markdown_code(text):
    """Remove fenced and inline Markdown code before extracting metadata."""
    visible_lines = []
    fence = None
    for line in (text or '').splitlines():
        match = FENCE_RE.match(line)
        if fence:
            if match and match.group(1)[0] == fence[0] and len(match.group(1)) >= len(fence):
                fence = None
            visible_lines.append('')
        elif match:
            fence = match.group(1)
            visible_lines.append('')
        else:
            visible_lines.append(line)
    return INLINE_CODE_RE.sub('', '\n'.join(visible_lines))


def delete_unused_tags(tags=None):
    """Delete tags that are no longer used by items or tag-based features."""
    candidates = Tag.objects.all() if tags is None else Tag.objects.filter(pk__in=[tag.pk for tag in tags])
    candidates.filter(items__isnull=True, kanbans__isnull=True, api_keys__isnull=True, tag_collections__isnull=True).exclude(
        name__in=Team.objects.values_list('slug', flat=True),
    ).delete()


class Tag(models.Model):
    name = models.SlugField(max_length=80, unique=True, allow_unicode=True)

    class Meta:
        ordering = ['name']

    def __str__(self):
        return f'#{self.name}'


class UserInvite(models.Model):
    email = models.EmailField()
    token = models.CharField(max_length=80, unique=True, editable=False)
    invited_by = models.ForeignKey(settings.AUTH_USER_MODEL, on_delete=models.CASCADE, related_name='sent_user_invites')
    created_at = models.DateTimeField(auto_now_add=True)
    accepted_at = models.DateTimeField(blank=True, null=True)

    class Meta:
        ordering = ['-created_at']

    def save(self, *args, **kwargs):
        if not self.token:
            self.token = secrets.token_urlsafe(32)
        super().save(*args, **kwargs)

    def __str__(self):
        return f'Benutzereinladung {self.email}'


class Team(models.Model):
    name = models.CharField(max_length=120)
    slug = models.SlugField(max_length=80, unique=True, allow_unicode=True, help_text='Team-Tag ohne #, z.B. my2dos')
    owner = models.ForeignKey(settings.AUTH_USER_MODEL, on_delete=models.CASCADE, related_name='owned_teams')
    created_at = models.DateTimeField(auto_now_add=True)

    class Meta:
        ordering = ['name']

    def __str__(self):
        return self.name


class TeamMembership(models.Model):
    class Role(models.TextChoices):
        OWNER = 'owner', 'Owner'
        ADMIN = 'admin', 'Admin'
        MEMBER = 'member', 'Mitglied'

    team = models.ForeignKey(Team, on_delete=models.CASCADE, related_name='memberships')
    user = models.ForeignKey(settings.AUTH_USER_MODEL, on_delete=models.CASCADE, related_name='team_memberships')
    role = models.CharField(max_length=10, choices=Role.choices, default=Role.MEMBER)
    created_at = models.DateTimeField(auto_now_add=True)

    class Meta:
        unique_together = [('team', 'user')]

    def __str__(self):
        return f'{self.user} in {self.team}'


class TeamInvite(models.Model):
    team = models.ForeignKey(Team, on_delete=models.CASCADE, related_name='invites')
    email = models.EmailField(blank=True)
    token = models.CharField(max_length=80, unique=True, editable=False)
    invited_by = models.ForeignKey(settings.AUTH_USER_MODEL, on_delete=models.CASCADE, related_name='sent_team_invites')
    created_at = models.DateTimeField(auto_now_add=True)
    accepted_at = models.DateTimeField(blank=True, null=True)

    class Meta:
        ordering = ['-created_at']

    def save(self, *args, **kwargs):
        if not self.token:
            self.token = secrets.token_urlsafe(32)
        super().save(*args, **kwargs)

    def __str__(self):
        return f'Einladung {self.team} {self.email}'


class Item(models.Model):
    class Kind(models.TextChoices):
        TODO = 'todo', _('Task')
        NOTE = 'note', _('Note')
        LINK = 'link', _('Link')
        JOURNAL = 'journal', _('Journal')

    class Visibility(models.TextChoices):
        PRIVATE = 'private', _('Private')
        TEAM = 'team', _('Team')
        PUBLIC = 'public', _('Public')

    owner = models.ForeignKey(settings.AUTH_USER_MODEL, on_delete=models.CASCADE, related_name='items')
    team = models.ForeignKey(Team, on_delete=models.SET_NULL, blank=True, null=True, related_name='items')
    kind = models.CharField(max_length=10, choices=Kind.choices, default=Kind.NOTE)
    content = models.TextField()
    comment = models.TextField(blank=True)
    visibility = models.CharField(max_length=10, choices=Visibility.choices, default=Visibility.PRIVATE)
    kanban_status = models.CharField(max_length=20, default='inbox', choices=[
        ('inbox', _('Inbox')),
        ('todo', 'Todo'),
        ('progress', _('In Progress')),
        ('done', _('Done')),
    ])
    is_done = models.BooleanField(default=False)
    completed_at = models.DateTimeField(blank=True, null=True)
    due_at = models.DateTimeField(blank=True, null=True)
    url = models.URLField(blank=True)
    tags = models.ManyToManyField(Tag, blank=True, related_name='items')
    linked_items = models.ManyToManyField('self', blank=True, symmetrical=False, related_name='backlinks')
    created_at = models.DateTimeField(auto_now_add=True)
    updated_at = models.DateTimeField(auto_now=True)

    class Meta:
        ordering = ['-created_at']

    def __str__(self):
        return self.content[:80]

    def get_absolute_url(self):
        return reverse('item_detail', args=[self.pk])

    @property
    def is_overdue(self):
        return self.kind == self.Kind.TODO and not self.is_done and self.due_at and self.due_at < timezone.now()

    @property
    def is_due_today(self):
        return self.kind == self.Kind.TODO and not self.is_done and self.due_at and timezone.localdate(self.due_at) == timezone.localdate()

    def sync_metadata(self):
        old_tags = list(self.tags.all())
        metadata_text = without_markdown_code(self.content)
        tag_names = {m.group(1).lower() for m in TAG_RE.finditer(metadata_text)}
        tags = [Tag.objects.get_or_create(name=name)[0] for name in tag_names]
        self.tags.set(tags)
        delete_unused_tags(old_tags)
        ids = [int(m.group(2)) for m in LINK_RE.finditer(f'{self.content}\n{self.comment}')]
        self.linked_items.set(Item.objects.filter(id__in=ids).exclude(id=self.id))


class Kanban(models.Model):
    owner = models.ForeignKey(settings.AUTH_USER_MODEL, on_delete=models.CASCADE, related_name='kanbans')
    name = models.CharField(max_length=120)
    tag = models.ForeignKey(Tag, on_delete=models.CASCADE, related_name='kanbans')
    created_at = models.DateTimeField(auto_now_add=True)

    class Meta:
        ordering = ['name']
        unique_together = [('owner', 'tag')]

    def __str__(self):
        return self.name


class Collection(models.Model):
    class Mode(models.TextChoices):
        MANUAL = 'manual', _('Manual collection')
        TAGS = 'tags', _('Tag collection')

    owner = models.ForeignKey(settings.AUTH_USER_MODEL, on_delete=models.CASCADE, related_name='collections')
    team = models.ForeignKey(Team, on_delete=models.SET_NULL, blank=True, null=True, related_name='collections')
    title = models.CharField(max_length=200)
    description = models.TextField(blank=True)
    visibility = models.CharField(max_length=10, choices=Item.Visibility.choices, default=Item.Visibility.PRIVATE)
    mode = models.CharField(max_length=10, choices=Mode.choices, default=Mode.MANUAL)
    filter_tags = models.ManyToManyField(Tag, blank=True, related_name='tag_collections')
    created_at = models.DateTimeField(auto_now_add=True)
    updated_at = models.DateTimeField(auto_now=True)

    class Meta:
        ordering = ['-updated_at']

    def __str__(self):
        return self.title

    def get_absolute_url(self):
        return reverse('collection_detail', args=[self.pk])


class CollectionSection(models.Model):
    collection = models.ForeignKey(Collection, on_delete=models.CASCADE, related_name='sections')
    item = models.ForeignKey(Item, on_delete=models.PROTECT, blank=True, null=True, related_name='collection_sections')
    sub_collection = models.ForeignKey(Collection, on_delete=models.PROTECT, blank=True, null=True, related_name='containing_sections')
    title = models.CharField(max_length=200, blank=True)
    position = models.PositiveIntegerField(default=0)
    created_at = models.DateTimeField(auto_now_add=True)

    class Meta:
        ordering = ['position', 'id']
        constraints = [
            models.CheckConstraint(
                check=(models.Q(item__isnull=False, sub_collection__isnull=True) | models.Q(item__isnull=True, sub_collection__isnull=False)),
                name='collection_section_exactly_one_target',
            ),
            models.UniqueConstraint(fields=['collection', 'item'], condition=models.Q(item__isnull=False), name='unique_collection_item'),
            models.UniqueConstraint(fields=['collection', 'sub_collection'], condition=models.Q(sub_collection__isnull=False), name='unique_collection_sub_collection'),
            models.UniqueConstraint(fields=['collection', 'position'], name='unique_collection_position'),
        ]

    def __str__(self):
        return f'{self.collection}: {self.title or self.item or self.sub_collection}'


class UserPreference(models.Model):
    user = models.OneToOneField(settings.AUTH_USER_MODEL, on_delete=models.CASCADE, related_name='preferences')
    language = models.CharField(max_length=10, blank=True, default='', choices=[('', _('Browser default')), ('de', 'Deutsch'), ('en', 'English')])
    default_item_kind = models.CharField(max_length=10, choices=Item.Kind.choices, default=Item.Kind.NOTE)
    show_notes = models.BooleanField(default=True)
    show_open_todos = models.BooleanField(default=True)
    show_done_todos = models.BooleanField(default=False)
    show_links = models.BooleanField(default=True)
    show_journal = models.BooleanField(default=False)
    due_first = models.BooleanField(default=True)
    overview_lines = models.PositiveSmallIntegerField(default=4)

    def __str__(self):
        return f'Einstellungen {self.user}'


class ApiKey(models.Model):
    owner = models.ForeignKey(settings.AUTH_USER_MODEL, on_delete=models.CASCADE, related_name='api_keys')
    name = models.CharField(max_length=120, default='API Key')
    token = models.CharField(max_length=80, unique=True, editable=False)
    tags = models.ManyToManyField(Tag, blank=True, related_name='api_keys')
    created_at = models.DateTimeField(auto_now_add=True)
    is_active = models.BooleanField(default=True)

    class Meta:
        ordering = ['-created_at']

    def save(self, *args, **kwargs):
        if not self.token:
            self.token = secrets.token_urlsafe(32)
        super().save(*args, **kwargs)

    def __str__(self):
        return self.name


class Attachment(models.Model):
    item = models.ForeignKey(Item, on_delete=models.CASCADE, related_name='attachments')
    file = models.FileField(upload_to='attachments/%Y/%m/')
    uploaded_at = models.DateTimeField(auto_now_add=True)

    def __str__(self):
        return self.file.name


@receiver(post_delete, sender=Item)
def clean_tags_after_item_delete(sender, instance, **kwargs):
    delete_unused_tags()