from django.conf import settings
from django.db import models
from django.utils.html import strip_tags
from django.utils.text import normalize_newlines, Truncator
from django.utils.translation import gettext_lazy as _

from shared.multilingual.utils import i18n_fields_list
from ..functional import firstof
from ..text import slimdown
from .slugs import DowngradingSlugField


from ..conf import USE_TRANSLATABLE_FIELDS


if USE_TRANSLATABLE_FIELDS:
    from shared.multilingual.utils.fields import (
        TranslatableCharField,
        TranslatableTextField
    )
    # TODO populate_from should use settings.LANGUAGE_CODE
    # FIXME Wrong spelling!
    SLUG_POPULATE_FROM = getattr(settings, 'SLUG_POPULATE_FROM', 'name_en')

else:
    TranslatableCharField = models.CharField
    TranslatableTextField = models.TextField
    SLUG_POPULATE_FROM = 'name'


# TODO Make slimdown optional through settings
# TODO Leave window_title alone, do not slimdown


class PageTitlesBehaviour:
    """
    Implements fallback behaviour.
    """

    def __str__(self):
        return strip_tags(slimdown(self.get_short_name()))

    def get_title(self):
        return self.get_first_title_line() or \
            self.name

    def get_short_name(self):
        return getattr(self, 'short_name', '') or \
            Truncator(self.name).words(5, truncate="...")

    def get_first_title_line(self):
        """
        First line of title field or self.name..
        """
        return normalize_newlines(getattr(self, 'long_title', '') or '').partition("\n")[0]

    def get_subtitle_lines(self):
        """
        All but first line of the long title field.
        """
        return normalize_newlines(getattr(self, 'long_title', '') or '').partition("\n")[2]

    def get_window_title(self):
        return firstof(
            getattr(self, 'window_title', None),
            strip_tags(slimdown(self.get_short_name())),
            strip_tags(slimdown(self.get_first_title_line())),
        )


PageTitlesFunctionMixin = PageTitlesBehaviour


class PageTitlesMixin(PageTitlesBehaviour, models.Model):
    """
    A model mixin containg title and slug fields for models serving 
    as web pages with an URL.

    name:           Main naming field, all other fields besides `slug` 
                    are optional.
    short_name:     For menus etc.
    long_title:     Long title, composed of title line (first line) and 
                    subtitle (all other lines)
    window_title:   Browser window title, also for search engine's results
    slug:           URL name

    """
    name = TranslatableCharField(_("Name"),
        max_length=250)
    sort_name = TranslatableCharField(_("Short Name"),
        max_length=250, null=True, blank=True,
        help_text=_("Optional, used for sorting."))
    short_name = TranslatableCharField(_("Short Name"),
        max_length=25, null=True, blank=True,
        help_text=_("Optional, used for menus etc."))
    long_title = TranslatableTextField(_("title/subtitle"),
        null=True, blank=True, max_length=500,
        help_text=_("Optional, long title for page content region. FIrst line is the title, other lines are the subtitle. Simplified Markdown."))
    window_title = TranslatableCharField(_("window title"),
        null=True, blank=True, max_length=300)
    slug = DowngradingSlugField(_("URL-Name"), max_length=200,
        populate_from=SLUG_POPULATE_FROM, unique_slug=True, blank=True)

    class Meta:
        abstract = True
        ordering = ['sort_name', 'name']


class PageTitlesAdminMixin:
    list_display = ['name', 'slug']
    search_fields = ['name', 'short_name', 'long_title', 'window_title']
    if USE_TRANSLATABLE_FIELDS:
        search_fields = i18n_fields_list(search_fields)
    prepopulated_fields = {
        'slug': [SLUG_POPULATE_FROM]
    }