utils.py

import inspect
import os
from collections import OrderedDict
from datetime import datetime
from typing import Any, Callable, Type, Generator, Tuple
from warnings import warn

from django.contrib import admin
from django.db import models
from django.utils.translation import gettext_lazy as _
from etc.toolbox import import_app_module, import_project_modules

from .settings import PREFS_MODULE_NAME
from .signals import prefs_save


class Frame:
    """Represents a frame object at a definite level of hierarchy.

    To be used as context manager:

        with Frame as f:
            ...

    """

    def __init__(self, stepback: int = 0):
        self.depth = stepback

    def __enter__(self):
        frame = inspect.currentframe().f_back

        for __ in range(self.depth):
            frame = frame.f_back

        self.frame = frame

        return self.frame

    def __exit__(self, exc_type, exc_val, exc_tb):
        del self.frame


class PatchedLocal:
    """Object of this class temporarily replace all module variables
    considered preferences.

    """
    def __init__(self, key: str, val: Any):
        self.key = key
        self.val = val


class Mimic:
    """Mimics other types by implementation of various special methods.

    This one is deprecated if favor of setting module proxying (proxy_settings_module()).

    """

    value: Any = None

    def __call__(self, *args, **kwargs):
        return self.value

    def __str__(self):
        return self.value.__str__()

    def __bool__(self):
        return bool(self.value)

    def __int__(self):
        return int(self.value)

    def __float__(self):
        return float(self.value)

    def __len__(self):
        return self.value.__len__()

    def __contains__(self, item):
        return self.value.__contains__(item)

    def __sub__(self, other):
        return self.value.__sub__(other)

    def __rsub__(self, other):
        return self.value.__rsub__(other)

    def __add__(self, other):
        return self.value.__add__(other)

    def __radd__(self, other):
        return self.value.__radd__(other)

    def __mul__(self, other):
        return self.value.__mul__(other)

    def __rmul__(self, other):
        return self.value.__rmul__(other)

    def __lt__(self, other):
        return self.value.__lt__(other)

    def __le__(self, other):
        return self.value.__le__(other)

    def __gt__(self, other):
        return self.value.__gt__(other)

    def __ge__(self, other):
        return self.value.__ge__(other)

    def __eq__(self, other):
        return self.value.__eq__(other)

    def __ne__(self, other):
        return self.value.__ne__(other)


class PrefProxy(Mimic):
    """Objects of this class replace app preferences."""

    def __init__(
            self,
            name: str,
            default: Any,
            category: str = None,
            field: models.Field = None,
            verbose_name: str = None,
            help_text: str = '',
            static: bool = True,
            readonly: bool = False
    ):
        """

        :param name: Preference name.

        :param default: Default (initial) value.

        :param category: Category name the preference belongs to.

        :param field: Django model field to represent this preference.

        :param verbose_name: Field verbose name.

        :param help_text: Field help text.

        :param static: Leave this preference static (do not store in DB).

        :param readonly: Make this field read only.

        """
        self.name = name
        self.category = category
        self.default = default
        self.static = static
        self.help_text = help_text

        if static:
            readonly = True

        self.readonly = readonly

        if verbose_name is None:
            verbose_name = name.replace('_', ' ').capitalize()

        self.verbose_name = verbose_name

        if field is None:
            self.field = get_field_for_proxy(self)

        else:
            self.field = field
            update_field_from_proxy(self.field, self)

    @property
    def value(self) -> Any:

        if self.static:
            val = self.default

        else:
            try:
                val = getattr(self, 'db_value')

            except AttributeError:
                val = self.default

        return self.field.to_python(val)

    def get_value(self) -> Any:
        warn('Please use .value instead .get_value().', DeprecationWarning, stacklevel=2)
        return self.value

    def __repr__(self):
        return f'{self.name} = {self.value}'


def get_field_for_proxy(pref_proxy: PrefProxy) -> models.Field:
    """Returns a field object instance for a given PrefProxy object.

    :param pref_proxy:

    """
    field = {
        bool: models.BooleanField,
        int:  models.IntegerField,
        float: models.FloatField,
        datetime: models.DateTimeField,

    }.get(type(pref_proxy.default), models.TextField)()

    update_field_from_proxy(field, pref_proxy)

    return field


def update_field_from_proxy(field_obj: models.Field, pref_proxy: PrefProxy):
    """Updates field object with data from a PrefProxy object.

    :param field_obj:

    :param pref_proxy:

    """
    attr_names = ('verbose_name', 'help_text', 'default')

    for attr_name in attr_names:
        setattr(field_obj, attr_name, getattr(pref_proxy, attr_name))


def get_pref_model_class(app: str, prefs: dict, get_prefs_func: Callable) -> Type[models.Model]:
    """Returns preferences model class dynamically crated for a given app or None on conflict."""

    module = f'{app}.{PREFS_MODULE_NAME}'

    model_dict = {
            '_prefs_app': app,
            '_get_prefs': staticmethod(get_prefs_func),
            '__module__': module,
            'Meta': type('Meta', (models.options.Options,), {
                'verbose_name': _('Preference'),
                'verbose_name_plural': _('Preferences'),
                'app_label': app,
                'managed': False,
            })
    }

    for field_name, val_proxy in prefs.items():
        model_dict[field_name] = val_proxy.field

    model = type('Preferences', (models.Model,), model_dict)

    def fake_save_base(self, *args, **kwargs):

        updated_prefs = {
            f.name: getattr(self, f.name)
            for f in self._meta.fields
            if not isinstance(f, models.fields.AutoField)
        }

        app_prefs = self._get_prefs(self._prefs_app)

        for pref in app_prefs.keys():
            if pref in updated_prefs:
                app_prefs[pref].db_value = updated_prefs[pref]

        self.pk = self._prefs_app  # Make Django 1.7 happy.
        prefs_save.send(sender=self, app=self._prefs_app, updated_prefs=updated_prefs)

        return True

    model.save_base = fake_save_base

    return model


def get_pref_model_admin_class(prefs: dict) -> Type[admin.ModelAdmin]:

    by_category = OrderedDict()
    readonly_fields = []

    for field_name, val_proxy in prefs.items():

        if val_proxy.readonly:
            readonly_fields.append(field_name)

        if val_proxy.category not in by_category:
            by_category[val_proxy.category] = []

        by_category[val_proxy.category].append(field_name)

    cl_model_admin_dict = {
        'has_add_permission': lambda *args: False,
        'has_delete_permission': lambda *args: False
    }

    if readonly_fields:
        cl_model_admin_dict['readonly_fields'] = readonly_fields

    fieldsets = []

    for category, cat_prefs in by_category.items():
        fieldsets.append((category, {'fields': cat_prefs}))

    if fieldsets:
        cl_model_admin_dict['fieldsets'] = fieldsets

    model = type('PreferencesAdmin', (admin.ModelAdmin,), cl_model_admin_dict)

    model.changelist_view = lambda self, request, **kwargs: self.change_view(request, '', **kwargs)

    model.get_object = lambda self, *args: (
        self.model(
            **{
                field_name: val_proxy.get_value() for field_name, val_proxy in
                self.model._get_prefs(self.model._prefs_app).items()
            }
        )
    )

    return model


def get_frame_locals(stepback: int = 0) -> dict:
    """Returns locals dictionary from a given frame.

    :param stepback:

    """
    with Frame(stepback=stepback) as frame:
        locals_dict = frame.f_locals

    return locals_dict


def traverse_local_prefs(stepback: int = 0) -> Generator[Tuple[str, dict], None, None]:
    """Generator to walk through variables considered as preferences
    in locals dict of a given frame.

    :param stepback:

    """
    locals_dict = get_frame_locals(stepback+1)
    for k in locals_dict:
        if not k.startswith('_') and k.upper() == k:
            yield k, locals_dict


def import_module(package: str, module_name: str):
    """Imports a module from a given package.

    :param package:
    :param module_name:

    """
    import_app_module(package, module_name)


def import_prefs():
    """Imports preferences modules from packages (apps) and project root."""
    
    # settings.py locals if autodiscover_siteprefs() is in urls.py
    settings_locals = get_frame_locals(3)

    if 'self' not in settings_locals:  # If not SiteprefsConfig.ready()
        # Try to import project-wide prefs.

        project_package = settings_locals['__package__']  # Expected project layout introduced in Django 1.4
        if not project_package:
            # Fallback to old layout.
            project_package = os.path.split(os.path.dirname(settings_locals['__file__']))[-1]

        import_module(project_package, PREFS_MODULE_NAME)

    import_project_modules(PREFS_MODULE_NAME)