from __future__ import unicode_literals

import warnings
from functools import partial

from django import forms
from django.apps import apps
from django.core import checks, exceptions
from django.db import connection, router
from django.db.backends import utils
from django.db.models import Q
from django.db.models.deletion import CASCADE, SET_DEFAULT, SET_NULL
from django.db.models.query_utils import PathInfo
from django.db.models.utils import make_model_tuple
from django.utils import six
from django.utils.deprecation import (
    RemovedInDjango20Warning, RemovedInDjango110Warning,
)
from django.utils.encoding import force_text, smart_text
from django.utils.functional import cached_property, curry
from django.utils.translation import ugettext_lazy as _
from django.utils.version import get_docs_version

from . import (
    AutoField, Field, IntegerField, PositiveIntegerField,
    PositiveSmallIntegerField,
)
from .related_descriptors import (
    ForwardManyToOneDescriptor, ManyToManyDescriptor,
    ReverseManyToOneDescriptor, ReverseOneToOneDescriptor,
)
from .related_lookups import (
    RelatedExact, RelatedGreaterThan, RelatedGreaterThanOrEqual, RelatedIn,
    RelatedIsNull, RelatedLessThan, RelatedLessThanOrEqual,
)
from .reverse_related import (
    ForeignObjectRel, ManyToManyRel, ManyToOneRel, OneToOneRel,
)

RECURSIVE_RELATIONSHIP_CONSTANT = 'self'


def resolve_relation(scope_model, relation):
    """
    Transform relation into a model or fully-qualified model string of the form
    "app_label.ModelName", relative to scope_model.

    The relation argument can be:
      * RECURSIVE_RELATIONSHIP_CONSTANT, i.e. the string "self", in which case
        the model argument will be returned.
      * A bare model name without an app_label, in which case scope_model's
        app_label will be prepended.
      * An "app_label.ModelName" string.
      * A model class, which will be returned unchanged.
    """
    # Check for recursive relations
    if relation == RECURSIVE_RELATIONSHIP_CONSTANT:
        relation = scope_model

    # Look for an "app.Model" relation
    if isinstance(relation, six.string_types):
        if "." not in relation:
            relation = "%s.%s" % (scope_model._meta.app_label, relation)

    return relation


def lazy_related_operation(function, model, *related_models, **kwargs):
    """
    Schedule `function` to be called once `model` and all `related_models`
    have been imported and registered with the app registry. `function` will
    be called with the newly-loaded model classes as its positional arguments,
    plus any optional keyword arguments.

    The `model` argument must be a model class. Each subsequent positional
    argument is another model, or a reference to another model - see
    `resolve_relation()` for the various forms these may take. Any relative
    references will be resolved relative to `model`.

    This is a convenience wrapper for `Apps.lazy_model_operation` - the app
    registry model used is the one found in `model._meta.apps`.
    """
    models = [model] + [resolve_relation(model, rel) for rel in related_models]
    model_keys = (make_model_tuple(m) for m in models)
    apps = model._meta.apps
    return apps.lazy_model_operation(partial(function, **kwargs), *model_keys)


def add_lazy_relation(cls, field, relation, operation):
    warnings.warn(
        "add_lazy_relation() has been superseded by lazy_related_operation() "
        "and related methods on the Apps class.",
        RemovedInDjango20Warning, stacklevel=2)
    # Rearrange args for new Apps.lazy_model_operation
    function = lambda local, related, field: operation(field, related, local)
    lazy_related_operation(function, cls, relation, field=field)


class RelatedField(Field):
    """
    Base class that all relational fields inherit from.
    """

    # Field flags
    one_to_many = False
    one_to_one = False
    many_to_many = False
    many_to_one = False

    @cached_property
    def related_model(self):
        # Can't cache this property until all the models are loaded.
        apps.check_models_ready()
        return self.remote_field.model

    def check(self, **kwargs):
        errors = super(RelatedField, self).check(**kwargs)
        errors.extend(self._check_related_name_is_valid())
        errors.extend(self._check_relation_model_exists())
        errors.extend(self._check_referencing_to_swapped_model())
        errors.extend(self._check_clashes())
        return errors

    def _check_related_name_is_valid(self):
        import re
        import keyword
        related_name = self.remote_field.related_name
        if related_name is None:
            return []
        is_valid_id = True
        if keyword.iskeyword(related_name):
            is_valid_id = False
        if six.PY3:
            if not related_name.isidentifier():
                is_valid_id = False
        else:
            if not re.match(r'^[a-zA-Z_][a-zA-Z0-9_]*\Z', related_name):
                is_valid_id = False
        if not (is_valid_id or related_name.endswith('+')):
            return [
                checks.Error(
                    "The name '%s' is invalid related_name for field %s.%s" %
                    (self.remote_field.related_name, self.model._meta.object_name,
                     self.name),
                    hint="Related name must be a valid Python identifier or end with a '+'",
                    obj=self,
                    id='fields.E306',
                )
            ]
        return []

    def _check_relation_model_exists(self):
        rel_is_missing = self.remote_field.model not in self.opts.apps.get_models()
        rel_is_string = isinstance(self.remote_field.model, six.string_types)
        model_name = self.remote_field.model if rel_is_string else self.remote_field.model._meta.object_name
        if rel_is_missing and (rel_is_string or not self.remote_field.model._meta.swapped):
            return [
                checks.Error(
                    ("Field defines a relation with model '%s', which "
                     "is either not installed, or is abstract.") % model_name,
                    hint=None,
                    obj=self,
                    id='fields.E300',
                )
            ]
        return []

    def _check_referencing_to_swapped_model(self):
        if (self.remote_field.model not in self.opts.apps.get_models() and
                not isinstance(self.remote_field.model, six.string_types) and
                self.remote_field.model._meta.swapped):
            model = "%s.%s" % (
                self.remote_field.model._meta.app_label,
                self.remote_field.model._meta.object_name
            )
            return [
                checks.Error(
                    ("Field defines a relation with the model '%s', "
                     "which has been swapped out.") % model,
                    hint="Update the relation to point at 'settings.%s'." % self.remote_field.model._meta.swappable,
                    obj=self,
                    id='fields.E301',
                )
            ]
        return []

    def _check_clashes(self):
        """
        Check accessor and reverse query name clashes.
        """
        from django.db.models.base import ModelBase

        errors = []
        opts = self.model._meta

        # `f.remote_field.model` may be a string instead of a model. Skip if model name is
        # not resolved.
        if not isinstance(self.remote_field.model, ModelBase):
            return []

        # Consider that we are checking field `Model.foreign` and the models
        # are:
        #
        #     class Target(models.Model):
        #         model = models.IntegerField()
        #         model_set = models.IntegerField()
        #
        #     class Model(models.Model):
        #         foreign = models.ForeignKey(Target)
        #         m2m = models.ManyToManyField(Target)

        # rel_opts.object_name == "Target"
        rel_opts = self.remote_field.model._meta
        # If the field doesn't install a backward relation on the target model
        # (so `is_hidden` returns True), then there are no clashes to check
        # and we can skip these fields.
        rel_is_hidden = self.remote_field.is_hidden()
        rel_name = self.remote_field.get_accessor_name()  # i. e. "model_set"
        rel_query_name = self.related_query_name()  # i. e. "model"
        field_name = "%s.%s" % (opts.object_name, self.name)  # i. e. "Model.field"

        # Check clashes between accessor or reverse query name of `field`
        # and any other field name -- i.e. accessor for Model.foreign is
        # model_set and it clashes with Target.model_set.
        potential_clashes = rel_opts.fields + rel_opts.many_to_many
        for clash_field in potential_clashes:
            clash_name = "%s.%s" % (rel_opts.object_name,
                clash_field.name)  # i. e. "Target.model_set"
            if not rel_is_hidden and clash_field.name == rel_name:
                errors.append(
                    checks.Error(
                        "Reverse accessor for '%s' clashes with field name '%s'." % (field_name, clash_name),
                        hint=("Rename field '%s', or add/change a related_name "
                              "argument to the definition for field '%s'.") % (clash_name, field_name),
                        obj=self,
                        id='fields.E302',
                    )
                )

            if clash_field.name == rel_query_name:
                errors.append(
                    checks.Error(
                        "Reverse query name for '%s' clashes with field name '%s'." % (field_name, clash_name),
                        hint=("Rename field '%s', or add/change a related_name "
                              "argument to the definition for field '%s'.") % (clash_name, field_name),
                        obj=self,
                        id='fields.E303',
                    )
                )

        # Check clashes between accessors/reverse query names of `field` and
        # any other field accessor -- i. e. Model.foreign accessor clashes with
        # Model.m2m accessor.
        potential_clashes = (r for r in rel_opts.related_objects if r.field is not self)
        for clash_field in potential_clashes:
            clash_name = "%s.%s" % (  # i. e. "Model.m2m"
                clash_field.related_model._meta.object_name,
                clash_field.field.name)
            if not rel_is_hidden and clash_field.get_accessor_name() == rel_name:
                errors.append(
                    checks.Error(
                        "Reverse accessor for '%s' clashes with reverse accessor for '%s'." % (field_name, clash_name),
                        hint=("Add or change a related_name argument "
                              "to the definition for '%s' or '%s'.") % (field_name, clash_name),
                        obj=self,
                        id='fields.E304',
                    )
                )

            if clash_field.get_accessor_name() == rel_query_name:
                errors.append(
                    checks.Error(
                        "Reverse query name for '%s' clashes with reverse query name for '%s'."
                        % (field_name, clash_name),
                        hint=("Add or change a related_name argument "
                              "to the definition for '%s' or '%s'.") % (field_name, clash_name),
                        obj=self,
                        id='fields.E305',
                    )
                )

        return errors

    def db_type(self, connection):
        # By default related field will not have a column as it relates to
        # columns from another table.
        return None

    def contribute_to_class(self, cls, name, virtual_only=False):

        super(RelatedField, self).contribute_to_class(cls, name, virtual_only=virtual_only)

        self.opts = cls._meta

        if not cls._meta.abstract:
            if self.remote_field.related_name:
                related_name = force_text(self.remote_field.related_name) % {
                    'class': cls.__name__.lower(),
                    'app_label': cls._meta.app_label.lower()
                }
                self.remote_field.related_name = related_name

            def resolve_related_class(model, related, field):
                field.remote_field.model = related
                field.do_related_class(related, model)
            lazy_related_operation(resolve_related_class, cls, self.remote_field.model, field=self)

    def get_forward_related_filter(self, obj):
        """
        Return the keyword arguments that when supplied to
        self.model.object.filter(), would select all instances related through
        this field to the remote obj. This is used to build the querysets
        returned by related descriptors. obj is an instance of
        self.related_field.model.
        """
        return {
            '%s__%s' % (self.name, rh_field.name): getattr(obj, rh_field.attname)
            for _, rh_field in self.related_fields
        }

    def get_reverse_related_filter(self, obj):
        """
        Complement to get_forward_related_filter(). Return the keyword
        arguments that when passed to self.related_field.model.object.filter()
        select all instances of self.related_field.model related through
        this field to obj. obj is an instance of self.model.
        """
        base_filter = {
            rh_field.attname: getattr(obj, lh_field.attname)
            for lh_field, rh_field in self.related_fields
        }
        descriptor_filter = self.get_extra_descriptor_filter(obj)
        base_q = Q(**base_filter)
        if isinstance(descriptor_filter, dict):
            return base_q & Q(**descriptor_filter)
        elif descriptor_filter:
            return base_q & descriptor_filter
        return base_q

    @property
    def swappable_setting(self):
        """
        Get the setting that this is powered from for swapping, or None
        if it's not swapped in / marked with swappable=False.
        """