import logging
from collections import namedtuple

from dal import autocomplete
from django.conf import settings
from django.db.models import Q

if getattr(settings, "LDAP_SERVER_URL", None):
    import ldap
else:
    # shared.tests.testcases.TestCaseMixin.mockLDAP needs
    # an ldap object to be in the scope
    ldap = None


django_logger = logging.getLogger("django.request")


class SearchUnit:
    """Base class for all the search utilities.

    A search unit should implement a `search` method taking a list of keywords as
    argument and returning an iterable of search results.
    """

    def search(self, _keywords):
        raise NotImplementedError(
            "Class implementing the SeachUnit interface should implement the search "
            "method"
        )


# ---
# Model-based search
# ---


class ModelSearch(SearchUnit):
    """Basic search engine for models based on filtering.

    The class should be configured through its `model` class attribute: the `search`
    method will return a queryset of instances of this model. The `search_fields`
    attributes indicates which fields to search in.

    Example:

    >>> from django.contrib.auth.models import User
    >>>
    >>> class UserSearch(ModelSearch):
    ...     model = User
    ...     search_fields = ["username", "first_name", "last_name"]
    >>>
    >>> user_search = UserSearch()  # has type ModelSearch[User]
    >>> user_search.search(["toto", "foo"])  # returns a queryset of Users
    """

    model = None
    search_fields = []

    def get_queryset_filter(self, keywords):
        filter_q = Q()

        if not keywords:
            return filter_q

        for keyword in keywords:
            kw_filter = Q()
            for field in self.search_fields:
                kw_filter |= Q(**{"{}__icontains".format(field): keyword})
            filter_q &= kw_filter

        return filter_q

    def search(self, keywords):
        """Returns the queryset of model instances matching all the keywords.

        The semantic of the search is the following: a model instance appears in the
        search results iff all of the keywords given as arguments occur in at least one
        of the search fields.
        """

        return self.model.objects.filter(self.get_queryset_filter(keywords))


class Select2QuerySetView(ModelSearch, autocomplete.Select2QuerySetView):
    """Compatibility layer between ModelSearch and Select2QuerySetView."""

    def get_queryset(self):
        keywords = self.q.split()
        return super().search(keywords)


# ---
# LDAP search
# ---

Clipper = namedtuple("Clipper", ["clipper", "fullname"])


class LDAPSearch(SearchUnit):
    ldap_server_url = getattr(settings, "LDAP_SERVER_URL", None)
    domain_component = "dc=spi,dc=ens,dc=fr"
    search_fields = ["cn", "uid"]

    def get_ldap_query(self, keywords):
        """Return a search query with the following semantics:

        A Clipper appears in the search results iff all of the keywords given as
        arguments occur in at least one of the search fields.
        """

        # Dumb but safe
        keywords = filter(str.isalnum, keywords)

        ldap_filters = []

        for keyword in keywords:
            ldap_filter = "(|{})".format(
                "".join(
                    "({}=*{}*)".format(field, keyword) for field in self.search_fields
                )
            )
            ldap_filters.append(ldap_filter)

        return "(&{})".format("".join(ldap_filters))

    def search(self, keywords):
        """Return a list of Clipper objects matching all the keywords."""

        query = self.get_ldap_query(keywords)

        if ldap is None or query == "(&)":
            return []

        try:
            ldap_obj = ldap.initialize(self.ldap_server_url)
            res = ldap_obj.search_s(
                self.domain_component, ldap.SCOPE_SUBTREE, query, self.search_fields
            )
            return [
                Clipper(
                    clipper=attrs["uid"][0].decode("utf-8"),
                    fullname=attrs["cn"][0].decode("utf-8"),
                )
                for (_, attrs) in res
            ]
        except ldap.LDAPError as err:
            django_logger.error("An LDAP error occurred", exc_info=err)
            return []


# ---
# Composition of autocomplete units
# ---


class Compose:
    """Search with several units and remove duplicate results.

    The `search_units` class attribute should be a list of tuples of the form `(name,
    uniq_key, search_unit)`.

    The `search` method produces a dictionary whose keys are the `name`s given in
    `search_units` and whose values are iterables produced by the different search
    units.

    The `uniq_key`s are used to remove duplicates: for instance, say that search unit
    1 has `uniq_key = "username"` and search unit 2 has `uniq_key = "clipper"`, then
    search results from unit 2 whose `.clipper` attribute is equal to the
    `.username` attribute of some result from unit 1 are omitted.

    Typical Example:

    >>> from django.contrib.auth.models import User
    >>>
    >>> class UserSearch(ModelSearch):
    ...     model = User
    ...     search_fields = ["username", "first_name", "last_name"]
    >>>
    >>> class UserAndClipperSearch(Compose):
    ...     search_units = [
    ...         ("users", "username", UserSearch),
    ...         ("clippers", "clipper", LDAPSearch),
    ...     ]

    In this example, clipper accounts that already have an associated user (i.e. with a
    username equal to the clipper login), will not appear in the results.
    """

    search_units = []

    def search(self, keywords):
        uniq_results = set()
        results = {}
        for name, uniq_key, search_unit in self.search_units:
            res = search_unit().search(keywords)
            res = [r for r in res if getattr(r, uniq_key) not in uniq_results]
            uniq_results |= set((getattr(r, uniq_key) for r in res))
            results[name] = res
        return results