from django.conf import settings
from django.db.models.sql import aggregates as sqlaggregates
from django.db.models.sql.compiler import SQLCompiler
from django.db.models.sql.constants import LOOKUP_SEP, MULTI, SINGLE
from django.db.models.sql.where import AND, OR, Constraint
from django.db.utils import DatabaseError, IntegrityError
from django.utils.tree import Node
import random

EMULATED_OPS = {
    'exact': lambda x, y: y in x if isinstance(x, (list,tuple)) else x == y,
    'iexact': lambda x, y: x.lower() == y.lower(),
    'startswith': lambda x, y: x.startswith(y),
    'istartswith': lambda x, y: x.lower().startswith(y.lower()),
    'isnull': lambda x, y: x is None if y else x is not None,
    'in': lambda x, y: x in y,
    'lt': lambda x, y: x < y,
    'lte': lambda x, y: x <= y,
    'gt': lambda x, y: x > y,
    'gte': lambda x, y: x >= y,
}

class NonrelQuery(object):
    # ----------------------------------------------
    # Public API
    # ----------------------------------------------
    def __init__(self, compiler, fields):
        self.fields = fields
        self.compiler = compiler
        self.connection = compiler.connection
        self.query = self.compiler.query
        self._negated = False

    def fetch(self, low_mark=0, high_mark=None):
        raise NotImplementedError('Not implemented')

    def count(self, limit=None):
        raise NotImplementedError('Not implemented')

    def delete(self):
        raise NotImplementedError('Not implemented')

    def order_by(self, ordering):
        raise NotImplementedError('Not implemented')

    # Used by add_filters()
    def add_filter(self, column, lookup_type, negated, db_type, value):
        raise NotImplementedError('Not implemented')

    # This is just a default implementation. You might want to override this
    # in case your backend supports OR queries
    def add_filters(self, filters):
        """Traverses the given Where tree and adds the filters to this query"""
        if filters.negated:
            self._negated = not self._negated

        if not self._negated and filters.connector != AND:
            raise DatabaseError('Only AND filters are supported')

        # Remove unneeded children from tree
        children = self._get_children(filters.children)

        if self._negated and filters.connector != OR and len(children) > 1:
            raise DatabaseError("When negating a whole filter subgroup "
                                "(e.g., a Q object) the subgroup filters must "
                                "be connected via OR, so the non-relational "
                                "backend can convert them like this: "
                                '"not (a OR b) => (not a) AND (not b)".')

        for child in children:
            if isinstance(child, Node):
                self.add_filters(child)
                continue

            column, lookup_type, db_type, value = self._decode_child(child)
            self.add_filter(column, lookup_type, self._negated, db_type, value)

        if filters.negated:
            self._negated = not self._negated

    # ----------------------------------------------
    # Internal API for reuse by subclasses
    # ----------------------------------------------
    def _decode_child(self, child):
        constraint, lookup_type, annotation, value = child
        packed, value = constraint.process(lookup_type, value, self.connection)
        alias, column, db_type = packed
        if alias and alias != self.query.model._meta.db_table:
            raise DatabaseError("This database doesn't support JOINs "
                                "and multi-table inheritance.")
        value = self._normalize_lookup_value(value, annotation, lookup_type)
        return column, lookup_type, db_type, value

    def _normalize_lookup_value(self, value, annotation, lookup_type):
        # Django fields always return a list (see Field.get_db_prep_lookup)
        # except if get_db_prep_lookup got overridden by a subclass
        if lookup_type not in ('in', 'range', 'year') and isinstance(value, (tuple, list)):
            if len(value) > 1:
                raise DatabaseError('Filter lookup type was: %s. Expected the '
                                'filters value not to be a list. Only "in"-filters '
                                'can be used with lists.'
                                % lookup_type)
            elif lookup_type == 'isnull':
                value = annotation
            else:
                value = value[0]

        if isinstance(value, unicode):
            value = unicode(value)
        elif isinstance(value, str):
            value = str(value)

        if lookup_type in ('startswith', 'istartswith'):
            value = value[:-1]
        elif lookup_type in ('endswith', 'iendswith'):
            value = value[1:]
        elif lookup_type in ('contains', 'icontains'):
            value = value[1:-1]

        return value

    def _get_children(self, children):
        # Filter out nodes that were automatically added by sql.Query, but are
        # not necessary with emulated negation handling code
        result = []
        for child in children:
            if isinstance(child, tuple):
                constraint = child[0]
                lookup_type = child[1]
                if lookup_type == 'isnull' and constraint.field is None:
                    continue
            result.append(child)
        return result

    def _matches_filters(self, entity, filters):
        # Filters without rules match everything
        if not filters.children:
            return True

        result = filters.connector == AND

        for child in filters.children:
            if isinstance(child, Node):
                submatch = self._matches_filters(entity, child)
            else:
                constraint, lookup_type, annotation, value = child
                packed, value = constraint.process(lookup_type, value, self.connection)
                alias, column, db_type = packed
                if alias != self.query.model._meta.db_table:
                    raise DatabaseError("This database doesn't support JOINs "
                                        "and multi-table inheritance.")

                # Django fields always return a list (see Field.get_db_prep_lookup)
                # except if get_db_prep_lookup got overridden by a subclass
                if lookup_type != 'in' and isinstance(value, (tuple, list)):
                    if len(value) > 1:
                        raise DatabaseError('Filter lookup type was: %s. '
                            'Expected the filters value not to be a list. '
                            'Only "in"-filters can be used with lists.'
                            % lookup_type)
                    elif lookup_type == 'isnull':
                        value = annotation
                    else:
                        value = value[0]

                submatch = EMULATED_OPS[lookup_type](entity[column], value)

            if filters.connector == OR and submatch:
                result = True
                break
            elif filters.connector == AND and not submatch:
                result = False
                break

        if filters.negated:
            return not result
        return result

    def _order_in_memory(self, lhs, rhs):
        for order in self.compiler._get_ordering():
            if LOOKUP_SEP in order:
                raise DatabaseError("JOINs in ordering not supported (%s)" % order)
            if order == '?':
                result = random.choice([1, 0, -1])
            else:
                column = order.lstrip('-')
                result = cmp(lhs.get(column), rhs.get(column))
                if order.startswith('-'):
                    result *= -1
            if result != 0:
                return result
        return 0

    def convert_value_from_db(self, db_type, value):
        return self.compiler.convert_value_from_db(db_type, value)

    def convert_value_for_db(self, db_type, value):
        return self.compiler.convert_value_for_db(db_type, value)

class NonrelCompiler(SQLCompiler):
    """
    Base class for non-relational compilers. Provides in-memory filter matching
    and ordering. Entities are assumed to be dictionaries where the keys are
    column names.
    """

    # ----------------------------------------------
    # Public API
    # ----------------------------------------------
    def results_iter(self):
        """
        Returns an iterator over the results from executing this query.
        """
        self.check_query()
        fields = self.get_fields()
        low_mark = self.query.low_mark
        high_mark = self.query.high_mark
        for entity in self.build_query(fields).fetch(low_mark, high_mark):
            yield self._make_result(entity, fields)

    def has_results(self):
        return self.get_count(check_exists=True)

    def execute_sql(self, result_type=MULTI):
        """
        Handles aggregate/count queries
        """
        aggregates = self.query.aggregate_select.values()
        # Simulate a count()
        if aggregates:
            assert len(aggregates) == 1
            aggregate = aggregates[0]
            assert isinstance(aggregate, sqlaggregates.Count)
            meta = self.query.get_meta()
            assert aggregate.col == '*' or aggregate.col == (meta.db_table, meta.pk.column)
            count = self.get_count()
            if result_type is SINGLE:
                return [count]
            elif result_type is MULTI:
                return [[count]]
        raise NotImplementedError('The database backend only supports count() queries')

    # ----------------------------------------------
    # Additional NonrelCompiler API
    # ----------------------------------------------
    def _make_result(self, entity, fields):
        result = []
        for field in fields:
            if not field.null and entity.get(field.column,
                    field.get_default()) is None:
                raise DatabaseError("Non-nullable field %s can't be None!" % field.name)
            result.append(self.convert_value_from_db(field.db_type(
                connection=self.connection), entity.get(field.column, field.get_default())))
        return result

    def check_query(self):
        if (len([a for a in self.query.alias_map if self.query.alias_refcount[a]]) > 1
                or self.query.distinct or self.query.extra or self.query.having):
            raise DatabaseError('This query is not supported by the database.')

    def get_count(self, check_exists=False):
        """
        Counts matches using the current filter constraints.
        """
        if check_exists:
            high_mark = 1
        else:
            high_mark = self.query.high_mark
        return self.build_query().count(high_mark)

    def build_query(self, fields=None):
        if fields is None:
            fields = self.get_fields()
        query = self.query_class(self, fields)
        query.add_filters(self.query.where)
        query.order_by(self._get_ordering())

        # This at least satisfies the most basic unit tests
        if settings.DEBUG:
            self.connection.queries.append({'sql': repr(query)})
        return query

    def get_fields(self):
        """
        Returns the fields which should get loaded from the backend by self.query
        """
        # We only set this up here because
        # related_select_fields isn't populated until
        # execute_sql() has been called.
        if self.query.select_fields:
            fields = self.query.select_fields + self.query.related_select_fields
        else:
            fields = self.query.model._meta.fields
        # If the field was deferred, exclude it from being passed
        # into `resolve_columns` because it wasn't selected.
        only_load = self.deferred_to_columns()
        if only_load:
            db_table = self.query.model._meta.db_table
            fields = [f for f in fields if db_table in only_load and
                      f.column in only_load[db_table]]

        query_model = self.query.model
        if query_model._meta.proxy:
            query_model = query_model._meta.proxy_for_model

        for field in fields:
            if field.model._meta != query_model._meta:
                raise DatabaseError('Multi-table inheritance is not supported '
                                    'by non-relational DBs.')
        return fields

    def _get_ordering(self):
        if not self.query.default_ordering:
            ordering = self.query.order_by
        else:
            ordering = self.query.order_by or self.query.get_meta().ordering
        result = []
        for order in ordering:
            if LOOKUP_SEP in order:
                raise DatabaseError("Ordering can't span tables on non-relational backends (%s)" % order)
            if order == '?':
                raise DatabaseError("Randomized ordering isn't supported by the backend")

            order = order.lstrip('+')

            descending = order.startswith('-')
            name = order.lstrip('-')
            if name == 'pk':
                name = self.query.get_meta().pk.name
                order = '-' + name if descending else name

            if self.query.standard_ordering:
                result.append(order)
            else:
                if descending:
                    result.append(name)
                else:
                    result.append('-' + name)
        return result

class NonrelInsertCompiler(object):
    def execute_sql(self, return_id=False):
        data = {}
        for (field, value), column in zip(self.query.values, self.query.columns):
            if field is not None:
                if not field.null and value is None:
                    raise DatabaseError("You can't set %s (a non-nullable "
                                        "field) to None!" % field.name)
                value = self.convert_value_for_db(field.db_type(connection=self.connection),
                    value)
            data[column] = value
        return self.insert(data, return_id=return_id)

class NonrelUpdateCompiler(object):
    def execute_sql(self, result_type=MULTI):
        # TODO: We don't yet support QuerySet.update() in Django-nonrel
        raise NotImplementedError('No updates')

class NonrelDeleteCompiler(object):
    def execute_sql(self, result_type=MULTI):
        self.build_query([self.query.get_meta().pk]).delete()
