"""

Code to manage the creation and SQL rendering of 'where' constraints.

"""

import datetime

from django.utils import tree

from django.db import connection

from django.db.models.fields import Field

from django.db.models.query_utils import QueryWrapper

from datastructures import EmptyResultSet, FullResultSet

# Connection types

AND = 'AND'

OR = 'OR'

class WhereNode(tree.Node):

    """

    Used to represent the SQL where-clause.

    The class is tied to the Query class that created it (in order to create

    The children in this tree are usually either Q-like objects or lists of

    """

    default = AND

        """

        Returns the SQL version of the where clause and the value to be

        substituted in. Returns None, None if this node is empty.

        If 'node' is provided, that is the root of the SQL generation

        (generally not needed except by the internal implementation for

        recursion).

        """

        if not qn:

            qn = connection.ops.quote_name

            return None, []

        result = []

        result_params = []

        empty = True

            try:

                if hasattr(child, 'as_sql'):

                    sql, params = child.as_sql(qn=qn)

                else:

                    sql, params = self.make_atom(child, qn)

            except EmptyResultSet:

                    # We can bail out early in this particular case (only).

                    raise

                    empty = False

                continue

            except FullResultSet:

                if self.connector == OR:

                        empty = True

                        break

                    # We match everything. No need for any constraints.

                    return '', []

                    empty = True

                continue

            empty = False

            if sql:

                result_params.extend(params)

        if empty:

            raise EmptyResultSet

    def make_atom(self, child, qn):

        """

        Returns the string for the SQL fragment and the parameters to use for

        it.

        """

        if table_alias:

            lhs = '%s.%s' % (qn(table_alias), qn(name))

        else:

            lhs = qn(name)

        field_sql = connection.ops.field_cast_sql(db_type) % lhs

            cast_sql = connection.ops.datetime_cast_sql()

        else:

            cast_sql = '%s'

        if isinstance(params, QueryWrapper):

            extra, params = params.data

        else:

            extra = ''

        if lookup_type in connection.operators:

            format = "%s %%s %s" % (connection.ops.lookup_cast(lookup_type),

                    extra)

            return (format % (field_sql,

                    connection.operators[lookup_type] % cast_sql), params)

        if lookup_type == 'in':

                raise EmptyResultSet

            if extra:

                return ('%s IN %s' % (field_sql, extra), params)

                    params)

        elif lookup_type in ('range', 'year'):

            return ('%s BETWEEN %%s and %%s' % field_sql, params)

        elif lookup_type in ('month', 'day'):

            return ('%s = %%s' % connection.ops.date_extract_sql(lookup_type,

                    field_sql), params)

        elif lookup_type == 'isnull':

        elif lookup_type == 'search':

            return (connection.ops.fulltext_search_sql(field_sql), params)

        elif lookup_type in ('regex', 'iregex'):

            return connection.ops.regex_lookup(lookup_type) % (field_sql, cast_sql), params

        raise TypeError('Invalid lookup_type: %r' % lookup_type)

    def relabel_aliases(self, change_map, node=None):

        """

        Relabels the alias values of any children. 'change_map' is a dictionary

        mapping old (current) alias values to the new values.

        """

        if not node:

            node = self

        for pos, child in enumerate(node.children):

            if hasattr(child, 'relabel_aliases'):

                child.relabel_aliases(change_map)

            elif isinstance(child, tree.Node):

                self.relabel_aliases(change_map, child)

            else:

                if child[0] in change_map:

                    node.children[pos] = (change_map[child[0]],) + child[1:]

class EverythingNode(object):

    """

    A node that matches everything.

    """

    def as_sql(self, qn=None):

        raise FullResultSet

    def relabel_aliases(self, change_map, node=None):

        return