"""

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 correct SQL).

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

    [table_alias, field_name, db_type, lookup_type, value_annotation,

    params]. However, a child could also be any class with as_sql() and

    relabel_aliases() methods.

    """

    default = AND

    def add(self, data, connector):

        """

        Add a node to the where-tree. If the data is a list or tuple, it is

        expected to be of the form (alias, col_name, field_obj, lookup_type,

        value), which is then slightly munged before being stored (to avoid

        storing any reference to field objects). Otherwise, the 'data' is

        stored unchanged and can be anything with an 'as_sql()' method.

        """

        # Because of circular imports, we need to import this here.

        from django.db.models.base import ObjectDoesNotExist

        if not isinstance(data, (list, tuple)):

            super(WhereNode, self).add(data, connector)

            return

        alias, col, field, lookup_type, value = data

        try:

            if field:

                params = field.get_db_prep_lookup(lookup_type, value)

                db_type = field.db_type()

            else:

                # This is possible when we add a comparison to NULL sometimes

                # (we don't really need to waste time looking up the associated

                # field object).

                params = Field().get_db_prep_lookup(lookup_type, value)

                db_type = None

        except ObjectDoesNotExist:

            # This can happen when trying to insert a reference to a null pk.

            # We break out of the normal path and indicate there's nothing to

            # match.

            super(WhereNode, self).add(NothingNode(), connector)

            return

        if isinstance(value, datetime.datetime):

            annotation = datetime.datetime

        else:

            annotation = bool(value)

        super(WhereNode, self).add((alias, col, db_type, lookup_type,

                annotation, params), connector)

    def as_sql(self, qn=None):

        """

        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

        if not self.children:

            return None, []

        result = []

        result_params = []

        empty = True

        for child in self.children:

            try:

                if hasattr(child, 'as_sql'):

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

                else:

                    # A leaf node in the tree.

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

            except EmptyResultSet:

                if self.connector == AND and not self.negated:

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

                    raise

                elif self.negated:

                    empty = False

                continue

            except FullResultSet:

                if self.connector == OR:

                    if self.negated:

                        empty = True

                        break

                    # We match everything. No need for any constraints.

                    return '', []

                if self.negated:

                    empty = True

                continue

            empty = False

            if sql:

                result.append(sql)

                result_params.extend(params)

        if empty:

            raise EmptyResultSet

        conn = ' %s ' % self.connector

        sql_string = conn.join(result)

        if sql_string:

            if self.negated:

                sql_string = 'NOT (%s)' % sql_string

            elif len(self.children) != 1:

                sql_string = '(%s)' % sql_string

        return sql_string, result_params

    def make_atom(self, child, qn):

        """

        Turn a tuple (table_alias, column_name, db_type, lookup_type,

        value_annot, params) into valid SQL.

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

        it.

        """

        table_alias, name, db_type, lookup_type, value_annot, params = child

        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

        if value_annot is datetime.datetime:

            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':

            if not value_annot:

                raise EmptyResultSet

            if extra:

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

            return ('%s IN (%s)' % (field_sql, ', '.join(['%s'] * len(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':

            return ('%s IS %sNULL' % (field_sql,

                (not value_annot and 'NOT ' or '')), ())

        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

class NothingNode(object):

    """

    A node that matches nothing.

    """

    def as_sql(self, qn=None):

        raise EmptyResultSet

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

        return