"""

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 EmptyShortCircuit(Exception):

    """

    Internal exception used to indicate that a "matches nothing" node should be

    added to the where-clause.

    """

    pass

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.

        """

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

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

            return

        obj, lookup_type, value = data

        if hasattr(value, '__iter__') and hasattr(value, 'next'):

            # Consume any generators immediately, so that we can determine

            # emptiness and transform any non-empty values correctly.

            value = list(value)

        if hasattr(obj, "process"):

            try:

                obj, params = obj.process(lookup_type, value)

            except (EmptyShortCircuit, EmptyResultSet):

                # There are situations where we want to short-circuit any

                # comparisons and make sure that nothing is returned. One

                # example is when checking for a NULL pk value, or the

                # equivalent.

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

                return

        else:

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

        # The "annotation" parameter is used to pass auxilliary information

        # about the value(s) to the query construction. Specifically, datetime

        # and empty values need special handling. Other types could be used

        # here in the future (using Python types is suggested for consistency).

        if isinstance(value, datetime.datetime):

            annotation = datetime.datetime

        elif hasattr(value, 'value_annotation'):

            annotation = value.value_annotation

        else:

            annotation = bool(value)

        super(WhereNode, self).add((obj, 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.

        """

        lvalue, lookup_type, value_annot, params = child

        if isinstance(lvalue, tuple):

            # A direct database column lookup.

            field_sql = self.sql_for_columns(lvalue, qn)

        else:

            # A smart object with an as_sql() method.

            field_sql = lvalue.as_sql(quote_func=qn)

        if value_annot is datetime.datetime:

            cast_sql = connection.ops.datetime_cast_sql()

        else:

            cast_sql = '%s'

        if hasattr(params, 'as_sql'):

            extra, params = params.as_sql(qn)

            cast_sql = ''

        else:

            extra = ''

        if lookup_type in connection.operators:

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

            return (format % (field_sql,

                              connection.operators[lookup_type] % cast_sql,

                              extra), 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', 'week_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 sql_for_columns(self, data, qn):

        """

        Returns the SQL fragment used for the left-hand side of a column

        constraint (for example, the "T1.foo" portion in the clause

        "WHERE ... T1.foo = 6").

        """

        table_alias, name, db_type = data

        if table_alias:

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

        else:

            lhs = qn(name)

        return connection.ops.field_cast_sql(db_type) % lhs

    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 isinstance(child[0], (list, tuple)):

                    elt = list(child[0])

                    if elt[0] in change_map:

                        elt[0] = change_map[elt[0]]

                        node.children[pos] = (tuple(elt),) + child[1:]

                else:

                    child[0].relabel_aliases(change_map)

                # Check if the query value also requires relabelling

                if hasattr(child[3], 'relabel_aliases'):

                    child[3].relabel_aliases(change_map)

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

class Constraint(object):

    """

    An object that can be passed to WhereNode.add() and knows how to

    pre-process itself prior to including in the WhereNode.

    """

    def __init__(self, alias, col, field):

        self.alias, self.col, self.field = alias, col, field

    def process(self, lookup_type, value):

        """

        Returns a tuple of data suitable for inclusion in a WhereNode

        instance.

        """

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

        from django.db.models.base import ObjectDoesNotExist

        try:

            if self.field:

                params = self.field.get_db_prep_lookup(lookup_type, value)

                db_type = self.field.db_type()

            else:

                # This branch is used at times when we add a comparison to NULL

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

                # field object at the calling location).

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

                db_type = None

        except ObjectDoesNotExist:

            raise EmptyShortCircuit

        return (self.alias, self.col, db_type), params