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from collections import defaultdict

from sqlalchemy import Table, Column, String, Integer, MetaData, ForeignKey

from sqlalchemy.sql import select, and_

from sqlalchemy.schema import Index

from sqlalchemy.sql.expression import desc

from dbworker import DBWorker

class XFeatures(DBWorker):

    """XFeatures are path properties that allow non-nested

       inheritance patterns. Currently used for storing permissions.

    """

    def __init__(self, **params):

        DBWorker.__init__(self, **params)

        metadata = MetaData()

        columns=[]

        columns.append(Column('feature_id', Integer, primary_key=True))

        columns.append(Column('path', String(2048)))

        self.xfeatures = Table('xfeatures', metadata, *columns, mysql_engine='InnoDB')

        # place an index on path

        Index('idx_features_path', self.xfeatures.c.path, unique=True)

        columns=[]

        columns.append(Column('feature_id', Integer,

                              ForeignKey('xfeatures.feature_id',

                                         ondelete='CASCADE'),

                              primary_key=True))

        columns.append(Column('key', Integer, primary_key=True,

                              autoincrement=False))

        columns.append(Column('value', String(255), primary_key=True))

        self.xfeaturevals = Table('xfeaturevals', metadata, *columns, mysql_engine='InnoDB')

        metadata.create_all(self.engine)

    def xfeature_inherit(self, path):

        """Return the (path, feature) inherited by the path, or None."""

        s = select([self.xfeatures.c.path, self.xfeatures.c.feature_id])

        s = s.where(self.xfeatures.c.path <= path)

        s = s.order_by(desc(self.xfeatures.c.path)).limit(1)

        r = self.conn.execute(s)

        row = r.fetchone()

        r.close()

        if row and path.startswith(row[0]):

            return row

        else:

            return None

    def xfeature_list(self, path):

        """Return the list of the (prefix, feature) pairs matching path.

           A prefix matches path if either the prefix includes the path,

           or the path includes the prefix.

        """

        inherited = self.xfeature_inherit(path)

        if inherited:

            return [inherited]

        s = select([self.xfeatures.c.path, self.xfeatures.c.feature_id])

        s = s.where(and_(self.xfeatures.c.path.like(self.escape_like(path) + '%', escape='\\'),

                     self.xfeatures.c.path != path))

        s = s.order_by(self.xfeatures.c.path)

        r = self.conn.execute(s)

        l = r.fetchall()

        r.close()

        return l

    def xfeature_create(self, path):

        """Create and return a feature for path.

           If the path already inherits a feature or

           bestows to paths already inheriting a feature,

           create no feature and return None.

           If the path has a feature, return it.

        """

        prefixes = self.xfeature_list(path)

        pl = len(prefixes)

        if (pl > 1) or (pl == 1 and prefixes[0][0] != path):

            return None

        if pl == 1 and prefixes[0][0] == path:

            return prefixes[0][1]

        s = self.xfeatures.insert()

        r = self.conn.execute(s, path=path)

        inserted_primary_key = r.inserted_primary_key[0]

        r.close()

        return inserted_primary_key

    def xfeature_destroy(self, path):

        """Destroy a feature and all its key, value pairs."""

        s = self.xfeatures.delete().where(self.xfeatures.c.path == path)

        r = self.conn.execute(s)

        r.close()

    def feature_dict(self, feature):

        """Return a dict mapping keys to list of values for feature."""

        s = select([self.xfeaturevals.c.key, self.xfeaturevals.c.value])

        s = s.where(self.xfeaturevals.c.feature_id == feature)

        r = self.conn.execute(s)

        d = defaultdict(list)

        for key, value in r.fetchall():

            d[key].append(value)

        r.close()

        return d

    def feature_set(self, feature, key, value):

        """Associate a key, value pair with a feature."""

        s = self.xfeaturevals.select()

        s = s.where(self.xfeaturevals.c.feature_id == feature)

        s = s.where(self.xfeaturevals.c.key == key)

        s = s.where(self.xfeaturevals.c.value == value)

        r = self.conn.execute(s)

        xfeaturevals = r.fetchall()

        r.close()

        if len(xfeaturevals) == 0:

            s = self.xfeaturevals.insert()

            r = self.conn.execute(s, feature_id=feature, key=key, value=value)

            r.close()

    def feature_setmany(self, feature, key, values):

        """Associate the given key, and values with a feature."""

        #TODO: more efficient way to do it

        for v in values:

            self.feature_set(feature, key, v)

    def feature_unset(self, feature, key, value):

        """Disassociate a key, value pair from a feature."""

        s = self.xfeaturevals.delete()

        s = s.where(and_(self.xfeaturevals.c.feature_id == feature,

                     self.xfeaturevals.c.key == key,

                     self.xfeaturevals.c.value == value))

        r = self.conn.execute(s)

        r.close()

    def feature_unsetmany(self, feature, key, values):

        """Disassociate the key for the values given, from a feature."""

        for v in values:

            conditional = and_(self.xfeaturevals.c.feature_id == feature,

                               self.xfeaturevals.c.key == key,

                               self.xfeaturevals.c.value == v)

            s = self.xfeaturevals.delete().where(conditional)

            r = self.conn.execute(s)

            r.close()

    def feature_get(self, feature, key):

        """Return the list of values for a key of a feature."""

        s = select([self.xfeaturevals.c.value])

        s = s.where(and_(self.xfeaturevals.c.feature_id == feature,

                     self.xfeaturevals.c.key == key))

        r = self.conn.execute(s)

        l = [row[0] for row in r.fetchall()]

        r.close()

        return l

    def feature_clear(self, feature, key):

        """Delete all key, value pairs for a key of a feature."""

        s = self.xfeaturevals.delete()

        s = s.where(and_(self.xfeaturevals.c.feature_id == feature,

                     self.xfeaturevals.c.key == key))

        r = self.conn.execute(s)

        r.close()