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from collections import defaultdict

from sqlalchemy import Table, Column, String, MetaData

from sqlalchemy.sql import select, and_

from sqlalchemy.schema import Index

from dbworker import DBWorker

class Groups(DBWorker):

    """Groups are named collections of members, belonging to an owner."""

    def __init__(self, **params):

        DBWorker.__init__(self, **params)

        metadata = MetaData()

        columns=[]

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

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

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

        self.groups = Table('groups', metadata, *columns)

        # place an index on member

        Index('idx_groups_member', self.groups.c.member)

        metadata.create_all(self.engine)

    def group_names(self, owner):

        """List all group names belonging to owner."""

        s = select([self.groups.c.name],

            self.groups.c.owner==owner).distinct()

        r = self.conn.execute(s)

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

        r.close()

        return l

    def group_dict(self, owner):

        """Return a dict mapping group names to member lists for owner."""

        s = select([self.groups.c.name, self.groups.c.member],

            self.groups.c.owner==owner)

        r = self.conn.execute(s)

        d = defaultdict(list)

        for group, member in r.fetchall():

            d[group].append(member)

        r.close()

        return d

    def group_add(self, owner, group, member):

        """Add a member to a group."""

        s = self.groups.select()

        s = s.where(self.groups.c.owner == owner)

        s = s.where(self.groups.c.name == group)

        s = s.where(self.groups.c.member == member)

        r = self.conn.execute(s)

        groups = r.fetchall()

        r.close()

        if len(groups) == 0:    

            s = self.groups.insert()

            r = self.conn.execute(s, owner=owner, name=group, member=member)

            r.close()

    def group_addmany(self, owner, group, members):

        """Add members to a group."""

        #TODO: more efficient way to do it

        for member in members:

            self.group_add(owner, group, member)

    def group_remove(self, owner, group, member):

        """Remove a member from a group."""

        s = self.groups.delete().where(and_(self.groups.c.owner==owner,

                                            self.groups.c.name==group,

                                            self.groups.c.member==member))

        r = self.conn.execute(s)

        r.close()

    def group_delete(self, owner, group):

        """Delete a group."""

        s = self.groups.delete().where(and_(self.groups.c.owner==owner,

                                            self.groups.c.name==group))

        r = self.conn.execute(s)

        r.close()

    def group_destroy(self, owner):

        """Delete all groups belonging to owner."""

        s = self.groups.delete().where(self.groups.c.owner==owner)

        r = self.conn.execute(s)

        r.close()

    def group_members(self, owner, group):

        """Return the list of members of a group."""

        s = select([self.groups.c.member], and_(self.groups.c.owner==owner,

                                                self.groups.c.name==group))

        r = self.conn.execute(s)

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

        r.close()

        return l

    def group_check(self, owner, group, member):

        """Check if a member is in a group."""

        s = select([self.groups.c.member], and_(self.groups.c.owner==owner,

                           self.groups.c.name==group,

                           self.groups.c.member==member))

        r = self.conn.execute(s)

        l = r.fetchone()

        r.close()

        return bool(l)

    def group_parents(self, member):

        """Return all (owner, group) tuples that contain member."""

        s = select([self.groups.c.owner, self.groups.c.name],

            self.groups.c.member==member)

        r = self.conn.execute(s)

        l = r.fetchall()

        r.close()

        return l