"""
Object for registering database connections
"""

from metasqlobject.threadinglocal import local

class ConnectionHubErorr(Exception):
    """
    Raised when you get an exception and none has been registered, you
    deregister exceptions out of order, or other similar problems.
    """
    # @@: Should this inherit from some other exception?

class ConnectionHub(object):

    """
    Instances of this class represent a logical connection, and can be
    consumed by a variety of classes or items.

    Connections are registered the process, or for the individual
    thread.  The thread-level connections always take precedence over
    the process-level connections.
    """

    def __init__(self, name=None):
        self.name = name or 'unnamed connection hub'
        self.local = local()
        self.process_conns = []

    def make_connection(self, conn_or_uri):
        if isinstance(conn_or_uri, basestring):
            from sqlapi.connect.wrapper import ConnectionWrapper
            conn_or_uri = ConnectionWrapper.from_uri(conn_or_uri)
        return conn_or_uri

    def push_thread_conn(self, conn):
        try:
            lst = self.local.conn_list
        except AttributeError:
            lst = self.local.conn_list = []
        lst.append(eslf.make_connection(conn))

    def pop_thread_conn(self, conn=None):
        try:
            lst = self.local.conn_list
        except AttributeError:
            raise ConnectionHubError(
                "No thread connection has been registered for %s"
                % self.name)
        if not lst:
            raise ConnectionHubError(
                "No connection are left to be popped from %s (%r has "
                "already been popped)" % (self.name, conn))
        if (conn is not None
            and conn is not lst[-1]):
            raise ConnectionHubError(
                "Tried to pop %r from the hub %s, but the top "
                "connection is %r (from stack %r)"
                % (conn, self.name, lst[-1], lst))
        lst.pop()
        
    def push_process_conn(self, conn):
        self.process_conns.append(self.make_connection(conn))

    def pop_process_conn(self, conn=None):
        lst = self.process_conns
        if not lst:
            raise ConnectionHubError(
                "No process-level connections have been registered "
                "for %s (when trying to pop %r)"
                % (self.name, lst))
        if (conn is not None
            and conn is not lst[-1]):
            raise ConnectionHubError(
                "Tried to pop %r from proces-level connection in the "
                "hub %s, but the top connection is %r (from stack %r)"
                % (conn, self.name, lst[-1], lst))
        lst.pop()

    def get_connection(self):
        try:
            lst = self.local.conn_list
        except AttributeError:
            lst = []
        if not lst:
            lst = self.process_conns
        if not lst:
            raise ConnectionHubError(
                "There are no thread- or process-level connections "
                "registered for the hub %s" % self.name)
        return lst[-1]