#
# Utility functions
#
# Various functions
#
# Copyright 2010 Greek Research and Technology Network
#

from synnefo.db.models import VirtualMachine
from synnefo.logic import credits

import synnefo.settings as settings

def id_from_instance_name(name):
    """Returns VirtualMachine's Django id, given a ganeti machine name.

    Strips the ganeti prefix atm. Needs a better name!

    """
    if not str(name).startswith(settings.BACKEND_PREFIX_ID):
        raise VirtualMachine.InvalidBackendIdError(str(name))
    ns = str(name).lstrip(settings.BACKEND_PREFIX_ID)
    if not ns.isdigit():
        raise VirtualMachine.InvalidBackendIdError(str(name))

    return int(ns)

def get_rsapi_state(vm):
    """Returns the API state for a virtual machine
    
    The API state for an instance of VirtualMachine is derived as follows:

    * If the deleted flag has been set, it is "DELETED".
    * Otherwise, it is a mapping of the last state reported by Ganeti
      (vm.operstate) through the RSAPI_STATE_FROM_OPER_STATE dictionary.
      
      The last state reported by Ganeti is set whenever Ganeti reports
      successful completion of an operation. If Ganeti says an OP_INSTANCE_STARTUP
      operation succeeded, vm.operstate is set to "STARTED".

    * To support any transitive states defined by the API (only REBOOT for the time
      being) this mapping is amended with information reported by Ganeti regarding
      any outstanding operation. If an OP_INSTANCE_STARTUP had succeeded previously
      and an OP_INSTANCE_REBOOT has been reported as in progress, the API state is
      "REBOOT".

    """
    try:
        r = VirtualMachine.RSAPI_STATE_FROM_OPER_STATE[vm.operstate]
    except KeyError:
        return "UNKNOWN"
    # A machine is DELETED if the deleted flag has been set
    if vm.deleted:
        return "DELETED"
    # A machine is in REBOOT if an OP_INSTANCE_REBOOT request is in progress
    if r == 'ACTIVE' and vm.backendopcode == 'OP_INSTANCE_REBOOT' and \
        vm.backendjobstatus in ('queued', 'waiting', 'running'):
        return "REBOOT"
    return r

def update_state(vm, new_operstate):
    """Wrapper around updates of the VirtualMachine.operstate field"""

    # Call charge() unconditionally before any change of
    # internal state.
    credits.charge(vm)
    vm.operstate = new_operstate