import os
import base64
from datetime import datetime
from planetstack.config import Config

class FailedDependency(Exception):
    pass

class SyncStep:
    """ A PlanetStack Sync step. 

    Attributes:
        psmodel        Model name the step synchronizes 
        dependencies    list of names of models that must be synchronized first if the current model depends on them
    """ 
    slow=False
    def get_prop(prop):
        try:
            sync_config_dir = Config().sync_config_dir
        except:
            sync_config_dir = '/etc/planetstack/sync'
        prop_config_path = '/'.join(sync_config_dir,self.name,prop)
        return open(prop_config_path).read().rstrip()

    def __init__(self, **args):
        """Initialize a sync step
           Keyword arguments:
                   name -- Name of the step
                provides -- PlanetStack models sync'd by this step
        """
        dependencies = []
        self.driver = args.get('driver')
        try:
            self.soft_deadline = int(self.get_prop('soft_deadline_seconds'))
        except:
            self.soft_deadline = 5 # 5 seconds

        return

    def fetch_pending(self):
        #return Sliver.objects.filter(ip=None)
        return []
    
    def check_dependencies(self, obj):
        for dep in self.dependencies:
            peer_object = getattr(obj, dep.lower())
            if (peer_object.pk==dep.pk):
                raise DependencyFailed

    def call(self, failed=[]):
        pending = self.fetch_pending()
        for o in pending:
            try:
                self.check_dependencies(o) # Raises exception if failed                    
                self.sync_record(o)
                o.enacted = datetime.now() # Is this the same timezone? XXX
                o.save(update_fields=['enacted'])
            except:
                failed.append(o)
        return failed

    def __call__(self, **args):
        return self.call(**args)