import errors
import units


__all__ = ['DeployedVersion', 'Schema',
           ]


class DeployedVersion(units.Unit):
    """Which schema version the current deployment has reached."""
    ID = units.UnitProperty(unicode)
    Version = units.UnitProperty(int)


class Schema(object):
    
    guid = ""
    latest = 0
    
    def __init__(self, arena):
        self.arena = arena
        arena.register(DeployedVersion)
        store = arena.storage(DeployedVersion)
        if not store.has_storage(DeployedVersion):
            store.create_storage(DeployedVersion)
        self._deployed_unit = None
    
    def _get_deployed_unit(self):
        if self._deployed_unit is None:
            box = self.arena.new_sandbox()
            self._deployed_unit = box.unit(DeployedVersion, ID=self.guid)
            if self._deployed_unit is None:
                self._deployed_unit = DeployedVersion(ID=self.guid, Version=0)
                box.memorize(self._deployed_unit)
        return self._deployed_unit
    
    def _get_dep(self):
        return self._get_deployed_unit().Version
    
    def _set_dep(self, newvalue):
        depunit = self._get_deployed_unit()
        depunit.Version = newvalue
        # Skip the sandbox, so we can save without repress
        self.arena.storage(DeployedVersion).save(depunit, forceSave=True)
    
    deployed = property(_get_dep, _set_dep, doc="Deployed version")
    
    def upgrade(self, version=None):
        """Upgrade deployment to version arg [latest]. Idempotent."""
        if version is None:
            version = self.latest
        
        for step in range(self.deployed, version):
            procedure = getattr(self, "upgrade_to_%s" % (step + 1), None)
            if procedure:
                procedure()
            self.deployed = step + 1
    
    def upgrade_to_0(self):
        pass
    
    def upgrade_to_1(self):
        classes = self.arena._registered_classes.keys()
        if DeployedVersion in classes:
            classes.remove(DeployedVersion)
        
        for cls in classes:
            self.arena.create_storage(cls)