"""
Base front end class for all async frontends.
"""
__docformat__ = "restructuredtext en"

#-------------------------------------------------------------------------------
#  Copyright (C) 2008  The IPython Development Team
#
#  Distributed under the terms of the BSD License.  The full license is in
#  the file COPYING, distributed as part of this software.
#-------------------------------------------------------------------------------


#-------------------------------------------------------------------------------
# Imports
#-------------------------------------------------------------------------------
import uuid

try:
    from zope.interface import Interface, Attribute, implements, classProvides
except ImportError:
    #zope.interface is not available
    Interface = object
    def Attribute(name, doc): pass
    def implements(interface): pass
    def classProvides(interface): pass



from frontendbase import FrontEndBase, IFrontEnd, IFrontEndFactory

from IPython.kernel.engineservice import IEngineCore
from IPython.kernel.core.history import FrontEndHistory

try:
    from twisted.python.failure import Failure
except ImportError:
    #Twisted not available
    Failure = Exception




class AsyncFrontEndBase(FrontEndBase):
    """
    Overrides FrontEndBase to wrap execute in a deferred result.
    All callbacks are made as callbacks on the deferred result.
    """
    
    implements(IFrontEnd)
    classProvides(IFrontEndFactory)
    
    def __init__(self, engine=None, history=None):
        assert(engine==None or IEngineCore.providedBy(engine))
        self.engine = IEngineCore(engine)
        if history is None:
                self.history = FrontEndHistory(input_cache=[''])
        else:
            self.history = history
    
    
    def execute(self, block, blockID=None):
        """Execute the block and return the deferred result.
        
        Parameters:
            block : {str, AST}
            blockID : any
                Caller may provide an ID to identify this block. 
                result['blockID'] := blockID
        
        Result:
            Deferred result of self.interpreter.execute
        """
        
        if(not self.is_complete(block)):
            return Failure(Exception("Block is not compilable"))
        
        if(blockID == None):
            blockID = uuid.uuid4() #random UUID
        
        d = self.engine.execute(block)
        d.addCallback(self._add_history, block=block)
        d.addCallbacks(self._add_block_id_for_result,
                errback=self._add_block_id_for_failure,
                callbackArgs=(blockID,),
                errbackArgs=(blockID,))
        d.addBoth(self.update_cell_prompt, blockID=blockID)
        d.addCallbacks(self.render_result, 
            errback=self.render_error)
        
        return d