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

# Tell nose to skip this module
__test__ = {}

#-------------------------------------------------------------------------------
#  Copyright (C) 2008-2011  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
#-------------------------------------------------------------------------------

# Third-party
from twisted.python.failure import Failure
from zope.interface import implements, classProvides

# From IPython
from IPython.external import guid

from IPython.frontend.frontendbase import (FrontEndBase, IFrontEnd,
                                           IFrontEndFactory)
from IPython.kernel.core.history import FrontEndHistory
from IPython.kernel.engineservice import IEngineCore

#-----------------------------------------------------------------------------
# Classes and functions
#-----------------------------------------------------------------------------

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 = guid.generate()

        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