from base64 import encodestring, decodestring
import pprint

def base64_decode(nb):
    """Base64 encode all bytes objects in the notebook."""
    for ws in nb.worksheets:
        for cell in ws.cells:
            if cell.cell_type == 'code':
                if 'png' in cell:
                    cell.png = bytes(decodestring(cell.png))
    return nb


def base64_encode(nb):
    """Base64 decode all binary objects in the notebook."""
    for ws in nb.worksheets:
        for cell in ws.cells:
            if cell.cell_type == 'code':
                if 'png' in cell:
                    cell.png = unicode(encodestring(cell.png))
    return nb


class NotebookReader(object):

    def reads(self, s, **kwargs):
        """Read a notebook from a string."""
        raise NotImplementedError("loads must be implemented in a subclass")

    def read(self, fp, **kwargs):
        """Read a notebook from a file like object"""
        return self.read(fp.read(), **kwargs)


class NotebookWriter(object):

    def writes(self, nb, **kwargs):
        """Write a notebook to a string."""
        raise NotImplementedError("loads must be implemented in a subclass")

    def write(self, nb, fp, **kwargs):
        """Write a notebook to a file like object"""
        return fp.write(self.writes(nb,**kwargs))