import importlib
import os

aliases = {
    'qt4': 'qt',
    'gtk2': 'gtk',
}

backends = [
    'qt', 'qt4', 'qt5',
    'gtk', 'gtk2', 'gtk3',
    'tk',
    'wx',
    'pyglet', 'glut',
    'osx',
    'asyncio'
]

registered = {}

def register(name, inputhook):
    """Register the function *inputhook* as an event loop integration."""
    registered[name] = inputhook

class UnknownBackend(KeyError):
    def __init__(self, name):
        self.name = name

    def __str__(self):
        return ("No event loop integration for {!r}. "
                "Supported event loops are: {}").format(self.name,
                                    ', '.join(backends + sorted(registered)))

def get_inputhook_name_and_func(gui):
    if gui in registered:
        return gui, registered[gui]

    if gui not in backends:
        raise UnknownBackend(gui)

    if gui in aliases:
        return get_inputhook_name_and_func(aliases[gui])

    gui_mod = gui
    if gui == 'qt5':
        os.environ['QT_API'] = 'pyqt5'
        gui_mod = 'qt'

    mod = importlib.import_module('IPython.terminal.pt_inputhooks.'+gui_mod)
    return gui, mod.inputhook
