cb_chain.py

"""Helper class to run a chain of callbacks on input data."""
from typing import Callable, Any


class CbChain(object):
    """Chain callbacks together.

    Instances of this object are themselves Callable. When called, it passes the supplied arguments to the first
    callback in the chain. The result of the first callback is fed to the second, the result of the second fed to
    the third, and so on.

    Sample usage:
    > p = CbChain(lambda x: x + 9).CbChain(lambda x: x * 3)
    > p(3)
    36

    Attributes

    cb: Callable
        The Callable to be run when this object is itself called.
    prev: CbChain
        The CbChain object whose callback should be run before the callback in this object.
    """
    def __init__(self, cb: Callable[..., Any]):
        self.cb = cb
        self.prev = None

    def CbChain(self, cb: Callable[..., Any]):
        """Returns a new Pipe object linked to the current with the supplied callback."""
        new_pipe = CbChain(cb)
        new_pipe.prev = self
        return new_pipe

    def __call__(self, *args, **kwargs) -> Any:
        """Runs the chain of callbacks on command line arguments."""
        if self.prev is not None:
            return self.cb(self.prev(*args, **kwargs))
        else:
            return self.cb(*args, **kwargs)