"""
Util for talking to the client program in order to retrieve
dynamic defaults for the UI
"""
import subprocess
from json import JSONDecodeError
from subprocess import CalledProcessError

import os

from gooey.python_bindings.types import Try, Success, Failure
from gooey.python_bindings.coms import deserialize_inbound


def communicate(cmd, encoding) -> Try:
    """
    Invoke the processes specified by `cmd`.
    Assumes that the process speaks JSON over stdout. Non-json response
    are treated as an error.

    Implementation Note: I don't know why, but `Popen` is like ~5-6x faster
    than `check_output`. in practice, it means waiting for ~1/10th
    of a second rather than ~7/10ths of a second. A
    difference which is pretty weighty when there's a
    user waiting on the other end.
    """
    try:
        proc = subprocess.Popen(
            cmd,
            stdout=subprocess.PIPE,
            stderr=subprocess.PIPE,
            env=os.environ.copy()
        )
        out, err = proc.communicate()
        if out and proc.poll() == 0:
            return Success(deserialize_inbound(out, encoding))
        else:
            return Failure(CalledProcessError(proc.returncode, cmd, output=out, stderr=err))
    except JSONDecodeError as e:
        return Failure(e)