"""Utilities for lambda-ripper-feeder."""
import os


def which(program):
    """Determine if an application is installed on the system."""

    def is_exe(file_path):
        return os.path.isfile(file_path) and os.access(file_path, os.X_OK)

    fpath, fname = os.path.split(program)
    if fpath:
        if is_exe(program):
            return program
    else:
        for path in os.environ['PATH'].split(os.pathsep):
            exe_file = os.path.join(path, program)
            if is_exe(exe_file):
                return exe_file

    return None