"""Utility functions.
"""
import contextlib
import functools
import multiprocessing

from milc import cli
from milc.subcommand import config


@contextlib.contextmanager
def parallelize():
    """Returns a function that can be used in place of a map() call.

    Attempts to use `mpire`, falling back to `multiprocessing` if it's not
    available. If parallelization is not requested, returns the original map()
    function.
    """

    # Work out if we've already got a config value for parallel searching
    if not cli.config.user.parallel_search:
        parallel_search = True
    else:
        parallel_search = cli.config.user.parallel_search

    # If we haven't already written a value, write it to the file
    if cli.config.user.parallel_search != parallel_search:
        cli.args.read_only = False
        cli.config.user.parallel_search = parallel_search
        config.set_config('user', 'parallel_search', parallel_search)
        cli.save_config()

    # Non-parallel searches use use `map()`
    if not parallel_search:
        yield map
        return

    # Prefer mpire's `WorkerPool` if it's available
    with contextlib.suppress(ImportError):
        from mpire import WorkerPool
        with WorkerPool() as pool:
            yield functools.partial(pool.imap_unordered, progress_bar=True)
        return

    # Otherwise fall back to multiprocessing's `Pool`
    with multiprocessing.Pool() as pool:
        yield pool.imap_unordered


def parallel_map(*args, **kwargs):
    """Effectively runs `map()` but executes it in parallel if necessary.
    """
    with parallelize() as map_fn:
        return map_fn(*args, **kwargs)