# -*- coding: utf-8 -*-

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# This file is part of QuTiP: Quantum Toolbox in Python.
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"""
Routines for running Python functions in parallel using process pools
from the multiprocessing library.
"""

import os
import platform
from multiprocessing import Pool
from qiskit.exceptions import QiskitError
from qiskit.util import local_hardware_info
from qiskit.tools.events.pubsub import Publisher

# Set parallel flag
os.environ['QISKIT_IN_PARALLEL'] = 'FALSE'

# Number of local physical cpus
CPU_COUNT = local_hardware_info()['cpus']


def parallel_map(task, values, task_args=tuple(), task_kwargs={},  # pylint: disable=W0102
                 num_processes=CPU_COUNT):
    """
    Parallel execution of a mapping of `values` to the function `task`. This
    is functionally equivalent to::

        result = [task(value, *task_args, **task_kwargs) for value in values]

    On Windows this function defaults to a serial implementation to avoid the
    overhead from spawning processes in Windows.

    Args:
        task (func): Function that is to be called for each value in ``values``.
        values (array_like): List or array of values for which the ``task``
                            function is to be evaluated.
        task_args (list): Optional additional arguments to the ``task`` function.
        task_kwargs (dict): Optional additional keyword argument to the ``task`` function.
        num_processes (int): Number of processes to spawn.

    Returns:
        result: The result list contains the value of
                ``task(value, *task_args, **task_kwargs)`` for
                    each value in ``values``.

    Raises:
        QiskitError: If user interrupts via keyboard.

    Events:
        terra.parallel.start: The collection of parallel tasks are about to start.
        terra.parallel.update: One of the parallel task has finished.
        terra.parallel.finish: All the parallel tasks have finished.
    """
    if len(values) == 1:
        return [task(values[0], *task_args, **task_kwargs)]

    Publisher().publish("terra.parallel.start", len(values))
    nfinished = [0]

    def _callback(_):
        nfinished[0] += 1
        Publisher().publish("terra.parallel.done", nfinished[0])

    # Run in parallel if not Win and not in parallel already
    if platform.system() != 'Windows' and num_processes > 1 \
       and os.getenv('QISKIT_IN_PARALLEL') == 'FALSE':
        os.environ['QISKIT_IN_PARALLEL'] = 'TRUE'
        try:
            pool = Pool(processes=num_processes)

            async_res = [pool.apply_async(task, (value,) + task_args, task_kwargs,
                                          _callback) for value in values]

            while not all([item.ready() for item in async_res]):
                for item in async_res:
                    item.wait(timeout=0.1)

            pool.terminate()
            pool.join()

        except KeyboardInterrupt:
            pool.terminate()
            pool.join()
            Publisher().publish("terra.parallel.finish")
            raise QiskitError('Keyboard interrupt in parallel_map.')

        Publisher().publish("terra.parallel.finish")
        os.environ['QISKIT_IN_PARALLEL'] = 'FALSE'
        return [ar.get() for ar in async_res]

    # Cannot do parallel on Windows , if another parallel_map is running in parallel,
    # or len(values) == 1.
    results = []
    for _, value in enumerate(values):
        result = task(value, *task_args, **task_kwargs)
        results.append(result)
        _callback(0)
    Publisher().publish("terra.parallel.finish")
    return results
