import g4gen
import multiprocessing
import numpy as np
import itertools

class G4GeneratorProcess(multiprocessing.Process):
    def __init__(self, idnum, material, input_queue, output_queue, seed=None):
        multiprocessing.Process.__init__(self)

        self.idnum = idnum
        self.material = material
        self.input_queue = input_queue
        self.output_queue = output_queue
        self.seed = seed
        self.daemon = True

    def run(self):
        gen = g4gen.G4Generator(self.material, seed=self.seed)
        while True:
            ev = self.input_queue.get()
            ev.photon_start = gen.generate_photons(ev)
            self.output_queue.put(ev)

def partition(num, partitions):
    '''Generator that returns num//partitions, with the last item including the remainder.

    Useful for partitioning a number into mostly equal parts while preserving the sum.

    >>> list(partition(800, 3))
    [266, 266, 268]
    >>> sum(list(partition(800, 3)))
    800
    '''
    step = num // partitions
    for i in xrange(partitions):
        if i < partitions - 1:
            yield step
        else:
            yield step + (num % partitions)

def queue_iterator(nelements, queue):
    for i in xrange(nelements):
        yield queue.get()

class G4ParallelGenerator(object):
    def __init__(self, nprocesses, material, base_seed=None):
        self.material = material
        self.vertex_queue = multiprocessing.Queue()
        self.photon_queue = multiprocessing.Queue()
        self.processes = [ G4GeneratorProcess(i, material, self.vertex_queue, self.photon_queue, seed=base_seed + i)
                           for i in xrange(nprocesses) ]
        for p in self.processes:
            p.start()

    def generate_events(self, nevents, vertex_iterator):
        # Doing this to avoid a deadlock caused by putting to one queue while getting from another
        for ev in itertools.islice(vertex_iterator, nevents):
            self.vertex_queue.put(ev)

        return queue_iterator(nevents, self.photon_queue)