import argparse
import sys

from pathlib import Path
from scandir import scandir

image_extensions = [".jpg", ".jpeg", ".png"]

def get_folder(path):
    output_dir = Path(path)
    output_dir.mkdir(parents=True, exist_ok=True)
    return output_dir

def get_image_paths(directory):
    return [x.path for x in scandir(directory) if
     any(map(lambda ext: x.name.lower().endswith(ext), image_extensions))]

class FullHelpArgumentParser(argparse.ArgumentParser):
    """
    Identical to the built-in argument parser, but on error
    it prints full help message instead of just usage information
    """
    def error(self, message):
        self.print_help(sys.stderr)
        args = {'prog': self.prog, 'message': message}
        self.exit(2, '%(prog)s: error: %(message)s\n' % args)

# From: https://stackoverflow.com/questions/7323664/python-generator-pre-fetch
import threading
import queue as Queue
class BackgroundGenerator(threading.Thread):
    def __init__(self, generator, prefetch=1): #See below why prefetch count is flawed
        threading.Thread.__init__(self)
        self.queue = Queue.Queue(prefetch)
        self.generator = generator
        self.daemon = True
        self.start()

    def run(self):
        # Put until queue size is reached. Note: put blocks only if put is called while queue has already reached max size
        # => this makes 2 prefetched items! One in the queue, one waiting for insertion!
        for item in self.generator:
            self.queue.put(item)
        self.queue.put(None)

    def iterator(self):
        while True:
            next_item = self.queue.get()
            if next_item is None:
                break
            yield next_item