#!/usr/bin/env python3

from operator import itemgetter
from timeit import default_timer as timer
import json
from random import randint

xs = [
    {
        'col0': randint(0, 500000),
        'col1': randint(0, 500000),
        'col2': randint(0, 500000),
        'col3': randint(0, 500000),
        'col4': randint(0, 500000),
        'col5': randint(0, 500000),
        'col6': randint(0, 500000),
        'col7': randint(0, 500000),
    }
    for i in range(500000)
]

##  `my_single_pass_sort` works better when fewer columns need be reversed:
##
##  -   when no column needs to be reversed, `my_single_pass_sort` takes about
##      25% time of `single_pass_sort`;
##
##  -   when 1 column need to be reversed, `my_single_pass_sort` takes about
##      80% time of `single_pass_sort`;
##
##  -   when all columns need to be reversed, `my_single_pass_sort` takes about
##      120% time of `single_pass_sort`;
specs = [
    (itemgetter('col0'), False),
    (itemgetter('col1'), False),
    (itemgetter('col2'), False),
    (itemgetter('col3'), False),
    (itemgetter('col4'), False),
    (itemgetter('col5'), False),
    (itemgetter('col6'), False),
    (itemgetter('col7'), False),
]

##  `multi_pass_sort` is usually much faster (2x) than the other two;
def multi_pass_sort(xs, specs):

    '''
    <https://mail.python.org/pipermail/python-ideas/2016-October/043045.html>
    '''

    for key, reverse in reversed(specs):
        xs.sort(key=key, reverse=reverse)

def _sorter(specs):
    keyfuncs, reversers = zip(*specs)

    class Wrapper(object):
        def __init__(self, obj):
            self.keys = tuple(f(obj) for f in keyfuncs)

        def __lt__(x, y):
            for a, b, r in zip(x.keys, y.keys, reversers):
                if a < b:
                    return not r
                if b < a:
                    return r
            return False    # all the keys are equal

    return Wrapper

def single_pass_sort(xs, specs):

    '''
    <https://mail.python.org/pipermail/python-ideas/2016-October/043126.html>
    '''

    xs.sort(key=_sorter(specs))

def my_single_pass_sort(xs, specs):

    '''
    <https://bugs.python.org/issue35010>
    '''

    def keygen(specs):
        class _:
            def __init__(self, v): self.v = v
            def __eq__(self, o): return o.v == self.v
            def __lt__(self, o): return o.v < self.v
        return lambda x: [ _(k(x)) if r else k(x) for k, r in specs ]
    xs.sort(key=keygen(specs))

t = timer()
#multi_pass_sort(xs, specs)
#single_pass_sort(xs, specs)
#my_single_pass_sort(xs, specs)
print(timer() - t)
#print(json.dumps(xs, indent=4))