Basic Python script to reverse a beatmap

reverser.py

import sys              
import os.path
from multiprocessing import Pool

def wline(file_, text=""):
    file_.write("%s\n" % text)

def _read_till_next_tag(file_, tag="", ignore_empty=True):
    lines = []

    for line in file_:

        # check if the line matches
        if line.strip() == tag:
            break

        # skip empty lines
        if line.strip() or not ignore_empty:
            lines.append(line)

    return lines

def _reverse_spinners(hitobjects):
    for i in range(len(hitobjects)):
        if int(hitobjects[i][3]) == 12:
            hitobjects[i][5] = str(int(hitobjects[i][5]) - int(hitobjects[-1 -i][2]) + int(hitobjects[i][2]))


def _reverse_and_switch_field(pairs, field):
    for i in range(len(pairs) // 2):
        pairs[i][field], pairs[-1 - i][field] = pairs[-1 - i][field], pairs[i][field]

def _reverse_slidershapes(hitobjects):
    for i in range(len(hitobjects)):
        elem = hitobjects[i]
        # Check whether object is a slider
        if int(elem[3]) & 2:

            # Reverse the points
            elem[5] = elem[5].split('|')
            points = elem[5][1:]
            points.reverse()
            elem[5] = [elem[5][0]] + points

            # join the strings
            elem[5] = join_list_elems([elem[5]], "|")[0]
            hitobjects[i] = elem

def copy_until(from_, to, until):
    for line in _read_till_next_tag(from_, until, False):
        to.write(line)

    to.write('')
    wline(to, until)

def join_list_elems(list_, sep=","):
    return [sep.join(elem) for elem in list_]

def reverse(bmap):

    # File where the reversed map will be written to
    reverse_file = bmap[:-4] + ' - reverse.osu'
    with open(bmap, 'r', encoding="utf8") as mfile, open(reverse_file, 'w', encoding="utf8") as rfile:

        # Copy the lines until we hit the timingpoints tag 
        copy_until(mfile, rfile, "[TimingPoints]")

        # Read and reverse timingpoints
        timingpoints = _read_till_next_tag(mfile, "[Colours]")
        timingpoints = [t.split(',', 1) for t in timingpoints]
        _reverse_and_switch_field(timingpoints, 0)

        # Write timingpoints
        for t in join_list_elems(timingpoints):
            rfile.write(t)

        # Write the colours tag into the file
        wline(rfile)
        wline(rfile, "[Colours]")

        # Copy the colours
        copy_until(mfile, rfile, "[HitObjects]")

        # Read and reverse hitobjects
        hitobjects = _read_till_next_tag(mfile)
        hitobjects = [h.split(',') for h in hitobjects]

        _reverse_and_switch_field(hitobjects, 2)

        # Reverse the slider shapes
        _reverse_slidershapes(hitobjects)

        _reverse_spinners(hitobjects)

        hitobjects = join_list_elems(hitobjects)
        hitobjects.reverse()

        # Write the hitobjects
        for h in hitobjects:
            rfile.write(h)

if __name__ == '__main__':
    maps = sys.argv[1:]
    p = Pool(len(maps))
    p.map(reverse, maps)
    p.close()
    p.join()
    print('\nDone...')