#!/usr/bin/env python3

import configparser
import math
import os
import sys

def main():
    action = parse_action()

    if action == "+":
        update_font_size(get_size_increment)
    elif action == "-":
        update_font_size(get_size_decrement)
    else:
        update_font_size(lambda _: action)

def parse_action():
    if len(sys.argv) != 2:
        print_help_exit()

    action = sys.argv[1]
    if action != "+" and action != "-" and not action.isdigit():
        print_help_exit()

    if action.isdigit():
        action = int(action)
        if action < 1:
            print_help_exit()

    return action

def print_help_exit():
    print("Usage: %s [+|-|22]", file=sys.stderr)
    sys.exit(1)

def get_size_increment(size):
    if size >= 40:
        return math.floor(size / 8) * 8 + 8
    if size >= 28:
        return math.floor(size / 4) * 4 + 4
    if size >= 18:
        return math.floor(size / 2) * 2 + 2
    return size + 1

def get_size_decrement(size):
    if size > 40:
        return math.ceil(size / 8) * 8 - 8
    if size > 28:
        return math.ceil(size / 4) * 4 - 4
    if size > 18:
        return math.ceil(size / 2) * 2 - 2
    return size - 1

def update_font_size(fn):
    filename = get_config_filename()
    config = configparser.RawConfigParser()
    config.optionxform = lambda key: key
    config.read(filename)

    font_name, old_size = config["Configuration"]["FontName"].rsplit(" ", 1)
    new_size = fn(int(old_size))
    config["Configuration"]["FontName"] = "%s %s" % (font_name, new_size)

    print("Updating font size:", old_size, "->", new_size)

    with open(filename+".new", "w") as f:
        config.write(f)
    os.rename(filename+".new", filename)

def get_config_filename():
    xdg_config_dir = os.environ.get("XDG_CONFIG_HOME", None)
    if not xdg_config_dir:
        xdg_config_dir = os.path.expanduser("~/.config")
    return os.path.join(xdg_config_dir, "xfce4", "terminal", "terminalrc")


if __name__ == "__main__":
    main()