Remove all unmodified css from customized buefy theme

original_theme.scss

// Import Bulma's core
@import "../../node_modules/bulma/sass/utilities/_all";

// Import Bulma and Buefy styles
@import "../../node_modules/bulma/bulma.sass";
@import "../../node_modules/buefy/src/scss/buefy";

strip_buefy_theme.py

# Python 3.8
import hashlib
import re
import shutil
import sys
from collections import defaultdict
from copy import deepcopy

import tinycss2
from tinycss2 import parse_stylesheet_bytes
from tinycss2.ast import QualifiedRule, AtRule

original_scss = 'original_theme.scss'
theme_scss = 'theme.scss'


def _convert(scss_file):
    import subprocess

    result = subprocess.run([shutil.which('npx'), 'node-sass', scss_file], stdout=subprocess.PIPE,
                            stderr=subprocess.PIPE)
    if result.stderr:
        print(result.stderr.decode(), file=sys.stderr)
        raise Exception(f'Error converting {scss_file}')
    return result.stdout


theme_css = _convert(theme_scss)
original_css = _convert(original_scss)

theme = parse_stylesheet_bytes(theme_css, skip_comments=True, skip_whitespace=True)
original = parse_stylesheet_bytes(original_css, skip_comments=True, skip_whitespace=True)


def _clean_str(content):
    return re.sub('[\r\n\t]', '', re.sub(' +', ' ', content)).strip()


def _get_rule_id(prelude):
    c = tinycss2.serialize(prelude)
    return _clean_str(c)


def _get_content(content):
    c = tinycss2.serialize(content)
    c = _clean_str(c)
    return hashlib.md5(c.encode()).hexdigest()


original_rules = defaultdict(list)
for item in original[0]:
    if isinstance(item, QualifiedRule):
        id = _get_rule_id(item.prelude)
        content_hash = _get_content(item.content)
        original_rules[id].append(content_hash)
    elif isinstance(item, AtRule):
        rule_id = _get_rule_id(item.prelude)
        for inner_item in tinycss2.parse_rule_list(item.content, skip_comments=True, skip_whitespace=True):
            inner_id = _get_rule_id(inner_item.prelude)
            content_hash = _get_content(inner_item.content)
            original_rules[(rule_id, inner_id)].append(content_hash)

modified_items = []
for item in theme[0]:
    if isinstance(item, QualifiedRule):
        id = _get_rule_id(item.prelude)
        if id in original_rules:
            content_hash = _get_content(item.content)
            if content_hash not in original_rules[id]:
                modified_items.append(item)
        else:
            modified_items.append(item)
    elif isinstance(item, AtRule):
        rule_item = item
        rule_id = _get_rule_id(rule_item.prelude)
        empty_rule_item = None
        for inner_item in tinycss2.parse_rule_list(rule_item.content, skip_comments=True, skip_whitespace=True):
            inner_id = _get_rule_id(inner_item.prelude)
            content_hash = _get_content(inner_item.content)
            if content_hash not in original_rules[(rule_id, inner_id)]:
                if empty_rule_item is None:
                    empty_rule_item = deepcopy(rule_item)
                    empty_rule_item.content = []
                    modified_items.append(empty_rule_item)
                empty_rule_item.content.append(inner_item)

print(tinycss2.serialize(modified_items))

theme.scss

// https://buefy.org/documentation/customization/
// Import Bulma's core
@import "~bulma/sass/utilities/_all";

// Set your colors
$primary: #8c67ef;
$primary-light: findLightColor($primary);
$primary-dark: findDarkColor($primary);
$primary-invert: findColorInvert($primary);
$twitter: #4099FF;
$twitter-invert: findColorInvert($twitter);

// Lists and maps
$custom-colors: null !default;
$custom-shades: null !default;

// Setup $colors to use as bulma classes (e.g. 'is-twitter')
$colors: mergeColorMaps(
    (
        "white": (
            $white,
            $black,
        ),
        "black": (
            $black,
            $white,
        ),
        "light": (
            $light,
            $light-invert,
        ),
        "dark": (
            $dark,
            $dark-invert,
        ),
        "primary": (
            $primary,
            $primary-invert,
            $primary-light,
            $primary-dark,
        ),
        "link": (
            $link,
            $link-invert,
            $link-light,
            $link-dark,
        ),
        "info": (
            $info,
            $info-invert,
            $info-light,
            $info-dark,
        ),
        "success": (
            $success,
            $success-invert,
            $success-light,
            $success-dark,
        ),
        "warning": (
            $warning,
            $warning-invert,
            $warning-light,
            $warning-dark,
        ),
        "danger": (
            $danger,
            $danger-invert,
            $danger-light,
            $danger-dark,
        ),
    ),
    $custom-colors
);

// Links
$link: $primary;
$link-invert: $primary-invert;
$link-focus-border: $primary;

// Import Bulma and Buefy styles
@import "~bulma";
@import "~buefy/src/scss/buefy";