Script to convert SCSS files from physical to logical values for RTL and vertical languages

to-logical.py

#
#   This script converts margins, padding, and borders to logical values,
#   allowing RTL and vertical languages to show correctly.
#   Supports both *.css and *.scss files.
#
#   Some renames are not yet implemented widely, and may require CSS plugin
#     https://github.com/csstools/postcss-logical
#   They have been commented out for now, but feel free to try them out.
#
#   Full spec:   https://drafts.csswg.org/css-logical/
#   Good blogs:  https://adrianroselli.com/2019/11/css-logical-properties.html
#                https://css-tricks.com/css-logical-properties/
#
#   Usage (recursive):      python3 convert-scss.py -r <path-to-scss-files-dir>
#
#   License: MIT

from pathlib import Path
import getopt, sys, re


def error(msg):
  print(msg)
  exit(1)


sides = {
  '-top': '-block-start',
  '-right': '-inline-end',
  '-bottom': '-block-end',
  '-left': '-inline-start',
}

renames = {
  # These are mostly unimplemented, might require https://github.com/csstools/postcss-logical
  # 'left': 'inset-inline-start',
  # 'right': 'inset-inline-end',
  # 'top': 'inset-block-start',
  # 'bottom': 'inset-block-end',

  'min-height': 'min-block-size',
  'max-height': 'max-block-size',
  'min-width': 'min-inline-size',
  'max-width': 'max-inline-size',
}

inline_start_end = {
  'left': 'inline-start',
  'right': 'inline-end',
}

aligns = {
  'text-align': {
    'left': 'start',
    'right': 'end',
    },
  # These are mostly unimplemented, might require https://github.com/csstools/postcss-logical
  # 'float': inline_start_end,
  # 'clear': inline_start_end,
}

def collapse_if_equal(val1, val2):
  return val1 if val1 == val2 else f"{val1} {val2}"


def replacer(match):
  # ^( *)(margin|padding|border)(-(?:left|right|top|bottom))?(-(?:size|style|color))?( *: *)([^;\n]+);( *//.*)?$
  original = match.group(0)
  spaces1 = match.group(1)
  typ = match.group(2)
  side = match.group(3) or ''
  extra = match.group(4) or ''
  spaces2 = match.group(5)
  values = match.group(6)
  comment = match.group(7) or ''
  # special lint controlling comment should be repeated
  dup_comment = comment if ('sass-lint:' in comment) else ''

  if not side:
    if typ == 'border':
      return original
    tokens = tokenize(values)
    important = ' ' + tokens[-1] if tokens[-1] == '!important' else ''
    if important:
      tokens = tokens[:-1]
    if len(tokens) == 1:
      return original  # single token stays as is
    if len(tokens) == 2:  # top-bottom  right-left
      # The *-block shorthand is not yet supported,  see
      #   https://developer.mozilla.org/en-US/docs/Web/CSS/margin-block
      return f"{spaces1}{typ}-block-start{extra}{spaces2}{tokens[0]}{important};{comment}\n" + \
             f"{spaces1}{typ}-block-end{extra}{spaces2}{tokens[0]}{important};{dup_comment}\n" + \
             f"{spaces1}{typ}-inline-start{extra}{spaces2}{tokens[1]}{important};{dup_comment}\n" + \
             f"{spaces1}{typ}-inline-end{extra}{spaces2}{tokens[1]}{important};{dup_comment}"
    if len(tokens) == 3:  # top  left-right  bottom
      return f"{spaces1}{typ}-block-start{extra}{spaces2}{tokens[0]}{important};{comment}\n" + \
             f"{spaces1}{typ}-block-end{extra}{spaces2}{tokens[2]}{important};{dup_comment}\n" + \
             f"{spaces1}{typ}-inline-start{extra}{spaces2}{tokens[1]}{important};{dup_comment}\n" + \
             f"{spaces1}{typ}-inline-end{extra}{spaces2}{tokens[1]}{important};{dup_comment}"
    if len(tokens) == 4:  # top  left-right  bottom
      return f"{spaces1}{typ}-block-start{extra}{spaces2}{tokens[0]}{important};{dup_comment}{comment}\n" + \
             f"{spaces1}{typ}-block-end{extra}{spaces2}{tokens[2]}{important};{dup_comment}\n" + \
             f"{spaces1}{typ}-inline-start{extra}{spaces2}{tokens[3]}{important};{dup_comment}\n" + \
             f"{spaces1}{typ}-inline-end{extra}{spaces2}{tokens[1]}{important};{dup_comment}"
    raise ValueError(f'Unexpected number of tokens {len(tokens)} in {original} -- {tokens}')

  return f"{spaces1}{typ}{sides[side]}{extra}{spaces2}{values};{comment}"

def renamer(match):
  # ^( *)(' + '|'.join(renames.keys()) + r')( *: *)([^;\n]+);( *//.*)?$
  original = match.group(0)
  spaces1 = match.group(1)
  typ = match.group(2)
  spaces2 = match.group(3)
  values = match.group(4)
  comment = match.group(5) or ''
  try:
    return f"{spaces1}{renames[typ]}{spaces2}{values};{comment}"
  except KeyError:
    return original

def aligner(match):
  # ^( *)(text-align|float|clear)( *: *)(left|right)( *);
  original = match.group(0)
  spaces1 = match.group(1)
  typ = match.group(2)
  spaces2 = match.group(3)
  values = match.group(4)
  spaces3 = match.group(5)
  try:
    return f"{spaces1}{typ}{spaces2}{aligns[typ][values]}{spaces3};"
  except KeyError:
    return original


def tokenize(string):
  # Original idea from https://stackoverflow.com/a/38212061/177275
  # Assume correct syntax / matching brackets
  brackets = 0
  start = 0
  results = []

  for idx, char in enumerate(string):
    if char == ' ':
      if start is not None and brackets == 0:
        results.append(string[start:idx])
        start = None
    else:
      if start is None:
        start = idx
      if char == '(' or char == '{':
        brackets += 1
      elif char == ')' or char == '}':
        brackets -= 1
        if brackets < 0:
          raise ValueError(f'failed to tokenize "{string}"')
  if start is not None:
    results.append(string[start:])
  results2 = []
  idx = 0
  while idx < len(results):
    if len(results[idx]) > 1 or results[idx] not in ('-', '+', '/', '*'):
      results2.append(results[idx])
    else:
      results2[-1] += ' ' + results[idx] + ' ' + results[idx + 1]
      idx += 1
    idx += 1
  return results2


def process(file_path):
  print(f"Processing {file_path}...")
  code = file_path.read_text()
  res = re.sub(
    r'^( *)(margin|padding|border)(-(?:left|right|top|bottom))?(-(?:size|style|color))?( *: *)([^;\n]+);( *//.*)?$',
    replacer, code, flags=re.MULTILINE)
  res = re.sub(
    r'^( *)(' + '|'.join(renames.keys()) + r')( *: *)([^;\n]+);( *//.*)?$',
    renamer, res, flags=re.MULTILINE)
  res = re.sub(
    r'^( *)(text-align|float|clear)( *: *)(left|right)( *);',
    aligner, res, flags=re.MULTILINE)
  if res != code:
    print(f"Modifying {file_path}")
    file_path.write_text(res)


# Use -r for recursive
opts, args = getopt.getopt(sys.argv[1:], 'r')
if len(args) != 1:
  error("Usage:  [-r]  <directory-or-file>\n\nUse -r for recursive")

recursive = opts and opts[0][0] == '-r'

root_path = Path(args[0])
if root_path.is_file():
  process(root_path)
else:
  for pattern in ('*.scss', '*.css'):
    for file in (root_path.rglob(pattern) if recursive else root_path.glob(pattern)):
      if file.is_file():
        process(root_path / file)