svg-tweak

#!/usr/bin/env python

import pathlib as pl, contextlib as cl
import os, sys, tempfile, stat, errno, re


p_err = lambda *a,**kw: print('ERROR:', *a, **kw, file=sys.stderr, flush=True) or 1

@cl.contextmanager
def safe_replacement(path, *open_args, mode=None, xattrs=None, **open_kws):
	'Context to atomically create/replace file-path in-place unless errors are raised'
	path, xattrs = str(path), None
	if mode is None:
		try: mode = stat.S_IMODE(os.lstat(path).st_mode)
		except FileNotFoundError: pass
	if xattrs is None and getattr(os, 'getxattr', None): # MacOS
		try: xattrs = dict((k, os.getxattr(path, k)) for k in os.listxattr(path))
		except FileNotFoundError: pass
		except OSError as err:
			if err.errno != errno.ENOTSUP: raise
	open_kws.update( delete=False,
		dir=os.path.dirname(path), prefix=os.path.basename(path)+'.' )
	if not open_args: open_kws.setdefault('mode', 'w')
	with tempfile.NamedTemporaryFile(*open_args, **open_kws) as tmp:
		try:
			if mode is not None: os.fchmod(tmp.fileno(), mode)
			if xattrs:
				for k, v in xattrs.items(): os.setxattr(path, k, v)
			yield tmp
			if not tmp.closed: tmp.flush()
			try: os.fdatasync(tmp)
			except AttributeError: pass # MacOS
			os.rename(tmp.name, path)
		finally:
			try: os.unlink(tmp.name)
			except FileNotFoundError: pass


def main(args=None):
	import argparse, textwrap
	dd = lambda text: re.sub( r' \t+', ' ',
		textwrap.dedent(text).strip('\n') + '\n' ).replace('\t', '  ')
	parser = argparse.ArgumentParser(usage='%(prog)s [options] [svg-file]',
		formatter_class=argparse.RawTextHelpFormatter, description=dd('''
			Tool to change something in an SVG file, according to specified options.'''))
	parser.add_argument('svg_file', nargs='?', help=dd('''
		SVG file to process and change in-place.
		Default is to read SVG from stdin stream and
			output resulting one to stdout, same as if "-" is specified.'''))

	parser.add_argument('-b', '--add-bg-color', metavar='color',
		help=dd('''
			Add background rectangle element with a solid color,
				removing transparency from the image that way.
			Useful to control when image viewers use backgrounds that
				make transparent SVG illegible, e.g. white-on-white or black-on-black.
			Pre-existing background elements are NOT removed, if any - only adds stuff.'''))

	opts = parser.parse_args(sys.argv[1:] if args is None else args)

	@cl.contextmanager
	def in_file(path):
		if not path or path == '-': return (yield sys.stdin)
		with open(path) as src: yield src

	@cl.contextmanager
	def out_func(path):
		if not path or path == '-': return (yield lambda s,end='': print(s, end=end))
		else: dst_file = safe_replacement(path)
		with dst_file as dst: yield lambda s,end='': print(s, file=dst, end=end)

	with in_file(opts.svg_file) as src, out_func(opts.svg_file) as out:
		out_buff = list()

		def src_read(a=0, n=10 * 2**20, tail=True):
			offset, out, buff = 0, list(), list(reversed(out_buff))
			while buff and n:
				if not (chunk := buff.pop()): continue
				offset += (m := len(chunk))
				if m <= a: a -= m; continue
				else: a, chunk = 0, chunk[a:]
				n -= len(chunk := chunk[:n])
				out.append(chunk)
			if n and tail: out.append(src.read(n))
			return ''.join(out)

		if opts.add_bg_color:
			s = src_read(n=50 * 2**10)
			for rx in r'</\s*defs\s*>', r'<\s*defs\s*/>', r'<svg\s*.*?>':
				if not (m := re.search(rx, s)): continue
				out_buff[:] = [ s[:m.end()],
					f'<rect fill="{opts.add_bg_color}" width="100%" height="100%" />',
					s[m.end():], src_read(len(s), tail=False) ]
				break
			else: return p_err('Failed to find <defs> or <svg> at the start of the file')

		out_buff.append(src_read(sum(len(c) for c in out_buff)))
		for s in out_buff: out(s)

if __name__ == '__main__':
	try: sys.exit(main())
	except BrokenPipeError: # stdout pipe closed
		os.dup2(os.open(os.devnull, os.O_WRONLY), sys.stdout.fileno())
		sys.exit(1)