script to fix up blog post markdown files

fixup-posts.py

#
# rewrite blog posts front matter to fix date format and title
# 2020.05.26  darell tan
#

import re
import os
import sys
import time

OLD_FMT  = '%d.%m.%Y, %H:%M'
NEW_FMT  = '%Y-%m-%d %H:%M:%S'
NEW_FMT2 = '%Y-%m-%d'

EOL_RE = re.compile(r'\s+$')

def date_can_parse(fmt, s):
	try:
		time.strptime(s, fmt)
		return True
	except:
		return False

def is_quoted(s):
	s = s.strip()
	return s[0] == s[-1] and s[0] in '"\''

def quotestr(s):
	if is_quoted(s):
		return s

	HAS_DQ = '"' in s
	HAS_SQ = "'" in s

	if HAS_DQ and not HAS_SQ:	# has double
		return "'%s'" % s
	elif HAS_SQ and not HAS_DQ:	# has single
		return '"%s"' % s
	elif HAS_DQ and HAS_SQ:		# has both
		return "'%s'" % s.replace("'", "''")

	# if it has funny chars, use double
	if ':' in s:
		return '"%s"' % s


def rewrite_file(fqn):
	changed = False
	contents = []
	with open(fqn, 'rb') as f:
		print fqn
		start = next(f)
		if '---' not in start:
			return

		contents.append(start)

		for l in f:
			contents.append(l)

			# end of front matter
			if l.strip().startswith('---'):
				break

			m = EOL_RE.search(l)
			tail = m.group(0) if m else ''

			# parse front matter k-v pairs
			k, v = l.strip().split(':', 1)
			k = k.strip()
			v = v.strip()

			if k == 'date':
				try:
					t = time.strptime(v, OLD_FMT)
				except:
					# new date format already, no need changes
					if date_can_parse(NEW_FMT, v) or date_can_parse(NEW_FMT2, v):
						continue

					# unable to parse
					raise

				t2 = time.strftime(NEW_FMT, t)

				contents[-1] = '%s: %s%s' % (k, t2, tail)
				changed = True
			elif k == 'title':
				if ':' in v and not is_quoted(v):
					contents[-1] = '%s: %s%s' % (k, quotestr(v), tail)
					changed = True

		# put remaining file contents
		contents.extend(f)

	# write the file back
	if changed:
		with open(fqn, 'wb') as f:
			f.write(''.join(contents))


assert os.path.isdir(sys.argv[1])

for root, _, files in os.walk(sys.argv[1]):
	for fn in files:
		fqn = os.path.join(root, fn)
		if fqn.endswith('.md'):
			try:
				rewrite_file(fqn)
			except:
				print('error processing file ' + fqn)
				raise