Correctly wrap JSON front-matter in markdown files

fix-json-frontmatter.py

#!/usr/bin/env python
#
# Script to wrap JSON front-matter in markdown files with `---` delimiters.
#
# This allows Prettier to be used on the markdown file (and it won't try and format the JSON front
# matter).
#
# I needed this to convert old Hugo markdown files that had JSON front-matter.
import os
import sys
import json
import tempfile


def fix_files(filepaths):
    for filepath in filepaths:
        fix_file(filepath)


def fix_file(filepath):
    with open(filepath, "r") as f:
        # Only process files where the first line is a brace opening a JSON object.
        line = f.readline().strip()
        if line != "{":
           return

        # Split the file contents into the front-matter object and the markdown content.
        front_matter, md_content = split_file(f)

        # Combine the content into a new file with the front-matter properly delimited.
        temp_fd, temp_filepath = tempfile.mkstemp()
        with os.fdopen(temp_fd, 'w') as g:
            g.write("---\n")
            g.write(json.dumps(front_matter, indent=4))
            g.write("\n---\n\n")
            g.write(md_content)

    # Copy the converted file into place.
    os.rename(temp_filepath, filepath)


def split_file(f):
    """
    Split a file into front-matter and markdown.
    """
    front_matter = None

    f.seek(0)
    json_lines = []
    md_lines = []
    for line in f.readlines():
        stripped_line = line.strip()
        if front_matter is None:
            json_lines.append(line)
        else:
            md_lines.append(line)

        if stripped_line == "}" and front_matter is None:
            json_str = "\n".join(json_lines)
            front_matter = json.loads(json_str)

    md_content = "".join(md_lines)

    return front_matter, md_content


fix_files(sys.argv[1:])