#!/usr/bin/env python3
"""Merge the auth-only patch into an existing, file-bind-mounted Element config."""

import argparse
import copy
import json
from pathlib import Path


def merge(current, patch):
    for key, value in patch.items():
        if isinstance(value, dict):
            if not isinstance(current.get(key), dict):
                current[key] = {}
            merge(current[key], value)
        else:
            current[key] = value


def main():
    parser = argparse.ArgumentParser(description=__doc__)
    parser.add_argument("config", type=Path)
    parser.add_argument("--write", action="store_true", help="write in place; otherwise print a preview")
    args = parser.parse_args()
    patch = json.loads(Path(__file__).with_name("auth-branding.patch.json").read_text())
    # r+ intentionally retains the inode: replacing this file would leave an
    # existing Docker single-file bind mount serving the old config.
    with args.config.open("r+" if args.write else "r", encoding="utf-8") as config_file:
        current = json.load(config_file)
        if not isinstance(current, dict):
            raise ValueError("Element config must be a JSON object")
        original = copy.deepcopy(current)
        merge(current, patch)
        for key in ("setting_defaults", "default_theme", "default_server_config", "default_server_name"):
            assert current.get(key) == original.get(key), f"Auth patch must preserve {key}"
        output = json.dumps(current, indent=2, ensure_ascii=False) + "\n"
        if args.write:
            config_file.seek(0)
            config_file.write(output)
            config_file.truncate()
        else:
            print(output, end="")


if __name__ == "__main__":
    main()