shell-json-set

#!/usr/bin/env python3
"""Set one top-level key of ~/.config/omarchy/shell.json from a fresh read.

  shell-json-set idle '{"lock": 300, "screensaver": 150}'

Read, change and replace happen in one short step, so a change another writer
made a moment ago (lock-explorer, the omarchy CLIs) is never overwritten from a
stale copy. Only the named key changes.
"""
import json, os, sys, tempfile

PATH = os.path.join(os.environ.get("HOME", ""), ".config/omarchy/shell.json")

# Config and theme files are read only when they are regular files (a symlink
# to one is fine, dotfile managers use them; a FIFO or device is not), and at
# most READ_LIMIT bytes, so a strange file cannot hang or flood the helper.
READ_LIMIT = 1024 * 1024


def read_capped(path, limit=READ_LIMIT):
    try:
        if not os.path.isfile(path) or os.path.getsize(path) > limit:
            return None
        with open(path, encoding="utf-8") as f:
            text = f.read(limit + 1)
        return text if len(text) <= limit else None
    except (OSError, UnicodeDecodeError):
        return None



def main(argv):
    if len(argv) != 2 or argv[0] not in ("idle",):
        print(__doc__, file=sys.stderr)
        return 2
    value = json.loads(argv[1])
    if argv[0] == "idle":
        if not isinstance(value, dict) or any(k not in ("lock", "screensaver") for k in value) \
                or any(not isinstance(v, int) or v < 0 or v > 86400 for v in value.values()):
            print("invalid idle value", file=sys.stderr)
            return 2
    target = os.path.realpath(PATH)
    text = read_capped(target)
    if text is None:
        print("shell.json is not a readable regular file", file=sys.stderr)
        return 1
    doc = json.loads(text)
    if not isinstance(doc, dict):
        print("shell.json is not an object", file=sys.stderr)
        return 1
    if doc.get(argv[0]) == value:
        return 0
    doc[argv[0]] = value
    fd, tmp = tempfile.mkstemp(prefix=".shell.json.", dir=os.path.dirname(target))
    with os.fdopen(fd, "w", encoding="utf-8") as f:
        f.write(json.dumps(doc, indent=2, ensure_ascii=False) + "\n")
    os.chmod(tmp, os.stat(target).st_mode & 0o777)
    os.replace(tmp, target)
    return 0


def _refused(err):
    """A readable line for a write the filesystem would not allow.

    A read-only ~/.config (home-manager and friends put one there), a file made
    immutable, or a full disk all arrive here as an OSError. The panel shows
    whatever comes back on stderr, and a Python traceback is no use to anybody.
    """
    home = os.environ.get("HOME", "")
    where = os.path.dirname(getattr(err, "filename", "") or "") or "that folder"
    return ("Could not write in %s: %s. Lacquer stopped there.\n"
            "A read-only folder, an immutable file or a full disk will do this."
            % (where.replace(home, "~") if home else where, err.strerror or err))


if __name__ == "__main__":
    try:
        sys.exit(main(sys.argv[1:]))
    except OSError as err:
        sys.exit(_refused(err))