"""Print services (`services/<name>/`) changed by the pushed commit, one per line.

Falls back to every service when the parent commit is unavailable (first commit or shallow clone),
so a deploy never silently skips a service.
"""

import re
import subprocess
import sys
from pathlib import Path

NAME = re.compile(r"^[a-z][a-z0-9-]{1,30}$")


def git(*args: str) -> str:
    return subprocess.run(["git", *args], check=True, capture_output=True, text=True).stdout


def all_services() -> list[str]:
    root = Path("services")
    return sorted(p.name for p in root.iterdir() if p.is_dir() and NAME.match(p.name)) if root.is_dir() else []


def changed_paths() -> list[str] | None:
    try:
        git("rev-parse", "--verify", "HEAD~1")
    except subprocess.CalledProcessError:
        try:
            git("fetch", "--deepen=1", "-q")
            git("rev-parse", "--verify", "HEAD~1")
        except subprocess.CalledProcessError:
            return None
    return git("diff", "--name-only", "HEAD~1", "HEAD").splitlines()


def main() -> None:
    paths = changed_paths()
    if paths is None:
        print("no parent commit — deploying all services", file=sys.stderr)
        services = all_services()
    else:
        existing = set(all_services())
        services = sorted({p.split("/")[1] for p in paths if p.startswith("services/") and p.count("/") >= 2} & existing)
    print("\n".join(services))


if __name__ == "__main__":
    main()