#!/usr/bin/env python3
"""Reject modifications to accepted Architecture Decision Records."""

from __future__ import annotations

import argparse
import subprocess
import sys
from pathlib import Path

ROOT = Path(__file__).resolve().parents[1]
ADR_PREFIX = "docs/adr/ADR-"


def _git(*args: str) -> str:
    return subprocess.check_output(
        ["git", *args],
        cwd=ROOT,
        text=True,
        stderr=subprocess.DEVNULL,
    ).strip()


def _exists_on(base: str, path: str) -> bool:
    try:
        _git("cat-file", "-e", f"{base}:{path}")
        return True
    except subprocess.CalledProcessError:
        return False


def find_modified_adrs(base: str) -> list[str]:
    try:
        diff_out = _git("diff", "--name-only", f"{base}...HEAD", "--", "docs/adr/")
    except subprocess.CalledProcessError:
        return []

    modified: list[str] = []
    for rel in diff_out.splitlines():
        if not rel.startswith(ADR_PREFIX) or not rel.endswith(".md"):
            continue
        if _exists_on(base, rel):
            modified.append(rel)
    return sorted(modified)


def run_check(base: str = "origin/main") -> int:
    modified = find_modified_adrs(base)
    if modified:
        print("Immutable ADR violation — accepted records cannot be edited:")
        for path in modified:
            print(f"  error: {path}")
        print(
            "\nReversal or refinement → new ADR-NNNN file. "
            "Never edit an existing ADR-*.md."
        )
        return 1

    print(f"ADR immutability OK (base {base})")
    return 0


def main() -> None:
    parser = argparse.ArgumentParser(description=__doc__)
    parser.add_argument(
        "--base",
        default="origin/main",
        help="Git ref to compare against (default: origin/main)",
    )
    args = parser.parse_args()
    sys.exit(run_check(base=args.base))


if __name__ == "__main__":
    main()