#!/usr/bin/env python3
"""Guard ADR numbering under docs/decisions/.

Fails when two ADRs share a ``NNNN`` prefix — the exact accident of two
``0006-*`` records landing from separate PRs cut off main at different times.
Runs in CI via pre-commit, so a duplicate number can't merge silently.

The scan is deliberately loose about *what* counts as an ADR file: it matches
any file whose name starts with four digits and a separator (``-`` or ``_``),
in any subdirectory and with any extension. A number collision must be caught
even if a file is named slightly off-convention (uppercase slug, ``.rst``) or
tucked into an archive subfolder — a strict ``NNNN-slug.md`` match would let
those slip past and give false confidence.
"""

import re
import sys
from pathlib import Path

ADR_FILE_RE = re.compile(r"^(\d{4})[-_]")


def main() -> int:
    decisions_dir = Path(__file__).parent.parent / "docs" / "decisions"
    if not decisions_dir.is_dir():
        return 0

    seen: dict[str, str] = {}
    errors: list[str] = []
    for path in sorted(decisions_dir.rglob("*")):
        if not path.is_file():
            continue
        match = ADR_FILE_RE.match(path.name)
        if not match:
            continue
        number = match.group(1)
        rel = str(path.relative_to(decisions_dir))
        if number in seen:
            errors.append(
                f"Duplicate ADR number {number}: {rel} collides with "
                f"{seen[number]}. Renumber one of them."
            )
        else:
            seen[number] = rel

    if errors:
        print("ADR numbering check failed:\n")
        for err in errors:
            print(f"  - {err}")
        return 1
    return 0


if __name__ == "__main__":
    sys.exit(main())