#!/usr/bin/env python3
"""Consistent, rotated bot.db backups (SPEC-012 OPS-13).

Run from cron on each host. Uses the sqlite3 online-backup API so the
snapshot is consistent even while the bot writes (WAL-safe), gzips it,
and keeps the newest N. Stdlib only.

Usage: python3 backup_db.py <bot.db> <backup-dir> [keep]
"""

import gzip
import os
import shutil
import sqlite3
import sys
import tempfile
import time
from pathlib import Path

DEFAULT_KEEP = 14
BACKUP_GLOB = "bot-*.db.gz"


def snapshot(src: Path, dest_gz: Path) -> None:
    """Write a consistent gzipped snapshot of src to dest_gz (OPS-13)."""
    fd, tmp_path = tempfile.mkstemp(suffix=".db", dir=str(dest_gz.parent))
    os.close(fd)
    tmp = Path(tmp_path)
    try:
        source = sqlite3.connect(str(src))
        try:
            target = sqlite3.connect(str(tmp))
            try:
                source.backup(target)  # atomic, WAL-safe online backup
            finally:
                target.close()
        finally:
            source.close()
        with open(tmp, "rb") as raw, gzip.open(str(dest_gz), "wb") as gz:
            shutil.copyfileobj(raw, gz)
        os.chmod(dest_gz, 0o600)  # conversation data
    finally:
        tmp.unlink(missing_ok=True)


def victims(existing: list, keep: int) -> list:
    """Given backup paths (any order), return the ones to delete, oldest first (OPS-14)."""
    ordered = sorted(existing)  # timestamped names sort chronologically
    return ordered[: max(0, len(ordered) - keep)]


def rotate(backup_dir: Path, keep: int) -> int:
    removed = 0
    for path in victims(list(backup_dir.glob(BACKUP_GLOB)), keep):
        Path(path).unlink(missing_ok=True)
        removed += 1
    return removed


def main() -> int:
    if len(sys.argv) < 3:
        print("usage: backup_db.py <bot.db> <backup-dir> [keep]", file=sys.stderr)
        return 2
    src = Path(sys.argv[1]).expanduser()
    backup_dir = Path(sys.argv[2]).expanduser()
    keep = int(sys.argv[3]) if len(sys.argv) > 3 else DEFAULT_KEEP
    if not src.exists():
        print(f"backup: source {src} missing", file=sys.stderr)
        return 1
    backup_dir.mkdir(parents=True, exist_ok=True)
    stamp = time.strftime("%Y%m%d-%H%M%S", time.gmtime())
    dest = backup_dir / f"bot-{stamp}.db.gz"
    snapshot(src, dest)
    removed = rotate(backup_dir, keep)
    print(f"backup: wrote {dest.name} ({dest.stat().st_size} bytes), rotated {removed} old")
    return 0


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