"""
db_snapshot.py — WAL-safe snapshot / restore helpers for seismo_relay.db and
the waveform store, backing the /db/snapshot, /db/waveforms/recent.zip and
/db/restore endpoints in server.py. Kept out of server.py so the logic is
unit-testable without HTTP.
"""
from __future__ import annotations
import sqlite3
import zipfile
from pathlib import Path


def snapshot_db(src_path: Path, dest_path: Path) -> Path:
    """WAL-safe copy of a live SQLite DB via the SQLite online backup API.
    Consistent even while the source is being written under WAL, and never
    blocks the source's writers."""
    src = sqlite3.connect(str(src_path))
    dest = sqlite3.connect(str(dest_path))
    try:
        with dest:
            src.backup(dest)
    finally:
        src.close()
        dest.close()
    return Path(dest_path)


def build_recent_waveforms_zip(db, store, n: int, dest_path: Path) -> dict:
    """Zip every on-disk file (event file + .h5/.a5.pkl/.sfm.json siblings) for
    the n most-recent events, arcname '<serial>/<filename>'. Events with no
    resolvable files on disk are skipped. Returns {'events': int, 'files': int}."""
    rows = db.query_events(limit=n, offset=0)
    events = 0
    files = 0
    with zipfile.ZipFile(dest_path, "w", compression=zipfile.ZIP_DEFLATED) as zf:
        for row in rows:
            serial = row.get("serial")
            fn = row.get("blastware_filename")
            if not serial or not fn:
                continue
            serial_dir = store.root / serial
            matched = sorted(serial_dir.glob(f"{fn}*")) if serial_dir.is_dir() else []
            matched = [p for p in matched if p.is_file()]
            if not matched:
                continue
            events += 1
            for p in matched:
                zf.write(p, arcname=f"{serial}/{p.name}")
                files += 1
    return {"events": events, "files": files}