"""Create safe runtime backups for the AtoCore machine store.

This module is intentionally conservative:

- The SQLite snapshot uses the online ``conn.backup()`` API and is safe to
  call while the database is in use.
- The project registry snapshot is a simple file copy of the canonical
  registry JSON.
- The Chroma snapshot is a *cold* directory copy. To stay safe it must be
  taken while no ingestion is running. The recommended pattern from the API
  layer is to acquire ``exclusive_ingestion()`` for the duration of the
  backup so refreshes and ingestions cannot run concurrently with the copy.

The backup metadata file records what was actually included so restore
tooling does not have to guess.
"""

from __future__ import annotations

import json
import shutil
import sqlite3
from datetime import datetime, UTC
from pathlib import Path

import atocore.config as _config
from atocore.models.database import init_db
from atocore.observability.logger import get_logger

log = get_logger("backup")


def create_runtime_backup(
    timestamp: datetime | None = None,
    include_chroma: bool = False,
) -> dict:
    """Create a hot SQLite backup plus registry/config metadata.

    When ``include_chroma`` is true the Chroma persistence directory is also
    snapshotted as a cold directory copy. The caller is responsible for
    ensuring no ingestion is running concurrently. The HTTP layer enforces
    this by holding ``exclusive_ingestion()`` around the call.
    """
    init_db()
    now = timestamp or datetime.now(UTC)
    stamp = now.strftime("%Y%m%dT%H%M%SZ")

    backup_root = _config.settings.resolved_backup_dir / "snapshots" / stamp
    db_backup_dir = backup_root / "db"
    config_backup_dir = backup_root / "config"
    chroma_backup_dir = backup_root / "chroma"
    metadata_path = backup_root / "backup-metadata.json"

    db_backup_dir.mkdir(parents=True, exist_ok=True)
    config_backup_dir.mkdir(parents=True, exist_ok=True)

    db_snapshot_path = db_backup_dir / _config.settings.db_path.name
    _backup_sqlite_db(_config.settings.db_path, db_snapshot_path)

    registry_snapshot = None
    registry_path = _config.settings.resolved_project_registry_path
    if registry_path.exists():
        registry_snapshot = config_backup_dir / registry_path.name
        registry_snapshot.write_text(
            registry_path.read_text(encoding="utf-8"), encoding="utf-8"
        )

    chroma_snapshot_path = ""
    chroma_files_copied = 0
    chroma_bytes_copied = 0
    if include_chroma:
        source_chroma = _config.settings.chroma_path
        if source_chroma.exists() and source_chroma.is_dir():
            chroma_backup_dir.mkdir(parents=True, exist_ok=True)
            chroma_files_copied, chroma_bytes_copied = _copy_directory_tree(
                source_chroma, chroma_backup_dir
            )
            chroma_snapshot_path = str(chroma_backup_dir)
        else:
            log.info(
                "chroma_snapshot_skipped_missing",
                path=str(source_chroma),
            )

    metadata = {
        "created_at": now.isoformat(),
        "backup_root": str(backup_root),
        "db_snapshot_path": str(db_snapshot_path),
        "db_size_bytes": db_snapshot_path.stat().st_size,
        "registry_snapshot_path": str(registry_snapshot) if registry_snapshot else "",
        "chroma_snapshot_path": chroma_snapshot_path,
        "chroma_snapshot_bytes": chroma_bytes_copied,
        "chroma_snapshot_files": chroma_files_copied,
        "chroma_snapshot_included": include_chroma,
        "vector_store_note": (
            "Chroma snapshot included as cold directory copy."
            if include_chroma and chroma_snapshot_path
            else "Chroma hot backup is not included; rerun with include_chroma=True under exclusive_ingestion()."
        ),
    }
    metadata_path.write_text(
        json.dumps(metadata, indent=2, ensure_ascii=True) + "\n",
        encoding="utf-8",
    )

    log.info(
        "runtime_backup_created",
        backup_root=str(backup_root),
        db_snapshot=str(db_snapshot_path),
        chroma_included=include_chroma,
        chroma_bytes=chroma_bytes_copied,
    )
    return metadata


def list_runtime_backups() -> list[dict]:
    """List all runtime backups under the configured backup directory."""
    snapshots_root = _config.settings.resolved_backup_dir / "snapshots"
    if not snapshots_root.exists() or not snapshots_root.is_dir():
        return []

    entries: list[dict] = []
    for snapshot_dir in sorted(snapshots_root.iterdir()):
        if not snapshot_dir.is_dir():
            continue
        metadata_path = snapshot_dir / "backup-metadata.json"
        entry: dict = {
            "stamp": snapshot_dir.name,
            "path": str(snapshot_dir),
            "has_metadata": metadata_path.exists(),
        }
        if metadata_path.exists():
            try:
                entry["metadata"] = json.loads(metadata_path.read_text(encoding="utf-8"))
            except json.JSONDecodeError:
                entry["metadata"] = None
                entry["metadata_error"] = "invalid_json"
        entries.append(entry)
    return entries


def validate_backup(stamp: str) -> dict:
    """Validate that a previously created backup is structurally usable.

    Checks:
    - the snapshot directory exists
    - the SQLite snapshot is openable and ``PRAGMA integrity_check`` returns ok
    - the registry snapshot, if recorded, parses as JSON
    - the chroma snapshot directory, if recorded, exists
    """
    snapshot_dir = _config.settings.resolved_backup_dir / "snapshots" / stamp
    result: dict = {
        "stamp": stamp,
        "path": str(snapshot_dir),
        "exists": snapshot_dir.exists(),
        "db_ok": False,
        "registry_ok": None,
        "chroma_ok": None,
        "errors": [],
    }
    if not snapshot_dir.exists():
        result["errors"].append("snapshot_directory_missing")
        return result

    metadata_path = snapshot_dir / "backup-metadata.json"
    if not metadata_path.exists():
        result["errors"].append("metadata_missing")
        return result

    try:
        metadata = json.loads(metadata_path.read_text(encoding="utf-8"))
    except json.JSONDecodeError as exc:
        result["errors"].append(f"metadata_invalid_json: {exc}")
        return result
    result["metadata"] = metadata

    db_path = Path(metadata.get("db_snapshot_path", ""))
    if not db_path.exists():
        result["errors"].append("db_snapshot_missing")
    else:
        try:
            with sqlite3.connect(str(db_path)) as conn:
                row = conn.execute("PRAGMA integrity_check").fetchone()
                result["db_ok"] = bool(row and row[0] == "ok")
                if not result["db_ok"]:
                    result["errors"].append(
                        f"db_integrity_check_failed: {row[0] if row else 'no_row'}"
                    )
        except sqlite3.DatabaseError as exc:
            result["errors"].append(f"db_open_failed: {exc}")

    registry_snapshot_path = metadata.get("registry_snapshot_path", "")
    if registry_snapshot_path:
        registry_path = Path(registry_snapshot_path)
        if not registry_path.exists():
            result["registry_ok"] = False
            result["errors"].append("registry_snapshot_missing")
        else:
            try:
                json.loads(registry_path.read_text(encoding="utf-8"))
                result["registry_ok"] = True
            except json.JSONDecodeError as exc:
                result["registry_ok"] = False
                result["errors"].append(f"registry_invalid_json: {exc}")

    chroma_snapshot_path = metadata.get("chroma_snapshot_path", "")
    if chroma_snapshot_path:
        chroma_dir = Path(chroma_snapshot_path)
        if chroma_dir.exists() and chroma_dir.is_dir():
            result["chroma_ok"] = True
        else:
            result["chroma_ok"] = False
            result["errors"].append("chroma_snapshot_missing")

    result["valid"] = not result["errors"]
    return result


def restore_runtime_backup(
    stamp: str,
    *,
    include_chroma: bool | None = None,
    pre_restore_snapshot: bool = True,
    confirm_service_stopped: bool = False,
) -> dict:
    """Restore a previously captured runtime backup.

    CRITICAL: the AtoCore service MUST be stopped before calling this.
    Overwriting a live SQLite database corrupts state and can break
    the running container's open connections. The caller must pass
    ``confirm_service_stopped=True`` as an explicit acknowledgment —
    otherwise this function refuses to run.

    The restore procedure:

    1. Validate the backup via ``validate_backup``; refuse on any error.
    2. (default) Create a pre-restore safety snapshot of the CURRENT
       state so the restore itself is reversible. The snapshot stamp
       is returned in the result for the operator to record.
    3. Remove stale SQLite WAL/SHM sidecar files next to the target db
       before copying — the snapshot is a self-contained main-file
       image from ``conn.backup()``, and leftover WAL/SHM from the old
       live db would desync against the restored main file.
    4. Copy the snapshot db over the target db path.
    5. Restore the project registry file if the snapshot captured one.
    6. Restore the Chroma directory if ``include_chroma`` resolves to
       true. When ``include_chroma is None`` the function defers to
       whether the snapshot captured Chroma (the common case).
    7. Run ``PRAGMA integrity_check`` on the restored db and report
       the result.

    Returns a dict describing what was restored. On refused restore
    (service still running, validation failed) raises ``RuntimeError``.
    """
    if not confirm_service_stopped:
        raise RuntimeError(
            "restore_runtime_backup refuses to run without "
            "confirm_service_stopped=True — stop the AtoCore container "
            "first (e.g. `docker compose down` from deploy/dalidou) "
            "before calling this function"
        )

    validation = validate_backup(stamp)
    if not validation.get("valid"):
        raise RuntimeError(
            f"backup {stamp} failed validation: {validation.get('errors')}"
        )
    metadata = validation.get("metadata") or {}

    pre_snapshot_stamp: str | None = None
    if pre_restore_snapshot:
        pre = create_runtime_backup(include_chroma=False)
        pre_snapshot_stamp = Path(pre["backup_root"]).name

    target_db = _config.settings.db_path
    source_db = Path(metadata.get("db_snapshot_path", ""))
    if not source_db.exists():
        raise RuntimeError(
            f"db snapshot not found at {source_db} — backup "
            f"metadata may be stale"
        )

    # Force sqlite to flush any lingering WAL into the main file and
    # release OS-level file handles on -wal/-shm before we swap the
    # main file. Passing through conn.backup() in the pre-restore
    # snapshot can leave sidecars momentarily locked on Windows;
    # an explicit checkpoint(TRUNCATE) is the reliable way to flush
    # and release. Best-effort: if the target db can't be opened
    # (missing, corrupt), fall through and trust the copy step.
    if target_db.exists():
        try:
            with sqlite3.connect(str(target_db)) as checkpoint_conn:
                checkpoint_conn.execute("PRAGMA wal_checkpoint(TRUNCATE)")
        except sqlite3.DatabaseError as exc:
            log.warning(
                "restore_pre_checkpoint_failed",
                target_db=str(target_db),
                error=str(exc),
            )

    # Remove stale WAL/SHM sidecars from the old live db so SQLite
    # can't read inconsistent state on next open. Tolerant to
    # Windows file-lock races — the subsequent copy replaces the
    # main file anyway, and the integrity check afterward is the
    # actual correctness signal.
    wal_path = target_db.with_name(target_db.name + "-wal")
    shm_path = target_db.with_name(target_db.name + "-shm")
    for stale in (wal_path, shm_path):
        if stale.exists():
            try:
                stale.unlink()
            except OSError as exc:
                log.warning(
                    "restore_sidecar_unlink_failed",
                    path=str(stale),
                    error=str(exc),
                )

    target_db.parent.mkdir(parents=True, exist_ok=True)
    shutil.copy2(source_db, target_db)

    registry_restored = False
    registry_snapshot_path = metadata.get("registry_snapshot_path", "")
    if registry_snapshot_path:
        src_reg = Path(registry_snapshot_path)
        if src_reg.exists():
            dst_reg = _config.settings.resolved_project_registry_path
            dst_reg.parent.mkdir(parents=True, exist_ok=True)
            shutil.copy2(src_reg, dst_reg)
            registry_restored = True

    chroma_snapshot_path = metadata.get("chroma_snapshot_path", "")
    if include_chroma is None:
        include_chroma = bool(chroma_snapshot_path)
    chroma_restored = False
    if include_chroma and chroma_snapshot_path:
        src_chroma = Path(chroma_snapshot_path)
        if src_chroma.exists() and src_chroma.is_dir():
            dst_chroma = _config.settings.chroma_path
            if dst_chroma.exists():
                shutil.rmtree(dst_chroma)
            shutil.copytree(src_chroma, dst_chroma)
            chroma_restored = True

    restored_integrity_ok = False
    integrity_error: str | None = None
    try:
        with sqlite3.connect(str(target_db)) as conn:
            row = conn.execute("PRAGMA integrity_check").fetchone()
            restored_integrity_ok = bool(row and row[0] == "ok")
            if not restored_integrity_ok:
                integrity_error = row[0] if row else "no_row"
    except sqlite3.DatabaseError as exc:
        integrity_error = f"db_open_failed: {exc}"

    result: dict = {
        "stamp": stamp,
        "pre_restore_snapshot": pre_snapshot_stamp,
        "target_db": str(target_db),
        "db_restored": True,
        "registry_restored": registry_restored,
        "chroma_restored": chroma_restored,
        "restored_integrity_ok": restored_integrity_ok,
    }
    if integrity_error:
        result["integrity_error"] = integrity_error

    log.info(
        "runtime_backup_restored",
        stamp=stamp,
        pre_restore_snapshot=pre_snapshot_stamp,
        registry_restored=registry_restored,
        chroma_restored=chroma_restored,
        integrity_ok=restored_integrity_ok,
    )
    return result


def _backup_sqlite_db(source_path: Path, dest_path: Path) -> None:
    source_conn = sqlite3.connect(str(source_path))
    dest_conn = sqlite3.connect(str(dest_path))
    try:
        source_conn.backup(dest_conn)
    finally:
        dest_conn.close()
        source_conn.close()


def _copy_directory_tree(source: Path, dest: Path) -> tuple[int, int]:
    """Copy a directory tree and return (file_count, total_bytes)."""
    if dest.exists():
        shutil.rmtree(dest)
    shutil.copytree(source, dest)

    file_count = 0
    total_bytes = 0
    for path in dest.rglob("*"):
        if path.is_file():
            file_count += 1
            total_bytes += path.stat().st_size
    return file_count, total_bytes


def main() -> None:
    """CLI entry point for the backup module.

    Supports four subcommands:

    - ``create``   run ``create_runtime_backup`` (default if none given)
    - ``list``     list all runtime backup snapshots
    - ``validate`` validate a specific snapshot by stamp
    - ``restore``  restore a specific snapshot by stamp

    The restore subcommand is the one used by the backup/restore drill
    and MUST be run only when the AtoCore service is stopped. It takes
    ``--confirm-service-stopped`` as an explicit acknowledgment.
    """
    import argparse

    parser = argparse.ArgumentParser(
        prog="python -m atocore.ops.backup",
        description="AtoCore runtime backup create/list/validate/restore",
    )
    sub = parser.add_subparsers(dest="command")

    p_create = sub.add_parser("create", help="create a new runtime backup")
    p_create.add_argument(
        "--chroma",
        action="store_true",
        help="also snapshot the Chroma vector store (cold copy)",
    )

    sub.add_parser("list", help="list runtime backup snapshots")

    p_validate = sub.add_parser("validate", help="validate a snapshot by stamp")
    p_validate.add_argument("stamp", help="snapshot stamp (e.g. 20260409T010203Z)")

    p_restore = sub.add_parser(
        "restore",
        help="restore a snapshot by stamp (service must be stopped)",
    )
    p_restore.add_argument("stamp", help="snapshot stamp to restore")
    p_restore.add_argument(
        "--confirm-service-stopped",
        action="store_true",
        help="explicit acknowledgment that the AtoCore container is stopped",
    )
    p_restore.add_argument(
        "--no-pre-snapshot",
        action="store_true",
        help="skip the pre-restore safety snapshot of current state",
    )
    chroma_group = p_restore.add_mutually_exclusive_group()
    chroma_group.add_argument(
        "--chroma",
        dest="include_chroma",
        action="store_true",
        default=None,
        help="force-restore the Chroma snapshot",
    )
    chroma_group.add_argument(
        "--no-chroma",
        dest="include_chroma",
        action="store_false",
        help="skip the Chroma snapshot even if it was captured",
    )

    args = parser.parse_args()
    command = args.command or "create"

    if command == "create":
        include_chroma = getattr(args, "chroma", False)
        result = create_runtime_backup(include_chroma=include_chroma)
    elif command == "list":
        result = {"backups": list_runtime_backups()}
    elif command == "validate":
        result = validate_backup(args.stamp)
    elif command == "restore":
        result = restore_runtime_backup(
            args.stamp,
            include_chroma=args.include_chroma,
            pre_restore_snapshot=not args.no_pre_snapshot,
            confirm_service_stopped=args.confirm_service_stopped,
        )
    else:  # pragma: no cover — argparse guards this
        parser.error(f"unknown command: {command}")

    print(json.dumps(result, indent=2, ensure_ascii=True))


if __name__ == "__main__":
    main()