"""Push/pull stack backups to remote destinations (SFTP, S3-compatible or NFS).

All operations are synchronous (paramiko / boto3 / docker); async callers
should wrap them with ``asyncio.to_thread``. Destination config is a plain
dict parsed from the ``BackupDestination.config`` JSON column.
"""
from __future__ import annotations

import io
import json
import logging
import os
import posixpath
import stat
import tarfile
import tempfile
from typing import Any

from models.backup_destination import BackupDestination

logger = logging.getLogger("stackpilot.backup_dest")


class DestinationError(Exception):
    pass


def parse_config(dest: BackupDestination) -> dict:
    try:
        return json.loads(dest.config or "{}")
    except json.JSONDecodeError:
        return {}


# --------------------------------------------------------------------------- #
# SFTP (paramiko)
# --------------------------------------------------------------------------- #


def _sftp_connect(cfg: dict):
    import paramiko

    host = cfg.get("host")
    if not host:
        raise DestinationError("SFTP host is required")
    port = int(cfg.get("port") or 22)
    username = cfg.get("username")
    transport = paramiko.Transport((host, port))
    try:
        pkey = None
        if cfg.get("private_key"):
            pkey = _load_key(cfg["private_key"])
        transport.connect(username=username, password=cfg.get("password") or None, pkey=pkey)
    except Exception as exc:  # noqa: BLE001
        transport.close()
        raise DestinationError(f"SFTP connection failed: {exc}") from exc
    return paramiko.SFTPClient.from_transport(transport), transport


def _load_key(key_str: str):
    import paramiko

    for cls in (paramiko.Ed25519Key, paramiko.ECDSAKey, paramiko.RSAKey):
        try:
            return cls.from_private_key(io.StringIO(key_str))
        except Exception:  # noqa: BLE001
            continue
    raise DestinationError("Could not parse SFTP private key")


def _sftp_makedirs(sftp, path: str) -> None:
    if not path or path in (".", "/"):
        return
    parts = path.strip("/").split("/")
    cur = "/" if path.startswith("/") else ""
    for p in parts:
        cur = posixpath.join(cur, p) if cur else p
        try:
            sftp.stat(cur)
        except IOError:
            sftp.mkdir(cur)


def _sftp_upload(cfg: dict, local_path: str, filename: str) -> str:
    sftp, transport = _sftp_connect(cfg)
    try:
        base = cfg.get("path") or "."
        if base not in (".", ""):
            _sftp_makedirs(sftp, base)
        remote = posixpath.join(base, filename) if base not in (".", "") else filename
        sftp.put(local_path, remote)
        return remote
    finally:
        sftp.close()
        transport.close()


def _sftp_list(cfg: dict) -> list[dict]:
    sftp, transport = _sftp_connect(cfg)
    try:
        base = cfg.get("path") or "."
        out = []
        try:
            entries = sftp.listdir_attr(base)
        except IOError:
            return []
        for e in entries:
            if stat.S_ISDIR(e.st_mode):
                continue
            if not e.filename.endswith(".tar.gz"):
                continue
            out.append({"name": e.filename, "size": e.st_size, "modified": e.st_mtime})
        return sorted(out, key=lambda x: x["modified"] or 0, reverse=True)
    finally:
        sftp.close()
        transport.close()


def _sftp_download(cfg: dict, name: str, local_path: str) -> None:
    sftp, transport = _sftp_connect(cfg)
    try:
        base = cfg.get("path") or "."
        remote = posixpath.join(base, name) if base not in (".", "") else name
        sftp.get(remote, local_path)
    finally:
        sftp.close()
        transport.close()


def _sftp_delete(cfg: dict, name: str) -> None:
    sftp, transport = _sftp_connect(cfg)
    try:
        base = cfg.get("path") or "."
        remote = posixpath.join(base, name) if base not in (".", "") else name
        sftp.remove(remote)
    finally:
        sftp.close()
        transport.close()


# --------------------------------------------------------------------------- #
# S3-compatible (boto3)
# --------------------------------------------------------------------------- #


def _s3_client(cfg: dict):
    import boto3

    bucket = cfg.get("bucket")
    if not bucket:
        raise DestinationError("S3 bucket is required")
    return boto3.client(
        "s3",
        endpoint_url=cfg.get("endpoint_url") or None,
        region_name=cfg.get("region") or None,
        aws_access_key_id=cfg.get("access_key") or None,
        aws_secret_access_key=cfg.get("secret_key") or None,
    )


def _s3_key(cfg: dict, filename: str) -> str:
    prefix = (cfg.get("prefix") or "").strip("/")
    return f"{prefix}/{filename}" if prefix else filename


def _s3_upload(cfg: dict, local_path: str, filename: str) -> str:
    client = _s3_client(cfg)
    key = _s3_key(cfg, filename)
    try:
        client.upload_file(local_path, cfg["bucket"], key)
    except Exception as exc:  # noqa: BLE001
        raise DestinationError(f"S3 upload failed: {exc}") from exc
    return key


def _s3_list(cfg: dict) -> list[dict]:
    client = _s3_client(cfg)
    prefix = (cfg.get("prefix") or "").strip("/")
    kwargs: dict[str, Any] = {"Bucket": cfg["bucket"]}
    if prefix:
        kwargs["Prefix"] = prefix + "/"
    try:
        resp = client.list_objects_v2(**kwargs)
    except Exception as exc:  # noqa: BLE001
        raise DestinationError(f"S3 list failed: {exc}") from exc
    out = []
    for obj in resp.get("Contents", []):
        name = obj["Key"].split("/")[-1]
        if not name.endswith(".tar.gz"):
            continue
        out.append(
            {
                "name": name,
                "size": obj.get("Size", 0),
                "modified": obj["LastModified"].timestamp() if obj.get("LastModified") else None,
            }
        )
    return sorted(out, key=lambda x: x["modified"] or 0, reverse=True)


def _s3_download(cfg: dict, name: str, local_path: str) -> None:
    client = _s3_client(cfg)
    try:
        client.download_file(cfg["bucket"], _s3_key(cfg, name), local_path)
    except Exception as exc:  # noqa: BLE001
        raise DestinationError(f"S3 download failed: {exc}") from exc


def _s3_delete(cfg: dict, name: str) -> None:
    client = _s3_client(cfg)
    client.delete_object(Bucket=cfg["bucket"], Key=_s3_key(cfg, name))


# --------------------------------------------------------------------------- #
# NFS — the Docker daemon mounts the export as a named volume; file I/O runs
# through a throwaway helper container (same pattern as volume backups), so
# the backend itself needs no mount privileges.
# --------------------------------------------------------------------------- #

_NFS_VOLUME_PREFIX = "stackpilot-nfs-dest-"


def _nfs_check_name(name: str) -> None:
    if not name or "/" in name or name in (".", "..") or name.startswith(".."):
        raise DestinationError(f"Invalid backup file name '{name}'")


def _nfs_subdir(cfg: dict) -> str:
    """Sanitized relative directory inside the export ('' = export root).

    Parts are restricted to a safe charset because the path is interpolated
    into helper-container shell commands.
    """
    import re

    raw = (cfg.get("subdir") or "").strip().strip("/")
    if not raw:
        return ""
    parts = [p for p in raw.split("/") if p]
    for p in parts:
        if p == ".." or not re.fullmatch(r"[A-Za-z0-9._-]+", p):
            raise DestinationError(
                "Subdirectory may only contain letters, digits, '.', '_' and '-'"
            )
    return "/".join(parts)


def _nfs_volume(dest: BackupDestination, cfg: dict) -> str:
    """Ensure the named volume describing this NFS mount exists; recreate it
    when the destination's server/path/options changed (opts are immutable)."""
    from docker_client import DockerError, get_client, safe_call

    server = (cfg.get("server") or "").strip()
    path = (cfg.get("path") or "").strip()
    if not server:
        raise DestinationError("NFS server is required")
    if not path.startswith("/"):
        raise DestinationError("NFS export path must be absolute (start with /)")
    options = (cfg.get("options") or "rw").strip().strip(",")
    driver_opts = {"type": "nfs", "o": f"addr={server},{options}", "device": f":{path}"}

    name = f"{_NFS_VOLUME_PREFIX}{dest.id}"
    client = get_client()
    try:
        vol = safe_call(client.volumes.get, name)
        if (vol.attrs.get("Options") or {}) != driver_opts:
            safe_call(vol.remove)
            raise DockerError("recreate", "options changed")
    except DockerError:
        safe_call(
            client.volumes.create,
            name=name,
            driver="local",
            driver_opts=driver_opts,
            labels={"stackpilot.nfs-destination": str(dest.id)},
        )
    return name


def _nfs_target(cfg: dict) -> str:
    sub = _nfs_subdir(cfg)
    return f"/nfs/{sub}" if sub else "/nfs"


def _nfs_run(volume: str, command: list[str]) -> str:
    """Run a helper container with the NFS volume at /nfs; return stdout."""
    import docker.errors

    from config import settings
    from docker_client import DockerError, get_client
    from services.stack_assets_service import ensure_helper_image

    client = get_client()
    ensure_helper_image(client)
    try:
        out = client.containers.run(
            settings.BACKUP_HELPER_IMAGE,
            command,
            volumes={volume: {"bind": "/nfs", "mode": "rw"}},
            remove=True,
        )
        return (out or b"").decode("utf-8", "replace")
    except docker.errors.ContainerError as exc:
        stderr = (exc.stderr or b"").decode("utf-8", "replace").strip()
        raise DestinationError(f"NFS operation failed: {stderr or exc}") from exc
    except (docker.errors.APIError, DockerError) as exc:
        # Mount errors surface here (unreachable server, bad export, ...).
        raise DestinationError(f"NFS mount failed: {exc}") from exc


def _nfs_helper(volume: str):
    """A created (not started) helper container for archive I/O on /nfs."""
    import docker.errors

    from config import settings
    from docker_client import DockerError, get_client, safe_call
    from services.stack_assets_service import ensure_helper_image

    client = get_client()
    ensure_helper_image(client)
    try:
        return safe_call(
            client.containers.create,
            settings.BACKUP_HELPER_IMAGE,
            command="true",
            volumes={volume: {"bind": "/nfs", "mode": "rw"}},
        )
    except (docker.errors.APIError, DockerError) as exc:
        raise DestinationError(f"NFS mount failed: {exc}") from exc


def _nfs_upload(dest: BackupDestination, cfg: dict, local_path: str, filename: str) -> str:
    import docker.errors

    _nfs_check_name(filename)
    volume = _nfs_volume(dest, cfg)
    target = _nfs_target(cfg)
    # Creates the subdir if needed AND fails early with a clear mount error.
    _nfs_run(volume, ["mkdir", "-p", target])
    container = _nfs_helper(volume)
    try:
        with tempfile.TemporaryFile() as tmp:
            with tarfile.open(fileobj=tmp, mode="w") as tar:
                tar.add(local_path, arcname=filename)
            tmp.seek(0)
            container.put_archive(target, tmp)
    except docker.errors.APIError as exc:
        raise DestinationError(f"NFS upload failed: {exc}") from exc
    finally:
        try:
            container.remove(force=True)
        except Exception:  # noqa: BLE001
            pass
    sub = _nfs_subdir(cfg)
    return posixpath.join(sub, filename) if sub else filename


def _nfs_list(dest: BackupDestination, cfg: dict) -> list[dict]:
    volume = _nfs_volume(dest, cfg)
    target = _nfs_target(cfg)
    out = _nfs_run(
        volume,
        ["sh", "-c", f"cd {target} 2>/dev/null && stat -c '%n|%s|%Y' *.tar.gz 2>/dev/null; true"],
    )
    entries = []
    for line in out.splitlines():
        parts = line.strip().split("|")
        if len(parts) != 3 or parts[0] == "*.tar.gz":
            continue
        try:
            entries.append({"name": parts[0], "size": int(parts[1]), "modified": int(parts[2])})
        except ValueError:
            continue
    return sorted(entries, key=lambda x: x["modified"] or 0, reverse=True)


def _nfs_download(dest: BackupDestination, cfg: dict, name: str, local_path: str) -> None:
    import docker.errors

    _nfs_check_name(name)
    volume = _nfs_volume(dest, cfg)
    target = _nfs_target(cfg)
    container = _nfs_helper(volume)
    try:
        bits, _ = container.get_archive(f"{target}/{name}")
        with tempfile.TemporaryFile() as tmp:
            for chunk in bits:
                tmp.write(chunk)
            tmp.seek(0)
            with tarfile.open(fileobj=tmp) as tar:
                member = next((m for m in tar.getmembers() if m.isreg()), None)
                fh = tar.extractfile(member) if member else None
                if fh is None:
                    raise DestinationError(f"'{name}' not found on NFS destination")
                with open(local_path, "wb") as out:
                    while chunk := fh.read(1024 * 1024):
                        out.write(chunk)
    except docker.errors.APIError as exc:
        raise DestinationError(f"NFS download failed (does '{name}' exist?): {exc}") from exc
    finally:
        try:
            container.remove(force=True)
        except Exception:  # noqa: BLE001
            pass


def _nfs_delete(dest: BackupDestination, cfg: dict, name: str) -> None:
    _nfs_check_name(name)
    volume = _nfs_volume(dest, cfg)
    _nfs_run(volume, ["rm", "-f", f"{_nfs_target(cfg)}/{name}"])


def _nfs_test(dest: BackupDestination, cfg: dict) -> bool:
    volume = _nfs_volume(dest, cfg)
    target = _nfs_target(cfg)
    _nfs_run(
        volume,
        ["sh", "-c", f"mkdir -p {target} && touch {target}/.stackpilot-test && rm -f {target}/.stackpilot-test"],
    )
    return True


# --------------------------------------------------------------------------- #
# Dispatch
# --------------------------------------------------------------------------- #


def upload(dest: BackupDestination, local_path: str, filename: str) -> str:
    cfg = parse_config(dest)
    if dest.type == "sftp":
        return _sftp_upload(cfg, local_path, filename)
    if dest.type == "s3":
        return _s3_upload(cfg, local_path, filename)
    if dest.type == "nfs":
        return _nfs_upload(dest, cfg, local_path, filename)
    raise DestinationError(f"Unknown destination type '{dest.type}'")


def list_backups(dest: BackupDestination) -> list[dict]:
    cfg = parse_config(dest)
    if dest.type == "sftp":
        return _sftp_list(cfg)
    if dest.type == "s3":
        return _s3_list(cfg)
    if dest.type == "nfs":
        return _nfs_list(dest, cfg)
    raise DestinationError(f"Unknown destination type '{dest.type}'")


def download(dest: BackupDestination, name: str, local_path: str) -> None:
    cfg = parse_config(dest)
    if dest.type == "sftp":
        _sftp_download(cfg, name, local_path)
    elif dest.type == "s3":
        _s3_download(cfg, name, local_path)
    elif dest.type == "nfs":
        _nfs_download(dest, cfg, name, local_path)
    else:
        raise DestinationError(f"Unknown destination type '{dest.type}'")


def delete(dest: BackupDestination, name: str) -> None:
    cfg = parse_config(dest)
    if dest.type == "sftp":
        _sftp_delete(cfg, name)
    elif dest.type == "s3":
        _s3_delete(cfg, name)
    elif dest.type == "nfs":
        _nfs_delete(dest, cfg, name)
    else:
        raise DestinationError(f"Unknown destination type '{dest.type}'")


def test(dest: BackupDestination) -> bool:
    """Connectivity check — validates reachability, auth and write access."""
    if dest.type == "nfs":
        return _nfs_test(dest, parse_config(dest))
    list_backups(dest)
    return True