import json
import logging
import os
import re
import shutil
import subprocess
import tarfile
import tempfile
from datetime import datetime, timezone
from pathlib import Path
from urllib.parse import urlparse

from app.core.config import settings

logger = logging.getLogger(__name__)

BACKUP_NAME_PATTERN = re.compile(r"^grade-archive_\d{8}_\d{6}\.tar\.gz$")
APP_VERSION = "1.0.0"


def backup_dir() -> Path:
    path = Path(settings.BACKUP_DIR)
    path.mkdir(parents=True, exist_ok=True)
    return path


def _pg_params() -> dict[str, str]:
    parsed = urlparse(settings.DATABASE_URL)
    return {
        "host": parsed.hostname or "127.0.0.1",
        "port": str(parsed.port or 5432),
        "user": parsed.username or "postgres",
        "password": parsed.password or "",
        "dbname": parsed.path.lstrip("/") or "student_archive",
    }


def _dump_database(dest: Path) -> None:
    pg = _pg_params()
    env = {**os.environ, "PGPASSWORD": pg["password"]}
    cmd = [
        "pg_dump",
        "-h",
        pg["host"],
        "-p",
        pg["port"],
        "-U",
        pg["user"],
        "-d",
        pg["dbname"],
        "--no-owner",
        "--no-privileges",
        "--clean",
        "--if-exists",
    ]
    with dest.open("w", encoding="utf-8") as out:
        subprocess.run(cmd, check=True, env=env, stdout=out)


def create_backup() -> Path:
    timestamp = datetime.now().strftime("%Y%m%d_%H%M%S")
    archive_path = backup_dir() / f"grade-archive_{timestamp}.tar.gz"
    work = Path(tempfile.mkdtemp(prefix="grade-archive-backup-"))
    try:
        db_file = work / "database.sql"
        _dump_database(db_file)
        manifest = {
            "app": "secondary-school-grade-archive",
            "version": APP_VERSION,
            "created_at": datetime.now(timezone.utc).isoformat(),
            "database": pg["dbname"] if (pg := _pg_params()) else "student_archive",
        }
        manifest_file = work / "manifest.json"
        manifest_file.write_text(json.dumps(manifest, ensure_ascii=False, indent=2), encoding="utf-8")

        uploads_dir = Path(settings.UPLOAD_DIR)
        with tarfile.open(archive_path, "w:gz") as tar:
            tar.add(db_file, arcname="database.sql")
            tar.add(manifest_file, arcname="manifest.json")
            if uploads_dir.is_dir():
                tar.add(uploads_dir, arcname="uploads")

        cleanup_old_backups()
        logger.info("Backup created: %s", archive_path)
        return archive_path
    finally:
        shutil.rmtree(work, ignore_errors=True)


def cleanup_old_backups() -> None:
    if settings.BACKUP_RETENTION_DAYS <= 0:
        return
    cutoff = datetime.now().timestamp() - settings.BACKUP_RETENTION_DAYS * 86400
    for item in backup_dir().glob("grade-archive_*.tar.gz"):
        if item.stat().st_mtime < cutoff:
            item.unlink(missing_ok=True)


def list_backups() -> list[dict]:
    items: list[dict] = []
    for path in sorted(backup_dir().glob("grade-archive_*.tar.gz"), reverse=True):
        stat = path.stat()
        items.append(
            {
                "filename": path.name,
                "size_bytes": stat.st_size,
                "created_at": datetime.fromtimestamp(stat.st_mtime, tz=timezone.utc),
            }
        )
    return items


def resolve_backup_file(filename: str) -> Path:
    if not BACKUP_NAME_PATTERN.match(filename):
        raise ValueError("无效的备份文件名")
    path = backup_dir() / filename
    if not path.is_file():
        raise FileNotFoundError(filename)
    return path


def restore_backup(archive_path: Path) -> None:
    work = Path(tempfile.mkdtemp(prefix="grade-archive-restore-"))
    try:
        with tarfile.open(archive_path, "r:gz") as tar:
            tar.extractall(work)

        db_file = work / "database.sql"
        if not db_file.is_file():
            raise ValueError("备份包缺少 database.sql")

        pg = _pg_params()
        env = {**os.environ, "PGPASSWORD": pg["password"]}

        subprocess.run(
            [
                "psql",
                "-h",
                pg["host"],
                "-p",
                pg["port"],
                "-U",
                pg["user"],
                "-d",
                pg["dbname"],
                "-v",
                "ON_ERROR_STOP=1",
                "-f",
                str(db_file),
            ],
            check=True,
            env=env,
        )

        uploads_src = work / "uploads"
        uploads_dest = Path(settings.UPLOAD_DIR)
        if uploads_src.is_dir():
            if uploads_dest.exists():
                shutil.rmtree(uploads_dest)
            shutil.copytree(uploads_src, uploads_dest)
        else:
            uploads_dest.mkdir(parents=True, exist_ok=True)

        logger.info("Backup restored from %s", archive_path)
    finally:
        shutil.rmtree(work, ignore_errors=True)