"""Export und Import von Beständen (CSV für Tabellen, JSON für Backups).

Der Import arbeitet ausschließlich additiv: Unbekanntes wird angelegt, Chargen
werden ergänzt – es wird nie etwas gelöscht oder überschrieben.
"""

from __future__ import annotations

import csv
import io
import json
from datetime import date, datetime, timezone

from fastapi import APIRouter, Depends, File, HTTPException, UploadFile, status
from fastapi.responses import Response
from sqlalchemy.orm import Session

from ..database import get_db
from ..deps import get_current_user, require_admin
from ..services.dates import MONTH, clean_precision, normalize_best_before
from ..models import (
    BaseUnit,
    DatePrecision,
    Group,
    Location,
    Lot,
    Movement,
    MovementType,
    Product,
    Unit,
    UnitKind,
    User,
)
from ..services.conversion import BASE_OF_KIND, display_unit_info, find_unit

router = APIRouter(tags=["transfer"])

CSV_FIELDS = [
    "barcode", "name", "marke", "einheit", "packungsgroesse", "gebinde",
    "gruppe", "mindestbestand", "menge", "menge_einheit", "mhd", "lagerort",
]
PACKAGE_TOKENS = {"packung", "package", "pkg", "pack"}


# --------------------------------------------------------------------------
# Export
# --------------------------------------------------------------------------
def _article_unit(product: Product) -> tuple[float, str]:
    """Faktor und Bezeichnung der Artikeleinheit (Gebinde, sonst Produkteinheit)."""
    unit_name, unit_factor = display_unit_info(product)
    if product.package_size and product.package_size > 0:
        return product.package_size, (product.package_label or "Packung")
    return unit_factor, unit_name


@router.get("/export/stock.csv")
def export_stock_csv(
    db: Session = Depends(get_db), _: User = Depends(get_current_user)
) -> Response:
    """Eine Zeile je Charge – direkt in Excel/LibreOffice bearbeitbar."""
    buf = io.StringIO()
    writer = csv.writer(buf, delimiter=";", lineterminator="\r\n")
    writer.writerow(CSV_FIELDS)

    for product in db.query(Product).order_by(Product.name).all():
        unit_name, _ = display_unit_info(product)
        factor, amount_label = _article_unit(product)
        base = [
            product.barcode or "",
            product.name,
            product.brand or "",
            unit_name,
            product.package_size if product.package_size else "",
            product.package_label or "",
            product.group.name if product.group else "",
            product.min_stock if product.min_stock is not None else "",
        ]
        lots = (
            db.query(Lot)
            .filter(Lot.product_id == product.id)
            .order_by(Lot.best_before.is_(None), Lot.best_before)
            .all()
        )
        if not lots:
            # Produkt ohne Bestand: Stammdaten trotzdem mitnehmen.
            writer.writerow(base + ["", "", "", ""])
            continue
        for lot in lots:
            location = db.get(Location, lot.location_id) if lot.location_id else None
            writer.writerow(
                base
                + [
                    round(lot.quantity / factor, 6),
                    amount_label,
                    _format_best_before(lot),
                    location.name if location else "",
                ]
            )

    # BOM, damit Excel die Umlaute korrekt erkennt.
    return Response(
        content="" + buf.getvalue(),
        media_type="text/csv; charset=utf-8",
        headers={"Content-Disposition": 'attachment; filename="bestand.csv"'},
    )


@router.get("/export/backup.json")
def export_backup_json(
    db: Session = Depends(get_db), _: User = Depends(get_current_user)
) -> Response:
    """Vollständiges Backup: Einheiten, Gruppen, Lagerorte, Produkte, Chargen."""
    locations = db.query(Location).order_by(Location.id).all()
    loc_name = {loc.id: loc.name for loc in locations}

    data = {
        "version": 1,
        "exported_at": datetime.now(timezone.utc).isoformat(),
        "units": [
            {"name": u.name, "kind": u.kind.value, "factor": u.factor}
            for u in db.query(Unit).order_by(Unit.id).all()
        ],
        "groups": [
            {
                "name": g.name,
                "min_stock": g.min_stock,
                "min_stock_unit": g.min_stock_unit.name if g.min_stock_unit else None,
            }
            for g in db.query(Group).order_by(Group.id).all()
        ],
        "locations": [
            {"name": loc.name, "parent": loc_name.get(loc.parent_id)}
            for loc in locations
        ],
        "products": [],
    }

    for p in db.query(Product).order_by(Product.id).all():
        unit_name, _ = display_unit_info(p)
        lots = db.query(Lot).filter(Lot.product_id == p.id).all()
        data["products"].append(
            {
                "barcode": p.barcode,
                "name": p.name,
                "brand": p.brand,
                "image_url": p.image_url,
                "unit": unit_name,
                "package_size": p.package_size,
                "package_label": p.package_label,
                "date_precision": p.date_precision,
                "group": p.group.name if p.group else None,
                "min_stock": p.min_stock,
                "min_stock_unit": p.min_stock_unit.name if p.min_stock_unit else None,
                "min_stock_in_packages": bool(p.min_stock_in_packages),
                "lots": [
                    {
                        "quantity": lot.quantity,
                        "best_before": lot.best_before.isoformat() if lot.best_before else None,
                        "best_before_precision": lot.best_before_precision,
                        "location": loc_name.get(lot.location_id),
                    }
                    for lot in lots
                ],
            }
        )

    return Response(
        content=json.dumps(data, ensure_ascii=False, indent=2),
        media_type="application/json; charset=utf-8",
        headers={"Content-Disposition": 'attachment; filename="project-good-backup.json"'},
    )


# --------------------------------------------------------------------------
# Import (nur additiv)
# --------------------------------------------------------------------------
def _num(value) -> float | None:
    if value is None:
        return None
    text = str(value).strip().replace(",", ".")
    if text == "":
        return None
    return float(text)


def _parse_date(value) -> date | None:
    text = (str(value) if value is not None else "").strip()
    if not text:
        return None
    for fmt in ("%Y-%m-%d", "%d.%m.%Y", "%d.%m.%y"):
        try:
            return datetime.strptime(text, fmt).date()
        except ValueError:
            continue
    raise ValueError(f"Datum nicht lesbar: {text}")


def _parse_best_before(value, precision=None) -> tuple[date | None, str]:
    """Liest ein MHD und erkennt dabei, ob nur Monat/Jahr angegeben war.

    Steht die Genauigkeit ausdrücklich in der Datei (JSON-Backup), gilt sie.
    Sonst wird sie aus der Schreibweise abgeleitet – "09/2026" ist eine
    Monatsangabe, "2026-09-07" eine tagesgenaue.
    """
    text = (str(value) if value is not None else "").strip()
    if not text:
        return None, DatePrecision.day.value

    if precision == DatePrecision.month.value:
        return normalize_best_before(_parse_date(text), MONTH), MONTH

    for fmt in ("%m/%Y", "%Y-%m", "%m.%Y"):
        try:
            parsed = datetime.strptime(text, fmt).date()
        except ValueError:
            continue
        return normalize_best_before(parsed, MONTH), MONTH

    return _parse_date(text), DatePrecision.day.value


def _format_best_before(lot: Lot) -> str:
    """Monatsangaben als "09/2026" schreiben, damit die Datei lesbar bleibt."""
    if not lot.best_before:
        return ""
    if lot.best_before_precision == MONTH:
        return lot.best_before.strftime("%m/%Y")
    return lot.best_before.isoformat()


IMPORT_MODES = {"add", "replace_listed", "replace_all"}


def _clear_lots(db: Session, product: Product, user: User) -> None:
    """Entfernt alle Chargen eines Produkts und protokolliert das als Korrektur."""
    lots = db.query(Lot).filter(Lot.product_id == product.id).all()
    total = float(sum(lot.quantity for lot in lots))
    for lot in lots:
        db.delete(lot)
    if total > 0:
        db.add(
            Movement(
                product_id=product.id,
                lot_id=None,
                user_id=user.id,
                type=MovementType.adjust,
                quantity=-total,
                unit_used="base",
                note="Import: Bestand ersetzt",
            )
        )
    db.flush()


def _clear_all_lots(db: Session, user: User) -> None:
    for product in db.query(Product).all():
        _clear_lots(db, product, user)


def _get_or_create_location(db: Session, name: str | None) -> Location | None:
    name = (name or "").strip()
    if not name:
        return None
    loc = db.query(Location).filter(Location.name == name).first()
    if loc is None:
        loc = Location(name=name)
        db.add(loc)
        db.flush()
    return loc


def _get_or_create_group(db: Session, name: str | None) -> Group | None:
    name = (name or "").strip()
    if not name:
        return None
    group = db.query(Group).filter(Group.name == name).first()
    if group is None:
        group = Group(name=name)
        db.add(group)
        db.flush()
    return group


def _get_or_create_product(db: Session, row: dict, created: list[str]) -> Product:
    """Sucht per Barcode, sonst per Name; legt das Produkt sonst an."""
    barcode = (row.get("barcode") or "").strip() or None
    name = (row.get("name") or "").strip()
    if barcode:
        product = db.query(Product).filter(Product.barcode == barcode).first()
        if product:
            return product
    if name:
        product = db.query(Product).filter(Product.name == name).first()
        if product:
            return product
    if not name:
        raise ValueError("Produktname fehlt")

    unit = find_unit(db, (row.get("einheit") or "Stück"))
    if unit is None:
        raise ValueError(f"Unbekannte Einheit: {row.get('einheit')}")
    group = _get_or_create_group(db, row.get("gruppe"))
    product = Product(
        barcode=barcode,
        name=name,
        brand=(row.get("marke") or "").strip() or None,
        base_unit=BASE_OF_KIND[unit.kind],
        display_unit_id=unit.id,
        package_size=_num(row.get("packungsgroesse")),
        package_label=(row.get("gebinde") or "").strip() or None,
        # Nur im JSON-Backup enthalten; aus der CSV kommt hier nichts.
        date_precision=clean_precision((row.get("mhd_genauigkeit") or "").strip() or None),
        group_id=group.id if group else None,
        min_stock=_num(row.get("mindestbestand")),
        source="import",
    )
    db.add(product)
    db.flush()
    created.append(product.name)
    return product


def _quantity_to_base(db: Session, product: Product, amount: float, token: str) -> float:
    """Rechnet eine Importmenge in Basiseinheiten um (kennt auch das Gebinde)."""
    text = (token or "").strip().lower()
    package_label = (product.package_label or "Packung").strip().lower()
    if text in PACKAGE_TOKENS or (text and text == package_label):
        if not product.package_size:
            raise ValueError(f"'{token}': keine Packungsgröße für {product.name} hinterlegt")
        return amount * product.package_size
    if not text:
        return amount  # ohne Angabe: Basiseinheiten
    unit = find_unit(db, text)
    if unit is None:
        raise ValueError(f"Unbekannte Einheit: {token}")
    return amount * unit.factor


def _import_csv(db: Session, content: bytes, user: User, mode: str) -> dict:
    text = content.decode("utf-8-sig", errors="replace")
    sample = text[:2048]
    delimiter = ";" if sample.count(";") >= sample.count(",") else ","
    reader = csv.DictReader(io.StringIO(text), delimiter=delimiter)

    created_products: list[str] = []
    lots_added = 0
    errors: list[str] = []
    cleared: set[int] = set()

    if mode == "replace_all":
        _clear_all_lots(db, user)

    for index, raw in enumerate(reader, start=2):  # Zeile 1 = Kopfzeile
        row = {(k or "").strip().lower(): (v if v is not None else "") for k, v in raw.items()}
        if not any(str(v).strip() for v in row.values()):
            continue
        try:
            product = _get_or_create_product(db, row, created_products)
            # Beim Ersetzen: Bestand des Produkts einmalig leeren, bevor die
            # Zeilen dieser Datei dazukommen.
            if mode == "replace_listed" and product.id not in cleared:
                _clear_lots(db, product, user)
                cleared.add(product.id)
            amount = _num(row.get("menge"))
            if amount is None or amount <= 0:
                continue  # Zeile ohne Bestand: nur Stammdaten
            quantity = _quantity_to_base(db, product, amount, row.get("menge_einheit", ""))
            location = _get_or_create_location(db, row.get("lagerort"))
            best_before, precision = _parse_best_before(row.get("mhd"))
            lot = Lot(
                product_id=product.id,
                quantity=quantity,
                best_before=best_before,
                best_before_precision=precision,
                location_id=location.id if location else None,
            )
            db.add(lot)
            db.flush()
            db.add(
                Movement(
                    product_id=product.id,
                    lot_id=lot.id,
                    user_id=user.id,
                    type=MovementType.in_,
                    quantity=quantity,
                    unit_used=row.get("menge_einheit") or "base",
                    note="Import",
                )
            )
            lots_added += 1
        except Exception as exc:  # eine fehlerhafte Zeile darf den Rest nicht stoppen
            errors.append(f"Zeile {index}: {exc}")

    return {
        "format": "csv",
        "mode": mode,
        "products_created": len(created_products),
        "products_cleared": len(cleared),
        "lots_added": lots_added,
        "errors": errors,
    }


def _import_json(db: Session, content: bytes, user: User, mode: str) -> dict:
    data = json.loads(content.decode("utf-8-sig", errors="replace"))
    created_products: list[str] = []
    lots_added = 0
    units_created = 0
    errors: list[str] = []
    cleared: set[int] = set()

    if mode == "replace_all":
        _clear_all_lots(db, user)

    for entry in data.get("units", []):
        try:
            if db.query(Unit).filter(Unit.name == entry["name"]).first():
                continue
            db.add(
                Unit(
                    name=entry["name"],
                    kind=UnitKind(entry.get("kind", "count")),
                    factor=float(entry.get("factor", 1)),
                    is_builtin=False,
                )
            )
            units_created += 1
        except Exception as exc:
            errors.append(f"Einheit {entry!r}: {exc}")
    db.flush()

    for entry in data.get("groups", []):
        _get_or_create_group(db, entry.get("name"))
    for entry in data.get("locations", []):
        _get_or_create_location(db, entry.get("name"))
    db.flush()
    # Übergeordnete Lagerorte nachziehen
    for entry in data.get("locations", []):
        parent_name = entry.get("parent")
        if not parent_name:
            continue
        child = db.query(Location).filter(Location.name == entry.get("name")).first()
        parent = db.query(Location).filter(Location.name == parent_name).first()
        if child and parent and child.parent_id is None and child.id != parent.id:
            child.parent_id = parent.id

    for entry in data.get("products", []):
        try:
            row = {
                "barcode": entry.get("barcode") or "",
                "name": entry.get("name") or "",
                "marke": entry.get("brand") or "",
                "einheit": entry.get("unit") or "Stück",
                "packungsgroesse": entry.get("package_size") or "",
                "gebinde": entry.get("package_label") or "",
                "mhd_genauigkeit": entry.get("date_precision") or "",
                "gruppe": entry.get("group") or "",
                "mindestbestand": entry.get("min_stock") if entry.get("min_stock") is not None else "",
            }
            product = _get_or_create_product(db, row, created_products)
            if mode == "replace_listed" and product.id not in cleared:
                _clear_lots(db, product, user)
                cleared.add(product.id)
            for lot_entry in entry.get("lots", []):
                quantity = float(lot_entry.get("quantity") or 0)
                if quantity <= 0:
                    continue
                location = _get_or_create_location(db, lot_entry.get("location"))
                best_before, precision = _parse_best_before(
                    lot_entry.get("best_before"), lot_entry.get("best_before_precision")
                )
                lot = Lot(
                    product_id=product.id,
                    quantity=quantity,
                    best_before=best_before,
                    best_before_precision=precision,
                    location_id=location.id if location else None,
                )
                db.add(lot)
                db.flush()
                db.add(
                    Movement(
                        product_id=product.id,
                        lot_id=lot.id,
                        user_id=user.id,
                        type=MovementType.in_,
                        quantity=quantity,
                        unit_used="base",
                        note="Import",
                    )
                )
                lots_added += 1
        except Exception as exc:
            errors.append(f"Produkt {entry.get('name')!r}: {exc}")

    return {
        "format": "json",
        "mode": mode,
        "units_created": units_created,
        "products_created": len(created_products),
        "products_cleared": len(cleared),
        "lots_added": lots_added,
        "errors": errors,
    }


@router.post("/import/stock")
def import_stock(
    mode: str = "add",
    file: UploadFile = File(...),
    db: Session = Depends(get_db),
    user: User = Depends(require_admin),
) -> dict:
    """Importiert CSV oder JSON.

    mode:
      add             – nur ergänzen (Standard, löscht nie etwas)
      replace_listed  – Bestand der in der Datei genannten Produkte ersetzen
      replace_all     – alle Bestände vorher leeren (vollständige Wiederherstellung)
    """
    if mode not in IMPORT_MODES:
        raise HTTPException(status.HTTP_400_BAD_REQUEST, f"Unbekannter Modus: {mode}")

    content = file.file.read()
    if not content:
        raise HTTPException(status.HTTP_400_BAD_REQUEST, "Datei ist leer")

    filename = (file.filename or "").lower()
    stripped = content.lstrip()[:1]
    is_json = filename.endswith(".json") or stripped in (b"{", b"[")

    try:
        result = (
            _import_json(db, content, user, mode)
            if is_json
            else _import_csv(db, content, user, mode)
        )
    except json.JSONDecodeError as exc:
        db.rollback()
        raise HTTPException(status.HTTP_400_BAD_REQUEST, f"JSON nicht lesbar: {exc}") from exc
    except Exception as exc:
        db.rollback()
        raise HTTPException(status.HTTP_400_BAD_REQUEST, f"Import fehlgeschlagen: {exc}") from exc

    db.commit()
    return result