from datetime import date
from decimal import Decimal

from fastapi import APIRouter, Depends, HTTPException
from pydantic import BaseModel, ConfigDict
from sqlalchemy import func, or_, select
from sqlalchemy.orm import Session

from app.auth import require_auth
from app.db import get_session
from app.models.tables import Account, Category, Transaction
from app.parsers.validate import dedup_hash
from app.services.categorize import apply_rules

router = APIRouter(prefix="/api/transactions", tags=["transactions"],
                   dependencies=[Depends(require_auth)])


class TransactionIn(BaseModel):
    account_id: int
    booking_date: date
    value_date: date | None = None
    amount: Decimal
    purpose: str = ""
    counterparty: str = ""
    force: bool = False


class TransactionOut(BaseModel):
    model_config = ConfigDict(from_attributes=True)
    id: int
    account_id: int
    statement_id: int | None = None
    booking_date: date
    value_date: date | None = None
    amount: Decimal
    purpose: str
    counterparty: str
    category_id: int | None = None
    status: str
    dedup_hash: str
    is_duplicate: bool


class TransactionPatch(BaseModel):
    category_id: int | None = None


def _apply_transaction_filters(
    stmt,
    account_id: int | None = None,
    date_from: date | None = None,
    date_to: date | None = None,
    category_id: int | None = None,
    q: str | None = None,
    status: str = "confirmed",
):
    """Wendet die Buchungs-Filter auf ein select()-Statement an. Wird sowohl fuer
    die Liste als auch fuer die dazugehoerige Gesamtanzahl (Pagination) genutzt,
    damit beide garantiert dieselben Ergebnisse zaehlen/zeigen."""
    if status:
        stmt = stmt.where(Transaction.status == status)
    if account_id is not None:
        stmt = stmt.where(Transaction.account_id == account_id)
    if date_from is not None:
        stmt = stmt.where(Transaction.booking_date >= date_from)
    if date_to is not None:
        stmt = stmt.where(Transaction.booking_date <= date_to)
    if category_id is not None:
        stmt = stmt.where(Transaction.category_id == category_id)
    if q:
        like = f"%{q}%"
        stmt = stmt.where(or_(Transaction.purpose.ilike(like),
                              Transaction.counterparty.ilike(like)))
    return stmt


@router.get("", response_model=list[TransactionOut])
def list_transactions(
    account_id: int | None = None,
    date_from: date | None = None,
    date_to: date | None = None,
    category_id: int | None = None,
    q: str | None = None,
    status: str = "confirmed",
    limit: int = 200,
    offset: int = 0,
    session: Session = Depends(get_session),
):
    stmt = _apply_transaction_filters(
        select(Transaction), account_id=account_id, date_from=date_from,
        date_to=date_to, category_id=category_id, q=q, status=status,
    )
    stmt = stmt.order_by(Transaction.booking_date, Transaction.id).offset(offset).limit(limit)
    return [TransactionOut.model_validate(t) for t in session.execute(stmt).scalars()]


def count_transactions(
    account_id: int | None = None,
    date_from: date | None = None,
    date_to: date | None = None,
    category_id: int | None = None,
    q: str | None = None,
    status: str = "confirmed",
    session: Session = Depends(get_session),
) -> int:
    """Gesamtanzahl der Buchungen fuer die gleichen Filter wie list_transactions
    (ohne limit/offset) - Grundlage fuer die Seitenzahl in der GUI-Pagination."""
    stmt = _apply_transaction_filters(
        select(func.count(Transaction.id)), account_id=account_id, date_from=date_from,
        date_to=date_to, category_id=category_id, q=q, status=status,
    )
    return session.execute(stmt).scalar_one()


@router.post("", response_model=TransactionOut, status_code=201)
def create_transaction(data: TransactionIn, session: Session = Depends(get_session)):
    if session.get(Account, data.account_id) is None:
        raise HTTPException(404, "Konto nicht gefunden")
    h = dedup_hash(data.account_id, data.booking_date, data.amount, data.purpose)
    existing = session.execute(
        select(Transaction).where(Transaction.dedup_hash == h)).scalar()
    if existing is not None and not data.force:
        raise HTTPException(409, "Buchung existiert bereits (Duplikat)")
    tx = Transaction(
        account_id=data.account_id,
        booking_date=data.booking_date,
        value_date=data.value_date,
        amount=data.amount,
        purpose=data.purpose,
        counterparty=data.counterparty,
        status="confirmed",
        dedup_hash=h,
        is_duplicate=existing is not None,
    )
    session.add(tx)
    session.commit()
    session.refresh(tx)
    apply_rules(session, [tx])
    session.commit()
    session.refresh(tx)
    return TransactionOut.model_validate(tx)


@router.patch("/{tx_id}", response_model=TransactionOut)
def patch_transaction(tx_id: int, data: TransactionPatch,
                      session: Session = Depends(get_session)):
    tx = session.get(Transaction, tx_id)
    if tx is None:
        raise HTTPException(404, "Buchung nicht gefunden")
    if "category_id" in data.model_fields_set:
        if data.category_id is not None and session.get(Category, data.category_id) is None:
            raise HTTPException(404, "Kategorie nicht gefunden")
        tx.category_id = data.category_id
    session.commit()
    session.refresh(tx)
    return TransactionOut.model_validate(tx)