aurum/backend/app/api/routes/transactions.py

from datetime import date as date_
from typing import Literal

from fastapi import APIRouter, Depends, HTTPException, Query
from sqlalchemy import func, select
from sqlalchemy.ext.asyncio import AsyncSession
from sqlalchemy.orm import selectinload

from app.api.deps import get_session
from app.models.category import Category
from app.models.enums import CategoryKind, TransactionType
from app.models.transaction import Transaction
from app.schemas.transaction import TransactionCreate, TransactionPage, TransactionRead, TransactionUpdate

router = APIRouter(prefix="/transactions", tags=["transactions"])

_EAGER = (selectinload(Transaction.account), selectinload(Transaction.category))

_TYPE_TO_CATEGORY_KIND = {
    TransactionType.INCOME: CategoryKind.INCOME,
    TransactionType.EXPENSE: CategoryKind.EXPENSE,
}


async def _ensure_category_matches_type(
    session: AsyncSession, category_id: int | None, transaction_type: TransactionType
) -> None:
    """A category picked for an income transaction must itself be an income
    category (and likewise for expense) — otherwise the dashboard's spending
    breakdown, which only joins EXPENSE-typed rows, would silently misclassify
    the entry."""
    if category_id is None:
        return
    expected_kind = _TYPE_TO_CATEGORY_KIND.get(transaction_type)
    category = await session.get(Category, category_id)
    if category is None:
        raise HTTPException(status_code=400, detail="Category not found")
    if expected_kind is not None and category.kind != expected_kind:
        raise HTTPException(
            status_code=400,
            detail=f"Category '{category.name}' is a {category.kind.value} category and cannot be used for a {transaction_type.value} transaction",
        )


@router.get("", response_model=TransactionPage)
async def list_transactions(
    year: int | None = Query(default=None, ge=2000, le=2100),
    month: int | None = Query(default=None, ge=1, le=12),
    start_date: date_ | None = Query(default=None),
    end_date: date_ | None = Query(default=None),
    account_id: int | None = None,
    category_id: int | None = None,
    type: TransactionType | None = None,
    sort: Literal["date_desc", "amount_desc", "amount_asc"] = Query(default="date_desc"),
    page: int = Query(default=1, ge=1),
    page_size: int = Query(default=20, ge=1, le=200),
    session: AsyncSession = Depends(get_session),
) -> TransactionPage:
    stmt = select(Transaction).options(*_EAGER)
    count_stmt = select(func.count()).select_from(Transaction)

    if year is not None:
        stmt = stmt.where(func.extract("year", Transaction.date) == year)
        count_stmt = count_stmt.where(func.extract("year", Transaction.date) == year)
    if month is not None:
        stmt = stmt.where(func.extract("month", Transaction.date) == month)
        count_stmt = count_stmt.where(func.extract("month", Transaction.date) == month)
    if start_date is not None:
        stmt = stmt.where(Transaction.date >= start_date)
        count_stmt = count_stmt.where(Transaction.date >= start_date)
    if end_date is not None:
        stmt = stmt.where(Transaction.date <= end_date)
        count_stmt = count_stmt.where(Transaction.date <= end_date)
    if account_id is not None:
        stmt = stmt.where(Transaction.account_id == account_id)
        count_stmt = count_stmt.where(Transaction.account_id == account_id)
    if category_id is not None:
        stmt = stmt.where(Transaction.category_id == category_id)
        count_stmt = count_stmt.where(Transaction.category_id == category_id)
    if type is not None:
        stmt = stmt.where(Transaction.type == type)
        count_stmt = count_stmt.where(Transaction.type == type)

    total = (await session.execute(count_stmt)).scalar_one()

    # id as a tiebreaker keeps pagination stable when many rows share a date/amount.
    if sort == "amount_desc":
        stmt = stmt.order_by(Transaction.amount.desc(), Transaction.id.desc())
    elif sort == "amount_asc":
        stmt = stmt.order_by(Transaction.amount.asc(), Transaction.id.desc())
    else:
        stmt = stmt.order_by(Transaction.date.desc(), Transaction.id.desc())
    stmt = stmt.offset((page - 1) * page_size).limit(page_size)

    result = await session.execute(stmt)
    items = list(result.scalars().all())

    return TransactionPage(items=items, total=total, page=page, page_size=page_size)


@router.get("/years", response_model=list[int])
async def list_transaction_years(session: AsyncSession = Depends(get_session)) -> list[int]:
    """Full range of years to offer in the year picker — from the earliest
    transaction through the current year, so a gap year with no activity
    still shows up (as zero) instead of silently disappearing from the UI."""
    bounds = await session.execute(select(func.min(Transaction.date), func.max(Transaction.date)))
    min_date, max_date = bounds.one()
    current_year = date_.today().year
    if min_date is None:
        return [current_year]
    return list(range(min_date.year, max(max_date.year, current_year) + 1))


@router.post("", response_model=TransactionRead, status_code=201)
async def create_transaction(payload: TransactionCreate, session: AsyncSession = Depends(get_session)) -> Transaction:
    await _ensure_category_matches_type(session, payload.category_id, payload.type)
    transaction = Transaction(**payload.model_dump())
    session.add(transaction)
    await session.commit()
    refreshed = await session.execute(
        select(Transaction).options(*_EAGER).where(Transaction.id == transaction.id)
    )
    return refreshed.scalar_one()


@router.patch("/{transaction_id}", response_model=TransactionRead)
async def update_transaction(
    transaction_id: int, payload: TransactionUpdate, session: AsyncSession = Depends(get_session)
) -> Transaction:
    transaction = await session.get(Transaction, transaction_id)
    if transaction is None:
        raise HTTPException(status_code=404, detail="Transaction not found")
    updates = payload.model_dump(exclude_unset=True)
    effective_type = updates.get("type", transaction.type)
    effective_category_id = updates.get("category_id", transaction.category_id)
    await _ensure_category_matches_type(session, effective_category_id, effective_type)
    for field, value in updates.items():
        setattr(transaction, field, value)
    await session.commit()
    refreshed = await session.execute(
        select(Transaction).options(*_EAGER).where(Transaction.id == transaction_id)
    )
    return refreshed.scalar_one()


@router.delete("/{transaction_id}", status_code=204)
async def delete_transaction(transaction_id: int, session: AsyncSession = Depends(get_session)) -> None:
    transaction = await session.get(Transaction, transaction_id)
    if transaction is None:
        raise HTTPException(status_code=404, detail="Transaction not found")
    await session.delete(transaction)
    await session.commit()