"""
Account Service — balance calculated from transactions.
Balance = sum of income - sum of expenses for an account,
plus any incoming transfers minus outgoing transfers.
"""

from decimal import Decimal
from sqlalchemy import func, case, or_, and_
from app.extensions import db
from app.models.account import Account
from app.models.transaction import Transaction


def calc_balance(account_id):
    """
    Recalculate and persist the balance for a given account.
    Uses a single aggregation query with CASE expressions instead of 4 queries.
    """
    row = db.session.query(
        func.coalesce(func.sum(case(
            (and_(Transaction.account_id == account_id,
                  Transaction.transaction_type == 'income'), Transaction.amount),
            else_=0
        )), 0),
        func.coalesce(func.sum(case(
            (and_(Transaction.account_id == account_id,
                  Transaction.transaction_type == 'expense'), Transaction.amount),
            else_=0
        )), 0),
        func.coalesce(func.sum(case(
            (and_(Transaction.account_id == account_id,
                  Transaction.transaction_type == 'transfer'), Transaction.amount),
            else_=0
        )), 0),
        func.coalesce(func.sum(case(
            (and_(Transaction.to_account_id == account_id,
                  Transaction.transaction_type == 'transfer'), Transaction.amount),
            else_=0
        )), 0),
    ).filter(
        or_(Transaction.account_id == account_id,
            Transaction.to_account_id == account_id)
    ).one()

    income, expense, transfer_out, transfer_in = (Decimal(str(v)) for v in row)
    balance = income - expense - transfer_out + transfer_in

    account = db.session.get(Account, account_id)
    if account:
        account.balance = balance
        db.session.commit()
    return balance


def recalc_all():
    """Recalculate balances for all accounts."""
    for account in Account.query.filter_by(is_active=True).all():
        calc_balance(account.id)


def get_total_assets():
    """Sum of all positive-balance accounts (non-credit)."""
    result = db.session.query(
        func.coalesce(func.sum(Account.balance), 0)
    ).filter(
        Account.is_active == True,
        Account.account_type != 'credit_card',
        Account.balance > 0
    ).scalar()
    return float(result)


def get_total_liabilities():
    """Sum of credit card balances (negative = owed)."""
    result = db.session.query(
        func.coalesce(func.sum(Account.balance), 0)
    ).filter(
        Account.is_active == True,
        Account.account_type == 'credit_card',
        Account.balance < 0
    ).scalar()
    return abs(float(result))