import uuid
from datetime import date, datetime, timezone
from decimal import Decimal

from dateutil.relativedelta import relativedelta
from sqlalchemy import and_, func, select, text
from sqlalchemy.ext.asyncio import AsyncSession

from app.db.models.account import Account
from app.db.models.budget import Budget
from app.db.models.category import Category
from app.db.models.net_worth_snapshot import NetWorthSnapshot
from app.db.models.transaction import Transaction
from app.schemas.report import (
    BudgetVsActualItem,
    BudgetVsActualReport,
    CashFlowPoint,
    CashFlowReport,
    CategoryBreakdownItem,
    CategoryBreakdownReport,
    IncomeExpensePoint,
    IncomeExpenseReport,
    NetWorthPoint,
    NetWorthReport,
    SpendingTrendPoint,
    SpendingTrendsReport,
)

LIABILITY_TYPES = {"credit_card", "loan", "mortgage"}


async def _current_net_worth(db: AsyncSession, user_id: uuid.UUID) -> tuple[Decimal, Decimal]:
    result = await db.execute(
        select(Account).where(
            Account.user_id == user_id,
            Account.include_in_net_worth == True,  # noqa: E712
            Account.is_active == True,  # noqa: E712
            Account.deleted_at.is_(None),
        )
    )
    accounts = result.scalars().all()
    assets = Decimal("0")
    liabilities = Decimal("0")
    for acc in accounts:
        bal = acc.current_balance or Decimal("0")
        if acc.type in LIABILITY_TYPES:
            liabilities += bal
        else:
            assets += bal
    return assets, liabilities


async def get_net_worth_report(
    db: AsyncSession, user_id: uuid.UUID, base_currency: str, months: int = 12
) -> NetWorthReport:
    cutoff = date.today() - relativedelta(months=months)
    result = await db.execute(
        select(NetWorthSnapshot)
        .where(NetWorthSnapshot.user_id == user_id, NetWorthSnapshot.date >= cutoff)
        .order_by(NetWorthSnapshot.date.asc())
    )
    snapshots = result.scalars().all()

    points = [
        NetWorthPoint(
            date=s.date,
            total_assets=s.total_assets,
            total_liabilities=s.total_liabilities,
            net_worth=s.net_worth,
            base_currency=s.base_currency,
        )
        for s in snapshots
    ]

    assets, liabilities = await _current_net_worth(db, user_id)
    current_nw = assets - liabilities

    change_30d = Decimal("0")
    change_30d_pct = Decimal("0")
    if points:
        past_nw = points[0].net_worth
        change_30d = current_nw - past_nw
        if past_nw != 0:
            change_30d_pct = (change_30d / abs(past_nw) * 100).quantize(Decimal("0.01"))

    return NetWorthReport(
        points=points,
        current_net_worth=current_nw,
        change_30d=change_30d,
        change_30d_pct=change_30d_pct,
        base_currency=base_currency,
    )


async def get_income_expense_report(
    db: AsyncSession, user_id: uuid.UUID, months: int = 12
) -> IncomeExpenseReport:
    cutoff = (date.today().replace(day=1) - relativedelta(months=months - 1))
    result = await db.execute(
        text("""
            SELECT
                TO_CHAR(date, 'YYYY-MM') AS month,
                SUM(CASE WHEN type = 'income' THEN amount ELSE 0 END) AS income,
                SUM(CASE WHEN type = 'expense' THEN ABS(amount) ELSE 0 END) AS expenses
            FROM transactions
            WHERE user_id = CAST(:uid AS uuid)
              AND status != 'void'
              AND deleted_at IS NULL
              AND date >= :cutoff
            GROUP BY TO_CHAR(date, 'YYYY-MM')
            ORDER BY month ASC
        """).bindparams(uid=str(user_id), cutoff=cutoff)
    )
    rows = result.fetchall()

    points = []
    total_income = Decimal("0")
    total_expenses = Decimal("0")
    for row in rows:
        inc = Decimal(str(row.income or 0))
        exp = Decimal(str(row.expenses or 0))
        points.append(IncomeExpensePoint(month=row.month, income=inc, expenses=exp, net=inc - exp))
        total_income += inc
        total_expenses += exp

    n = len(points) or 1
    return IncomeExpenseReport(
        points=points,
        total_income=total_income,
        total_expenses=total_expenses,
        avg_monthly_income=(total_income / n).quantize(Decimal("0.01")),
        avg_monthly_expenses=(total_expenses / n).quantize(Decimal("0.01")),
        currency="GBP",
    )


async def get_cash_flow_report(
    db: AsyncSession, user_id: uuid.UUID, date_from: date, date_to: date
) -> CashFlowReport:
    result = await db.execute(
        text("""
            SELECT
                date,
                SUM(CASE WHEN amount > 0 THEN amount ELSE 0 END) AS inflow,
                SUM(CASE WHEN amount < 0 THEN ABS(amount) ELSE 0 END) AS outflow
            FROM transactions
            WHERE user_id = CAST(:uid AS uuid)
              AND status != 'void'
              AND deleted_at IS NULL
              AND date BETWEEN :df AND :dt
              AND type IN ('income', 'expense')
            GROUP BY date
            ORDER BY date ASC
        """).bindparams(uid=str(user_id), df=date_from, dt=date_to)
    )
    rows = result.fetchall()

    points = []
    running = Decimal("0")
    total_inflow = Decimal("0")
    total_outflow = Decimal("0")
    for row in rows:
        inflow = Decimal(str(row.inflow or 0))
        outflow = Decimal(str(row.outflow or 0))
        running += inflow - outflow
        total_inflow += inflow
        total_outflow += outflow
        points.append(
            CashFlowPoint(
                date=row.date,
                inflow=inflow,
                outflow=outflow,
                net=inflow - outflow,
                running_balance=running,
            )
        )

    return CashFlowReport(
        points=points,
        total_inflow=total_inflow,
        total_outflow=total_outflow,
        currency="GBP",
    )


async def get_category_breakdown(
    db: AsyncSession,
    user_id: uuid.UUID,
    date_from: date,
    date_to: date,
    txn_type: str = "expense",
) -> CategoryBreakdownReport:
    result = await db.execute(
        select(
            Transaction.category_id,
            func.sum(func.abs(Transaction.amount)).label("total"),
            func.count(Transaction.id).label("cnt"),
        )
        .where(
            Transaction.user_id == user_id,
            Transaction.type == txn_type,
            Transaction.status != "void",
            Transaction.date >= date_from,
            Transaction.date <= date_to,
            Transaction.deleted_at.is_(None),
        )
        .group_by(Transaction.category_id)
        .order_by(func.sum(func.abs(Transaction.amount)).desc())
    )
    rows = result.fetchall()

    grand_total = Decimal("0")
    raw = []
    for row in rows:
        amt = Decimal(str(row.total or 0))
        grand_total += amt
        if row.category_id:
            cat_result = await db.execute(select(Category).where(Category.id == row.category_id))
            category = cat_result.scalar_one_or_none()
            cat_name = category.name if category else "Uncategorised"
        else:
            cat_name = "Uncategorised"
        raw.append((row.category_id, cat_name, amt, row.cnt))

    items = [
        CategoryBreakdownItem(
            category_id=str(cat_id) if cat_id else None,
            category_name=name,
            amount=amt,
            percent=(amt / grand_total * 100).quantize(Decimal("0.01")) if grand_total > 0 else Decimal("0"),
            transaction_count=cnt,
        )
        for cat_id, name, amt, cnt in raw
    ]

    return CategoryBreakdownReport(
        items=items,
        total=grand_total,
        currency="GBP",
        date_from=date_from,
        date_to=date_to,
    )


async def get_budget_vs_actual(db: AsyncSession, user_id: uuid.UUID) -> BudgetVsActualReport:
    from app.services.budget_service import list_budgets, _period_bounds
    today = date.today()
    budgets = await list_budgets(db, user_id, active_only=True)

    items = []
    total_budgeted = Decimal("0")
    total_actual = Decimal("0")

    for budget in budgets:
        period_start, period_end = _period_bounds(budget.period, today)
        cat_result = await db.execute(select(Category).where(Category.id == budget.category_id))
        category = cat_result.scalar_one_or_none()
        cat_name = category.name if category else "Unknown"

        spent_result = await db.execute(
            select(func.coalesce(func.sum(func.abs(Transaction.amount)), Decimal("0")))
            .where(
                and_(
                    Transaction.user_id == user_id,
                    Transaction.category_id == budget.category_id,
                    Transaction.type == "expense",
                    Transaction.status != "void",
                    Transaction.date >= period_start,
                    Transaction.date <= period_end,
                    Transaction.deleted_at.is_(None),
                )
            )
        )
        actual = Decimal(str(spent_result.scalar() or 0))
        variance = budget.amount - actual
        pct = (actual / budget.amount * 100).quantize(Decimal("0.01")) if budget.amount > 0 else Decimal("0")

        items.append(
            BudgetVsActualItem(
                budget_id=str(budget.id),
                budget_name=budget.name,
                category_name=cat_name,
                budgeted=budget.amount,
                actual=actual,
                variance=variance,
                percent_used=pct,
            )
        )
        total_budgeted += budget.amount
        total_actual += actual

    return BudgetVsActualReport(
        items=items,
        total_budgeted=total_budgeted,
        total_actual=total_actual,
        currency="GBP",
    )


async def get_spending_trends(
    db: AsyncSession, user_id: uuid.UUID, months: int = 6
) -> SpendingTrendsReport:
    cutoff = (date.today().replace(day=1) - relativedelta(months=months - 1))
    result = await db.execute(
        text("""
            SELECT
                TO_CHAR(t.date, 'YYYY-MM') AS month,
                COALESCE(c.name, 'Uncategorised') AS category_name,
                SUM(ABS(t.amount)) AS amount
            FROM transactions t
            LEFT JOIN categories c ON c.id = t.category_id
            WHERE t.user_id = CAST(:uid AS uuid)
              AND t.type = 'expense'
              AND t.status != 'void'
              AND t.deleted_at IS NULL
              AND t.date >= :cutoff
            GROUP BY TO_CHAR(t.date, 'YYYY-MM'), c.name
            ORDER BY month ASC, amount DESC
        """).bindparams(uid=str(user_id), cutoff=cutoff)
    )
    rows = result.fetchall()

    points = [
        SpendingTrendPoint(month=row.month, category_name=row.category_name, amount=Decimal(str(row.amount or 0)))
        for row in rows
    ]
    categories = list(dict.fromkeys(p.category_name for p in points))

    return SpendingTrendsReport(points=points, categories=categories, currency="GBP")


async def take_net_worth_snapshot(db: AsyncSession, user_id: uuid.UUID, base_currency: str) -> None:
    today = date.today()
    existing = await db.execute(
        select(NetWorthSnapshot).where(
            NetWorthSnapshot.user_id == user_id,
            NetWorthSnapshot.date == today,
        )
    )
    if existing.scalar_one_or_none():
        return

    assets, liabilities = await _current_net_worth(db, user_id)
    snapshot = NetWorthSnapshot(
        id=uuid.uuid4(),
        user_id=user_id,
        date=today,
        total_assets=assets,
        total_liabilities=liabilities,
        net_worth=assets - liabilities,
        base_currency=base_currency,
        breakdown={},
        created_at=datetime.now(timezone.utc),
    )
    db.add(snapshot)
    await db.flush()