import calendar
import uuid
from collections import defaultdict
from datetime import UTC, date, datetime
from typing import Any

from sqlalchemy import func
from sqlalchemy.orm import Session

from app.audit import service as audit
from app.budgeting.models import (
    BudgetPeriod,
    ExpectedIncome,
    ExpectedIncomeMatch,
    FundingMovement,
    PeriodClosure,
    PlanAssignment,
)
from app.categorization.service import resolve_category_name
from app.errors import bad_request, conflict, not_found
from app.identity.models import User
from app.ledger.models import Account, Category, Operation, Posting
from app.ledger.service import ensure_period_open_for_date as _ledger_guard  # noqa: F401


def validate_year_month(year: int, month: int) -> None:
    if not 1 <= month <= 12 or year < 2000:
        raise bad_request("BUDGET_PERIOD_INVALID", "Invalid year/month")


def period_bounds(year: int, month: int) -> tuple[date, date]:
    start = date(year, month, 1)
    if month == 12:
        end = date(year + 1, 1, 1)
    else:
        end = date(year, month + 1, 1)
    return start, end


def shift_month(d: date, months: int) -> date:
    index = d.year * 12 + (d.month - 1) + months
    year, month = divmod(index, 12)
    month += 1
    return date(year, month, min(d.day, calendar.monthrange(year, month)[1]))


def get_period(db: Session, *, space_id: uuid.UUID, period_id: uuid.UUID) -> BudgetPeriod:
    period = db.query(BudgetPeriod).filter_by(id=period_id, space_id=space_id).one_or_none()
    if period is None:
        raise not_found("BUDGET_PERIOD_NOT_FOUND", "Budget period not found")
    return period


def get_or_create_period(
    db: Session, *, space_id: uuid.UUID, year: int, month: int
) -> BudgetPeriod:
    validate_year_month(year, month)
    period = (
        db.query(BudgetPeriod).filter_by(space_id=space_id, year=year, month=month).one_or_none()
    )
    if period is None:
        period = BudgetPeriod(space_id=space_id, year=year, month=month, status="open")
        db.add(period)
        db.flush()
    return period


def list_periods(db: Session, *, space_id: uuid.UUID) -> list[BudgetPeriod]:
    return (
        db.query(BudgetPeriod)
        .filter_by(space_id=space_id)
        .order_by(BudgetPeriod.year.desc(), BudgetPeriod.month.desc())
        .all()
    )


def _previous_ym(year: int, month: int) -> tuple[int, int]:
    return (year - 1, 12) if month == 1 else (year, month - 1)


def _closure_snapshot(db: Session, *, space_id: uuid.UUID, year: int, month: int) -> dict | None:
    period = (
        db.query(BudgetPeriod)
        .filter_by(space_id=space_id, year=year, month=month, status="closed")
        .one_or_none()
    )
    if period is None:
        return None
    closure = (
        db.query(PeriodClosure)
        .filter_by(period_id=period.id)
        .order_by(PeriodClosure.closed_at.desc())
        .first()
    )
    return closure.snapshot if closure else None


def _balance_until(db: Session, account: Account, end: date) -> int:
    total = (
        db.query(func.coalesce(func.sum(Posting.amount_kopecks), 0))
        .join(Operation, Operation.id == Posting.operation_id)
        .filter(
            Posting.account_id == account.id,
            Operation.status == "confirmed",
            func.coalesce(Operation.posted_on, Operation.occurred_on) <= end,
        )
        .scalar()
    )
    return account.opening_amount_kopecks + int(total or 0)


def compute_period_state(db: Session, *, space_id: uuid.UUID, period: BudgetPeriod) -> dict:
    """Deterministic budget state.

    Resource model:
    - income lands in the general pool;
    - categorized debit/cash expenses consume their category's available amount;
    - uncategorized debit/cash expenses reduce the pool directly (unallocated deficit);
    - credit expenses grow debt; the funded portion of a credit expense moves from
      the category into the account's credit reserve (derived, not stored);
    - a credit payment is covered by the credit reserve first, the remainder
      reduces the pool (which may go negative);
    - a refund on a credit card reduces debt and releases any surplus reserve;
    - a same-period refund restores the parent purchase's category; a refund on
      an uncategorized expense restores the pool;
    - transfers into the system savings envelope are carved out of the pool as
      its backing; transfers back out return to the pool;
    - adjustments reconcile a stored balance through one signed posting and are
      excluded from income/expense totals, category spend and cash flow;
    - monthly categories fold their residual into the pool at close; savings
      envelopes and credit reserves persist via all-time/ snapshot carries.
    """
    start, end = period_bounds(period.year, period.month)

    accounts = db.query(Account).filter_by(space_id=space_id).all()
    account_by_id = {a.id: a for a in accounts}
    savings_account = next((a for a in accounts if a.system_key == "savings"), None)
    # Archived categories stay in the computation: any plan/funding/operations
    # history in the selected period must keep affecting totals.
    categories = db.query(Category).filter_by(space_id=space_id).all()

    ops = (
        db.query(Operation)
        .filter(
            Operation.space_id == space_id,
            Operation.status == "confirmed",
            Operation.occurred_on >= start,
            Operation.occurred_on < end,
        )
        .all()
    )

    income_total = 0
    monthly_consumption: dict[Any, int] = defaultdict(int)
    envelope_consumption_total: dict[Any, int] = defaultdict(int)
    credit_expense_period: dict[Any, int] = defaultdict(int)
    asset_expense_period_uncategorized = 0
    portions_by_account: dict[Any, int] = defaultdict(int)
    expense_account_by_cat: dict[Any, dict] = defaultdict(lambda: defaultdict(int))
    payments_by_account: dict[Any, int] = defaultdict(int)
    refunds_to_credit_by_account: dict[Any, int] = defaultdict(int)
    refund_back_uncategorized_period = 0
    # Net transfers into the system savings envelope for this month (+ into,
    # - back out). Adjustments are excluded from every flow aggregate.
    savings_net_period = 0

    for op in ops:
        if op.type == "income":
            income_total += op.amount_kopecks
        elif op.type == "expense":
            account = account_by_id[op.account_id]
            if account.kind == "credit":
                credit_expense_period[op.category_id] += op.amount_kopecks
                expense_account_by_cat[op.category_id][account.id] += op.amount_kopecks
            if op.category_id is None:
                if account.kind != "credit":
                    asset_expense_period_uncategorized += op.amount_kopecks
            else:
                monthly_consumption[op.category_id] += op.amount_kopecks
        elif op.type == "transfer":
            counter = (
                account_by_id.get(op.counter_account_id)
                if op.counter_account_id is not None
                else None
            )
            if counter is not None and counter.kind == "credit":
                payments_by_account[counter.id] += op.amount_kopecks
            source = account_by_id.get(op.account_id)
            if counter is not None and counter.system_key == "savings":
                savings_net_period += op.amount_kopecks
            if source is not None and source.system_key == "savings":
                savings_net_period -= op.amount_kopecks
        elif op.type == "refund":
            parent_account = account_by_id.get(op.account_id)
            parent = db.get(Operation, op.parent_operation_id) if op.parent_operation_id else None
            if parent_account is not None and parent_account.kind == "credit":
                refunds_to_credit_by_account[parent_account.id] += op.amount_kopecks
            elif parent is not None and parent.category_id is not None:
                same_period = start <= parent.occurred_on < end
                if same_period:
                    monthly_consumption[parent.category_id] -= op.amount_kopecks
                else:
                    refund_back_uncategorized_period += op.amount_kopecks
            else:
                refund_back_uncategorized_period += op.amount_kopecks

    # Funding movements of this period and all-time envelope funding.
    funded_period: dict[Any, int] = defaultdict(int)
    for kind, sign in (("fund", 1), ("unfund", -1)):
        rows = (
            db.query(FundingMovement.category_id, func.sum(FundingMovement.amount_kopecks))
            .filter(
                FundingMovement.space_id == space_id,
                FundingMovement.period_id == period.id,
                FundingMovement.kind == kind,
            )
            .group_by(FundingMovement.category_id)
            .all()
        )
        for category_id, total in rows:
            funded_period[category_id] += sign * int(total or 0)
    funding_total = sum(funded_period.values())

    funded_all_time: dict[Any, int] = defaultdict(int)
    for kind, sign in (("fund", 1), ("unfund", -1)):
        rows = (
            db.query(FundingMovement.category_id, func.sum(FundingMovement.amount_kopecks))
            .filter(
                FundingMovement.space_id == space_id,
                FundingMovement.kind == kind,
            )
            .group_by(FundingMovement.category_id)
            .all()
        )
        for category_id, total in rows:
            funded_all_time[category_id] += sign * int(total or 0)

    # All-time envelope consumption up to period end.
    for cat in categories:
        if cat.kind != "savings_envelope" or cat.system_key == "savings":
            continue
        consumed = (
            db.query(func.coalesce(func.sum(Operation.amount_kopecks), 0))
            .filter(
                Operation.space_id == space_id,
                Operation.status == "confirmed",
                Operation.type == "expense",
                Operation.category_id == cat.id,
                Operation.occurred_on < end,
            )
            .scalar()
        )
        restored = 0
        refunds = (
            db.query(Operation)
            .filter(
                Operation.space_id == space_id,
                Operation.status == "confirmed",
                Operation.type == "refund",
                Operation.occurred_on < end,
                Operation.parent_operation_id.is_not(None),
            )
            .all()
        )
        for refund in refunds:
            parent = db.get(Operation, refund.parent_operation_id)
            if (
                parent is not None
                and parent.category_id == cat.id
                and parent.occurred_on.year == refund.occurred_on.year
                and parent.occurred_on.month == refund.occurred_on.month
            ):
                restored += refund.amount_kopecks
        envelope_consumption_total[cat.id] += int(consumed or 0) - restored

    # Credit funded portions per category (period-scoped derivation).
    credit_funded_portion: dict[Any, int] = defaultdict(int)
    for category_id, credit_amount in list(credit_expense_period.items()):
        if category_id is None:
            continue
        noncredit_consumption = monthly_consumption[category_id] - credit_amount
        available = funded_period[category_id] - noncredit_consumption
        portion = min(max(available, 0), credit_amount)
        credit_funded_portion[category_id] += portion
        if credit_amount:
            allocation = expense_account_by_cat[category_id]
            remaining = portion
            for index, (account_id, amount) in enumerate(allocation.items()):
                account_portion = (
                    remaining if index == len(allocation) - 1 else portion * amount // credit_amount
                )
                portions_by_account[account_id] += account_portion
                remaining -= account_portion

    prev_snapshot = _closure_snapshot(
        db,
        space_id=space_id,
        year=_previous_ym(period.year, period.month)[0],
        month=_previous_ym(period.year, period.month)[1],
    )
    carry_pool = int(prev_snapshot.get("carry_pool", 0)) if prev_snapshot else 0
    carry_reserves: dict[str, int] = (
        {k: int(v) for k, v in prev_snapshot.get("credit_reserves", {}).items()}
        if prev_snapshot
        else {}
    )

    # Reserve and debt per credit account.
    credit_reserves: dict[str, int] = {}
    credit_debt: dict[str, int] = {}
    releases_payment_total = 0
    surplus_release_total = 0
    for account in accounts:
        if account.kind != "credit":
            continue
        key = str(account.id)
        reserve = carry_reserves.get(key, 0) + portions_by_account[account.id]
        payment = payments_by_account[account.id]
        covered = min(reserve, payment)
        releases_payment_total += covered
        reserve -= covered
        reserve -= refunds_to_credit_by_account[account.id]
        debt = max(-_balance_until(db, account, end), 0)
        surplus = max(0, reserve - debt)
        surplus_release_total += surplus
        credit_reserves[key] = min(max(reserve, 0), debt)
        credit_debt[key] = debt

    uncategorized_outflow = asset_expense_period_uncategorized - refund_back_uncategorized_period
    payments_total = sum(payments_by_account.values())

    pool = (
        carry_pool
        + income_total
        - uncategorized_outflow
        - (payments_total - releases_payment_total)
        + surplus_release_total
        - funding_total
        - savings_net_period
    )

    monthly_rows: list[dict[str, Any]] = []
    monthly_residual_total = 0
    for cat in categories:
        if cat.kind != "monthly":
            continue
        available = funded_period[cat.id] - monthly_consumption[cat.id]
        monthly_residual_total += available
        monthly_rows.append(
            {
                "category_id": str(cat.id),
                "name": resolve_category_name(cat),
                "name_key": cat.system_key,
                "archived": cat.archived,
                "planned": 0,
                "funded": funded_period[cat.id],
                "spent": monthly_consumption[cat.id],
                "available": available,
            }
        )
    # All-time net transfer movement into the system savings account (+ in, - out).
    savings_net_all_time = 0
    if savings_account is not None:
        savings_net_all_time = int(
            db.query(func.coalesce(func.sum(Posting.amount_kopecks), 0))
            .join(Operation, Operation.id == Posting.operation_id)
            .filter(
                Posting.account_id == savings_account.id,
                Operation.status == "confirmed",
                Operation.type == "transfer",
            )
            .scalar()
            or 0
        )

    envelope_rows: list[dict[str, Any]] = []
    for cat in categories:
        if cat.kind != "savings_envelope" or cat.system_key == "credit_reserve":
            continue
        if cat.system_key == "savings":
            # System savings envelope: funded shows the net transfer movement of
            # the selected month, spent is always zero and available tracks the
            # linked account balance at month end (adjustments included).
            available = _balance_until(db, savings_account, end) if savings_account else 0
            envelope_rows.append(
                {
                    "category_id": str(cat.id),
                    "name": resolve_category_name(cat),
                    "name_key": cat.system_key,
                    "archived": cat.archived,
                    "system": True,
                    "funded_total": savings_net_all_time,
                    "planned": 0,
                    "funded": savings_net_period,
                    "spent": 0,
                    "available": available,
                }
            )
            continue
        available = funded_all_time[cat.id] - envelope_consumption_total[cat.id]
        envelope_rows.append(
            {
                "category_id": str(cat.id),
                "name": resolve_category_name(cat),
                "name_key": cat.system_key,
                "archived": cat.archived,
                "system": cat.system_key is not None,
                "funded_total": funded_all_time[cat.id],
                "planned": 0,
                "funded": funded_period[cat.id],
                "spent": funded_all_time[cat.id] - available,
                "available": available,
            }
        )

    assignments = db.query(PlanAssignment).filter_by(period_id=period.id).all()
    planned_by_cat = {a.category_id: a.planned_kopecks for a in assignments}
    for row in monthly_rows:
        cid = uuid.UUID(str(row["category_id"]))
        row["planned"] = planned_by_cat.get(cid, 0)
    planned_total = sum(planned_by_cat.values())

    expected = db.query(ExpectedIncome).filter_by(period_id=period.id).all()
    expected_total = sum(e.amount_kopecks for e in expected)
    matched_by_expected: dict[Any, int] = defaultdict(int)
    for m in (
        db.query(ExpectedIncomeMatch)
        .filter(ExpectedIncomeMatch.expected_income_id.in_([e.id for e in expected] or [None]))
        .all()
        if expected
        else []
    ):
        matched_by_expected[m.expected_income_id] += m.amount_kopecks

    uncategorized_count = sum(1 for op in ops if op.type == "expense" and op.category_id is None)
    negative_envelopes = [
        str(row["name"] or row["name_key"] or row["category_id"])
        for row in envelope_rows
        if int(row["available"]) < 0
    ]

    warnings = []
    if planned_total > carry_pool + expected_total:
        warnings.append("plan_imbalance")
    for key, debt in credit_debt.items():
        if debt > credit_reserves.get(key, 0):
            warnings.append("underfunded_credit_debt")
            break
    if uncategorized_count:
        warnings.append("uncategorized_expenses")
    if negative_envelopes:
        warnings.append("negative_envelopes")

    return {
        "period": {
            "id": str(period.id),
            "year": period.year,
            "month": period.month,
            "status": period.status,
        },
        "pool": pool,
        "carry_pool": carry_pool,
        "income_total": income_total,
        "planned_total": planned_total,
        "expected_income_total": expected_total,
        "expected_incomes": [
            {
                "id": str(e.id),
                "expected_on": e.expected_on.isoformat(),
                "amount_kopecks": e.amount_kopecks,
                "source_name": e.source_name,
                "matched_kopecks": matched_by_expected.get(e.id, 0),
            }
            for e in expected
        ],
        "monthly_categories": monthly_rows,
        "envelopes": envelope_rows,
        "credit_reserves": credit_reserves,
        "credit_debt": credit_debt,
        "uncategorized_expenses": uncategorized_count,
        "warnings": warnings,
        "close_blockers": (
            []
            if period.status == "closed"
            else _close_blockers(
                db,
                space_id=space_id,
                period=period,
                uncategorized_count=uncategorized_count,
                negative_envelopes=negative_envelopes,
            )
        ),
    }


def _close_blockers(
    db: Session,
    *,
    space_id: uuid.UUID,
    period: BudgetPeriod,
    uncategorized_count: int,
    negative_envelopes: list[str],
) -> list[dict]:
    from app.imports.models import HoldResolution, SourceRecord, StatementDocument

    blockers = []
    unresolved = (
        db.query(StatementDocument.id)
        .filter(
            StatementDocument.space_id == space_id,
            StatementDocument.status.in_(
                ["uploaded", "queued", "processing", "ready", "review_required"]
            ),
        )
        .count()
    )
    if unresolved:
        blockers.append({"code": "IMPORTS_UNRESOLVED", "count": unresolved})
    start, end = period_bounds(period.year, period.month)
    unresolved_holds = (
        db.query(SourceRecord.id)
        .join(
            StatementDocument,
            (StatementDocument.space_id == SourceRecord.space_id)
            & (StatementDocument.id == SourceRecord.document_id),
        )
        .outerjoin(HoldResolution, HoldResolution.hold_source_record_id == SourceRecord.id)
        .filter(
            SourceRecord.space_id == space_id,
            SourceRecord.bank_status == "hold",
            StatementDocument.status == "confirmed",
            StatementDocument.active_parse_run_id == SourceRecord.parse_run_id,
            HoldResolution.id.is_(None),
            SourceRecord.occurred_on >= start,
            SourceRecord.occurred_on < end,
        )
        .count()
    )
    if unresolved_holds:
        blockers.append({"code": "IMPORT_UNRESOLVED_HOLDS", "count": unresolved_holds})
    if uncategorized_count:
        blockers.append({"code": "BUDGET_UNCATEGORIZED_EXPENSES", "count": uncategorized_count})
    if negative_envelopes:
        blockers.append({"code": "BUDGET_NEGATIVE_ENVELOPE", "categories": negative_envelopes})
    return blockers


def require_open(period: BudgetPeriod) -> None:
    if period.status != "open":
        raise conflict(
            "BUDGET_PERIOD_CLOSED", "Budget period is closed", details={"period_id": str(period.id)}
        )


def get_category(db: Session, *, space_id: uuid.UUID, category_id: uuid.UUID) -> Category:
    category = db.query(Category).filter_by(id=category_id, space_id=space_id).one_or_none()
    if category is None:
        raise not_found("BUDGET_CATEGORY_NOT_FOUND", "Category not found")
    return category


def create_category(
    db: Session,
    *,
    space_id: uuid.UUID,
    user: User,
    kind: str,
    name: str,
) -> Category:
    if kind not in ("monthly", "savings_envelope"):
        raise bad_request("BUDGET_CATEGORY_KIND_INVALID", "Unknown category kind")
    trimmed = name.strip()
    if not trimmed:
        raise bad_request("BUDGET_CATEGORY_NAME_REQUIRED", "Category name is required")
    category = Category(space_id=space_id, kind=kind, custom_name=trimmed[:200])
    db.add(category)
    db.flush()
    audit.record(
        db,
        event_type="category.created",
        space_id=space_id,
        user_id=user.id,
        detail={"category_id": str(category.id)},
    )
    return category


def ensure_credit_reserve_category(
    db: Session, *, space_id: uuid.UUID, account: Account
) -> Category:
    category = (
        db.query(Category)
        .filter_by(space_id=space_id, system_key="credit_reserve", linked_account_id=account.id)
        .one_or_none()
    )
    if category is None:
        category = Category(
            space_id=space_id,
            kind="savings_envelope",
            system_key="credit_reserve",
            linked_account_id=account.id,
        )
        db.add(category)
        db.flush()
    return category


def list_categories(
    db: Session, *, space_id: uuid.UUID, include_archived: bool = False
) -> list[Category]:
    query = db.query(Category).filter_by(space_id=space_id)
    if not include_archived:
        query = query.filter(Category.archived.is_(False))
    return query.order_by(Category.created_at).all()


def archive_category(
    db: Session, *, space_id: uuid.UUID, user: User, category_id: uuid.UUID
) -> Category:
    category = get_category(db, space_id=space_id, category_id=category_id)
    if category.system_key is not None:
        raise conflict("BUDGET_CATEGORY_SYSTEM", "System categories cannot be archived")
    category.archived = True
    audit.record(
        db,
        event_type="category.archived",
        space_id=space_id,
        user_id=user.id,
        detail={"category_id": str(category.id)},
    )
    return category


def update_category_definition(
    db: Session,
    *,
    space_id: uuid.UUID,
    user: User,
    category_id: uuid.UUID,
    name: str | None = None,
    archived: bool | None = None,
) -> Category:
    """Rename and/or archive/restore one user category definition.

    System categories reject both changes; ``archived=False`` restores an
    archived user category. History (plans, funding, operations) is preserved.
    """
    category = get_category(db, space_id=space_id, category_id=category_id)
    if category.system_key is not None:
        raise conflict("BUDGET_CATEGORY_SYSTEM", "System categories cannot be renamed or archived")
    changes: dict[str, bool | str] = {}
    if name is not None:
        trimmed = name.strip()
        if not trimmed:
            raise bad_request("BUDGET_CATEGORY_NAME_REQUIRED", "Category name is required")
        category.custom_name = trimmed[:200]
        changes["renamed"] = True
    if archived is not None:
        category.archived = archived
        changes["archived"] = archived
    if changes:
        audit.record(
            db,
            event_type="category.updated",
            space_id=space_id,
            user_id=user.id,
            detail={"category_id": str(category.id), **changes},
        )
    return category


def set_assignments(
    db: Session,
    *,
    space_id: uuid.UUID,
    user: User,
    period: BudgetPeriod,
    items: list[dict],
) -> list[PlanAssignment]:
    require_open(period)
    result = []
    for item in items:
        category = get_category(db, space_id=space_id, category_id=item["category_id"])
        if category.system_key is not None:
            raise conflict("BUDGET_CATEGORY_SYSTEM", "System categories cannot be planned")
        if category.archived:
            raise conflict("BUDGET_CATEGORY_ARCHIVED", "Category is archived")
        planned = item["planned_kopecks"]
        if planned < 0:
            raise bad_request("BUDGET_PLANNED_NEGATIVE", "Planned amount cannot be negative")
        assignment = (
            db.query(PlanAssignment)
            .filter_by(period_id=period.id, category_id=category.id)
            .one_or_none()
        )
        if assignment is None:
            assignment = PlanAssignment(
                space_id=space_id,
                period_id=period.id,
                category_id=category.id,
                planned_kopecks=planned,
            )
            db.add(assignment)
        else:
            assignment.planned_kopecks = planned
        result.append(assignment)
    db.flush()
    audit.record(
        db,
        event_type="budget.assignments_set",
        space_id=space_id,
        user_id=user.id,
        detail={"period_id": str(period.id), "count": len(result)},
    )
    return result


def add_expected_income(
    db: Session,
    *,
    space_id: uuid.UUID,
    user: User,
    period: BudgetPeriod,
    expected_on: date,
    amount_kopecks: int,
    source_name: str | None,
    note: str | None = None,
) -> ExpectedIncome:
    require_open(period)
    if amount_kopecks <= 0:
        raise bad_request("MONEY_AMOUNT_MUST_BE_POSITIVE", "Amount must be positive")
    income = ExpectedIncome(
        space_id=space_id,
        period_id=period.id,
        expected_on=expected_on,
        amount_kopecks=amount_kopecks,
        source_name=source_name,
        note=note,
    )
    db.add(income)
    db.flush()
    return income


def match_expected_income(
    db: Session,
    *,
    space_id: uuid.UUID,
    user: User,
    expected_income_id: uuid.UUID,
    operation_id: uuid.UUID,
    amount_kopecks: int | None = None,
) -> ExpectedIncomeMatch:
    expected = (
        db.query(ExpectedIncome).filter_by(id=expected_income_id, space_id=space_id).one_or_none()
    )
    if expected is None:
        raise not_found("BUDGET_EXPECTED_INCOME_NOT_FOUND", "Expected income not found")
    operation = db.query(Operation).filter_by(id=operation_id, space_id=space_id).one_or_none()
    if operation is None or operation.type != "income" or operation.status != "confirmed":
        raise not_found("BUDGET_INCOME_OPERATION_NOT_FOUND", "Confirmed income operation not found")
    existing = db.query(ExpectedIncomeMatch).filter_by(operation_id=operation.id).one_or_none()
    if existing is not None:
        raise conflict("BUDGET_INCOME_ALREADY_MATCHED", "Income already matched to expected income")
    amount = (
        amount_kopecks
        if amount_kopecks is not None
        else min(operation.amount_kopecks, expected.amount_kopecks)
    )
    if amount <= 0 or amount > operation.amount_kopecks:
        raise bad_request(
            "BUDGET_MATCH_AMOUNT_INVALID",
            "Match amount must be within the income operation",
        )
    match = ExpectedIncomeMatch(
        space_id=space_id,
        expected_income_id=expected.id,
        operation_id=operation.id,
        amount_kopecks=amount,
    )
    db.add(match)
    db.flush()
    return match


def fund(
    db: Session,
    *,
    space_id: uuid.UUID,
    user: User,
    period: BudgetPeriod,
    category_id: uuid.UUID,
    amount_kopecks: int,
    kind: str,
    note: str | None = None,
) -> FundingMovement:
    require_open(period)
    if kind not in ("fund", "unfund"):
        raise bad_request("BUDGET_FUNDING_KIND_INVALID", "Unknown funding kind")
    if amount_kopecks <= 0:
        raise bad_request("MONEY_AMOUNT_MUST_BE_POSITIVE", "Amount must be positive")
    category = get_category(db, space_id=space_id, category_id=category_id)
    if category.system_key is not None:
        raise conflict("BUDGET_CATEGORY_SYSTEM", "System categories cannot be funded")
    if category.archived:
        raise conflict("BUDGET_CATEGORY_ARCHIVED", "Category is archived")
    movement = FundingMovement(
        space_id=space_id,
        period_id=period.id,
        category_id=category_id,
        kind=kind,
        amount_kopecks=amount_kopecks,
        note=note,
        created_by_user_id=user.id,
    )
    db.add(movement)
    db.flush()
    return movement


def close_period(db: Session, *, space_id: uuid.UUID, user: User, period: BudgetPeriod) -> dict:
    period = (
        db.query(BudgetPeriod).filter_by(id=period.id, space_id=space_id).with_for_update().one()
    )
    require_open(period)
    previous_year, previous_month = _previous_ym(period.year, period.month)
    earlier_period = (
        db.query(BudgetPeriod)
        .filter(
            BudgetPeriod.space_id == space_id,
            (BudgetPeriod.year < period.year)
            | ((BudgetPeriod.year == period.year) & (BudgetPeriod.month < period.month)),
        )
        .order_by(BudgetPeriod.year.desc(), BudgetPeriod.month.desc())
        .with_for_update()
        .first()
    )
    if earlier_period is not None and (
        earlier_period.year != previous_year
        or earlier_period.month != previous_month
        or earlier_period.status != "closed"
    ):
        raise conflict(
            "BUDGET_CLOSE_OUT_OF_ORDER",
            "Close the previous calendar month before this period",
            details={"year": previous_year, "month": previous_month},
        )
    state = compute_period_state(db, space_id=space_id, period=period)
    if state["close_blockers"]:
        raise conflict(
            "BUDGET_CLOSE_BLOCKED",
            "Period has blocking issues",
            details={"blockers": state["close_blockers"]},
        )
    monthly_residual = sum(row["available"] for row in state["monthly_categories"])
    snapshot = {
        "period": state["period"],
        "closed_at": datetime.now(UTC).isoformat(),
        "pool": state["pool"],
        "carry_pool": state["pool"] + monthly_residual,
        "income_total": state["income_total"],
        "planned_total": state["planned_total"],
        "monthly_categories": state["monthly_categories"],
        "envelopes": state["envelopes"],
        "credit_reserves": state["credit_reserves"],
        "credit_debt": state["credit_debt"],
        "warnings": state["warnings"],
    }
    closure = PeriodClosure(
        space_id=space_id,
        period_id=period.id,
        snapshot=snapshot,
        closed_at=datetime.now(UTC),
        closed_by_user_id=user.id,
    )
    period.status = "closed"
    db.add(closure)
    db.flush()
    audit.record(
        db,
        event_type="budget.closed",
        space_id=space_id,
        user_id=user.id,
        detail={"period_id": str(period.id)},
    )
    return snapshot


def reopen_period(
    db: Session, *, space_id: uuid.UUID, user: User, period: BudgetPeriod
) -> list[BudgetPeriod]:
    period = (
        db.query(BudgetPeriod).filter_by(id=period.id, space_id=space_id).with_for_update().one()
    )
    if period.status != "closed":
        raise conflict("BUDGET_PERIOD_NOT_CLOSED", "Only closed periods can be reopened")
    affected = (
        db.query(BudgetPeriod)
        .filter(
            BudgetPeriod.space_id == space_id,
            BudgetPeriod.status == "closed",
            (BudgetPeriod.year > period.year)
            | ((BudgetPeriod.year == period.year) & (BudgetPeriod.month >= period.month)),
        )
        .order_by(BudgetPeriod.year, BudgetPeriod.month)
        .all()
    )
    for p in affected:
        p.status = "open"
    db.flush()
    audit.record(
        db,
        event_type="budget.reopened",
        space_id=space_id,
        user_id=user.id,
        detail={"period_id": str(period.id), "impacted": [str(p.id) for p in affected]},
    )
    return affected


def copy_previous_month(
    db: Session, *, space_id: uuid.UUID, user: User, period: BudgetPeriod
) -> dict:
    require_open(period)
    prev_year, prev_month = _previous_ym(period.year, period.month)
    previous = (
        db.query(BudgetPeriod)
        .filter_by(space_id=space_id, year=prev_year, month=prev_month)
        .one_or_none()
    )
    if previous is None:
        raise not_found("BUDGET_PREVIOUS_PERIOD_MISSING", "Previous month period does not exist")
    copied_assignments = 0
    for assignment in db.query(PlanAssignment).filter_by(period_id=previous.id).all():
        category = get_category(db, space_id=space_id, category_id=assignment.category_id)
        if category.archived:
            continue
        existing = (
            db.query(PlanAssignment)
            .filter_by(period_id=period.id, category_id=assignment.category_id)
            .one_or_none()
        )
        if existing is None:
            db.add(
                PlanAssignment(
                    space_id=space_id,
                    period_id=period.id,
                    category_id=assignment.category_id,
                    planned_kopecks=assignment.planned_kopecks,
                )
            )
        else:
            existing.planned_kopecks = assignment.planned_kopecks
        copied_assignments += 1
    copied_expected = 0
    for expected in db.query(ExpectedIncome).filter_by(period_id=previous.id).all():
        db.add(
            ExpectedIncome(
                space_id=space_id,
                period_id=period.id,
                expected_on=shift_month(expected.expected_on, 1),
                amount_kopecks=expected.amount_kopecks,
                source_name=expected.source_name,
                note=expected.note,
            )
        )
        copied_expected += 1
    db.flush()
    audit.record(
        db,
        event_type="budget.copied",
        space_id=space_id,
        user_id=user.id,
        detail={
            "period_id": str(period.id),
            "assignments": copied_assignments,
            "expected": copied_expected,
        },
    )
    return {"assignments_copied": copied_assignments, "expected_incomes_copied": copied_expected}