from __future__ import annotations

from dataclasses import asdict, dataclass
from datetime import UTC, date, datetime, time, timedelta
from decimal import Decimal

from sqlalchemy import func, select, text
from sqlalchemy.orm import Session

from app.models.budget import BudgetAllocation, BudgetReservation, BudgetTransaction
from app.models.financial_record import ExpenseClaim
from app.models.risk_observation import RiskObservation
from app.services.demo_company_simulation_catalog import (
    BUDGETED_STATUSES,
    SIM_BUDGET_PREFIX,
    SIM_PROJECT_CODE,
    SIM_RESERVATION_PREFIX,
    SIM_RISK_PREFIX,
    SIM_TRANSACTION_PREFIX,
    build_simulation_reimbursement_no,
    target_budget_usage,
)


@dataclass(frozen=True, slots=True)
class SimulationRebalanceSummary:
    mode: str
    claims: int
    main_period_claims: int
    recent_claims: int
    period_start: str
    period_end: str
    max_daily_count: int
    budget_transactions: int
    budget_reservations: int
    risk_observations: int
    allocation_missing_count: int

    def to_dict(self) -> dict[str, object]:
        return asdict(self)


class HalfYearExpenseSimulationRebalancer:
    """Rebalance existing simulation rows without deleting business records."""

    def __init__(
        self,
        db: Session,
        *,
        start_date: date = date(2026, 1, 1),
        end_date: date = date(2026, 6, 2),
        recent_sample_days: int = 2,
    ) -> None:
        self.db = db
        self.start_date = start_date
        self.end_date = end_date
        self.main_period_end = date(end_date.year, end_date.month, 1) - timedelta(days=1)
        self.recent_sample_days = max(1, recent_sample_days)

    def preview(self) -> SimulationRebalanceSummary:
        return self._run(apply=False)

    def apply(self) -> SimulationRebalanceSummary:
        return self._run(apply=True)

    def _run(self, *, apply: bool) -> SimulationRebalanceSummary:
        claims = self._simulation_claims()
        plans = self._claim_plans(claims)
        allocation_map = self._allocation_map()
        allocation_missing_count = self._count_missing_allocations(plans, allocation_map)
        day_counts: dict[date, int] = {}
        for _claim, plan in plans:
            day_counts[plan["day"]] = day_counts.get(plan["day"], 0) + 1

        if apply and plans:
            self._apply_claim_plans(plans, allocation_map)
            self._rebalance_allocation_amounts()
            self.db.flush()

        recent_count = sum(1 for _claim, plan in plans if plan["day"] >= date(2026, 6, 1))
        return SimulationRebalanceSummary(
            mode="apply" if apply else "dry-run",
            claims=len(claims),
            main_period_claims=len(claims) - recent_count,
            recent_claims=recent_count,
            period_start=self.start_date.isoformat(),
            period_end=self.end_date.isoformat(),
            max_daily_count=max(day_counts.values()) if day_counts else 0,
            budget_transactions=self._sim_transaction_count(),
            budget_reservations=self._sim_reservation_count(),
            risk_observations=self._sim_risk_count(),
            allocation_missing_count=allocation_missing_count,
        )

    def _simulation_claims(self) -> list[ExpenseClaim]:
        return list(
            self.db.scalars(
                select(ExpenseClaim)
                .where(ExpenseClaim.project_code == SIM_PROJECT_CODE)
                .order_by(ExpenseClaim.claim_no.asc(), ExpenseClaim.id.asc())
            ).all()
        )

    def _claim_plans(self, claims: list[ExpenseClaim]) -> list[tuple[ExpenseClaim, dict[str, object]]]:
        recent_count = self._recent_count(len(claims))
        main_count = max(len(claims) - recent_count, 0)
        main_days = self._date_range(self.start_date, self.main_period_end)
        recent_days = self._date_range(date(2026, 6, 1), self.end_date)
        plans: list[tuple[ExpenseClaim, dict[str, object]]] = []
        for index, claim in enumerate(claims):
            if index < main_count:
                day = self._spread_day(index, main_count, main_days)
            else:
                recent_index = index - main_count
                day = recent_days[recent_index % len(recent_days)]
            occurred_at = datetime.combine(day, time(hour=8 + (index % 9)), tzinfo=UTC)
            submitted_at = None
            if self._status(claim) != "draft":
                submitted_at = datetime.combine(day, time(hour=9 + (index % 7)), tzinfo=UTC)
            updated_at = self._updated_at(claim, occurred_at, submitted_at, index)
            final_claim_no = build_simulation_reimbursement_no(occurred_at, index + 1)
            period_key = f"{occurred_at.year}Q{((occurred_at.month - 1) // 3) + 1}"
            subject_code = "meal" if str(claim.expense_type or "") == "entertainment" else str(claim.expense_type or "")
            plans.append(
                (
                    claim,
                    {
                        "sequence": index + 1,
                        "day": day,
                        "occurred_at": occurred_at,
                        "submitted_at": submitted_at,
                        "updated_at": updated_at,
                        "claim_no": final_claim_no,
                        "period_key": period_key,
                        "subject_code": subject_code,
                    },
                )
            )
        return plans

    def _apply_claim_plans(
        self,
        plans: list[tuple[ExpenseClaim, dict[str, object]]],
        allocation_map: dict[tuple[str | None, str, str], str],
    ) -> None:
        claim_ids = [claim.id for claim, _plan in plans]
        transactions_by_claim = self._transactions_by_claim_id(claim_ids)
        reservations_by_claim = self._reservations_by_claim_id(claim_ids)
        observations_by_claim = self._observations_by_claim_id(claim_ids)

        for claim, plan in plans:
            claim.claim_no = f"SIM-TEMP-{claim.id}"
        self.db.flush()

        for claim, plan in plans:
            claim_no = str(plan["claim_no"])
            occurred_at = plan["occurred_at"]
            submitted_at = plan["submitted_at"]
            updated_at = plan["updated_at"]
            allocation_id = allocation_map.get(
                (
                    claim.department_id,
                    str(plan["period_key"]),
                    str(plan["subject_code"]),
                )
            )
            claim.claim_no = claim_no
            claim.occurred_at = occurred_at
            claim.submitted_at = submitted_at
            claim.created_at = occurred_at
            claim.updated_at = updated_at
            claim.reason = self._normalized_reason(claim.reason, occurred_at.date())

            self.db.execute(
                text(
                    """
                    update expense_claim_items
                    set item_date = :item_date, updated_at = :updated_at
                    where claim_id = :claim_id
                    """
                ),
                {
                    "item_date": occurred_at.date(),
                    "updated_at": updated_at,
                    "claim_id": claim.id,
                },
            )

            for transaction in transactions_by_claim.get(claim.id, []):
                transaction.source_no = claim_no
                transaction.created_at = submitted_at or occurred_at
                if allocation_id:
                    transaction.allocation_id = allocation_id

            for reservation in reservations_by_claim.get(claim.id, []):
                reservation.source_no = claim_no
                reservation.created_at = submitted_at or occurred_at
                reservation.updated_at = updated_at
                if allocation_id:
                    reservation.allocation_id = allocation_id

            for observation in observations_by_claim.get(claim.id, []):
                observation.subject_key = claim_no
                observation.subject_label = claim_no
                observation.claim_no = claim_no
                observation.created_at = submitted_at or occurred_at
                observation.updated_at = updated_at

    def _allocation_map(self) -> dict[tuple[str | None, str, str], str]:
        rows = self.db.scalars(
            select(BudgetAllocation).where(BudgetAllocation.project_code == SIM_PROJECT_CODE)
        ).all()
        return {
            (row.department_id, row.period_key, row.subject_code): row.id
            for row in rows
        }

    def _count_missing_allocations(
        self,
        plans: list[tuple[ExpenseClaim, dict[str, object]]],
        allocation_map: dict[tuple[str | None, str, str], str],
    ) -> int:
        missing = {
            (claim.department_id, str(plan["period_key"]), str(plan["subject_code"]))
            for claim, plan in plans
            if self._status(claim) in BUDGETED_STATUSES
            and (claim.department_id, str(plan["period_key"]), str(plan["subject_code"])) not in allocation_map
        }
        return len(missing)

    def _rebalance_allocation_amounts(self) -> None:
        allocations = list(
            self.db.scalars(
                select(BudgetAllocation)
                .where(BudgetAllocation.budget_no.like(f"{SIM_BUDGET_PREFIX}%"))
                .order_by(BudgetAllocation.period_key.asc(), BudgetAllocation.subject_code.asc())
            ).all()
        )
        transactions = list(
            self.db.scalars(
                select(BudgetTransaction).where(
                    BudgetTransaction.transaction_no.like(f"{SIM_TRANSACTION_PREFIX}%")
                )
            ).all()
        )
        used_by_allocation: dict[str, Decimal] = {}
        for transaction in transactions:
            used_by_allocation[transaction.allocation_id] = (
                used_by_allocation.get(transaction.allocation_id, Decimal("0.00"))
                + Decimal(transaction.amount or 0)
            )
        for index, allocation in enumerate(allocations):
            used = used_by_allocation.get(allocation.id, Decimal("0.00"))
            usage = target_budget_usage(allocation.period_key, allocation.subject_code, index)
            allocation.original_amount = max(
                (used / usage).quantize(Decimal("0.01")) if usage > 0 else used,
                Decimal("3000.00"),
            )
            allocation.updated_by = "simulation_rebalance"
            allocation.updated_at = datetime.now(UTC)

    def _transactions_by_claim_id(self, claim_ids: list[str]) -> dict[str, list[BudgetTransaction]]:
        rows = self.db.scalars(
            select(BudgetTransaction)
            .where(BudgetTransaction.transaction_no.like(f"{SIM_TRANSACTION_PREFIX}%"))
            .where(BudgetTransaction.source_id.in_(claim_ids))
        ).all()
        return self._group_by_source_id(rows)

    def _reservations_by_claim_id(self, claim_ids: list[str]) -> dict[str, list[BudgetReservation]]:
        rows = self.db.scalars(
            select(BudgetReservation)
            .where(BudgetReservation.reservation_no.like(f"{SIM_RESERVATION_PREFIX}%"))
            .where(BudgetReservation.source_id.in_(claim_ids))
        ).all()
        return self._group_by_source_id(rows)

    def _observations_by_claim_id(self, claim_ids: list[str]) -> dict[str, list[RiskObservation]]:
        rows = self.db.scalars(
            select(RiskObservation)
            .where(RiskObservation.observation_key.like(f"{SIM_RISK_PREFIX}%"))
            .where(RiskObservation.claim_id.in_(claim_ids))
        ).all()
        grouped: dict[str, list[RiskObservation]] = {}
        for row in rows:
            if row.claim_id:
                grouped.setdefault(row.claim_id, []).append(row)
        return grouped

    @staticmethod
    def _group_by_source_id(rows: object) -> dict[str, list[object]]:
        grouped: dict[str, list[object]] = {}
        for row in rows:
            grouped.setdefault(row.source_id, []).append(row)
        return grouped

    def _recent_count(self, total: int) -> int:
        if total <= 0:
            return 0
        return min(24, max(12, total // 50))

    @staticmethod
    def _date_range(start: date, end: date) -> list[date]:
        days = max((end - start).days, 0)
        return [start + timedelta(days=index) for index in range(days + 1)]

    @staticmethod
    def _spread_day(index: int, count: int, days: list[date]) -> date:
        if not days:
            raise ValueError("days cannot be empty")
        if count <= 1:
            return days[0]
        day_index = round(index * (len(days) - 1) / (count - 1))
        jitter = ((index * 17) % 5) - 2
        return days[max(0, min(len(days) - 1, day_index + jitter))]

    @staticmethod
    def _updated_at(
        claim: ExpenseClaim,
        occurred_at: datetime,
        submitted_at: datetime | None,
        index: int,
    ) -> datetime:
        base = submitted_at or occurred_at
        status = HalfYearExpenseSimulationRebalancer._status(claim)
        if status == "paid":
            return base + timedelta(days=2 + (index % 3), hours=index % 5)
        if status in {"approved", "pending_payment"}:
            return base + timedelta(days=1 + (index % 2), hours=index % 4)
        if status in {"returned", "rejected"}:
            return base + timedelta(hours=6 + (index % 8))
        return base + timedelta(hours=2 + (index % 4))

    @staticmethod
    def _normalized_reason(reason: str, day: date) -> str:
        text = str(reason or "").strip()
        for month in range(1, 7):
            text = text.replace(f"{month}月", f"{day.month}月")
        return text

    @staticmethod
    def _status(claim: ExpenseClaim) -> str:
        return str(claim.status or "").strip().lower()

    def _sim_transaction_count(self) -> int:
        return int(
            self.db.scalar(
                select(func.count()).select_from(BudgetTransaction).where(
                    BudgetTransaction.transaction_no.like(f"{SIM_TRANSACTION_PREFIX}%")
                )
            )
            or 0
        )

    def _sim_reservation_count(self) -> int:
        return int(
            self.db.scalar(
                select(func.count()).select_from(BudgetReservation).where(
                    BudgetReservation.reservation_no.like(f"{SIM_RESERVATION_PREFIX}%")
                )
            )
            or 0
        )

    def _sim_risk_count(self) -> int:
        return int(
            self.db.scalar(
                select(func.count()).select_from(RiskObservation).where(
                    RiskObservation.observation_key.like(f"{SIM_RISK_PREFIX}%")
                )
            )
            or 0
        )