import logging
import uuid

from sqlalchemy import func, select
from sqlalchemy.exc import IntegrityError, SQLAlchemyError
from sqlalchemy.ext.asyncio import AsyncSession

from backend.app.models.archive import PrintArchive
from backend.app.models.finance import TransactionType, UserWallet, WalletTransaction
from backend.app.services.finance_balance import sync_personal_wallet_balance
from backend.app.services.finance_budget import is_billing_enabled, release_budget_reservation

logger = logging.getLogger(__name__)


class BillingRunIdCollisionError(RuntimeError):
    """A billing idempotency key points at a different physical print run."""


async def _get_balance_after_for_transaction(
    db: AsyncSession,
    user_id: int,
    cost_center_id: int | None,
    amount: float,
) -> float:
    """Calculate balance_after for a transaction.

    For cost-center transactions: sum of ALL transactions for that cost center (global).
    For personal transactions (cost_center_id=None): user's wallet balance (personal).

    Args:
        user_id: The user making the transaction
        cost_center_id: The cost center (None for personal)
        amount: The transaction amount (positive/negative)

    Returns:
        The balance after this transaction would be applied
    """
    try:
        if cost_center_id is None:
            # Personal transaction: use user wallet balance
            wallet = (await db.execute(select(UserWallet).where(UserWallet.user_id == user_id))).scalar_one_or_none()
            if wallet is None:
                return float(amount)
            return float(wallet.balance) + amount
        else:
            # Cost-center transaction: sum of ALL transactions for this cost center (global, not per-user)
            result = await db.execute(
                select(func.coalesce(func.sum(WalletTransaction.amount), 0.0)).where(
                    WalletTransaction.cost_center_id == cost_center_id,
                    WalletTransaction.is_voided.is_(False),
                )
            )
            current_balance = float(result.scalar() or 0.0)
            return current_balance + amount
    except SQLAlchemyError as e:
        logger.error(f"Database error in _get_balance_after_for_transaction: {e}", exc_info=True)
        raise


def _calculate_partial_charge(
    archive: PrintArchive,
    base_cost: float,
    *,
    filament_usage: tuple[float | None, float | None] | None = None,
) -> tuple[float, str]:
    """Calculate proportional charge for partial prints based on filament usage.

    Returns (charge_amount, description_suffix) where:
    - charge_amount: absolute cost to charge (0 if insufficient data)
    - description_suffix: reason/details for transaction description
    """
    try:
        # Only apply proportional calculation for non-completed prints
        if archive.status == "completed":
            return round(float(base_cost), 2), ""

        if filament_usage is not None:
            actual_grams, planned_grams = filament_usage
            filament_used = float(actual_grams or 0.0)
            filament_planned = float(planned_grams) if planned_grams is not None else None
        else:
            # Backwards-compatible fallback for recalculation and callers that
            # do not have per-run telemetry. At print completion main.py passes
            # the measured/progress-scaled run usage explicitly: the archive
            # field is the slicer's planned amount and must not be mistaken for
            # the amount consumed by an aborted run.
            filament_used = float(archive.filament_used_grams or 0.0)
            filament_planned = None

            if archive.extra_data and isinstance(archive.extra_data, dict):
                filament_planned = archive.extra_data.get("filament_grams_total")
                if filament_planned is not None:
                    filament_planned = float(filament_planned)

        # If we don't have reliable planned filament data, do not guess a partial charge.
        # Charging a failed/aborted print without an estimated baseline can overcharge users.
        if filament_planned is None or filament_planned <= 0:
            return 0.0, f"[{archive.status}: insufficient filament data]"

        # Calculate proportional cost
        filament_ratio = min(1.0, max(0.0, filament_used / filament_planned))  # Clamp to [0, 1]
        charge = float(base_cost) * filament_ratio

        # Round charges to 2 decimals for consistent persistence
        charge = round(charge, 2)

        suffix = f"[{archive.status}: {filament_ratio:.1%} filament ({filament_used:.1f}g/{filament_planned:.1f}g)]"
        return charge, suffix
    except ValueError as e:
        logger.error(f"Value error in _calculate_partial_charge: {e}", exc_info=True)
        raise


async def apply_print_charge_for_archive(
    db: AsyncSession,
    archive_id: int,
    *,
    charged_user_id: int | None = None,
    cost_center_id: int | None = None,
    print_queue_id: int | None = None,
    print_run_id: str | None = None,
    base_cost_override: float | None = None,
    filament_usage: tuple[float | None, float | None] | None = None,
) -> bool:
    """Apply an idempotent wallet charge for a print archive.

    Charges completed prints at full cost, and partial/failed prints proportionally
    based on actual filament used vs. planned filament.

    Returns True when a new wallet transaction was created.
    """
    try:
        if not await is_billing_enabled(db):
            if print_queue_id is not None:
                await release_budget_reservation(
                    db, source_type="print_queue", source_id=print_queue_id, status="released"
                )
            else:
                await release_budget_reservation(db, print_archive_id=archive_id, status="released")
            logger.info("Billing is disabled; skipping print charge for archive ID %s.", archive_id)
            return False

        archive = (
            await db.execute(select(PrintArchive).where(PrintArchive.id == archive_id).with_for_update())
        ).scalar_one_or_none()
        if archive is None:
            logger.warning(f"Archive with ID {archive_id} not found.")
            return False

        effective_run_id = print_run_id or archive.billing_run_id
        # The archive-level flag is retained only for legacy deleted charges.
        # A new scheduler dispatch clears it while persisting its new run UUID;
        # current deletions are represented by a voided transaction instead.
        if archive.wallet_charge_skipped:
            logger.info(f"Wallet charge skipped for archive ID {archive_id}.")
            return False

        # Accept completed, aborted, cancelled, and failed prints
        if archive.status not in ("completed", "aborted", "cancelled", "failed"):
            logger.info(f"Archive ID {archive_id} has status {archive.status}, which is not chargeable.")
            return False

        actual_user_id = charged_user_id if charged_user_id is not None else archive.created_by_id
        if actual_user_id is None:
            logger.warning(f"Archive ID {archive_id} has no creator ID.")
            return False

        base_cost = float(base_cost_override if base_cost_override is not None else (archive.cost or 0.0))
        if base_cost <= 0:
            logger.info(f"Base cost for archive ID {archive_id} is zero or negative.")
            return False

        # New dispatches persist a UUID before sending the printer command.
        # Generate one here only for legacy/in-flight rows created before that
        # migration; the locked archive row makes this fallback durable.
        if not effective_run_id:
            effective_run_id = str(uuid.uuid4())
            archive.billing_run_id = effective_run_id

        tx_conditions = [
            WalletTransaction.transaction_type == TransactionType.PRINT_CHARGE.value,
            WalletTransaction.print_run_id == effective_run_id,
        ]

        existing_tx = (await db.execute(select(WalletTransaction).where(*tx_conditions))).scalar_one_or_none()
        if existing_tx is not None:
            if existing_tx.print_archive_id != archive.id:
                logger.critical(
                    "BILLING RUN ID COLLISION: run %s belongs to archive %s, not archive %s; charge aborted",
                    effective_run_id,
                    existing_tx.print_archive_id,
                    archive.id,
                )
                raise BillingRunIdCollisionError(
                    f"Billing run ID {effective_run_id} is already assigned to another archive"
                )
            logger.info(f"Transaction already exists for archive ID {archive_id}.")
            if existing_tx.is_voided:
                logger.info("Print charge for run %s was voided by an administrator.", effective_run_id)
            return False

        # Calculate charge (full for completed, partial for others)
        charge, reason_suffix = _calculate_partial_charge(
            archive,
            base_cost,
            filament_usage=filament_usage,
        )
        if charge <= 0:
            if print_queue_id is not None:
                await release_budget_reservation(
                    db, source_type="print_queue", source_id=print_queue_id, status="released"
                )
            else:
                await release_budget_reservation(db, print_archive_id=archive.id, status="released")
            logger.info(f"Calculated charge for archive ID {archive_id} is zero or negative.")
            return False

        actual_cost_center_id = cost_center_id if cost_center_id is not None else archive.cost_center_id

        wallet = (await db.execute(select(UserWallet).where(UserWallet.user_id == actual_user_id))).scalar_one_or_none()
        if wallet is None:
            wallet = UserWallet(user_id=actual_user_id, balance=0.0, currency="EUR")
            db.add(wallet)
            await db.flush()
            logger.info("Created new wallet for user ID %s.", actual_user_id)

        label = archive.print_name or archive.filename or f"Archive {archive.id}"
        description = f"Print charge: {label}{' ' + reason_suffix if reason_suffix else ''}"

        balance_after = await _get_balance_after_for_transaction(db, actual_user_id, actual_cost_center_id, -charge)
        if balance_after is not None:
            balance_after = round(float(balance_after), 2)

        tx = WalletTransaction(
            user_id=actual_user_id,
            cost_center_id=actual_cost_center_id,
            transaction_type=TransactionType.PRINT_CHARGE.value,
            amount=-charge,
            balance_after=balance_after,
            description=description,
            created_by_user_id=None,
            print_run_id=effective_run_id,
            print_archive_id=archive.id,
            print_queue_id=print_queue_id,
        )
        # Limit a concurrent deduplication conflict to a savepoint. The caller
        # owns the outer transaction, which may already contain archive-owner
        # backfills and other completion updates that must survive this race.
        try:
            async with db.begin_nested():
                db.add(tx)
                # Flush inside the savepoint to detect unique/index conflicts.
                await db.flush()
        except IntegrityError as e:
            # Distinguish a legitimate concurrent retry of this exact run from
            # a collision or an unrelated constraint failure. Only the former
            # is an idempotent no-op; everything else must remain loud so the
            # caller rolls back and the budget reservation stays active.
            concurrent_tx = (await db.execute(select(WalletTransaction).where(*tx_conditions))).scalar_one_or_none()
            if concurrent_tx is not None and concurrent_tx.print_archive_id == archive.id:
                logger.info("Transaction already exists for archive ID %s (concurrent), skipping", archive_id)
                return False
            logger.critical(
                "Failed to persist billing charge for archive %s and run %s: %s",
                archive_id,
                effective_run_id,
                e,
                exc_info=True,
            )
            if concurrent_tx is not None:
                raise BillingRunIdCollisionError(
                    f"Billing run ID {effective_run_id} is already assigned to another archive"
                ) from e
            raise

        # Rebuild from the canonical personal-ledger definition. A shared cost
        # center charge must not debit the user's personal wallet.
        new_wallet_balance = await sync_personal_wallet_balance(db, wallet)

        # Consume matching budget reservations after the transaction is persisted
        if print_queue_id is not None:
            await release_budget_reservation(db, source_type="print_queue", source_id=print_queue_id, status="consumed")
        else:
            await release_budget_reservation(db, print_archive_id=archive.id, status="consumed")
        logger.info(f"Applied print charge for archive ID {archive_id}. New balance: {new_wallet_balance}.")
        return True
    except SQLAlchemyError as e:
        logger.error(f"Database error in apply_print_charge_for_archive: {e}", exc_info=True)
        raise
    except ValueError as e:
        logger.error(f"Value error in apply_print_charge_for_archive: {e}", exc_info=True)
        return False