from __future__ import annotations

from dataclasses import dataclass

from django.db import transaction

from apps.users.models import UserWallet

from .models import CallRecord, PointsLedger, normalize_resolution


class BillingOperationError(RuntimeError):
    code = "billing_operation_error"


class InsufficientPointsError(BillingOperationError):
    code = "insufficient_points"

    def __init__(self, *, required_points: int, available_points: int):
        self.required_points = required_points
        self.available_points = available_points
        super().__init__("Insufficient points. Please recharge before calling this API.")


class InvalidCallStateError(BillingOperationError):
    code = "invalid_call_state"

    def __init__(self, message: str):
        super().__init__(message)


@dataclass(frozen=True)
class CallCharge:
    call_record: CallRecord
    ledger_entry: PointsLedger
    points_cost: int
    balance_after: int


@dataclass(frozen=True)
class RefundResult:
    call_record: CallRecord
    ledger_entry: PointsLedger | None
    points_refunded: int
    balance_after: int
    refunded: bool


def _validate_positive_points(points: int) -> int:
    if isinstance(points, bool) or not isinstance(points, int) or points <= 0:
        raise ValueError("points must be a positive integer")
    return points


def _locked_wallet_for_user(user) -> UserWallet:
    wallet, _created = UserWallet.objects.select_for_update().get_or_create(user=user)
    return wallet


def precharge_call(
    *,
    user,
    points_cost: int,
    operation_type: str,
    alias: str,
    model_used: str = "",
    resolution: str | None = None,
    api_key=None,
    prompt: str = "",
) -> CallCharge:
    points_cost = _validate_positive_points(points_cost)
    normalized_alias = str(alias or "").strip()
    normalized_resolution = normalize_resolution(resolution)

    with transaction.atomic():
        wallet = _locked_wallet_for_user(user)
        if wallet.points_balance < points_cost:
            raise InsufficientPointsError(
                required_points=points_cost,
                available_points=wallet.points_balance,
            )

        wallet.points_balance -= points_cost
        wallet.save(update_fields=("points_balance", "updated_at"))

        call_record = CallRecord.objects.create(
            user=user,
            api_key=api_key,
            operation_type=operation_type,
            alias=normalized_alias,
            model_used=str(model_used or "").strip(),
            resolution=normalized_resolution,
            prompt=str(prompt or ""),
            points_cost=points_cost,
            status=CallRecord.Status.PENDING,
        )
        ledger_entry = PointsLedger.objects.create(
            user=user,
            change_type=PointsLedger.ChangeType.CONSUME,
            points_delta=-points_cost,
            balance_after=wallet.points_balance,
            ref_call=call_record,
        )

    return CallCharge(
        call_record=call_record,
        ledger_entry=ledger_entry,
        points_cost=points_cost,
        balance_after=ledger_entry.balance_after,
    )


def mark_call_success(
    call_record: CallRecord,
    *,
    result_ref: str = "",
    result_summary: str = "",
    upstream_latency_ms: int | None = None,
) -> CallRecord:
    with transaction.atomic():
        locked_call = CallRecord.objects.select_for_update().get(pk=call_record.pk)
        if locked_call.status == CallRecord.Status.FAILED:
            raise InvalidCallStateError("Cannot mark a failed call as successful.")

        locked_call.status = CallRecord.Status.SUCCESS
        locked_call.result_ref = str(result_ref or "")
        locked_call.result_summary = str(result_summary or "")
        locked_call.upstream_latency_ms = upstream_latency_ms
        locked_call.error_message = ""
        locked_call.save(
            update_fields=(
                "status",
                "result_ref",
                "result_summary",
                "upstream_latency_ms",
                "error_message",
                "updated_at",
            )
        )

    return locked_call


def refund_call_points(
    call_record: CallRecord,
    *,
    error_message: str = "",
    reason: str = "",
) -> RefundResult:
    with transaction.atomic():
        locked_call = CallRecord.objects.select_for_update().get(pk=call_record.pk)
        if locked_call.status == CallRecord.Status.SUCCESS:
            raise InvalidCallStateError("Cannot refund a successful call via failure refund.")

        existing_refund = (
            PointsLedger.objects.filter(
                ref_call=locked_call,
                change_type=PointsLedger.ChangeType.REFUND,
            )
            .order_by("id")
            .first()
        )
        if existing_refund is not None:
            if locked_call.status != CallRecord.Status.FAILED:
                locked_call.status = CallRecord.Status.FAILED
                locked_call.error_message = str(error_message or locked_call.error_message or "")
                locked_call.save(update_fields=("status", "error_message", "updated_at"))
            return RefundResult(
                call_record=locked_call,
                ledger_entry=existing_refund,
                points_refunded=0,
                balance_after=existing_refund.balance_after,
                refunded=False,
            )

        points_cost = _validate_positive_points(locked_call.points_cost)
        wallet = _locked_wallet_for_user(locked_call.user)
        wallet.points_balance += points_cost
        wallet.save(update_fields=("points_balance", "updated_at"))

        locked_call.status = CallRecord.Status.FAILED
        locked_call.error_message = str(error_message or "")
        locked_call.save(update_fields=("status", "error_message", "updated_at"))

        ledger_reason = str(reason or error_message or "Call failed; refund precharged points.").strip()
        ledger_entry = PointsLedger.objects.create(
            user=locked_call.user,
            change_type=PointsLedger.ChangeType.REFUND,
            points_delta=points_cost,
            balance_after=wallet.points_balance,
            ref_call=locked_call,
            reason=ledger_reason,
        )

    return RefundResult(
        call_record=locked_call,
        ledger_entry=ledger_entry,
        points_refunded=points_cost,
        balance_after=ledger_entry.balance_after,
        refunded=True,
    )