ANTOOZA-BACKEND/Application/Features/Api/Paper/PlaceOrder/Handler.cs

using Application.Abstractions.Data;
using Application.Abstractions.Messaging;
using Application.Helpers;
using Domain.Entities.Paper.ValueObject;
using Domain.Entities.Stocks.ValueObject;
using Microsoft.EntityFrameworkCore;
using SharedKernel.Results;
using PaperOrderEntity = Domain.Entities.Paper.PaperOrder;

namespace Application.Features.Api.Paper.PlaceOrder;

/// <summary>
/// 모의투자 주문 접수 — FillRule/TargetDate/CancelableUntil 서버 산정 + 예약/상한 검증 (d4 §③/§⑤).
/// 매수: ReservedAmount = ceil(종가×수량×1.35) + 예상수수료, 1주문 상한(Equity×OrderMaxPctBp) 검증, 계좌 예약.
/// 매도: 포지션 가용 수량 검증 후 매도 예약. 실제 기표는 배치(M2).
/// </summary>
internal sealed class Handler(IAppDbContext db) : ICommandHandler<Command, Result<Response>>
{
    public async Task<Result<Response>> Handle(Command request, CancellationToken ct)
    {
        var paper = await db.Config.AsNoTracking().OrderByDescending(c => c.ID).Select(c => c.Paper).FirstOrDefaultAsync(ct);

        if (paper is null || !paper.Enabled)
        {
            return Result.Failure<Response>(Error.Problem("Paper.Disabled", "모의투자가 비활성화되어 있습니다."));
        }

        if (request.Quantity <= 0)
        {
            return Result.Failure<Response>(Error.Problem("Paper.InvalidQuantity", "수량은 1 이상이어야 합니다."));
        }

        var code = request.StockCode?.Trim() ?? "";

        if (code.Length != 6)
        {
            return Result.Failure<Response>(Error.Problem("Paper.InvalidCode", "종목코드가 올바르지 않습니다."));
        }

        // 종목 존재 + 거래 상태 검증
        var stock = await db.Stock.AsNoTracking()
            .Where(c => c.Code == code)
            .Select(c => new { c.ID, c.TradingStatus, c.IsActive })
            .FirstOrDefaultAsync(ct);

        if (stock is null || !stock.IsActive)
        {
            return Result.Failure<Response>(Error.NotFound("Paper.StockNotFound", "종목을 찾을 수 없습니다."));
        }

        if (stock.TradingStatus != TradingStatus.Normal)
        {
            return Result.Failure<Response>(Error.Problem("Paper.StockNotTradable", "거래정지 또는 관리종목은 주문할 수 없습니다."));
        }

        var account = await db.PaperAccount.FirstOrDefaultAsync(c => c.MemberID == request.MemberID, ct);

        if (account is null)
        {
            return Result.Failure<Response>(Error.NotFound("Paper.NoAccount", "모의투자 계좌가 없습니다. 먼저 입금해 주세요."));
        }

        // 최근 종가
        var latestClose = await PaperValuation.GetLatestCloseAsync(db, code, ct);

        if (latestClose is null || latestClose.Value <= 0)
        {
            return Result.Failure<Response>(Error.Problem("Paper.NoPrice", "종목 시세가 없어 주문할 수 없습니다."));
        }

        // 체결 계획 (KST + 휴장일)
        var holidayList = await db.MarketHoliday.AsNoTracking().Select(c => c.Date).ToListAsync(ct);
        var holidays = holidayList.ToHashSet();
        var nowKst = PaperTradingClock.NowKst();
        var (fillRule, targetDate, cancelableUntilKst) = PaperTradingClock.Plan(nowKst, holidays);
        var cancelableUntilUtc = PaperTradingClock.ToUtc(cancelableUntilKst);

        var close = latestClose.Value;
        var orderNotional = close * request.Quantity;

        decimal reservedAmount;

        if (request.Side == PaperOrderSide.Buy)
        {
            // 1주문 상한: 주문금액 ≤ Equity × OrderMaxPctBp / 10000
            var positions = await db.PaperPosition.AsNoTracking()
                .Where(c => c.AccountID == account.ID && c.Quantity > 0)
                .Select(c => new { c.StockCode, c.Quantity })
                .ToListAsync(ct);

            var codes = positions.Select(c => c.StockCode).Distinct().ToList();
            var latestCloses = await PaperValuation.GetLatestClosesAsync(db, codes, ct);
            var equity = PaperValuation.ComputeEquity(account.Token, account.ReservedToken, positions.Select(c => (c.StockCode, c.Quantity)), latestCloses);
            var maxNotional = equity * paper.OrderMaxPctBp / 10000m;

            if (orderNotional > maxNotional)
            {
                return Result.Failure<Response>(Error.Problem("Paper.OrderTooLarge", $"1주문 한도({paper.OrderMaxPctBp / 100m:0.##}% = {(long)maxNotional:N0} 토큰)를 초과합니다."));
            }

            // 매수 예약금 = ceil(종가 × 수량 × 1.35) + 예상수수료 (가격제한폭 ±30% + 연휴 갭 여유)
            var priceReserve = Math.Ceiling(orderNotional * 1.35m);
            var estFee = Math.Floor(orderNotional * paper.FeeRateBp / 10000m);
            reservedAmount = priceReserve + estFee;

            if (account.Token < reservedAmount)
            {
                return Result.Failure<Response>(Error.Conflict("Paper.InsufficientToken", $"잔액이 부족합니다. 예약 필요: {(long)reservedAmount:N0} / 가용: {(long)account.Token:N0}."));
            }

            account.ReserveForBuy(reservedAmount);
        }
        else
        {
            // 매도: 포지션 가용 수량 검증
            var position = await db.PaperPosition.FirstOrDefaultAsync(c => c.AccountID == account.ID && c.StockCode == code, ct);

            if (position is null || position.Quantity - position.ReservedQuantity < request.Quantity)
            {
                return Result.Failure<Response>(Error.Conflict("Paper.InsufficientPosition", "매도 가능한 보유 수량이 부족합니다."));
            }

            position.ReserveSell(request.Quantity);
            reservedAmount = 0;
        }

        var order = PaperOrderEntity.Create(
            account.ID,
            code,
            request.Side,
            fillRule,
            request.Quantity,
            reservedAmount,
            targetDate,
            cancelableUntilUtc);

        db.PaperOrder.Add(order);

        await db.SaveChangesAsync(ct);

        return Result.Success(new Response(
            order.ID,
            order.Side,
            order.FillRule,
            order.TargetDate,
            order.CancelableUntil,
            order.Quantity,
            order.ReservedAmount));
    }
}