ANTOOZA-BACKEND/Domain/Entities/Store/Coupon.cs

using System.ComponentModel.DataAnnotations;
using System.ComponentModel.DataAnnotations.Schema;
using Domain.Entities.Store.ValueObject;

namespace Domain.Entities.Store;

/// <summary>
/// 쿠폰 메타. 실제 코드 풀은 CouponCode 1:N 으로 관리.
/// ProductID 필수 (어떤 Digital 상품에 발급할 쿠폰인지), GameID 필수 (사용자 정책: 게임 필수 연결).
/// </summary>
public class Coupon
{
    [ForeignKey(nameof(ProductID))]
    public virtual Product? Product { get; private set; }

    [ForeignKey(nameof(GameID))]
    public virtual Game? Game { get; private set; }

    [Key]
    public int ID { get; private set; }

    public int ProductID { get; private set; }

    public int GameID { get; private set; }

    public string Name { get; private set; } = default!;

    public DateTime? ExpiresAt { get; private set; }

    public CouponUsagePolicy UsagePolicy { get; private set; } = CouponUsagePolicy.SingleUse;

    /// <summary>누적 발급 가능 코드 수 (CouponCode 풀의 총 row 수). 통계용.</summary>
    public int GeneratedCount { get; private set; }

    /// <summary>실제 사용된 코드 수 (Status=Used). 통계용.</summary>
    public int UsedCount { get; private set; }

    /// <summary>잔여 코드 부족 알림 임계치 (Available 코드가 이 값 미만이면 Admin 알림).</summary>
    public int LowStockThreshold { get; private set; } = 10;

    public DateTime CreatedAt { get; private set; } = DateTime.UtcNow;

    public DateTime? UpdatedAt { get; private set; }

    private Coupon() { }

    public static Coupon Create(
        int productID,
        int gameID,
        string name,
        CouponUsagePolicy usagePolicy = CouponUsagePolicy.SingleUse,
        DateTime? expiresAt = null,
        int lowStockThreshold = 10
    ) {
        if (productID <= 0)
        {
            throw new ArgumentOutOfRangeException(nameof(productID), "Product is required.");
        }

        if (gameID <= 0)
        {
            throw new ArgumentOutOfRangeException(nameof(gameID), "Game is required.");
        }

        if (string.IsNullOrWhiteSpace(name))
        {
            throw new ArgumentException("Name is required.", nameof(name));
        }

        if (name.Length > 200)
        {
            throw new ArgumentOutOfRangeException(nameof(name));
        }

        if (lowStockThreshold < 0)
        {
            throw new ArgumentOutOfRangeException(nameof(lowStockThreshold));
        }

        return new Coupon
        {
            ProductID = productID,
            GameID = gameID,
            Name = name,
            UsagePolicy = usagePolicy,
            ExpiresAt = expiresAt,
            LowStockThreshold = lowStockThreshold
        };
    }

    public void Update(string name, DateTime? expiresAt, int lowStockThreshold)
    {
        if (string.IsNullOrWhiteSpace(name))
        {
            throw new ArgumentException("Name is required.", nameof(name));
        }

        if (lowStockThreshold < 0)
        {
            throw new ArgumentOutOfRangeException(nameof(lowStockThreshold));
        }

        Name = name;
        ExpiresAt = expiresAt;
        LowStockThreshold = lowStockThreshold;
        UpdatedAt = DateTime.UtcNow;
    }

    /// <summary>BulkUpload 후 발급 가능 코드 수 누적.</summary>
    public void IncreaseGeneratedCount(int delta)
    {
        if (delta <= 0)
        {
            throw new ArgumentOutOfRangeException(nameof(delta));
        }

        GeneratedCount += delta;
        UpdatedAt = DateTime.UtcNow;
    }

    /// <summary>코드 1개가 Used 상태로 전이될 때 호출 (실제 사용 보고용 — 결제 발급 시점이 아니라 사용자가 사용 누른 시점).</summary>
    public void IncreaseUsedCount(int delta = 1)
    {
        if (delta <= 0)
        {
            throw new ArgumentOutOfRangeException(nameof(delta));
        }

        UsedCount += delta;
        UpdatedAt = DateTime.UtcNow;
    }
}