ANTOOZA-BACKEND/Application/Features/Admin/Store/Coupon/ExportCodes/Handler.cs

using Application.Abstractions.Data;
using Application.Abstractions.Messaging;
using Domain.Entities.Store.ValueObject;
using Microsoft.EntityFrameworkCore;
using SharedKernel.Helpers;
using SharedKernel.Results;

namespace Application.Features.Admin.Store.Coupon.ExportCodes;

/// <summary>
/// CSV 양식 (DB 컬럼명 기준):
///   ID, Code, Status, IssuedToMemberID, IssuedToMemberName, IssuedToMemberEmail, IssuedAt, UsedAt, CreatedAt
///
/// Status 인코딩 (사용자 결정 — Option A):
///   0 = Available (미배포)
///   1 = Reserved/Issued/Used (배포된 상태로 묶음)
///
/// 일시는 KST 로 출력 (UTC → Local 변환).
/// </summary>
public sealed class Handler(IAppDbContext db) : IQueryHandler<Query, Result<Response>>
{
    private static readonly string[] Header =
    [
        "ID",
        "Code",
        "Status",
        "IssuedToMemberID",
        "IssuedToMemberName",
        "IssuedToMemberEmail",
        "IssuedAt",
        "UsedAt",
        "CreatedAt"
    ];

    public async Task<Result<Response>> Handle(Query request, CancellationToken ct)
    {
        var coupon = await db.Coupon.AsNoTracking()
            .Where(c => c.ID == request.CouponID)
            .Select(c => new { c.ID, c.Name })
            .FirstOrDefaultAsync(ct);

        if (coupon is null)
        {
            return Result.Failure<Response>(Error.NotFound("Coupon.NotFound", "쿠폰을 찾을 수 없습니다."));
        }

        var rows = await db.CouponCode.AsNoTracking()
            .Include(c => c.IssuedToMember)
            .Where(c => c.CouponID == request.CouponID)
            .OrderBy(c => c.ID)
            .Select(c => new
            {
                c.ID,
                c.Code,
                c.Status,
                c.IssuedToMemberID,
                Name = c.IssuedToMember != null ? c.IssuedToMember.Name : null,
                Email = c.IssuedToMember != null ? c.IssuedToMember.Email : null,
                c.IssuedAt,
                c.UsedAt,
                c.CreatedAt
            })
            .ToListAsync(ct);

        var csvRows = new List<string[]> { Header };

        foreach (var r in rows)
        {
            var status = r.Status == CouponCodeStatus.Available ? "0" : "1";
            var memberID = r.IssuedToMemberID?.ToString() ?? "";
            var name = r.Name ?? "";
            var email = r.Email ?? "";
            var issuedAt = r.IssuedAt.HasValue
                ? DateTime.SpecifyKind(r.IssuedAt.Value, DateTimeKind.Utc).ToLocalTime().ToString("yyyy-MM-dd HH:mm:ss")
                : "";
            var usedAt = r.UsedAt.HasValue
                ? DateTime.SpecifyKind(r.UsedAt.Value, DateTimeKind.Utc).ToLocalTime().ToString("yyyy-MM-dd HH:mm:ss")
                : "";
            var createdAt = DateTime.SpecifyKind(r.CreatedAt, DateTimeKind.Utc).ToLocalTime().ToString("yyyy-MM-dd HH:mm:ss");

            csvRows.Add([
                r.ID.ToString(),
                r.Code,
                status,
                memberID,
                name,
                email,
                issuedAt,
                usedAt,
                createdAt
            ]);
        }

        var bytes = CsvHelper.WriteUtf8Bom(csvRows);
        var fileName = $"coupon-codes-{request.CouponID}-{DateTime.Now:yyyyMMdd-HHmmss}.csv";

        return Result.Success(new Response(bytes, fileName));
    }
}