using MediatR;
using TakeoutSaaS.Application.App.Billings.Commands;
using TakeoutSaaS.Domain.Tenants.Repositories;

namespace TakeoutSaaS.Application.App.Billings.Handlers;

/// <summary>
/// 处理逾期账单命令处理器（后台任务）。
/// </summary>
public sealed class ProcessOverdueBillingsCommandHandler(
    ITenantBillingRepository billingRepository)
    : IRequestHandler<ProcessOverdueBillingsCommand, int>
{
    /// <inheritdoc />
    public async Task<int> Handle(ProcessOverdueBillingsCommand request, CancellationToken cancellationToken)
    {
        // 1. 查询逾期账单（到期日已过且未支付）
        var overdueBillings = await billingRepository.GetOverdueBillingsAsync(cancellationToken);
        if (overdueBillings.Count == 0)
        {
            return 0;
        }

        // 2. (空行后) 标记为逾期并更新通知时间
        var now = DateTime.UtcNow;
        var updatedCount = 0;
        foreach (var billing in overdueBillings)
        {
            var before = billing.Status;
            billing.MarkAsOverdue();

            if (before != billing.Status)
            {
                billing.OverdueNotifiedAt ??= now;
                await billingRepository.UpdateAsync(billing, cancellationToken);
                updatedCount++;
            }
        }

        // 3. (空行后) 持久化
        if (updatedCount > 0)
        {
            await billingRepository.SaveChangesAsync(cancellationToken);
        }

        return updatedCount;
    }
}