using MediatR;
using TakeoutSaaS.Application.App.Tenants.Commands;
using TakeoutSaaS.Application.App.Tenants.Dto;
using TakeoutSaaS.Domain.Tenants.Entities;
using TakeoutSaaS.Domain.Tenants.Enums;
using TakeoutSaaS.Domain.Tenants.Repositories;
using TakeoutSaaS.Shared.Abstractions.Constants;
using TakeoutSaaS.Shared.Abstractions.Exceptions;
using TakeoutSaaS.Shared.Abstractions.Ids;

namespace TakeoutSaaS.Application.App.Tenants.Handlers;

/// <summary>
/// 套餐升降配处理器。
/// </summary>
public sealed class ChangeTenantSubscriptionPlanCommandHandler(
    ITenantRepository tenantRepository,
    IIdGenerator idGenerator)
    : IRequestHandler<ChangeTenantSubscriptionPlanCommand, TenantSubscriptionDto>
{
    /// <inheritdoc />
    public async Task<TenantSubscriptionDto> Handle(ChangeTenantSubscriptionPlanCommand request, CancellationToken cancellationToken)
    {
        // 1. 校验租户与订阅存在性
        _ = await tenantRepository.FindByIdAsync(request.TenantId, cancellationToken)
            ?? throw new BusinessException(ErrorCodes.NotFound, "租户不存在");

        var subscription = await tenantRepository.FindSubscriptionByIdAsync(request.TenantId, request.TenantSubscriptionId, cancellationToken)
            ?? throw new BusinessException(ErrorCodes.NotFound, "订阅不存在");

        var previousPackage = subscription.TenantPackageId;

        // 2. 根据立即生效或排期设置目标套餐
        if (request.Immediate)
        {
            subscription.TenantPackageId = request.TargetPackageId;
            subscription.ScheduledPackageId = null;
        }
        else
        {
            subscription.ScheduledPackageId = request.TargetPackageId;
        }

        // 3. 更新订阅并记录变更历史
        await tenantRepository.UpdateSubscriptionAsync(subscription, cancellationToken);
        await tenantRepository.AddSubscriptionHistoryAsync(new TenantSubscriptionHistory
        {
            Id = idGenerator.NextId(),
            TenantId = subscription.TenantId,
            TenantSubscriptionId = subscription.Id,
            FromPackageId = previousPackage,
            ToPackageId = request.TargetPackageId,
            ChangeType = SubscriptionChangeType.Upgrade,
            EffectiveFrom = subscription.EffectiveFrom,
            EffectiveTo = subscription.EffectiveTo,
            Notes = request.Notes
        }, cancellationToken);

        // 4. 记录审计日志
        await tenantRepository.AddAuditLogAsync(new TenantAuditLog
        {
            TenantId = subscription.TenantId,
            Action = TenantAuditAction.SubscriptionPlanChanged,
            Title = request.Immediate ? "套餐立即变更" : "套餐排期变更",
            Description = request.Notes,
            PreviousStatus = null,
            CurrentStatus = null
        }, cancellationToken);

        // 5. 保存并返回 DTO
        await tenantRepository.SaveChangesAsync(cancellationToken);

        return subscription.ToSubscriptionDto()
               ?? throw new BusinessException(ErrorCodes.InternalServerError, "订阅更新失败");
    }
}