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>
/// 新建/续费订阅处理器。
/// </summary>
public sealed class CreateTenantSubscriptionCommandHandler(
    ITenantRepository tenantRepository,
    IIdGenerator idGenerator)
    : IRequestHandler<CreateTenantSubscriptionCommand, TenantSubscriptionDto>
{
    /// <inheritdoc />
    public async Task<TenantSubscriptionDto> Handle(CreateTenantSubscriptionCommand request, CancellationToken cancellationToken)
    {
        // 1. 校验订阅时长
        if (request.DurationMonths <= 0)
        {
            throw new BusinessException(ErrorCodes.BadRequest, "订阅时长必须大于 0");
        }

        // 2. 获取租户与当前订阅
        var tenant = await tenantRepository.FindByIdAsync(request.TenantId, cancellationToken)
            ?? throw new BusinessException(ErrorCodes.NotFound, "租户不存在");

        var current = await tenantRepository.GetActiveSubscriptionAsync(request.TenantId, cancellationToken);
        var from = current?.EffectiveTo ?? tenant.EffectiveTo ?? DateTime.UtcNow;
        var effectiveFrom = from > DateTime.UtcNow ? from : DateTime.UtcNow;
        var effectiveTo = effectiveFrom.AddMonths(request.DurationMonths);

        // 3. 创建订阅实体
        var subscription = new TenantSubscription
        {
            Id = idGenerator.NextId(),
            TenantId = tenant.Id,
            TenantPackageId = request.TenantPackageId,
            EffectiveFrom = effectiveFrom,
            EffectiveTo = effectiveTo,
            NextBillingDate = effectiveTo,
            Status = SubscriptionStatus.Active,
            AutoRenew = request.AutoRenew,
            Notes = request.Notes
        };

        // 4. 记录订阅与历史
        await tenantRepository.AddSubscriptionAsync(subscription, cancellationToken);
        await tenantRepository.AddSubscriptionHistoryAsync(new TenantSubscriptionHistory
        {
            Id = idGenerator.NextId(),
            TenantId = tenant.Id,
            TenantSubscriptionId = subscription.Id,
            FromPackageId = current?.TenantPackageId ?? request.TenantPackageId,
            ToPackageId = request.TenantPackageId,
            ChangeType = current == null ? SubscriptionChangeType.New : SubscriptionChangeType.Renew,
            EffectiveFrom = effectiveFrom,
            EffectiveTo = effectiveTo,
            Amount = null,
            Currency = null,
            Notes = request.Notes
        }, cancellationToken);

        // 5. 记录审计
        await tenantRepository.AddAuditLogAsync(new TenantAuditLog
        {
            TenantId = tenant.Id,
            Action = TenantAuditAction.SubscriptionUpdated,
            Title = current == null ? "创建订阅" : "续费订阅",
            Description = $"套餐 {request.TenantPackageId} 时长 {request.DurationMonths} 月"
        }, cancellationToken);

        // 6. 保存变更
        await tenantRepository.SaveChangesAsync(cancellationToken);

        // 7. 返回 DTO
        return subscription.ToSubscriptionDto()
               ?? throw new BusinessException(ErrorCodes.InternalServerError, "订阅生成失败");
    }
}