using Microsoft.EntityFrameworkCore;
using System.Reflection;
using TakeoutSaaS.Shared.Abstractions.Entities;
using TakeoutSaaS.Shared.Abstractions.Ids;
using TakeoutSaaS.Shared.Abstractions.Security;
using TakeoutSaaS.Shared.Abstractions.Tenancy;

namespace TakeoutSaaS.Infrastructure.Common.Persistence;

/// <summary>
/// 多租户感知 DbContext：自动应用租户过滤并填充租户字段。
/// </summary>
public abstract class TenantAwareDbContext(
    DbContextOptions options,
    ITenantProvider tenantProvider,
    ICurrentUserAccessor? currentUserAccessor = null,
    IIdGenerator? idGenerator = null) : AppDbContext(options, currentUserAccessor, idGenerator)
{
    /// <summary>
    /// 当前请求租户 ID。
    /// </summary>
    protected long CurrentTenantId => tenantProvider.GetCurrentTenantId();

    /// <summary>
    /// 保存前填充租户元数据并执行基础处理。
    /// </summary>
    protected override void OnBeforeSaving()
    {
        ApplyTenantMetadata();
        base.OnBeforeSaving();
    }

    /// <summary>
    /// 应用租户过滤器到所有实现 <see cref="IMultiTenantEntity"/> 的实体。
    /// </summary>
    /// <param name="modelBuilder">模型构建器。</param>
    protected void ApplyTenantQueryFilters(ModelBuilder modelBuilder)
    {
        foreach (var entityType in modelBuilder.Model.GetEntityTypes())
        {
            if (!typeof(IMultiTenantEntity).IsAssignableFrom(entityType.ClrType))
            {
                continue;
            }

            var methodInfo = typeof(TenantAwareDbContext)
                .GetMethod(nameof(SetTenantFilter), BindingFlags.Instance | BindingFlags.NonPublic)!
                .MakeGenericMethod(entityType.ClrType);

            methodInfo.Invoke(this, new object[] { modelBuilder });
        }
    }

    /// <summary>
    /// 为具体实体设置租户过滤器。
    /// </summary>
    /// <typeparam name="TEntity">实体类型。</typeparam>
    /// <param name="modelBuilder">模型构建器。</param>
    private void SetTenantFilter<TEntity>(ModelBuilder modelBuilder)
        where TEntity : class, IMultiTenantEntity
    {
        modelBuilder.Entity<TEntity>().HasQueryFilter(entity => entity.TenantId == CurrentTenantId);
    }

    /// <summary>
    /// 为新增实体填充租户 ID。
    /// </summary>
    private void ApplyTenantMetadata()
    {
        var tenantId = CurrentTenantId;

        foreach (var entry in ChangeTracker.Entries<IMultiTenantEntity>())
        {
            if (entry.State == EntityState.Added && entry.Entity.TenantId == 0 && tenantId != 0)
            {
                entry.Entity.TenantId = tenantId;
            }
        }
    }
}