using System.ComponentModel.DataAnnotations;
using System.Text;

namespace Util.Domains {
    /// <summary>
    /// 领域实体
    /// </summary>
    /// <typeparam name="TKey">标识类型</typeparam>
    public abstract class EntityBase<TKey> {

        #region 构造方法

        /// <summary>
        /// 初始化领域实体
        /// </summary>
        /// <param name="id">标识</param>
        protected EntityBase( TKey id ) {
            Id = id;
        }

        #endregion

        #region 字段

        /// <summary>
        /// 描述
        /// </summary>
        private StringBuilder _description;

        #endregion

        #region Id(标识)

        /// <summary>
        /// 标识
        /// </summary>
        [Required]
        public TKey Id { get; private set; }

        #endregion

        #region Equals(相等运算)

        /// <summary>
        /// 相等运算
        /// </summary>
        public override bool Equals( object entity ) {
            if ( entity == null )
                return false;
            if ( !( entity is EntityBase<TKey> ) )
                return false;
            return this == (EntityBase<TKey>)entity;
        }

        #endregion

        #region GetHashCode(获取哈希)

        /// <summary>
        /// 获取哈希
        /// </summary>
        public override int GetHashCode() {
            return Id.GetHashCode();
        }

        #endregion

        #region ==(相等比较)

        /// <summary>
        /// 相等比较
        /// </summary>
        /// <param name="entity1">领域实体1</param>
        /// <param name="entity2">领域实体2</param>
        public static bool operator ==( EntityBase<TKey> entity1, EntityBase<TKey> entity2 ) {
            if ( (object)entity1 == null && (object)entity2 == null )
                return true;
            if ( (object)entity1 == null || (object)entity2 == null )
                return false;
            if ( entity1.Id == null )
                return false;
            if ( entity1.Id.Equals( default( TKey ) ) )
                return false;
            return entity1.Id.Equals( entity2.Id );
        }

        #endregion

        #region !=(不相等比较)

        /// <summary>
        /// 不相等比较
        /// </summary>
        /// <param name="entity1">领域实体1</param>
        /// <param name="entity2">领域实体2</param>
        public static bool operator !=( EntityBase<TKey> entity1, EntityBase<TKey> entity2 ) {
            return !( entity1 == entity2 );
        }

        #endregion

        #region ToString(输出领域对象的状态)

        /// <summary>
        /// 输出领域对象的状态
        /// </summary>
        public override string ToString() {
            _description = new StringBuilder();
            AddDescriptions();
            return _description.ToString().TrimEnd().TrimEnd( ',' );
        }

        /// <summary>
        /// 添加描述
        /// </summary>
        protected virtual void AddDescriptions() {
        }

        /// <summary>
        /// 添加描述
        /// </summary>
        protected void AddDescription( string description ) {
            if ( string.IsNullOrWhiteSpace( description ) )
                return;
            _description.Append( description );
        }

        /// <summary>
        /// 添加描述
        /// </summary>
        prot