using System.Collections.Generic;

namespace System.Linq.Expressions
{
    public static class ExpressionHelper
    {
        /// <summary>
        /// 将多个条件 使用 OR 连接成一个表达式
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="predicates">多个条件表达式</param>
        /// <returns></returns>
        public static Expression<Func<T, bool>> WhereOr<T>(
            IReadOnlyList<Expression<Func<T, bool>>> predicates)
        {
            if (predicates.Count == 0) return x => false; // no matches!
            if (predicates.Count == 1) return predicates[0]; // simple
            var param = Expression.Parameter(typeof(T), "x");
            Expression body = Expression.Invoke(predicates[0], param);
            for (int i = 1; i < predicates.Count; i++)
            {
                body = Expression.OrElse(body, Expression.Invoke(predicates[i], param));
            }
            var lambda = Expression.Lambda<Func<T, bool>>(body, param);
            return lambda;
        }
    }
}