using System;
using System.Linq.Expressions;

namespace IRaCIS.Infra.Data.ExpressionExtend
{
    /// <summary>
    /// 合并表达式 And Or  Not扩展
    /// </summary>
    public static class ExpressionExtend
    {
        /// <summary>
        /// 合并表达式 expr1 AND expr2
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="expr1"></param>
        /// <param name="expr2"></param>
        /// <returns></returns>
        public static Expression<Func<T, bool>> And<T>(this Expression<Func<T, bool>> expr1, Expression<Func<T, bool>> expr2)
        {
            if (expr1 == null) return expr2;
            else if (expr2 == null) return expr1;

            //return Expression.Lambda<Func<T, bool>>(Expression.AndAlso(expr1.Body, expr2.Body), expr1.Parameters);
            ParameterExpression newParameter = Expression.Parameter(typeof(T), "c");
            NewExpressionVisitor visitor = new NewExpressionVisitor(newParameter);

            var left = visitor.Replace(expr1.Body);
            var right = visitor.Replace(expr2.Body);
            var body = Expression.And(left, right);
            return Expression.Lambda<Func<T, bool>>(body, newParameter);

        }
        /// <summary>
        /// 合并表达式 expr1 or expr2
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="expr1"></param>
        /// <param name="expr2"></param>
        /// <returns></returns>
        public static Expression<Func<T, bool>> Or<T>(this Expression<Func<T, bool>> expr1, Expression<Func<T, bool>> expr2)
        {
            if (expr1 == null) return expr2;
            else if (expr2 == null) return expr1;

            ParameterExpression newParameter = Expression.Parameter(typeof(T), "c");
            NewExpressionVisitor visitor = new NewExpressionVisitor(newParameter);

            var left = visitor.Replace(expr1.Body);
            var right = visitor.Replace(expr2.Body);
            var body = Expression.Or(left, right);
            return Expression.Lambda<Func<T, bool>>(body, newParameter);
        }
        public static Expression<Func<T, bool>> Not<T>(this Expression<Func<T, bool>> expr)
        {
            if (expr == null) return null;
            var candidateExpr = expr.Parameters[0];
            var body = Expression.Not(expr.Body);
            return Expression.Lambda<Func<T, bool>>(body, candidateExpr);
        }
    }
}