using System;
using System.Collections.Generic;
using System.Linq;
using System.Linq.Expressions;
using System.Text;
using System.Threading.Tasks;

namespace DG.Core
{
    public static class PredicateExtensionses
    {
        public static Expression<Func<T, bool>> True<T>() { return f => true; }

        public static Expression<Func<T, bool>> False<T>() { return f => false; }

        public static Expression<Func<T, bool>> And<T>(this Expression<Func<T, bool>> expLeft, Expression<Func<T, bool>> expRight)
        {
            var candidateExpr = Expression.Parameter(typeof(T), "candidate");
            var parameterReplacer = new ParameterReplacer(candidateExpr);

            var left = parameterReplacer.Replace(expLeft.Body);
            var right = parameterReplacer.Replace(expRight.Body);
            var body = Expression.And(left, right);

            return Expression.Lambda<Func<T, bool>>(body, candidateExpr);
        }

        public static Expression<Func<T, bool>> Or<T>(this Expression<Func<T, bool>> expLeft, Expression<Func<T, bool>> expRight)
        {
            var candidateExpr = Expression.Parameter(typeof(T), "candidate");
            var parameterReplacer = new ParameterReplacer(candidateExpr);

            var left = parameterReplacer.Replace(expLeft.Body);
            var right = parameterReplacer.Replace(expRight.Body);
            var body = Expression.OrElse(left, right);

            return Expression.Lambda<Func<T, bool>>(body, candidateExpr);
        }
        /// <summary>
        /// And ((a or b )and (x or d))关系，但是and后面里面的关系是Or的关系，如 a.resid='' and ((a.channel>=1 and a.channel<10) or (a.channel>=50 and a.channel<60))
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="expLeft"></param>
        /// <param name="expRight"></param>
        /// <returns></returns>
        public static Expression<Func<T, bool>> AndListOr<T>(this Expression<Func<T, bool>> expLeft, Expression<Func<T, bool>>[] predicates)
        {
            var candidateExpr = Expression.Parameter(typeof(T), "candidate");
            var parameterReplacer = new ParameterReplacer(candidateExpr);
            var left = parameterReplacer.Replace(expLeft.Body);
            Expression<Func<T, bool>> lambda = predicates[0];
            for (int i = 1; i < predicates.Length; i++)
            {
                lambda = lambda.Or(predicates[i]);
            }
            var right = parameterReplacer.Replace(lambda.Body);
            var body = Expression.And(left, right);

            return Expression.Lambda<Func<T, bool>>(body, candidateExpr);
        }

        /// <summary>
        /// 传入条件之间为OR查询
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="source"></param>
        /// <param name="predicates"></param>
        /// <returns></returns>
        public static IQueryable<T> WhereOR<T>(this IQueryable<T> source, params Expression<Func<T, bool>>[] predicates)
        {
            if (source == null) throw new ArgumentNullException("source");
            if (predicates == null) throw new ArgumentNullException("predicates");
            if (predicates.Length == 0) return source.Where(x => true);
            if (predicates.Length == 1) return source.Where(predicates[0]);

            var param = Expression.Parameter(typeof(T), "x");
            Expression body = Expression.Invoke(predicates[0], param);
            for (int i = 1; i < predicates.Length; i++)
            {
                body = Expression.OrElse(body, Expression.Invoke(predicates[i], param));
            }
            var lambda = Expression.Lambda<Func<T, bool>>(body, param);
            return source.Where(lambda);
        }
    }

    internal class ParameterReplacer : ExpressionVisitor
    {
        public ParameterReplacer(ParameterExpression paramExpr)
        {
            this.ParameterExpression = paramExpr;
        }

        public ParameterExpression ParameterExpression { get; private set; }

        public Expression Replace(Expression expr)
        {
            return this.Visit(expr);
        }

        protected override Expression VisitParameter(ParameterExpression p)
        {
            return this.ParameterExpression;
        }
    }
}