using System;
using System.Linq;
using System.Linq.Expressions;

namespace CRM.Core.BLL
{
    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.Or(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]);

            Expression<Func<T, bool>> lambda = predicates[0];
            for (int i = 1; i < predicates.Length; i++)
            {
                lambda = lambda.Or(predicates[i]);
            }
            return source.Where(lambda);
        }

        //public static Expression<Func<T, bool>> Or<T>(this Expression<Func<T, bool>> first, Expression<Func<T, bool>> second)
        //{
        //    return ParameterRebinder.Compose(first, second, Expression.Or);
        //}
    }

    //public class ParameterRebinder : ExpressionVisitor
    //{
    //    public static Expression<T> Compose<T>(Expression<T> first, Expression<T> second, Func<Expression, Expression, Expression> merge)
    //    {
    //        // build parameter map (from parameters of second to parameters of first) 
    //        var map = first.Parameters.Select((f, i) => new { f, s = second.Parameters[i] }).ToDictionary(p => p.s, p => p.f);

    //        // replace parameters in the second lambda expression with parameters from the first 
    //        var secondBody = ReplaceParameters(map, second.Body);

    //        // apply composition of lambda expression bodies to parameters from the first expression  
    //        return Expression.Lambda<T>(merge(first.Body, secondBody), first.Parameters);
    //    }

    //}

    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;
        }
    }
}