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

namespace CallCenter.Utility.Linq
{
    public static class PredicateExtensionses
    {
        public static Expression<Func<T, bool>> True<T>()
        {
            return f => true;
        }
        public static Expression<Func<T, bool>> All<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>> exp_left, Expression<Func<T, bool>> exp_right)
        {
            var candidateExpr = Expression.Parameter(typeof(T), "candidate");

            var parameterReplacer = new ParameterReplacer(candidateExpr);

            var left = parameterReplacer.Replace(exp_left.Body);
            var right = parameterReplacer.Replace(exp_right.Body);

            var body = Expression.And(left, right);
            exp_left = Expression.Lambda<Func<T, bool>>(body, candidateExpr);
            return Expression.Lambda<Func<T, bool>>(body, candidateExpr);
        }

        public static Expression<Func<T, bool>> Or<T>(this Expression<Func<T, bool>> exp_left, Expression<Func<T, bool>> exp_right)
        {
            var candidateExpr = Expression.Parameter(typeof(T), "candidate");

            var parameterReplacer = new ParameterReplacer(candidateExpr);

            var left = parameterReplacer.Replace(exp_left.Body);
            var right = parameterReplacer.Replace(exp_right.Body);

            var body = Expression.Or(left, right);

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



    }
    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;
        }
    }
}
