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

namespace SurfacePlot3D.Members
{
    public static class PredicateBuilder
    {
        public static Expression<Func<T, Boolean>> True<T>() { return f => true; }
        public static Expression<Func<T, Boolean>> False<T>() { return f => false; }

        public static Expression<Func<T, bool>> Or<T>
            (
                this Expression<Func<T, bool>> expr1
              , Expression<Func<T, bool>> expr2
            )
        {
            var invokedExpr = Expression.Invoke(expr2, expr1.Parameters.Cast<Expression>());
            return Expression.Lambda<Func<T, Boolean>>(Expression.OrElse(expr1.Body, invokedExpr), expr1.Parameters);
        }

        public static Expression<Func<T, Boolean>> And<T>(this Expression<Func<T, Boolean>> expr1, Expression<Func<T, Boolean>> expr2)
        {
            var invokedExpr = Expression.Invoke(expr2, expr1.Parameters.Cast<Expression>());
            return Expression.Lambda<Func<T, Boolean>>(Expression.AndAlso(expr1.Body, invokedExpr), expr1.Parameters);
        }
    }
}