// From below CodeProject article
// https://www.codeproject.com/Articles/894936/Manipulate-your-expression-trees-with-elegance

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

namespace ManipulateExpressionTrees
{
    public static class ReflectionHelpers
    {
        public static Expression<TDelegate> GetRidOfCompile<TDelegate>(this Expression<TDelegate> expression)
        {
            var visitor = new CompileMethodVisitor();
            return Expression.Lambda<TDelegate>(
                visitor.Visit(expression.Body),
                expression.Parameters);
        }

        public static Expression<TDelegate> GetRidOfInterfaceCast<TDelegate>(this Expression<TDelegate> expression)
        {
            var visitor = new InterfaceCastVisitor();
            return Expression.Lambda<TDelegate>(
                visitor.Visit(expression.Body),
                expression.Parameters);
        }


        private class CompileMethodVisitor : ExpressionVisitor
        {
            protected override Expression VisitInvocation(InvocationExpression node)
            {
                if (node.NodeType != ExpressionType.Invoke)
                    return base.VisitInvocation(node);

                var source = node.Expression as MethodCallExpression;

                if (source == null)
                    return base.VisitInvocation(node);

                var methodInfo = source.Method;

                if (methodInfo.DeclaringType == null ||
                    !methodInfo.DeclaringType.IsGenericType)
                    return base.VisitInvocation(node);

                var methodDeclaringType = methodInfo.DeclaringType.GetGenericTypeDefinition();
                if (methodDeclaringType != typeof(Expression<>))
                    return base.VisitInvocation(node);

                var expr = (LambdaExpression)Evaluate(source.Object);

                var body = expr.Body;
                for (int i = 0; i < expr.Parameters.Count; i++)
                {
                    var visitor = new ParameterUpdateVisitor(expr.Parameters[i], node.Arguments[i]);
                    body = visitor.Visit(body);
                }
                return body;
            }

            private object Evaluate(Expression exp)
            {
                return Expression.Lambda(exp).Compile().DynamicInvoke();
            }
        }

        private class InterfaceCastVisitor : ExpressionVisitor
        {
            protected override Expression VisitMember(MemberExpression node)
            {
                var interfaceProperty = node.Member;

                if (interfaceProperty.MemberType != MemberTypes.Property)
                    return base.VisitMember(node);

                var interfaceType = interfaceProperty.DeclaringType;

                if (interfaceType == null || !interfaceType.IsInterface)
                    return base.VisitMember(node);

                var interfaceCast = node.Expression as UnaryExpression;
                if (interfaceCast == null ||
                    interfaceCast.NodeType != ExpressionType.Convert)
                    return base.VisitMember(node);

                var instanceType = interfaceCast.Operand.Type;

                var instanceProperty = GetImplementedProperty(instanceType, interfaceProperty);

                return Expression.MakeMemberAccess(
                    base.Visit(interfaceCast.Operand),
                    instanceProperty);
            }

            private PropertyInfo GetImplementedProperty(Type classType, MemberInfo interfaceProperty)
            {
                return classType.GetProperty(interfaceProperty.Name);
            }
        }


        /// <summary>
        /// updates the parameter in the expression
        /// </summary>
        private class ParameterUpdateVisitor : ExpressionVisitor
        {
            private readonly ParameterExpression oldParameter;
            private readonly Expression newParameter;

            public ParameterUpdateVisitor(ParameterExpression oldParameter, Expression newParameter)
            {
                this.oldParameter = oldParameter;
                this.newParameter = newParameter;
            }

            protected override Expression VisitParameter(ParameterExpression node)
            {
                if (object.ReferenceEquals(node, oldParameter))
                    return newParameter;

                return base.VisitParameter(node);
            }
        }

    }
}