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[TestFixture]
public class ExpressionTreeFixture
{
    [Test]
    public void a_plus_abs_b_should_equal_9()
    {
        a_plus_abs_b(5, -4).ShouldEqual(9);
    }

    private int a_plus_abs_b(int a, int b)
    {

        var operation = b > 0 
            ? ExpressionType.Add 
            : ExpressionType.Subtract;

        var maths = Expression
                        .MakeBinary(operation, 
                                Expression.Constant(a),
                                Expression.Constant(b));

        return Expression.Lambda<Func<int>>(maths).Compile()();
    }
}

[TestFixture]
public class ExpressionTreeFixture
{
    [Test]
    public void a_plus_abs_b_should_equal_9()
    {
        a_plus_abs_b(5, -4).ShouldEqual(9);
    }

    private int a_plus_abs_b(int a, int b)
    {

        var operation = b > 0 
            ? ExpressionType.Add 
            : ExpressionType.Subtract;

        var maths = Expression
                        .MakeBinary(operation, 
                                Expression.Constant(a),
                                Expression.Constant(b));

        return Expression.Lambda<Func<int>>(maths).Compile()();
    }
}

  public class ASTTester
    {
        [Test]
        public void fun_with_ast()
        {
            /*
             * (define (a-plus-abs-b a b)
             *      ((if (> b 0) + -) a b))
             */
            a_plus_abs_b(5, -4)().ShouldEqual(9);
            5.PlusAbs(-4).ShouldEqual(9);
            cool()(5, -4).ShouldEqual(9);
            cool()(5, 0).ShouldEqual(5);

            boo(-4)(5).ShouldEqual(9);

            var func = GetPredicateBuilder<MyClass>(
                ReflectionHelper.GetProperty<MyClass>(x => x.Name).ToMemberExpression<MyClass>());

            func("something").Compile()(new MyClass(){Name = "has something in it"}).ShouldBeTrue();
        } 


        public int add(int a, int b)
        {
            return a + b;
        }

        public int subtract(int a, int b)
        {
            return a - b;
        }

        public Func<int, int> boo(int b)
        {
            var plus = new Func<int, int>(a => add(a, b));
            var minus = new Func<int, int>(a => subtract(a, b));

            return (b > 0) ? plus : minus;
        }


        public class MyClass
        {
            public string Name { get; set; }
        }
        private Func<int> a_plus_abs_b(int a, int b)
        {
//            if (b > 0) return a + b;
//            return a - b;

            var operation = b > 0 ? ExpressionType.Add : ExpressionType.Subtract;
            var maths = Expression.MakeBinary(operation, Expression.Constant(a), Expression.Constant(b));
           
            return Expression.Lambda<Func<int>>(maths).Compile();
        }

        private Func<int,int,int> cool ()
        {
            ParameterExpression a = Expression.Parameter(typeof (int), "a");
            ParameterExpression b = Expression.Parameter(typeof (int), "b");

            var greaterThanZero = Expression.MakeBinary(ExpressionType.GreaterThan, b, Expression.Constant(0));
            
            var maths = Expression.Condition(greaterThanZero, 
                Expression.MakeBinary(ExpressionType.Add, a, b),
                Expression.MakeBinary(ExpressionType.Subtract, a, b));

            
            return Expression.Lambda<Func<int, int, int>>(maths, a, b).Compile();
        }

        private static readonly MethodInfo _indexOfMethod =
                ReflectionHelper.GetMethod<string>(s => s.IndexOf("", StringComparison.InvariantCultureIgnoreCase));
       
        public Func<object, Expression<Func<T, bool>>> GetPredicateBuilder<T>(MemberExpression propertyPath)
        {
            return valueToCheck =>
            {
                

                ConstantExpression valueToCheckConstant = Expression.Constant(valueToCheck);
                
                //THECALL(x) =  (x.Name ?? "").IndexOf("something", StringComparison.InvariantCultureIgnoreCase)

                MethodCallExpression indexOfCall =
                    Expression.Call(Expression.Coalesce(propertyPath, Expression.Constant(String.Empty)), _indexOfMethod,
                                    valueToCheckConstant,
                                    Expression.Constant(StringComparison.InvariantCultureIgnoreCase));
                
                
                // let THEOPERATION(x) =  [>, THECALL(x), 0 ]
                var operation = false ? ExpressionType.LessThan : ExpressionType.GreaterThanOrEqual;
                BinaryExpression comparison = Expression.MakeBinary(operation, indexOfCall,
                                                                    Expression.Constant(0));

                // let THEFUNC = (x) => THEOPERATION(X)
                ParameterExpression lambdaParameter = propertyPath.GetParameter<T>();
               // ParameterExpression lambdaParameter = Expression.Parameter(typeof (T), "entity");
                return Expression.Lambda<Func<T, bool>>(comparison, lambdaParameter);
            };
        }
    }

    public static class IntExtension
    {
        public static int PlusAbs(this int a, int b)
        {
            var operation = b > 0 ? ExpressionType.Add : ExpressionType.Subtract;
            var maths = Expression.MakeBinary(operation, Expression.Constant(a), Expression.Constant(b));

            return Expression.Lambda<Func<int>>(maths).Compile()();
        }
    }

public Func<int,int,int> a_plus_abs_b ()
{
    ParameterExpression a = Expression.Parameter(typeof (int), "a");
    ParameterExpression b = Expression.Parameter(typeof (int), "b");

    var greaterThanZero = Expression.MakeBinary(ExpressionType.GreaterThan, b, Expression.Constant(0));

    var maths = Expression.Condition(greaterThanZero, 
            Expression.MakeBinary(ExpressionType.Add, a, b),
            Expression.MakeBinary(ExpressionType.Subtract, a, b));


    return Expression.Lambda<Func<int, int, int>>(maths, a, b).Compile();
}

[TestFixture]
public class ExpressionTreeFixture
{
    [Test]
    public void a_plus_abs_b_should_equal_9()
    {
        5.PlusAbs(-4).ShouldEqual(9);
    }
}

public static class IntExtension
{
    public static int PlusAbs(this int a, int b)
    {
        var operation = b > 0 
            ? ExpressionType.Add 
            : ExpressionType.Subtract;

        var maths = Expression
            .MakeBinary(operation, 
                    Expression.Constant(a),
                    Expression.Constant(b));

        return Expression.Lambda<Func<int>>(maths).Compile()();
    }
}

[TestFixture]
public class ExpressionTreeFixture
{
    [Test]
    public void a_plus_abs_b_should_equal_9()
    {
        5.PlusAbs(-4).ShouldEqual(9);
    }
}
 public static class IntExtension
    {
        public static int PlusAbs(this int a, int b)
        {
        var operation = b > 0 
            ? ExpressionType.Add 
            : ExpressionType.Subtract;

        var maths = Expression
                        .MakeBinary(operation, 
                                Expression.Constant(a),
                                Expression.Constant(b));

        return Expression.Lambda<Func<int>>(maths).Compile()();
        }
    }

        if (b > 0) return a + b;
        return a - b;

public int add(int a, int b)
{
    return a + b;
}

public int subtract(int a, int b)
{
    return a - b;
}

public Func<int, int> boo(int b)
{
    var plus = new Func<int, int>(a => add(a, b));
    var minus = new Func<int, int>(a => subtract(a, b));

    return (b > 0) ? plus : minus;
}