public static ParameterExpression GetParameterExpression()

in tools/AutoMapper/XpressionMapper/Extensions/VisitorExtensions.cs [105:139]
30 lines of code
17 McCabe index (conditional complexity)

        public static ParameterExpression GetParameterExpression(this Expression expression)
        {
            if (expression == null)
                return null;

            //the node represents parameter of the expression
            switch (expression.NodeType)
            {
                case ExpressionType.Parameter:
                    return (ParameterExpression)expression;
                case ExpressionType.Quote:
                    return GetParameterExpression(GetMemberExpression((LambdaExpression)((UnaryExpression)expression).Operand));
                case ExpressionType.Lambda:
                    return GetParameterExpression(GetMemberExpression((LambdaExpression)expression));
                case ExpressionType.ConvertChecked:
                case ExpressionType.Convert:
                    var ue = expression as UnaryExpression;
                    return GetParameterExpression(ue?.Operand);
                case ExpressionType.MemberAccess:
                    return GetParameterExpression(((MemberExpression)expression).Expression);
                case ExpressionType.Call:
                    var methodExpression = expression as MethodCallExpression;
                    var memberExpression = methodExpression?.Object as MemberExpression;//Method is an instance method

                    var isExtension = methodExpression != null && methodExpression.Method.IsDefined(typeof(ExtensionAttribute), true);
                    if (isExtension && memberExpression == null && methodExpression.Arguments.Count > 0)
                        memberExpression = methodExpression.Arguments[0] as MemberExpression;//Method is an extension method based on the type of methodExpression.Arguments[0] and methodExpression.Arguments[0] is a member expression.

                    return isExtension && memberExpression == null && methodExpression.Arguments.Count > 0
                        ? GetParameterExpression(methodExpression.Arguments[0])
                        : (memberExpression == null ? null : GetParameterExpression(memberExpression.Expression));
            }

            return null;
        }