ExternalFunction.cs

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// 
//  Copyright 2010-2015 Deveel
// 
//    Licensed under the Apache License, Version 2.0 (the "License");
//    you may not use this file except in compliance with the License.
//    You may obtain a copy of the License at
// 
//        http://www.apache.org/licenses/LICENSE-2.0
// 
//    Unless required by applicable law or agreed to in writing, software
//    distributed under the License is distributed on an "AS IS" BASIS,
//    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
//    See the License for the specific language governing permissions and
//    limitations under the License.
//

using System;
using System.Reflection;

using Deveel.Data.Types;

namespace Deveel.Data.Routines {
    public sealed class ExternalFunction : Function {
        private MethodInfo method;

        public ExternalFunction(FunctionInfo functionInfo) 
            : base(functionInfo) {
            if (functionInfo.FunctionType != FunctionType.External)
                throw new ArgumentException("The information specified are not pointing to any external function.");
        }

        public override InvokeResult Execute(InvokeContext context) {
            if (method == null)
                method = DiscoverMethod();

            if (method == null)
                throw new InvalidOperationException();

            var args = context.EvaluatedArguments;

            try {
                var methodArgs = ConvertArguments(method, args);
                var result = method.Invoke(null, methodArgs);

                return  context.Result(ConvertValue(result, ReturnType()));
            } catch (Exception) {
                throw;
            }
        }

        private DataObject ConvertValue(object value, SqlType sqlType) {
            throw new NotImplementedException();
        }

        private object[] ConvertArguments(MethodInfo methodInfo, DataObject[] args) {
            var methodParams = methodInfo.GetParameters();

            if (methodParams.Length != args.Length)
                throw new InvalidOperationException();      // TODO: support the case of the Unbounded parameters

            var values = new object[args.Length];
            for (int i = 0; i < args.Length; i++) {
                var paramType = methodParams[i].ParameterType;
                var sqlType = PrimitiveTypes.FromType(paramType);

                values[i] = sqlType.ConvertTo(args[i].Value, paramType);
            }

            return values;
        }

        public override SqlType ReturnType(InvokeContext context) {
            if (method == null)
                method = DiscoverMethod();

            return base.ReturnType(context);
        }

        private MethodInfo DiscoverMethod() {
            var type = FunctionInfo.ExternalType;
            var methodName = FunctionInfo.ExternalMethodName;
            if (String.IsNullOrEmpty(methodName))
                methodName = FunctionInfo.RoutineName.Name;

            throw new NotImplementedException();
        }
    }
}