using LinFu.IoC.Interfaces;

namespace LinFu.IoC
{
    /// <summary>
    ///     Represents the default implementation for the <see cref="IGetService" /> interface.
    /// </summary>
    public class DefaultGetServiceBehavior :
        IGetService
    {
        private readonly IServiceContainer _container;
        private readonly ICreateInstance _creator;
        private readonly IPostProcessor _postProcessor;
        private readonly IPreProcessor _preProcessor;

        /// <summary>
        ///     Initializes the class with the given <paramref name="container" /> instance.
        /// </summary>
        /// <param name="container">The target service container.</param>
        public DefaultGetServiceBehavior(IServiceContainer container)
        {
            _container = container;
            _creator = new DefaultCreator();
            _preProcessor = new CompositePreProcessor(container.PreProcessors);
            _postProcessor = new CompositePostProcessor(container.PostProcessors);
        }

        /// <summary>
        ///     Initializes the class with the given <paramref name="container" /> instance.
        /// </summary>
        /// <param name="container">The target service container.</param>
        /// <param name="creator">The <see cref="ICreateInstance" /> instance responsible for instantiating service types.</param>
        /// <param name="preProcessor">The <see cref="IPreProcessor" /> that will allow users to intercept a given service request.</param>
        /// <param name="postProcessor">
        ///     The <see cref="IPostProcessor" /> instance that will handle the results of a given service
        ///     request.
        /// </param>
        public DefaultGetServiceBehavior(IServiceContainer container, ICreateInstance creator,
            IPreProcessor preProcessor, IPostProcessor postProcessor)
        {
            _container = container;
            _creator = creator;
            _preProcessor = preProcessor;
            _postProcessor = postProcessor;
        }


        /// <summary>
        ///     Instantiates the service described by the <paramref name="serviceRequest" />.
        /// </summary>
        /// <param name="serviceRequest">
        ///     The <see cref="IServiceRequest" /> that describes the service that needs to be
        ///     instantiated.
        /// </param>
        /// <returns>A valid object reference if the service can be found; otherwise, it will return <c>null</c>.</returns>
        public virtual object GetService(IServiceRequest serviceRequest)
        {
            // Allow users to intercept the instantiation process
            if (_preProcessor != null)
                _preProcessor.Preprocess(serviceRequest);

            var factoryRequest = new FactoryRequest
            {
                ServiceType = serviceRequest.ServiceType,
                ServiceName = serviceRequest.ServiceName,
                Arguments = serviceRequest.ActualArguments,
                Container = _container
            };

            var instance = _creator.CreateFrom(factoryRequest, serviceRequest.ActualFactory);

            // Postprocess the results
            var result = new ServiceRequestResult
            {
                ServiceName = serviceRequest.ServiceName,
                ActualResult = instance,
                Container = _container,
                OriginalResult = instance,
                ServiceType = serviceRequest.ServiceType,
                AdditionalArguments = serviceRequest.ActualArguments
            };

            if (_postProcessor != null)
                _postProcessor.PostProcess(result);

            return result.ActualResult ?? result.OriginalResult;
        }
    }
}