/src/LinFu.IoC/Configuration/Loaders/PreprocessorLoader.cs

 1using System;
 2using System.Collections.Generic;
 3using System.IO;
 4using System.Linq;
 5using LinFu.IoC.Interfaces;
 6using LinFu.Reflection;
 7
 8namespace LinFu.IoC.Configuration.Loaders
 9{
10    /// <summary>
11    ///     A class that automatically loads <see cref="IPreProcessor" />
12    ///     instances and configures a loader to inject those postprocessors
13    ///     into a container upon initialization.
14    /// </summary>
15    internal class PreProcessorLoader : IActionLoader<IServiceContainer, Type>
16    {
17        /// <summary>
18        ///     Determines if the plugin loader can load the <paramref name="inputType" />.
19        /// </summary>
20        /// <remarks>The target type must implement the <see cref="IPreProcessor" /> interface before it can be loaded into memory.</remarks>
21        /// <param name="inputType">The target type that might contain the target instance.</param>
22        /// <returns><c>true</c> if the type can be loaded; otherwise, it returns <c>false</c>.</returns>
23        public bool CanLoad(Type inputType)
24        {
25            try
26            {
27                // The type must have a default constructor
28                var defaultConstructor = inputType.GetConstructor(new Type[0]);
29                if (defaultConstructor == null)
30                    return false;
31
32                // It must have the PreprocessorAttribute defined
33                var attributes = inputType.GetCustomAttributes(typeof(PreprocessorAttribute), true);
34                var attributeList = attributes.Cast<PreprocessorAttribute>();
35
36                if (attributeList.Count() == 0)
37                    return false;
38
39                return typeof(IPreProcessor).IsAssignableFrom(inputType);
40            }
41            catch (TypeInitializationException)
42            {
43                // Ignore the error
44                return false;
45            }
46            catch (FileNotFoundException)
47            {
48                // Ignore the error
49                return false;
50            }
51        }
52
53        /// <summary>
54        ///     Loads a set of <see cref="IPreProcessor" /> instances
55        ///     so that they can be loaded into a container upon initialization.
56        /// </summary>
57        /// <param name="inputType">The type that will be used to configure the target loader.</param>
58        /// <returns>A set of <see cref="Action{TTarget}" /> instances. This cannot be <c>null</c>.</returns>
59        public IEnumerable<Action<IServiceContainer>> Load(Type inputType)
60        {
61            var defaultResult = new Action<IServiceContainer>[0];
62
63            // Create the postprocessor instance
64            var instance = Activator.CreateInstance(inputType) as IPreProcessor;
65            if (instance == null)
66                return defaultResult;
67
68            // Inject the postprocessor into any service containers
69            // that will be configured by the current loader instance
70            Action<IServiceContainer> assignPreprocessor =
71                container => container.PreProcessors.Add(instance);
72
73            return new[] {assignPreprocessor};
74        }
75    }
76}