ServiceCollectionAssemblyBinding.cs

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using System;
using System.Reflection;

namespace IoCContainer_net4_sharp5
{
    // Lets say you want a singleton where the type bond comes from an assembly:
    // new ServiceCollectionAssemblyBinding ("org.bigcorp.bestcode", new ServiceCollectionSingletonBinding ())
    //LATER multi-domain/and_or AppDomain.CurrentDomain.SetupInformation.ShadowCopy*
    /// <summary>Extends the <c>"ServiceCollection"</c> with the ability to load services from assemblies not known at compile time.</summary>
    public class ServiceCollectionAssemblyBinding : ServiceCollectionBinding
    {
        private string _asm_fname = "";
        private Assembly _asm = null;
        private string _iface_name = "";
        private string _impl_name = "";

        /// <summary>This is a decorator that isn't hosting any services - a binding that does so is required.</summary>
        private ServiceCollectionAssemblyBinding(string assembly_file_name, Assembly assembly, ServiceCollectionBinding binding)
            : base (binding)
        {
            if (null == binding)
                throw new ArgumentException ("Can't decorate null. Perhaps IDecorate<decorated> or something?", "binding");
            if (null == assembly && string.IsNullOrEmpty (assembly_file_name))
                throw new ArgumentException ("Try specifying a valid assembly file name. Test it using Assembly.Load().", "assembly_file_name");
            if (string.IsNullOrEmpty (assembly_file_name) && null == assembly)
                throw new ArgumentException ("Try specifying a valid assembly. Use Assembly.Load().", "assembly");
            _asm_fname = assembly_file_name;
            _asm = assembly;
        }

        private void EnsureInitialStateOk()
        {
            if (string.IsNullOrEmpty (_asm_fname) && null == _asm)
                throw new Exception ("You forgot to call the big private constructor.");
        }

        /// <summary>Construct via assembly file name - full path could be required.</summary>
        public ServiceCollectionAssemblyBinding(string assembly_fname, ServiceCollectionBinding binding)
            : this (assembly_fname, assembly: null, binding: binding) { }
        /// <summary>Construct via assembly reference.</summary>
        public ServiceCollectionAssemblyBinding(Assembly assembly, ServiceCollectionBinding binding)
            : this (assembly_file_name: "", assembly: assembly, binding: binding) { }
        // etc. When adding new constructors, please do call the big private constructor above, or bad things will happen.

        public override object Create(IInstanceBuilder builder, Type type, object[] args)
        {
            LoadTypes ();
            return base.Create (builder, type, args);
        }

        // Returns not null or throws any exception you can imagine.
        // type_name: the complete type name: foo.bar.fancy_type for example
        private static Type LoadType(Assembly assembly, string type_name)
        {
            Type result = null;
            try
            {
                result = assembly.GetType (name: type_name, throwOnError: true, ignoreCase: false);
                if (null == result)
                    throw new Exception (".net framework bug: \"" + Environment.Version.ToString () + "\"");
            }
            catch (TypeLoadException e)
            {
                throw new ArgumentException (string.Format ("\"{0}\" not found at \"{1}\"", type_name, assembly.FullName), "Bind.iface", e);
            }
            catch (Exception e)
            {
                throw new Exception (string.Format ("Unhandled exception while looking for \"{0}\" at \"{1}\"", type_name, assembly.FullName), e);
            }
            return result;
        }

        private void LoadTypes()
        {
            EnsureInitialStateOk ();
            if (null != Interface && null != Implementation) return; // no Transient Assembly loading

            // This is a scary function - be aware! - loading assemblies is never simple. Assume (this time only) time consuming.
            //TODONT optimize; no point: you can't know what will happen during the next call or how much time it will take because:
            //       S.o. could employ custom missing dependencies resolution, where s.o. could ask the user, via an interactive UI,
            //       to locate the missing dependencies, who can go, to lets say dinner, leaving the file dialog open and locate them the
            //       next week if he decides to; or s.o. could invoke the CodeDOM to build something on the fly; or s.o. could invoke
            //       some network deployment wonder to deliver the required assemblies. Good enough?
            if (null == _asm) _asm = Assembly.LoadFile (_asm_fname);

            Interface = new Type[] { LoadType (assembly: _asm, type_name: _iface_name) };
            Implementation = new Type[] { LoadType (assembly: _asm, type_name: _impl_name) };
        }

        /// <summary>Bind via full (including all namespaces) type names as a string.</summary>
        public ServiceCollectionAssemblyBinding Bind(string iface, string impl)
        {
            _iface_name = iface;
            _impl_name = impl;
            LoadTypes ();
            return this;
        }
    }// public class ServiceCollectionAssemblyBinding
}