ServiceCollectionBinding.cs

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using System;
using System.Collections.Generic;
using System.Linq;

namespace IoCContainer_net4_sharp5
{
    // Adapt your binding to the service collection. The idea is to enable you to extend the ServiceCollection.
    // Instead of .AddScoped(), .AddSingleton(), you .Register(Scoped), .Register(Singleton), ...
    //  * Lowers responsibilities per class
    //  * Create binding per type if needs be - you could do your private type setup at the binding
    // ServiceCollection is a singleton by design, so there is no explicit contract here. Access it via its public static interface if needs be.
    // Direct descendants of ServiceCollectionBinding that init the base decorator with null and then call the base methods will
    // be rewarded with CantBeImplementedException; just don't do that.
    /// <summary>
    /// Adapts your binding to the service collection. Employs Visitor (to abstract away the actual object construction) and
    /// Decorator (to simplify adapter code) as well.
    /// </summary>
    public abstract class ServiceCollectionBinding
    {
        // Avoids "if (null == _b)"
        private class ServiceCollectionBindingIfNull : ServiceCollectionBinding
        {
            private static readonly string DIRECTIONS = "Turn back.";
            public class CantBeImplementedException : NotImplementedException { public CantBeImplementedException() : base (DIRECTIONS) { } }
            public override object Create(IInstanceBuilder b, Type t, object[] a) { throw new CantBeImplementedException (); }
        }
        protected ServiceCollectionBinding _b = null;
        protected ServiceCollectionBinding() { }
        public ServiceCollectionBinding(ServiceCollectionBinding binding = null) { _b = binding ?? new ServiceCollectionBindingIfNull (); }

        /// <summary>Returns Implementation by Interface.</summary>
        public Type GetImplementationType(Type iface)
        {
            if (!Set)
            {
                if (iface != Interface.First ())
                    throw new ArgumentException ("Fixme: odd interface request", "iface");
                return Implementation.First ();
            }
            var tmp = Implementation.Where (t => iface.IsAssignableFrom (t));
            //TODO verify tmp vs tmp2; IsSubclassOf() works not
            //var tmp2 = Implementation.Where (t => null != t.GetInterface (iface.Name)).ToArray ();
            if (tmp.Count () <= 0)
                throw new ArgumentException (string.Format ("No implementor of \"{0}\" found", iface.FullName), "iface");
            if (tmp.Count () > 1)
                throw new ArgumentException (string.Format ("Too many implementors of \"{0}\" found", iface.FullName), "iface");
            return tmp.First ();
        }

        // These will be called by the ServiceCollection "build()" thread. Consider them a model.
        //TODO should this arg list become ServiceCollectionBindingCreateArguments? It should.
        /// <summary>
        /// Lets the <c>"builder"</c> create the service instance of <c>"impl_type"</c> using <c>"args"</c> constructor parameters.
        /// </summary>
        public virtual object Create(IInstanceBuilder builder, Type impl_type, object[] args) { return _b.Create (builder, impl_type, args); }
        
        /// <summary>The service Interface(s) associated with this binding</summary>
        public IEnumerable<Type> Interface { get; protected set; }

        /// <summary>The service Implementation(s) associated with this binding</summary>
        public IEnumerable<Type> Implementation { get; protected set; }

        // When this is true the IEnumerable becomes the key i.e. you state that your binding manages distinct "Interface"s -
        // not the ServiceCollection. The dependencies are looked for at the set 1st.
        /// <summary>Whether or not the binding encapsulates its own private service collection.</summary>
        public bool Set { get; protected set; }
    }// public abstract class ServiceCollectionBinding
}