private object CreateInstance()

in sources/Google.Solutions.IapDesktop.Core/ObjectModel/ServiceRegistry.cs [75:172]
73 lines of code
10 McCabe index (conditional complexity)

        private object CreateInstance(Type serviceType)
        {
            //
            // Check for ctor(IServiceProvider).
            //
            var constructorWithServiceProvider = serviceType.GetConstructor(
                BindingFlags.Public | BindingFlags.Instance,
                null,
                new[] { typeof(IServiceProvider) },
                null);
            if (constructorWithServiceProvider != null)
            {
                return Activator.CreateInstance(serviceType, (IServiceProvider)this);
            }

            //
            // Check for ctor(IServiceCategoryProvider).
            //
            var constructorWithServiceCategoryProvider = serviceType.GetConstructor(
                BindingFlags.Public | BindingFlags.Instance,
                null,
                new[] { typeof(IServiceCategoryProvider) },
                null);
            if (constructorWithServiceCategoryProvider != null)
            {
                return Activator.CreateInstance(serviceType, (IServiceCategoryProvider)this);
            }

            //
            // Check other constructors and see if there is one for which all
            // parameters can be bound to a service. Analyze the one with the most
            // parameters first.
            //
            bool IsSupportedConstructorArgumentType(Type t)
            {
                if (t == serviceType)
                {
                    // Don't allow recursion
                    return false;
                }

                if (IsServiceRegistered(t))
                {
                    return true;
                }
                else if (IsDecorator(t) && t.GetGenericArguments().All(IsServiceRegistered))
                {
                    return true;
                }
                else
                {
                    return false;
                }
            }

            foreach (var constructor in serviceType.GetConstructors()
                .OrderByDescending(c => c.GetParameters().Length))
            {
                if (constructor
                    .GetParameters()
                    .Select(p => p.ParameterType)
                    .All(t => IsSupportedConstructorArgumentType(t)))
                {
                    // We have services for all parameters.
                    var parameterValues = constructor
                        .GetParameters()
                        .Select(p => GetService(p.ParameterType))
                        .ToArray();

                    return Activator.CreateInstance(
                        serviceType,
                        parameterValues);
                }
                else
                {
#if DEBUG
                    Debug.WriteLine($"ServiceRegistry: {serviceType} has an unsuitable ctor: {constructor}");

                    foreach (var t in constructor
                        .GetParameters()
                        .Select(p => p.ParameterType)
                        .Where(t => !IsSupportedConstructorArgumentType(t))
                        .ToList())
                    {
                        Debug.WriteLine($"  > Unsupported argument type: {t}");
                    }
#endif

                    //
                    // There is at least one parameter that we do not
                    // have a suitable service for.
                    //
                }
            }

            throw new UnknownServiceException(
                $"Class {serviceType.Name} lacks a suitable constructor to serve as service");
        }