namespace System.Web.Mvc {
    using System;

    public abstract class BuildManagerViewEngine : VirtualPathProviderViewEngine {
        private IBuildManager _buildManager;
        private IViewPageActivator _viewPageActivator;
        private IResolver<IViewPageActivator> _activatorResolver;

        protected BuildManagerViewEngine()
            : this(null, null, null) {
        }

        protected BuildManagerViewEngine(IViewPageActivator viewPageActivator)
            : this(viewPageActivator, null, null) {
        }

        internal BuildManagerViewEngine(IViewPageActivator viewPageActivator, IResolver<IViewPageActivator> activatorResolver, IDependencyResolver dependencyResolver) {
            if (viewPageActivator != null) {
                _viewPageActivator = viewPageActivator;
            }
            else {
                _activatorResolver = activatorResolver ?? new SingleServiceResolver<IViewPageActivator>(
                    () => null,
                    new DefaultViewPageActivator(dependencyResolver),
                    "BuildManagerViewEngine constructor"
                );
            }
        }

        internal IBuildManager BuildManager {
            get {
                if (_buildManager == null)
                    _buildManager = new BuildManagerWrapper();
                return _buildManager;
            }
            set {
                _buildManager = value;
            }
        }

        protected override bool FileExists(ControllerContext controllerContext, string virtualPath) {
            return BuildManager.FileExists(virtualPath);
        }

        protected IViewPageActivator ViewPageActivator {
            get {
                if (_viewPageActivator != null) {
                    return _viewPageActivator;
                }
                _viewPageActivator = _activatorResolver.Current;
                return _viewPageActivator;
            }
        }

        internal class DefaultViewPageActivator : IViewPageActivator {
            Func<IDependencyResolver> _resolverThunk;

            public DefaultViewPageActivator()
                : this(null) {
            }

            public DefaultViewPageActivator(IDependencyResolver resolver) {
                if (resolver == null) {
                    _resolverThunk = () => DependencyResolver.Current;
                }
                else {
                    _resolverThunk = () => resolver;
                }
            }

            public object Create(ControllerContext controllerContext, Type type) {
                return _resolverThunk().GetService(type) ?? Activator.CreateInstance(type);
            }
        }
    }
}