Umbraco-CMS/src/Umbraco.Core/Dynamics/ExtensionMethodFinder.cs

using System;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.Linq;
using System.Reflection;
using System.Runtime.CompilerServices;
using System.Linq.Expressions;
using System.Web.Services.Description;
using Umbraco.Core.Cache;

namespace Umbraco.Core.Dynamics
{
	/// <summary>
	/// Utility class for finding extension methods on a type to execute
	/// </summary>
    internal static class ExtensionMethodFinder
	{
        /// <summary>
        /// The static cache for extension methods found that match the criteria that we are looking for
        /// </summary>
        private static readonly ConcurrentDictionary<Tuple<Type, string, int>, MethodInfo[]> MethodCache = new ConcurrentDictionary<Tuple<Type, string, int>, MethodInfo[]>();

        /// <summary>
        /// Returns the enumerable of all extension method info's in the app domain = USE SPARINGLY!!!
        /// </summary>
        /// <returns></returns>
        /// <remarks>
        /// We cache this as a sliding 5 minute exiration, in unit tests there's over 1100 methods found, surely that will eat up a bit of memory so we want
        /// to make sure we give it back.
        /// </remarks>
	    private static IEnumerable<MethodInfo> GetAllExtensionMethodsInAppDomain(IRuntimeCacheProvider runtimeCacheProvider)
        {
            if (runtimeCacheProvider == null) throw new ArgumentNullException("runtimeCacheProvider");

            return runtimeCacheProvider.GetCacheItem<MethodInfo[]>(typeof (ExtensionMethodFinder).Name, () => TypeFinder.GetAssembliesWithKnownExclusions()
                // assemblies that contain extension methods
                .Where(a => a.IsDefined(typeof (ExtensionAttribute), false))
                // types that contain extension methods
                .SelectMany(a => a.GetTypes()
                    .Where(t => t.IsDefined(typeof (ExtensionAttribute), false) && t.IsSealed && t.IsGenericType == false && t.IsNested == false))
                // actual extension methods
                .SelectMany(t => t.GetMethods(BindingFlags.Static | BindingFlags.Public)
                    .Where(m => m.IsDefined(typeof (ExtensionAttribute), false)))
                // and also IEnumerable<T> extension methods - because the assembly is excluded
                .Concat(typeof (Enumerable).GetMethods(BindingFlags.Static | BindingFlags.Public))
                //If we don't do this then we'll be scanning all assemblies each time!
                .ToArray(),
                
                //only cache for 5 minutes
                timeout: TimeSpan.FromMinutes(5), 

                //each time this is accessed it will be for 5 minutes longer
                isSliding:true);
        }

	    /// <summary>
	    /// Returns all extension methods found matching the definition
	    /// </summary>
	    /// <param name="runtimeCache">
	    /// The runtime cache is used to temporarily cache all extension methods found in the app domain so that 
	    /// while we search for individual extension methods, the process will be reasonably 'quick'. We then statically
	    /// cache the MethodInfo's that we are looking for and then the runtime cache will expire and give back all that memory.
	    /// </param>
	    /// <param name="thisType"></param>
	    /// <param name="name"></param>
	    /// <param name="argumentCount">
	    /// The arguments EXCLUDING the 'this' argument in an extension method
	    /// </param>
	    /// <returns></returns>
	    /// <remarks>
	    /// NOTE: This will be an intensive method to call! Results will be cached based on the key (args) of this method
	    /// </remarks>
	    internal static IEnumerable<MethodInfo> GetAllExtensionMethods(IRuntimeCacheProvider runtimeCache, Type thisType, string name, int argumentCount)
		{
		    var key = new Tuple<Type, string, int>(thisType, name, argumentCount);

		    return MethodCache.GetOrAdd(key, tuple =>
		    {
                var candidates = GetAllExtensionMethodsInAppDomain(runtimeCache);

                // filter by name	
                var filtr1 = candidates.Where(m => m.Name == name);

                // filter by args count
                // ensure we add + 1 to the arg count because the 'this' arg is not included in the count above!
                var filtr2 = filtr1.Where(m => m.GetParameters().Length == argumentCount + 1);

                // filter by first parameter type (target of the extension method)
                // ie find the right overload that can take genericParameterType
                // (which will be either DynamicNodeList or List<DynamicNode> which is IEnumerable)
                var filtr3 = filtr2.Select(x =>
                {
                    var t = x.GetParameters()[0].ParameterType; // exists because of +1 above
                    var bindings = new Dictionary<string, Type>();
                    if (TypeHelper.MatchType(thisType, t, bindings) == false) return null;

                    // create the generic method if necessary
                    if (x.ContainsGenericParameters == false) return x;
                    var targs = t.GetGenericArguments().Select(y => bindings[y.Name]).ToArray();
                    return x.MakeGenericMethod(targs);
                }).Where(x => x != null);

		        return filtr3.ToArray();
		    });
		    
        }

        private static MethodInfo DetermineMethodFromParams(IEnumerable<MethodInfo> methods, Type genericType, IEnumerable<object> args)
		{
			MethodInfo methodToExecute = null;

            //Given the args, lets get the types and compare the type sequence to try and find the correct overload
            var argTypes = args.Select(o =>
            {
                var oe = (o as Expression);
                return oe != null ? oe.Type : o.GetType();
            });

            var methodsWithArgTypes = methods.Select(method => new
            {
                method,
                //skip the first arg because that is the extension method type ('this') that we are looking for
                types = method.GetParameters().Select(pi => pi.ParameterType).Skip(1)
            });

            //This type comparer will check 
            var typeComparer = new DelegateEqualityComparer<Type>(
                //Checks if the argument type passed in can be assigned from the parameter type in the method. For 
                // example, if the argument type is HtmlHelper<MyModel> but the method parameter type is HtmlHelper then
                // it will match because the argument is assignable to that parameter type and will be able to execute
                TypeHelper.IsTypeAssignableFrom, 
                //This will not ever execute but if it does we need to get the hash code of the string because the hash
                // code of a type is random
                type => type.FullName.GetHashCode());

            var firstMatchingOverload = methodsWithArgTypes
                .FirstOrDefault(m => m.types.SequenceEqual(argTypes, typeComparer));

            if (firstMatchingOverload != null)
            {
                methodToExecute = firstMatchingOverload.method;
            }

			return methodToExecute;
		}

        public static MethodInfo FindExtensionMethod(IRuntimeCacheProvider runtimeCache, Type thisType, object[] args, string name, bool argsContainsThis)
        {
            Type genericType = null;
            if (thisType.IsGenericType)
            {
                genericType = thisType.GetGenericArguments()[0];
            }

            args = args
                //if the args contains 'this', remove the first one since that is 'this' and we don't want to use
                //that in the method searching
                .Skip(argsContainsThis ? 1 : 0)
                .ToArray();

            var methods = GetAllExtensionMethods(runtimeCache, thisType, name, args.Length).ToArray();
            
            return DetermineMethodFromParams(methods, genericType, args);
        }
    }
}