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

using System;
using System.Collections.Generic;
using System.Linq;
using System.Reflection;
using System.Web.Compilation;
using System.Runtime.CompilerServices;
using System.Collections;
using System.Linq.Expressions;

namespace Umbraco.Core.Dynamics
{
	/// <summary>
	/// Utility class for finding extension methods on a type to execute
	/// </summary>
    internal static class ExtensionMethodFinder
    {	
		/// <summary>
		/// Returns all extension methods found matching the definition
		/// </summary>
		/// <param name="thisType"></param>
		/// <param name="name"></param>
		/// <param name="argumentCount"></param>
		/// <param name="argsContainsThis"></param>
		/// <returns></returns>
		/// <remarks>
		/// TODO: NOTE: This will be an intensive method to call!! Results should be cached!
		/// </remarks>
        private static IEnumerable<MethodInfo> GetAllExtensionMethods(Type thisType, string name, int argumentCount, bool argsContainsThis)
        {
			//only scan assemblies we know to contain extension methods (user assemblies)
        	var assembliesToScan = TypeFinder.GetAssembliesWithKnownExclusions();        	

            //get extension methods from runtime
            var candidates = (
				from assembly in assembliesToScan
                where assembly.IsDefined(typeof(ExtensionAttribute), false)
                from type in assembly.GetTypes()
                where (type.IsDefined(typeof(ExtensionAttribute), false)
                    && type.IsSealed && !type.IsGenericType && !type.IsNested)
                from method in type.GetMethods(BindingFlags.Static | BindingFlags.Public)
                // this filters extension methods
                where method.IsDefined(typeof(ExtensionAttribute), false)
                select method
                );

            //add the extension methods defined in IEnumerable
            candidates = candidates.Concat(typeof(Enumerable).GetMethods(BindingFlags.Static | BindingFlags.Public));            

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

            var isGenericAndRightParamCount = methodsByName.Where(m => m.GetParameters().Length == argumentCount + (argsContainsThis ? 0 : 1));

            //find the right overload that can take genericParameterType
            //which will be either DynamicNodeList or List<DynamicNode> which is IEnumerable`

            var withGenericParameterType = isGenericAndRightParamCount.Select(m => new { m, t = FirstParameterType(m) });

            var methodsWhereArgZeroIsTargetType = (from method in withGenericParameterType
                                                   where
                                                   method.t != null && MethodArgZeroHasCorrectTargetType(method.m, method.t, thisType)
                                                   select method);

            return methodsWhereArgZeroIsTargetType.Select(mt => mt.m);
        }
        
		private static bool MethodArgZeroHasCorrectTargetType(MethodInfo method, Type firstArgumentType, Type thisType)
        {
            //This is done with seperate method calls because you can't debug/watch lamdas - if you're trying to figure
            //out why the wrong method is returned, it helps to be able to see each boolean result

            return

            // is it defined on me?
            MethodArgZeroHasCorrectTargetTypeTypeMatchesExactly(method, firstArgumentType, thisType) ||

            // or on any of my interfaces?
           MethodArgZeroHasCorrectTargetTypeAnInterfaceMatches(method, firstArgumentType, thisType) ||

            // or on any of my base types?
            MethodArgZeroHasCorrectTargetTypeIsASubclassOf(method, firstArgumentType, thisType) ||

           //share a common interface (e.g. IEnumerable)
            MethodArgZeroHasCorrectTargetTypeShareACommonInterface(method, firstArgumentType, thisType);


        }

        private static bool MethodArgZeroHasCorrectTargetTypeShareACommonInterface(MethodInfo method, Type firstArgumentType, Type thisType)
        {
            Type[] interfaces = firstArgumentType.GetInterfaces();
            if (interfaces.Length == 0)
            {
                return false;
            }
            bool result = interfaces.All(i => thisType.GetInterfaces().Contains(i));
            return result;
        }

        private static bool MethodArgZeroHasCorrectTargetTypeIsASubclassOf(MethodInfo method, Type firstArgumentType, Type thisType)
        {
            bool result = thisType.IsSubclassOf(firstArgumentType);
            return result;
        }

        private static bool MethodArgZeroHasCorrectTargetTypeAnInterfaceMatches(MethodInfo method, Type firstArgumentType, Type thisType)
        {
            bool result = thisType.GetInterfaces().Contains(firstArgumentType);
            return result;
        }

        private static bool MethodArgZeroHasCorrectTargetTypeTypeMatchesExactly(MethodInfo method, Type firstArgumentType, Type thisType)
        {
            bool result = (thisType == firstArgumentType);
            return result;
        }
        
		private static Type FirstParameterType(MethodInfo m)
        {
            ParameterInfo[] p = m.GetParameters();
            if (p.Any())
            {
                return p.First().ParameterType;
            }
            return null;
        }

		private static MethodInfo DetermineMethodFromParams(IEnumerable<MethodInfo> methods, Type genericType, IEnumerable<object> args)
		{
			if (!methods.Any())
			{
				return null;
			}
			MethodInfo methodToExecute = null;
			if (methods.Count() > 1)
			{
				//Given the args, lets get the types and compare the type sequence to try and find the correct overload
				var argTypes = args.ToList().ConvertAll(o =>
				{
					var oe = (o as Expression);
					if (oe != null)
					{
						return oe.Type.FullName;
					}
					return o.GetType().FullName;
				});
				var methodsWithArgTypes = methods.Select(method => new { method, types = method.GetParameters().Select(pi => pi.ParameterType.FullName) });
				var firstMatchingOverload = methodsWithArgTypes.FirstOrDefault(m => m.types.SequenceEqual(argTypes));
				if (firstMatchingOverload != null)
				{
					methodToExecute = firstMatchingOverload.method;
				}
			}

			if (methodToExecute == null)
			{
				var firstMethod = methods.FirstOrDefault();
				// NH: this is to ensure that it's always the correct one being chosen when using the LINQ extension methods
				if (methods.Count() > 1)
				{
					var firstGenericMethod = methods.FirstOrDefault(x => x.IsGenericMethodDefinition);
					if (firstGenericMethod != null)
					{
						firstMethod = firstGenericMethod;
					}
				}

				if (firstMethod != null)
				{
					if (firstMethod.IsGenericMethodDefinition)
					{
						if (genericType != null)
						{
							methodToExecute = firstMethod.MakeGenericMethod(genericType);
						}
					}
					else
					{
						methodToExecute = firstMethod;
					}
				}
			}
			return methodToExecute;
		}

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

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