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namespace System.Web.Mvc {
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Linq;
public class FilterProviderCollection : Collection<IFilterProvider> {
private static FilterComparer _filterComparer = new FilterComparer();
private IResolver<IEnumerable<IFilterProvider>> _serviceResolver;
public FilterProviderCollection() {
_serviceResolver = new MultiServiceResolver<IFilterProvider>(() => Items);
}
public FilterProviderCollection(IList<IFilterProvider> providers)
: base(providers) {
_serviceResolver = new MultiServiceResolver<IFilterProvider>(() => Items);
}
internal FilterProviderCollection(IResolver<IEnumerable<IFilterProvider>> serviceResolver, params IFilterProvider[] providers)
: base(providers) {
_serviceResolver = serviceResolver ?? new MultiServiceResolver<IFilterProvider>(
() => Items
);
}
private IEnumerable<IFilterProvider> CombinedItems {
get {
return _serviceResolver.Current;
}
}
private static bool AllowMultiple(object filterInstance) {
IMvcFilter mvcFilter = filterInstance as IMvcFilter;
if (mvcFilter == null) {
return true;
}
return mvcFilter.AllowMultiple;
}
public IEnumerable<Filter> GetFilters(ControllerContext controllerContext, ActionDescriptor actionDescriptor) {
if (controllerContext == null) {
throw new ArgumentNullException("controllerContext");
}
if (actionDescriptor == null) {
throw new ArgumentNullException("actionDescriptor");
}
IEnumerable<Filter> combinedFilters =
CombinedItems.SelectMany(fp => fp.GetFilters(controllerContext, actionDescriptor))
.OrderBy(filter => filter, _filterComparer);
// Remove duplicates from the back forward
return RemoveDuplicates(combinedFilters.Reverse()).Reverse();
}
private IEnumerable<Filter> RemoveDuplicates(IEnumerable<Filter> filters) {
HashSet<Type> visitedTypes = new HashSet<Type>();
foreach (Filter filter in filters) {
object filterInstance = filter.Instance;
Type filterInstanceType = filterInstance.GetType();
if (!visitedTypes.Contains(filterInstanceType) || AllowMultiple(filterInstance)) {
yield return filter;
visitedTypes.Add(filterInstanceType);
}
}
}
private class FilterComparer : IComparer<Filter> {
public int Compare(Filter x, Filter y) {
// Nulls always have to be less than non-nulls
if (x == null && y == null) {
return 0;
}
if (x == null) {
return -1;
}
if (y == null) {
return 1;
}
// Sort first by order...
if (x.Order < y.Order) {
return -1;
}
if (x.Order > y.Order) {
return 1;
}
// ...then by scope
if (x.Scope < y.Scope) {
return -1;
}
if (x.Scope > y.Scope) {
return 1;
}
return 0;
}
}
}
}
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