namespace System.Web.ModelBinding {
    using System;
    using System.Collections;
    using System.Collections.Generic;
    using System.Diagnostics.CodeAnalysis;
    using System.Globalization;
    
    internal static class CollectionModelBinderUtil {

        public static void CreateOrReplaceCollection<TElement>(ModelBindingContext bindingContext, IEnumerable<TElement> incomingElements, Func<ICollection<TElement>> creator) {
            ICollection<TElement> collection = bindingContext.Model as ICollection<TElement>;
            if (collection == null || collection.IsReadOnly) {
                collection = creator();
                bindingContext.Model = collection;
            }

            collection.Clear();
            foreach (TElement element in incomingElements) {
                collection.Add(element);
            }
        }

        public static void CreateOrReplaceDictionary<TKey, TValue>(ModelBindingContext bindingContext, IEnumerable<KeyValuePair<TKey, TValue>> incomingElements, Func<IDictionary<TKey, TValue>> creator) {
            IDictionary<TKey, TValue> dictionary = bindingContext.Model as IDictionary<TKey, TValue>;
            if (dictionary == null || dictionary.IsReadOnly) {
                dictionary = creator();
                bindingContext.Model = dictionary;
            }

            dictionary.Clear();
            foreach (var element in incomingElements) {
                if (element.Key != null) {
                    dictionary[element.Key] = element.Value;
                }
            }
        }

        // supportedInterfaceType: type that is updatable by this binder
        // newInstanceType: type that will be created by the binder if necessary
        // openBinderType: model binder type
        // modelMetadata: metadata for the model to bind
        //
        // example: GetGenericBinder(typeof(IList<>), typeof(List<>), typeof(ListBinder<>), ...) means that the ListBinder<T>
        // type can update models that implement IList<T>, and if for some reason the existing model instance is not
        // updatable the binder will create a List<T> object and bind to that instead. This method will return a ListBinder<T>
        // or null, depending on whether the type and updatability checks succeed.
        public static IModelBinder GetGenericBinder(Type supportedInterfaceType, Type newInstanceType, Type openBinderType, ModelMetadata modelMetadata) {
            Type[] typeArguments = GetTypeArgumentsForUpdatableGenericCollection(supportedInterfaceType, newInstanceType, modelMetadata);
            return (typeArguments != null) ? (IModelBinder)Activator.CreateInstance(openBinderType.MakeGenericType(typeArguments)) : null;
        }

        [SuppressMessage("Microsoft.Globalization", "CA1304:SpecifyCultureInfo", MessageId = "System.Web.ModelBinding.ValueProviderResult.ConvertTo(System.Type)", Justification = @"The default CultureInfo used by ValueProvider is fine.")]
        public static IEnumerable<string> GetIndexNamesFromValueProviderResult(ValueProviderResult vpResultIndex) {
            IEnumerable<string> indexNames = null;
            if (vpResultIndex != null) {
                string[] indexes = (string[])(vpResultIndex.ConvertTo(typeof(string[])));
                if (indexes != null && indexes.Length > 0) {
                    indexNames = indexes;
                }
            }
            return indexNames;
        }

        public static IEnumerable<string> GetZeroBasedIndexes() {
            for (int i = 0; ; i++) {
                yield return i.ToString(CultureInfo.InvariantCulture);
            }
        }

        // Returns the generic type arguments for the model type if updatable, else null.
        // supportedInterfaceType: open type (like IList<>) of supported interface, must implement ICollection<>
        // newInstanceType: open type (like List<>) of object that will be created, must implement supportedInterfaceType
        public static Type[] GetTypeArgumentsForUpdatableGenericCollection(Type supportedInterfaceType, Type newInstanceType, ModelMetadata modelMetadata) {
            /*
             * Check that we can extract proper type arguments from the model.
             */

            if (!modelMetadata.ModelType.IsGenericType || modelMetadata.ModelType.IsGenericTypeDefinition) {
                // not a closed generic type
                return null;
            }

            Type[] modelTypeArguments = modelMetadata.ModelType.GetGenericArguments();
            if (modelTypeArguments.Length != supportedInterfaceType.GetGenericArguments().Length) {
                // wrong number of generic type arguments
                return null;
            }

            /*
             * Is it possible just to change the reference rather than update the collection in-place?
             */

            if (!modelMetadata.IsReadOnly) {
                Type closedNewInstanceType = newInstanceType.MakeGenericType(modelTypeArguments);
                if (modelMetadata.ModelType.IsAssignableFrom(closedNewInstanceType)) {
                    return modelTypeArguments;
                }
            }

            /*
             * At this point, we know we can't change the reference, so we need to verify that
             * the model instance can be updated in-place.
             */

            Type closedSupportedInterfaceType = supportedInterfaceType.MakeGenericType(modelTypeArguments);
            if (!closedSupportedInterfaceType.IsInstanceOfType(modelMetadata.Model)) {
                return null; // not instance of correct interface
            }

            Type closedCollectionType = TypeHelpers.ExtractGenericInterface(closedSupportedInterfaceType, typeof(ICollection<>));
            bool collectionInstanceIsReadOnly = (bool)closedCollectionType.GetProperty("IsReadOnly").GetValue(modelMetadata.Model, null);
            if (collectionInstanceIsReadOnly) {
                return null;
            }
            else {
                return modelTypeArguments;
            }
        }

    }
}