// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.

using System;
using System.Linq;
using Microsoft.AspNetCore.Mvc.ApplicationModels;
using Microsoft.AspNetCore.Mvc.ViewFeatures;

namespace Microsoft.AspNetCore.Mvc.ApplicationModels
{
    internal class AutoValidateAntiforgeryPageApplicationModelProvider : IPageApplicationModelProvider
    {
        // The order is set to execute after the DefaultPageApplicationModelProvider.
        public int Order => -1000 + 10;

        public void OnProvidersExecuted(PageApplicationModelProviderContext context)
        {
        }

        public void OnProvidersExecuting(PageApplicationModelProviderContext context)
        {
            if (context == null)
            {
                throw new ArgumentNullException(nameof(context));
            }

            var pageApplicationModel = context.PageApplicationModel;

            // ValidateAntiforgeryTokenAttribute relies on order to determine if it's the effective policy.
            // When two antiforgery filters of the same order are added to the application model, the effective policy is determined
            // by whatever appears later in the list (closest to the action). This causes filters listed on the model to be pre-empted
            // by the one added here. We'll resolve this unusual behavior by skipping the addition of the AutoValidateAntiforgeryTokenAttribute
            // when another already exists.
            if (!pageApplicationModel.Filters.OfType<IAntiforgeryPolicy>().Any())
            {
                // Always require an antiforgery token on post
                pageApplicationModel.Filters.Add(new AutoValidateAntiforgeryTokenAttribute());
            }
        }
    }
}
