IActionDescriptorProvider

namespace Microsoft.AspNetCore.Mvc.Abstractions
{
    /// <summary>
    /// Defines a contract for specifying <see cref="ActionDescriptor"/> instances.
    /// </summary>
    /// <remarks>
    /// <para>
    /// On application initialization, MVC invokes all registered instances of <see cref="IActionDescriptorProvider"/> to 
    /// perform <see cref="ActionDescriptor" /> discovery. 
    /// <see cref="IActionDescriptorProvider"/> instances are invoked in the ascending sort order of <see cref="Order"/>.  
    /// </para>
    /// <para>
    /// Each provider has its <see cref="OnProvidersExecuting"/> method
    /// called in sequence and given the same instance of <see cref="ActionInvokerProviderContext"/>. Then each
    /// provider has its <see cref="OnProvidersExecuted"/> method called in the reverse order. Each instance has
    /// an opportunity to add or modify <see cref="ActionDescriptorProviderContext.Results"/>.
    /// </para>
    /// <para>
    /// As providers are called in a predefined sequence, each provider has a chance to observe and decorate the
    /// result of the providers that have already run. 
    /// </para>
    /// </remarks>
    public interface IActionDescriptorProvider
    {
        /// <summary>
        /// Gets the order value for determining the order of execution of providers. Providers execute in
        /// ascending numeric value of the <see cref="Order"/> property.
        /// </summary>
        /// <remarks>
        /// <para>
        /// Providers are executed in an ordering determined by an ascending sort of the <see cref="Order"/> property.
        /// A provider with a lower numeric value of <see cref="Order"/> will have its
        /// <see cref="OnProvidersExecuting"/> called before that of a provider with a higher numeric value of
        /// <see cref="Order"/>. The <see cref="OnProvidersExecuted"/> method is called in the reverse ordering after
        /// all calls to <see cref="OnProvidersExecuting"/>. A provider with a lower numeric value of
        /// <see cref="Order"/> will have its <see cref="OnProvidersExecuted"/> method called after that of a provider
        /// with a higher numeric value of <see cref="Order"/>.
        /// </para>
        /// <para>
        /// If two providers have the same numeric value of <see cref="Order"/>, then their relative execution order
        /// is undefined.
        /// </para>
        /// </remarks>
        int Order { get; }

        /// <summary>
        /// Called to execute the provider. 
        /// <see cref="Order"/> for details on the order of execution of <see cref="OnProvidersExecuting(ActionDescriptorProviderContext)"/>.
        /// </summary>
        /// <param name="context">The <see cref="ActionDescriptorProviderContext"/>.</param>
        void OnProvidersExecuting(ActionDescriptorProviderContext context);

        /// <summary>
        /// Called to execute the provider, after the <see cref="OnProvidersExecuting"/> methods of all providers,
        /// have been called.
        /// <see cref="Order"/> for details on the order of execution of <see cref="OnProvidersExecuted(ActionDescriptorProviderContext)"/>.
        /// </summary>
        /// <param name="context">The <see cref="ActionDescriptorProviderContext"/>.</param>
        void OnProvidersExecuted(ActionDescriptorProviderContext context);
    }
}