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

using System.Reflection;
using Microsoft.AspNetCore.Mvc.Abstractions;
using Microsoft.AspNetCore.Mvc.ApplicationParts;
using Microsoft.AspNetCore.Mvc.Controllers;

namespace Microsoft.AspNetCore.Mvc.ApplicationModels;

internal sealed class ControllerActionDescriptorProvider : IActionDescriptorProvider
{
    private readonly ApplicationPartManager _partManager;
    private readonly ApplicationModelFactory _applicationModelFactory;

    public ControllerActionDescriptorProvider(
        ApplicationPartManager partManager,
        ApplicationModelFactory applicationModelFactory)
    {
        ArgumentNullException.ThrowIfNull(partManager);
        ArgumentNullException.ThrowIfNull(applicationModelFactory);

        _partManager = partManager;
        _applicationModelFactory = applicationModelFactory;
    }

    public int Order => -1000;

    /// <inheritdoc />
    public void OnProvidersExecuting(ActionDescriptorProviderContext context)
    {
        ArgumentNullException.ThrowIfNull(context);

        foreach (var descriptor in GetDescriptors())
        {
            context.Results.Add(descriptor);
        }
    }

    /// <inheritdoc />
    public void OnProvidersExecuted(ActionDescriptorProviderContext context)
    {
        // After all of the providers have run, we need to provide a 'null' for each all of route values that
        // participate in action selection.
        //
        // This is important for scenarios like Razor Pages, that use the 'page' route value. An action that
        // uses 'page' shouldn't match when 'action' is set, and an action that uses 'action' shouldn't match when
        // 'page is specified.
        //
        // Or for another example, consider areas. A controller that's not in an area needs a 'null' value for
        // area so it can't match when the route produces an 'area' value.
        var keys = new HashSet<string>(StringComparer.OrdinalIgnoreCase);
        for (var i = 0; i < context.Results.Count; i++)
        {
            var action = context.Results[i];
            foreach (var key in action.RouteValues.Keys)
            {
                keys.Add(key);
            }
        }

        for (var i = 0; i < context.Results.Count; i++)
        {
            var action = context.Results[i];
            foreach (var key in keys)
            {
                if (!action.RouteValues.ContainsKey(key))
                {
                    action.RouteValues.Add(key, null);
                }
            }
        }
    }

    internal IEnumerable<ControllerActionDescriptor> GetDescriptors()
    {
        var controllerTypes = GetControllerTypes();
        var application = _applicationModelFactory.CreateApplicationModel(controllerTypes);
        return ControllerActionDescriptorBuilder.Build(application);
    }

    private IEnumerable<TypeInfo> GetControllerTypes()
    {
        var feature = new ControllerFeature();
        _partManager.PopulateFeature(feature);

        return feature.Controllers;
    }
}