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

using System.Linq;
using Microsoft.AspNetCore.Mvc.ApplicationParts;
using Microsoft.AspNetCore.Mvc.Razor.Compilation;
using Microsoft.AspNetCore.Mvc.RazorPages;
using Microsoft.AspNetCore.Razor.Hosting;
using Microsoft.Extensions.Logging;
using Microsoft.Extensions.Options;

namespace Microsoft.AspNetCore.Mvc.ApplicationModels;

#pragma warning disable CA1852 // Seal internal types
internal class CompiledPageRouteModelProvider : IPageRouteModelProvider
#pragma warning restore CA1852 // Seal internal types
{
    private const string RazorPageDocumentKind = "mvc.1.0.razor-page";
    private const string RouteTemplateKey = "RouteTemplate";
    private readonly ApplicationPartManager _applicationManager;
    private readonly RazorPagesOptions _pagesOptions;
    private readonly PageRouteModelFactory _routeModelFactory;

    public CompiledPageRouteModelProvider(
        ApplicationPartManager applicationManager,
        IOptions<RazorPagesOptions> pagesOptionsAccessor,
        ILogger<CompiledPageRouteModelProvider> logger)
    {
        _applicationManager = applicationManager ?? throw new ArgumentNullException(nameof(applicationManager));
        _pagesOptions = pagesOptionsAccessor?.Value ?? throw new ArgumentNullException(nameof(pagesOptionsAccessor));
        _routeModelFactory = new PageRouteModelFactory(_pagesOptions, logger);
    }

    public int Order => -1000;

    public void OnProvidersExecuting(PageRouteModelProviderContext context)
    {
        ArgumentNullException.ThrowIfNull(context);

        CreateModels(context);
    }

    public void OnProvidersExecuted(PageRouteModelProviderContext context)
    {
        ArgumentNullException.ThrowIfNull(context);
    }

    private IEnumerable<CompiledViewDescriptor> GetViewDescriptors(ApplicationPartManager applicationManager)
    {
        ArgumentNullException.ThrowIfNull(applicationManager);

        var viewsFeature = GetViewFeature(applicationManager);

        var visited = new HashSet<string>(StringComparer.OrdinalIgnoreCase);
        foreach (var viewDescriptor in viewsFeature.ViewDescriptors)
        {
            if (!visited.Add(viewDescriptor.RelativePath))
            {
                // Already seen an descriptor with a higher "order"
                continue;
            }

            if (IsRazorPage(viewDescriptor))
            {
                yield return viewDescriptor;
            }
        }

        static bool IsRazorPage(CompiledViewDescriptor viewDescriptor)
        {
            if (viewDescriptor.Item != null)
            {
                return viewDescriptor.Item.Kind == RazorPageDocumentKind;
            }

            return false;
        }
    }

    protected virtual ViewsFeature GetViewFeature(ApplicationPartManager applicationManager)
    {
        var viewsFeature = new ViewsFeature();
        applicationManager.PopulateFeature(viewsFeature);
        return viewsFeature;
    }

    private void CreateModels(PageRouteModelProviderContext context)
    {
        var rootDirectory = _pagesOptions.RootDirectory;
        if (!rootDirectory.EndsWith("/", StringComparison.Ordinal))
        {
            rootDirectory = rootDirectory + "/";
        }

        var areaRootDirectory = "/Areas/";
        foreach (var viewDescriptor in GetViewDescriptors(_applicationManager))
        {
            var relativePath = viewDescriptor.RelativePath;
            var routeTemplate = GetRouteTemplate(viewDescriptor);
            PageRouteModel? routeModel = null;

            // When RootDirectory and AreaRootDirectory overlap (e.g. RootDirectory = '/', AreaRootDirectory = '/Areas'), we
            // only want to allow a page to be associated with the area route.
            if (relativePath.StartsWith(areaRootDirectory, StringComparison.OrdinalIgnoreCase))
            {
                routeModel = _routeModelFactory.CreateAreaRouteModel(relativePath, routeTemplate);
            }
            else if (relativePath.StartsWith(rootDirectory, StringComparison.OrdinalIgnoreCase))
            {
                routeModel = _routeModelFactory.CreateRouteModel(relativePath, routeTemplate);
            }

            if (routeModel != null)
            {
                context.RouteModels.Add(routeModel);
            }
        }
    }

    internal static string? GetRouteTemplate(CompiledViewDescriptor viewDescriptor)
    {
        if (viewDescriptor.Item != null)
        {
            return viewDescriptor.Item.Metadata
                .OfType<RazorCompiledItemMetadataAttribute>()
                .FirstOrDefault(f => f.Key == RouteTemplateKey)
                ?.Value;
        }

        return null;
    }
}