// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
 
using System.Diagnostics;
using System.Linq;
using Microsoft.AspNetCore.Mvc.Infrastructure;
using Microsoft.AspNetCore.Mvc.RazorPages;
using Microsoft.AspNetCore.Razor.Language;
using Microsoft.Extensions.Options;
using Microsoft.Extensions.Primitives;
 
namespace Microsoft.AspNetCore.Mvc.Razor.RuntimeCompilation;
 
internal sealed class PageActionDescriptorChangeProvider : IActionDescriptorChangeProvider
{
    private readonly RuntimeCompilationFileProvider _fileProvider;
    private readonly string[] _searchPatterns;
    private readonly string[] _additionalFilesToTrack;
 
    public PageActionDescriptorChangeProvider(
        RazorProjectEngine projectEngine,
        RuntimeCompilationFileProvider fileProvider,
        IOptions<RazorPagesOptions> razorPagesOptions)
    {
        ArgumentNullException.ThrowIfNull(projectEngine);
        ArgumentNullException.ThrowIfNull(fileProvider);
        ArgumentNullException.ThrowIfNull(razorPagesOptions);
 
        _fileProvider = fileProvider;
 
        var rootDirectory = razorPagesOptions.Value.RootDirectory;
        Debug.Assert(!string.IsNullOrEmpty(rootDirectory));
        rootDirectory = rootDirectory.TrimEnd('/');
 
        // Search pattern that matches all cshtml files under the Pages RootDirectory
        var pagesRootSearchPattern = rootDirectory + "/**/*.cshtml";
 
        // Search pattern that matches all cshtml files under the Pages AreaRootDirectory
        var areaRootSearchPattern = "/Areas/**/*.cshtml";
 
        _searchPatterns = new[]
        {
                pagesRootSearchPattern,
                areaRootSearchPattern
            };
 
        // pagesRootSearchPattern will miss _ViewImports outside the RootDirectory despite these influencing
        // compilation. e.g. when RootDirectory = /Dir1/Dir2, the search pattern will ignore changes to
        // [/_ViewImports.cshtml, /Dir1/_ViewImports.cshtml]. We need to additionally account for these.
        var importFeatures = projectEngine.ProjectFeatures.OfType<IImportProjectFeature>().ToArray();
        var fileAtPagesRoot = projectEngine.FileSystem.GetItem(rootDirectory + "/Index.cshtml", fileKind: null);
 
        _additionalFilesToTrack = GetImports(importFeatures, fileAtPagesRoot);
    }
 
    public IChangeToken GetChangeToken()
    {
        var fileProvider = _fileProvider.FileProvider;
 
        var changeTokens = new IChangeToken[_additionalFilesToTrack.Length + _searchPatterns.Length];
        for (var i = 0; i < _additionalFilesToTrack.Length; i++)
        {
            changeTokens[i] = fileProvider.Watch(_additionalFilesToTrack[i]);
        }
 
        for (var i = 0; i < _searchPatterns.Length; i++)
        {
            var wildcardChangeToken = fileProvider.Watch(_searchPatterns[i]);
            changeTokens[_additionalFilesToTrack.Length + i] = wildcardChangeToken;
        }
 
        return new CompositeChangeToken(changeTokens);
    }
 
    private static string[] GetImports(
        IImportProjectFeature[] importFeatures,
        RazorProjectItem file)
    {
        return importFeatures
            .SelectMany(f => f.GetImports(file))
            .Where(f => f.FilePath != null)
            .Select(f => f.FilePath)
            .ToArray();
    }
}