{

// ReSharper disable EmptyConstructor

/// <summary>

/// Initializes a new <see cref="DocumentLoader"/> instance.

/// </summary>

protected DocumentLoader()

{

// the help file builder (SHFB) insists on an empty constructor here

}

// ReSharper restore EmptyConstructor

/// <summary>

/// Gets the default document loader.

/// </summary>

public static DocumentLoader Default => DefaultImpl.Instance;

/// <summary>

/// Gets or sets the maximum size of the document loader's cache.

/// </summary>

/// <remarks>

/// This property specifies the maximum number of documents to be cached by the document

/// loader. For the default document loader, its initial value is 1024.

/// </remarks>

/// <seealso cref="Default"/>

public virtual uint MaxCacheSize

{

get => 0;

set => throw new NotSupportedException("Loader does not support caching");

}

/// <summary>

/// Loads a document.

/// </summary>

/// <param name="settings">Document access settings for the operation.</param>

/// <param name="sourceInfo">An optional structure containing meta-information for the requesting document.</param>

/// <param name="specifier">A string specifying the document to be loaded.</param>

/// <param name="category">An optional category for the requested document.</param>

/// <param name="contextCallback">An optional context callback for the requested document.</param>

/// <returns>A <see cref="Document"/> instance that represents the loaded document.</returns>

/// <remarks>

/// A loaded document must have an absolute <see cref="DocumentInfo.Uri">URI</see>. Once a

/// load operation has completed successfully, subsequent requests that resolve to the same

/// URI are expected to return the same <see cref="Document"/> reference, although loaders

/// are not required to manage document caches of unlimited size.

/// </remarks>

public virtual Document LoadDocument(DocumentSettings settings, DocumentInfo? sourceInfo, string specifier, DocumentCategory category, DocumentContextCallback contextCallback)

{

MiscHelpers.VerifyNonBlankArgument(specifier, nameof(specifier), "Invalid document specifier");

try

{

return LoadDocumentAsync(settings, sourceInfo, specifier, category, contextCallback).Result;

}

catch (AggregateException exception)

{

exception = exception.Flatten();

if (exception.InnerExceptions.Count == 1)

{

throw new FileLoadException(null, specifier, exception.InnerExceptions[0]);

}

throw new FileLoadException(null, specifier, exception);

}

}

/// <summary>

/// Loads a document asynchronously.

/// </summary>

/// <param name="settings">Document access settings for the operation.</param>

/// <param name="sourceInfo">An optional structure containing meta-information for the requesting document.</param>

/// <param name="specifier">A string specifying the document to be loaded.</param>

/// <param name="category">An optional category for the requested document.</param>

/// <param name="contextCallback">An optional context callback for the requested document.</param>

/// <returns>A task that represents the asynchronous operation. Upon completion, the task's result is a <see cref="Document"/> instance that represents the loaded document.</returns>

/// <remarks>

/// A loaded document must have an absolute <see cref="DocumentInfo.Uri">URI</see>. Once a

/// load operation has completed successfully, subsequent requests that resolve to the same

/// URI are expected to return the same <see cref="Document"/> reference, although loaders

/// are not required to manage document caches of unlimited size.

/// </remarks>

public abstract Task<Document> LoadDocumentAsync(DocumentSettings settings, DocumentInfo? sourceInfo, string specifier, DocumentCategory category, DocumentContextCallback contextCallback);

/// <summary>

/// Discards all cached documents.

/// </summary>

public virtual void DiscardCachedDocuments()

{

}

#region Nested type: DefaultImpl

private sealed class DefaultImpl : DocumentLoader

{

public static readonly DefaultImpl Instance = new DefaultImpl();

private static readonly IReadOnlyCollection<string> relativePrefixes = new List<string>

{

"." + Path.DirectorySeparatorChar,

"." + Path.AltDirectorySeparatorChar,

".." + Path.DirectorySeparatorChar,

".." + Path.AltDirectorySeparatorChar,

};

private readonly List<Document> cache = new List<Document>();

private DefaultImpl()

{

MaxCacheSize = 1024;

}

private static async Task<List<Uri>> GetCandidateUrisAsync(DocumentSettings settings, DocumentInfo? sourceInfo, Uri uri)

{

var candidateUris = new List<Uri>();

if (string.IsNullOrWhiteSpace(settings.FileNameExtensions))

{

candidateUris.Add(uri);

}

else

{

foreach (var testUri in ApplyFileNameExtensions(sourceInfo, uri, settings.FileNameExtensions))

{

if (await IsCandidateUriAsync(settings, testUri).ConfigureAwait(false))

{

candidateUris.Add(testUri);

}

}

}

return candidateUris;

}

private static async Task<List<Uri>> GetCandidateUrisAsync(DocumentSettings settings, DocumentInfo? sourceInfo, string specifier)

{

var candidateUris = new List<Uri>();

var rawUris = GetRawUris(settings, sourceInfo, specifier).Distinct();

if (!string.IsNullOrWhiteSpace(settings.FileNameExtensions))

{

rawUris = rawUris.SelectMany(uri => ApplyFileNameExtensions(sourceInfo, uri, settings.FileNameExtensions));

}

foreach (var testUri in rawUris)

{

if (await IsCandidateUriAsync(settings, testUri).ConfigureAwait(false))

{

candidateUris.Add(testUri);

}

}

return candidateUris;

}

private static IEnumerable<Uri> GetRawUris(DocumentSettings settings, DocumentInfo? sourceInfo, string specifier)

{

Uri baseUri;

Uri uri;

if (sourceInfo.HasValue && SpecifierMayBeRelative(settings, specifier))

{

baseUri = GetBaseUri(sourceInfo.Value);

if ((baseUri != null) && Uri.TryCreate(baseUri, specifier, out uri))

{

yield return uri;

}

}

var searchPath = settings.SearchPath;

if (!string.IsNullOrWhiteSpace(searchPath))

{

foreach (var url in searchPath.SplitSearchPath())

{

if (Uri.TryCreate(url, UriKind.Absolute, out baseUri) && TryCombineSearchUri(baseUri, specifier, out uri))

{

yield return uri;

}

}

}

if (MiscHelpers.Try(out var path, () => Path.Combine(Directory.GetCurrentDirectory(), specifier)) && Uri.TryCreate(path, UriKind.Absolute, out uri))

{

yield return uri;

}

if (MiscHelpers.Try(out path, () => Path.Combine(AppDomain.CurrentDomain.BaseDirectory, specifier)) && Uri.TryCreate(path, UriKind.Absolute, out uri))

{

yield return uri;

}

using (var process = Process.GetCurrentProcess())

{

var module = process.MainModule;

if ((module != null) && Uri.TryCreate(module.FileName, UriKind.Absolute, out baseUri) && Uri.TryCreate(baseUri, specifier, out uri))

{

yield return uri;

}

}

}

private static IEnumerable<Uri> ApplyFileNameExtensions(DocumentInfo? sourceInfo, Uri uri, string fileNameExtensions)

{

yield return uri;

var builder = new UriBuilder(uri);

var path = builder.Path;

if (!string.IsNullOrEmpty(Path.GetFileName(path)) && !Path.HasExtension(path))

{

string sourceFileNameExtension = null;

if (sourceInfo.HasValue)

{

sourceFileNameExtension = Path.GetExtension((sourceInfo.Value.Uri != null) ? new UriBuilder(sourceInfo.Value.Uri).Path : sourceInfo.Value.Name);

if (!string.IsNullOrEmpty(sourceFileNameExtension))

{

builder.Path = Path.ChangeExtension(path, sourceFileNameExtension);

yield return builder.Uri;

}

}

foreach (var fileNameExtension in fileNameExtensions.SplitSearchPath())

{

var testFileNameExtension = fileNameExtension.StartsWith(".", StringComparison.Ordinal) ? fileNameExtension : "." + fileNameExtension;

if (!testFileNameExtension.Equals(sourceFileNameExtension, StringComparison.OrdinalIgnoreCase))

{

builder.Path = Path.ChangeExtension(path, testFileNameExtension);

yield return builder.Uri;

}

}

}

}

private static bool SpecifierMayBeRelative(DocumentSettings settings, string specifier)

{

return !settings.AccessFlags.HasFlag(DocumentAccessFlags.EnforceRelativePrefix) || relativePrefixes.Any(specifier.StartsWith);

}

private static Uri GetBaseUri(DocumentInfo sourceInfo)

{

var sourceUri = sourceInfo.Uri;

if ((sourceUri == null) && !Uri.TryCreate(sourceInfo.Name, UriKind.RelativeOrAbsolute, out sourceUri))

{

return null;

}

if (!sourceUri.IsAbsoluteUri)

{

return null;

}

return sourceUri;

}

private static bool TryCombineSearchUri(Uri searchUri, string specifier, out Uri uri)

{

var searchUrl = searchUri.AbsoluteUri;

if (!searchUrl.EndsWith("/", StringComparison.Ordinal))

{

searchUri = new Uri(searchUrl + "/");

}

return Uri.TryCreate(searchUri, specifier, out uri);

}

private static async Task<bool> IsCandidateUriAsync(DocumentSettings settings, Uri uri)

{

return uri.IsFile ?

settings.AccessFlags.HasFlag(DocumentAccessFlags.EnableFileLoading) && File.Exists(uri.LocalPath) :

settings.AccessFlags.HasFlag(DocumentAccessFlags.EnableWebLoading) && await WebDocumentExistsAsync(uri).ConfigureAwait(false);

}

private static async Task<bool> WebDocumentExistsAsync(Uri uri)

{

using (var client = new HttpClient())

{

using (var request = new HttpRequestMessage(HttpMethod.Head, uri))

{

using (var response = await client.SendAsync(request).ConfigureAwait(false))

{

return response.IsSuccessStatusCode;

}

}

}

}

private async Task<Document> LoadDocumentAsync(DocumentSettings settings, Uri uri, DocumentCategory category, DocumentContextCallback contextCallback)

{

var cachedDocument = GetCachedDocument(uri);

if (cachedDocument != null)

{

return cachedDocument;

}

string contents;

var flags = settings.AccessFlags;

if (uri.IsFile)

{

if (!flags.HasFlag(DocumentAccessFlags.EnableFileLoading))

{

throw new UnauthorizedAccessException("The script engine is not configured for loading documents from the file system");

}

using (var reader = new StreamReader(uri.LocalPath))

{

contents = await reader.ReadToEndAsync().ConfigureAwait(false);

}

}

else

{

if (!flags.HasFlag(DocumentAccessFlags.EnableWebLoading))

{

throw new UnauthorizedAccessException("The script engine is not configured for downloading documents from the Web");

}

using (var client = new WebClient())

{

contents = await client.DownloadStringTaskAsync(uri).ConfigureAwait(false);

}

}

var documentInfo = new DocumentInfo(uri) { Category = category, ContextCallback = contextCallback };

var callback = settings.LoadCallback;

callback?.Invoke(ref documentInfo);

return CacheDocument(new StringDocument(documentInfo, contents));

}

private Document GetCachedDocument(Uri uri)

{

lock (cache)

{

for (var index = 0; index < cache.Count; index++)

{

var cachedDocument = cache[index];

if (cachedDocument.Info.Uri == uri)

{

cache.RemoveAt(index);

cache.Insert(0, cachedDocument);

return cachedDocument;

}

}

return null;

}

}

private Document CacheDocument(Document document)

{

lock (cache)

{

var cachedDocument = cache.FirstOrDefault(testDocument => testDocument.Info.Uri == document.Info.Uri);

if (cachedDocument != null)

{

Debug.Assert(cachedDocument.Contents.ReadToEnd().SequenceEqual(document.Contents.ReadToEnd()));

return cachedDocument;

}

var maxCacheSize = Math.Max(16, Convert.ToInt32(Math.Min(MaxCacheSize, int.MaxValue)));

while (cache.Count >= maxCacheSize)

{

cache.RemoveAt(cache.Count - 1);

}

cache.Insert(0, document);

return document;

}

}

#region DocumentLoader overrides

public override uint MaxCacheSize { get; set; }

public override async Task<Document> LoadDocumentAsync(DocumentSettings settings, DocumentInfo? sourceInfo, string specifier, DocumentCategory category, DocumentContextCallback contextCallback)

{

MiscHelpers.VerifyNonNullArgument(settings, nameof(settings));

MiscHelpers.VerifyNonBlankArgument(specifier, nameof(specifier), "Invalid document specifier");

if ((settings.AccessFlags & DocumentAccessFlags.EnableAllLoading) == DocumentAccessFlags.None)

{

throw new UnauthorizedAccessException("The script engine is not configured for loading documents");

}

if (category == null)

{

category = sourceInfo.HasValue ? sourceInfo.Value.Category : DocumentCategory.Script;

}

List<Uri> candidateUris;

if (Uri.TryCreate(specifier, UriKind.RelativeOrAbsolute, out var uri) && uri.IsAbsoluteUri)

{

candidateUris = await GetCandidateUrisAsync(settings, sourceInfo, uri).ConfigureAwait(false);

}

else

{

candidateUris = await GetCandidateUrisAsync(settings, sourceInfo, specifier).ConfigureAwait(false);

}

if (candidateUris.Count < 1)

{

throw new FileNotFoundException(null, specifier);

}

if (candidateUris.Count == 1)

{

return await LoadDocumentAsync(settings, candidateUris[0], category, contextCallback).ConfigureAwait(false);

}

var exceptions = new List<Exception>(candidateUris.Count);

foreach (var candidateUri in candidateUris)

{

var task = LoadDocumentAsync(settings, candidateUri, category, contextCallback);

try

{

return await task.ConfigureAwait(false);

}

catch (Exception exception)

{

if ((task.Exception != null) && task.Exception.InnerExceptions.Count == 1)

{

Debug.Assert(ReferenceEquals(task.Exception.InnerExceptions[0], exception));

exceptions.Add(exception);

}

else

{

exceptions.Add(task.Exception);

}

}

}

if (exceptions.Count < 1)

{

MiscHelpers.AssertUnreachable();

throw new FileNotFoundException(null, specifier);

}

if (exceptions.Count == 1)

{

MiscHelpers.AssertUnreachable();

throw new FileLoadException(exceptions[0].Message, specifier, exceptions[0]);

}

throw new AggregateException(exceptions).Flatten();

}

public override void DiscardCachedDocuments()

{

lock (cache)

{

cache.Clear();

}

base.DiscardCachedDocuments();

}

#endregion

}

#endregion