// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
 
using System.Text;
using Microsoft.Extensions.FileProviders;
 
namespace Microsoft.AspNetCore.Components.WebView;
 
internal sealed class StaticContentProvider
{
    private readonly IFileProvider _fileProvider;
    private readonly Uri _appBaseUri;
    private readonly string _hostPageRelativePath;
    private static readonly FileExtensionContentTypeProvider ContentTypeProvider = new();
    private static readonly ManifestEmbeddedFileProvider _manifestProvider =
        new ManifestEmbeddedFileProvider(typeof(StaticContentProvider).Assembly);
 
    public StaticContentProvider(IFileProvider fileProvider, Uri appBaseUri, string hostPageRelativePath)
    {
        _fileProvider = fileProvider ?? throw new ArgumentNullException(nameof(fileProvider));
        _appBaseUri = appBaseUri ?? throw new ArgumentNullException(nameof(appBaseUri));
        _hostPageRelativePath = hostPageRelativePath ?? throw new ArgumentNullException(nameof(hostPageRelativePath));
    }
 
    public bool TryGetResponseContent(string requestUri, bool allowFallbackOnHostPage, out int statusCode, out string statusMessage, out Stream content, out IDictionary<string, string> headers)
    {
        var fileUri = new Uri(requestUri);
        if (_appBaseUri.IsBaseOf(fileUri))
        {
            var relativePath = _appBaseUri.MakeRelativeUri(fileUri).ToString();
 
            // Content in the file provider takes first priority
            // Next we may fall back on supplying the host page to support deep linking
            // If there's no match, fall back on serving embedded framework content
            string contentType;
            var found = TryGetFromFileProvider(relativePath, out content, out contentType)
                || (allowFallbackOnHostPage && TryGetFromFileProvider(_hostPageRelativePath, out content, out contentType))
                || TryGetFrameworkFile(relativePath, out content, out contentType);
 
            if (found)
            {
                statusCode = 200;
                statusMessage = "OK";
                headers = GetResponseHeaders(contentType);
            }
            else
            {
                content = new MemoryStream(Encoding.UTF8.GetBytes($"There is no content at {relativePath}"));
                statusCode = 404;
                statusMessage = "Not found";
                headers = GetResponseHeaders("text/plain");
            }
 
            // Always respond to requests within the base URI, even if there's no matching file
            return true;
        }
        else
        {
            // URL isn't within application base path, so let the network handle it
            statusCode = default;
            statusMessage = default;
            headers = default;
            content = default;
            return false;
        }
    }
 
    private bool TryGetFromFileProvider(string relativePath, out Stream content, out string contentType)
    {
        if (!string.IsNullOrEmpty(relativePath))
        {
            var fileInfo = _fileProvider.GetFileInfo(relativePath);
            if (fileInfo.Exists)
            {
                content = fileInfo.CreateReadStream();
                contentType = GetResponseContentTypeOrDefault(fileInfo.Name);
                return true;
            }
        }
 
        content = default;
        contentType = default;
        return false;
    }
 
    private static bool TryGetFrameworkFile(string relativePath, out Stream content, out string contentType)
    {
        // We're not trying to simulate everything a real webserver does. We don't need to
        // support querystring parameters, for example. It's enough to require an exact match.
        var file = _manifestProvider.GetFileInfo(relativePath);
        if (file.Exists)
        {
            content = file.CreateReadStream();
            contentType = GetResponseContentTypeOrDefault(relativePath);
            return true;
        }
 
        content = default;
        contentType = default;
        return false;
    }
 
    private static string GetResponseContentTypeOrDefault(string path)
        => ContentTypeProvider.TryGetContentType(path, out var matchedContentType)
        ? matchedContentType
        : "application/octet-stream";
 
    private static IDictionary<string, string> GetResponseHeaders(string contentType)
        => new Dictionary<string, string>()
        {
                { "Content-Type", contentType },
                { "Cache-Control", "no-cache, max-age=0, must-revalidate, no-store" },
        };
}