using System.Text.RegularExpressions;

namespace Uwaa.HTTP.Routing;

/// <summary>
/// Special router which serves static files from the filesystem.
/// </summary>
public partial class FileEndpoint : RouterBase
{
    static MIMEType GuessMIMEType(string extension)
    {
        return extension switch
        {
            ".txt" => new("text", "plain"),
            ".htm" or "html" => new("text", "html"),
            ".js" => new("text", "javascript"),
            ".css" => new("text", "css"),
            ".csv" => new("text", "csv"),

            ".bin" => new("application", "octet-stream"),
            ".zip" => new("application", "zip"),
            ".7z" => new("application", "x-7z-compressed"),
            ".gz" => new("application", "gzip"),
            ".xml" => new("application", "xml"),
            ".pdf" => new("application", "pdf"),
            ".json" => new("application", "json"),

            ".bmp" => new("image", "bmp"),
            ".png" => new("image", "png"),
            ".jpg" or "jpeg" => new("image", "jpeg"),
            ".gif" => new("image", "gif"),
            ".webp" => new("image", "webp"),
            ".svg" => new("image", "svg+xml"),
            ".ico" => new("image", "vnd.microsoft.icon"),

            ".mid" or ".midi" => new("audio", "midi"),
            ".mp3" => new("audio", "mpeg"),
            ".ogg" or ".oga" or ".opus" => new("audio", "ogg"),
            ".wav" => new("audio", "wav"),
            ".weba" => new("audio", "webm"),

            ".webm" => new("video", "webm"),
            ".mp4" => new("video", "mp4"),
            ".mpeg" => new("video", "mpeg"),
            ".ogv" => new("video", "ogg"),

            ".otf" => new("font", "otf"),
            ".ttf" => new("font", "ttf"),
            ".woff" => new("font", "woff"),
            ".woff2" => new("font", "woff2"),

            _ => new("application", "octet-stream"), //Unknown
        };
    }

    /// <summary>
    /// The source directory from which assets should be served.
    /// </summary>
    public string Directory;

    public override HttpMethod Method => HttpMethod.GET;

    public override int Arguments => 1;

    public FileEndpoint(string directory)
    {
        Directory = directory;
    }

    protected override async Task<HttpResponse?> GetResponseInner(HttpRequest req, HttpClientInfo info, ArraySegment<string> path)
    {
        string? asset = path[0];
        if (string.IsNullOrWhiteSpace(asset))
            return null;

        if (FilenameChecker().IsMatch(asset))
            return HttpResponse.BadRequest("Illegal chars in asset path");

        string assetPath = $"{Directory}/{asset}";
        FileInfo fileInfo = new FileInfo(assetPath);
        MIMEType mime;
        if (string.IsNullOrEmpty(fileInfo.Extension))
        {
            mime = new MIMEType("text", "html");
            assetPath += ".htm";
        }
        else
        {
            mime = GuessMIMEType(fileInfo.Extension);
        }

        if (!File.Exists(assetPath))
            return null;

        return new HttpContent(mime, await File.ReadAllBytesAsync(assetPath));
    }

    /// <summary>
    /// Ensures filenames are legal.
    /// </summary>
    /// <remarks>
    /// Enforcing a set of legal characters in filenames reduces the potential attack surface against the server.
    /// </remarks>
    /// <returns>Returns a regular expression which checks for invalid characters.</returns>
    [GeneratedRegex(@"[^a-zA-Z0-9_\-.()\[\] ]")]
    private static partial Regex FilenameChecker();
}