using System.IO;
using System.Text.RegularExpressions;

namespace Futonizer.Services;

/// <summary>
/// Recognises subtitle files by extension and extracts a normalized episode
/// code (e.g. "S04E06") from a filename, used to match dropped subtitle
/// files to the video file with the same episode code.
/// </summary>
public static class SubtitleMatcher
{
    /// <summary>
    /// Every subtitle container/format extension mkvmerge (and therefore
    /// Futonizer) can mux in: SubRip, (Advanced) SubStation Alpha, VobSub,
    /// WebVTT, HDMV/PGS, Universal Subtitle Format, SAMI, TTML/DFXP, EBU-STL,
    /// MicroDVD/SubViewer (both commonly saved with a plain ".sub" extension),
    /// and Kate.
    /// </summary>
    public static readonly string[] SupportedExtensions =
    {
        ".srt", ".ass", ".ssa", ".sub", ".idx", ".vtt", ".webvtt",
        ".sup", ".pgs", ".usf", ".smi", ".sami", ".ttml", ".dfxp",
        ".stl", ".kate",
    };

    public static bool IsSubtitleFile(string path)
    {
        string ext = Path.GetExtension(path);
        return !string.IsNullOrEmpty(ext)
               && SupportedExtensions.Contains(ext, StringComparer.OrdinalIgnoreCase);
    }

    // "S04E06", "S4E6", "S04 E06", "S04-E06", "S04.E06" — the standard scene/anime tagging scheme.
    private static readonly Regex SeasonEpisodeRegex =
        new(@"S(\d{1,4})[\s._-]*E(\d{1,4})", RegexOptions.IgnoreCase | RegexOptions.Compiled);

    // Fallback: "4x06" style season x episode separator.
    private static readonly Regex SeasonXEpisodeRegex =
        new(@"(?<![\d.])(\d{1,2})x(\d{2,3})(?!\d)", RegexOptions.IgnoreCase | RegexOptions.Compiled);

    /// <summary>
    /// Extracts and normalizes the episode code from a filename (e.g.
    /// "Show.S4E6.1080p.mkv" and "Show - 04x06 - Title.srt" both return
    /// "S04E06"), so files can be matched regardless of zero-padding or
    /// separator style. Returns null if no episode code is found.
    /// </summary>
    public static string? ExtractEpisodeCode(string fileName)
    {
        var match = SeasonEpisodeRegex.Match(fileName);
        if (!match.Success)
            match = SeasonXEpisodeRegex.Match(fileName);

        if (!match.Success) return null;

        if (!int.TryParse(match.Groups[1].Value, out int season)) return null;
        if (!int.TryParse(match.Groups[2].Value, out int episode)) return null;

        return $"S{season:D2}E{episode:D2}";
    }
}