using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text.RegularExpressions;

namespace TinfoilVibeServer.Utilities;

/// <summary>
/// Streams a multipart RAR as a single, seekable stream.
/// Supports:
///   • myGame.rar            (single volume)
///   • myGame.r00 / r01 …    (RAR 4.x style)
///   • myGame.part01.rar …   (WinRAR “part” style)
/// </summary>
public static class MultiPartRarHelper
{
    public static string GetBaseNameForRarVolume(string fileName)
    {
        string baseName = string.Empty;
        // Multipart – remove the ".rNN" or ".partNN" suffix
        var m = Regex.Match(fileName,
            @"^(?<base>.+?)(\.r\d\d|\.part\d\d)\.rar$",
            RegexOptions.IgnoreCase);
        if (!m.Success)
        {
            if (fileName.EndsWith(".rar", StringComparison.OrdinalIgnoreCase))
            {
                // Single‑volume archive – just drop the suffix
                baseName = fileName.Substring(0, fileName.Length - 4);
            }
        }
        else
        {
            baseName = m.Groups["base"].Value;
        }
        return baseName;
    }

    /// <summary>
    /// Returns the list of files that belong to the same multipart set.
    /// </summary>
    public static List<string> DiscoverVolumes(string dir, string baseName)
    {
        // Pattern:  <base>.(rar | rNN | partNN.rar)
        string pattern =
            $@"^{Regex.Escape(baseName)}(\.rar|\.r\d\d|\.part\d\d\.rar)$";

        return Directory.GetFiles(dir)
            .Where(f => Regex.IsMatch(Path.GetFileName(f), pattern, RegexOptions.IgnoreCase))
            .OrderBy(f => GetPartNumber(Path.GetFileName(f), baseName))
            .ToList();
    }
    
    /// <summary>
    /// Gives each file a numeric key that guarantees the correct order.
    /// 0 → .rar   (first volume)
    /// 1 → .r00   or .part01
    /// 2 → .r01   or .part02
    /// … and so on.
    /// </summary>
    private static int GetPartNumber(string fileName, string baseName)
    {
        // 1️⃣  ".rar"   → 0
        if (fileName.Equals($"{baseName}.rar", StringComparison.OrdinalIgnoreCase))
            return 0;

        // 2️⃣  ".rNN" or ".partNN.rar"
        var m = Regex.Match(fileName,
            $@"\.r(?<num>\d\d)$|\.part(?<num>\d\d)\.rar$",
            RegexOptions.IgnoreCase);

        if (m.Success)
        {
            int partNum = int.Parse(m.Groups["num"].Value);
            return partNum + 1;   // so r00 → 1, r01 → 2; part01 → 1, part02 → 2
        }

        // 3️⃣  unknown pattern – treat as first part
        return 0;
    }

}