using System.Diagnostics;
using System.Security.Cryptography;
using System.Text.RegularExpressions;

namespace MSCO.Server;

/// <summary>Eine Mod, die der Server an seine Spieler verteilt (data/mods/&lt;id&gt;.dll).</summary>
public sealed record ServerMod(string Id, string Name, string Version, string Sha256, byte[] Data)
{
    public int Size => Data.Length;
}

/// <summary>
/// Server-Mods: MSCO-Mods (DLLs) in data/mods. Beim Beitreten bekommt jeder Spieler die Liste; fehlende Mods lädt die
/// MSCO-Mod nach Zustimmung des Spielers vom Server herunter (MsgType.ModFileRequest). Verwalten: Dateien in den Ordner
/// legen bzw. im Web-Panel unter "Mods" hochladen, danach "mods reload" (Panel: automatisch).
/// </summary>
public static class ModStore
{
    public const int MaxModBytes = 20 * 1024 * 1024;
    public const int MaxMods = 30;
    static readonly Regex IdPattern = new("^[A-Za-z0-9_.-]{1,64}$");

    public static string Folder(string dataDir) => Path.Combine(dataDir, "mods");

    /// <summary>Alle Mods aus data/mods lesen (ungültige werden mit Meldung übersprungen).</summary>
    public static List<ServerMod> Load(string dataDir, Action<string> log)
    {
        var list = new List<ServerMod>();
        string dir = Folder(dataDir);
        if (!Directory.Exists(dir)) return list;
        foreach (string file in Directory.GetFiles(dir, "*.dll").OrderBy(f => f, StringComparer.OrdinalIgnoreCase))
        {
            if (list.Count >= MaxMods) { log?.Invoke($"More than {MaxMods} mods in data/mods - the rest is ignored"); break; }
            try
            {
                byte[] data = File.ReadAllBytes(file);
                string id = Path.GetFileNameWithoutExtension(file);
                string error = Check(id, data);
                if (error != null) { log?.Invoke($"Mod {Path.GetFileName(file)} skipped: {error}"); continue; }
                list.Add(Describe(file, id, data));
            }
            catch (Exception e) { log?.Invoke($"Mod {Path.GetFileName(file)} could not be read: {e.Message}"); }
        }
        return list;
    }

    static ServerMod Describe(string file, string id, byte[] data)
    {
        string name = id, version = "";
        try
        {
            var info = FileVersionInfo.GetVersionInfo(file);
            if (!string.IsNullOrWhiteSpace(info.ProductName)) name = info.ProductName.Trim();
            version = (info.ProductVersion ?? info.FileVersion ?? "").Split('+')[0].Trim();
        }
        catch { }
        string sha = Convert.ToHexString(SHA256.HashData(data)).ToLowerInvariant();
        return new ServerMod(id, Clip(name, 64), Clip(version, 32), sha, data);
    }

    static string Clip(string s, int max) => s.Length > max ? s[..max] : s;

    static string Check(string id, byte[] data)
    {
        if (!IdPattern.IsMatch(id)) return "the file name may only contain letters, digits, '.', '-' and '_'";
        if (data.Length < 64 || data.Length > MaxModBytes) return $"size must be up to {MaxModBytes / 1024 / 1024} MB";
        if (data[0] != 0x4d || data[1] != 0x5a) return "not a .NET DLL";
        return null;
    }

    /// <summary>Mod hochladen (Panel). Gibt einen Fehler oder null zurück.</summary>
    public static string Add(string dataDir, string fileName, byte[] data)
    {
        fileName = Path.GetFileName(fileName ?? "");
        if (!fileName.EndsWith(".dll", StringComparison.OrdinalIgnoreCase)) return "Choose a .dll file";
        string id = Path.GetFileNameWithoutExtension(fileName);
        string error = Check(id, data);
        if (error != null) return "This mod cannot be used: " + error;
        string dir = Folder(dataDir);
        Directory.CreateDirectory(dir);
        if (!File.Exists(Path.Combine(dir, id + ".dll")) && Directory.GetFiles(dir, "*.dll").Length >= MaxMods)
            return $"At most {MaxMods} mods";
        string target = Path.Combine(dir, id + ".dll"), tmp = target + ".upload";
        File.WriteAllBytes(tmp, data);
        File.Move(tmp, target, true);
        return null;
    }

    public static bool Remove(string dataDir, string id)
    {
        if (!IdPattern.IsMatch(id ?? "")) return false;
        string file = Path.Combine(Folder(dataDir), id + ".dll");
        if (!File.Exists(file)) return false;
        File.Delete(file);
        return true;
    }
}