using System;
using System.Collections.Generic;
using System.IO;
using System.Reflection;
using System.Security.Cryptography;

namespace MSCO
{
    /// <summary>
    /// Lädt MSCO-Mods und ruft sie auf. Eigene Mods: &lt;Spiel&gt;\MSCO\Mods\*.dll (immer aktiv). Mods eines Servers:
    /// &lt;Spiel&gt;\MSCO\Mods\Servers\&lt;id&gt;.dll - nur aktiv, solange man auf einem Server ist, der sie verlangt.
    /// Fehler einer Mod werden abgefangen und protokolliert; wirft sie ständig Fehler, wird sie abgeschaltet.
    /// </summary>
    public static class ModLoader
    {
        public sealed class LoadedMod
        {
            public MscoMod Mod;
            public string File, Sha256;
            public bool FromServer, Active;
            public int Errors;
            public string Error;
        }

        const int MaxErrors = 50;
        static readonly List<LoadedMod> mods = new List<LoadedMod>();
        static bool localLoaded;

        public static IList<LoadedMod> All { get { return mods.AsReadOnly(); } }
        public static string Folder { get { return Path.Combine(Bootstrap.Folder ?? ".", "Mods"); } }
        public static string ServerFolder { get { return Path.Combine(Folder, "Servers"); } }
        public static string ServerFile(string id) { return Path.Combine(ServerFolder, id + ".dll"); }

        /// <summary>Eigene Mods einmal beim ersten Hauptmenü laden.</summary>
        public static void LoadLocal()
        {
            if (localLoaded) return;
            localLoaded = true;
            try
            {
                Directory.CreateDirectory(Folder);
                foreach (string file in Directory.GetFiles(Folder, "*.dll"))
                    Load(file, false);
                if (mods.Count > 0) MscoLog.Info("[MSCO] " + mods.Count + " mod(s) loaded from " + Folder);
            }
            catch (Exception e) { MscoLog.Warning("[MSCO] Could not load mods: " + e.Message); }
        }

        public static string Sha256Of(byte[] data)
        {
            using (var sha = SHA256.Create())
                return BitConverter.ToString(sha.ComputeHash(data)).Replace("-", "").ToLowerInvariant();
        }

        public static LoadedMod FindBySha(string sha)
        {
            foreach (LoadedMod m in mods) if (string.Equals(m.Sha256, sha, StringComparison.OrdinalIgnoreCase)) return m;
            return null;
        }

        /// <summary>
        /// DLL laden (aus den Bytes - die Datei bleibt frei, und eine neue Version einer Server-Mod kann neben der alten
        /// geladen werden) und alle MscoMod-Klassen darin anlegen. Gibt die erste Mod zurück (oder null).
        /// </summary>
        public static LoadedMod Load(string file, bool fromServer)
        {
            LoadedMod first = null;
            try
            {
                byte[] data = System.IO.File.ReadAllBytes(file);
                string sha = Sha256Of(data);
                LoadedMod existing = FindBySha(sha);
                if (existing != null) return existing;

                Assembly asm = Assembly.Load(data);
                Type[] types;
                try { types = asm.GetTypes(); }
                catch (ReflectionTypeLoadException e) { types = Array.FindAll(e.Types, t => t != null); }
                foreach (Type t in types)
                {
                    if (t.IsAbstract || !typeof(MscoMod).IsAssignableFrom(t)) continue;
                    MscoMod mod;
                    try { mod = (MscoMod)Activator.CreateInstance(t); }
                    catch (Exception e)
                    {
                        MscoLog.Warning("[MSCO] Mod " + t.FullName + " could not be created: " + (e.InnerException ?? e).Message);
                        continue;
                    }
                    var loaded = new LoadedMod { Mod = mod, File = file, Sha256 = sha, FromServer = fromServer, Active = !fromServer };
                    mods.Add(loaded);
                    if (first == null) first = loaded;
                    MscoLog.Info("[MSCO] Mod loaded: " + Safe(() => mod.Name, t.Name) + " " + Safe(() => mod.Version, "") +
                                 (fromServer ? " (from the server)" : ""));
                    Call(loaded, m => m.OnLoad());
                }
                if (first == null) MscoLog.Warning("[MSCO] " + Path.GetFileName(file) + " contains no MSCO mod (class deriving from MscoMod)");
            }
            catch (Exception e)
            {
                MscoLog.Warning("[MSCO] Could not load mod " + Path.GetFileName(file) + ": " + e.Message);
            }
            return first;
        }

        static string Safe(Func<string> get, string fallback)
        {
            try { return get() ?? fallback; } catch { return fallback; }
        }

        /// <summary>Server-Mods für die aktuelle Sitzung einschalten (alle anderen Server-Mods aus).</summary>
        public static void ActivateServerMods(ICollection<string> shas)
        {
            foreach (LoadedMod m in mods)
                if (m.FromServer && m.Error == null) m.Active = shas != null && shas.Contains(m.Sha256);
        }

        // ---------------------------------------------------------------- Aufrufe

        static void Call(LoadedMod m, Action<MscoMod> action)
        {
            try { action(m.Mod); }
            catch (Exception e)
            {
                m.Errors++;
                if (m.Errors <= 3) MscoLog.Warning("[MSCO] Mod " + Safe(() => m.Mod.Name, "?") + ": " + e);
                if (m.Errors >= MaxErrors)
                {
                    m.Active = false;
                    m.Error = e.Message;
                    MscoLog.Warning("[MSCO] Mod " + Safe(() => m.Mod.Name, "?") + " was turned off (too many errors)");
                }
            }
        }

        static void Each(Action<MscoMod> action)
        {
            for (int i = 0; i < mods.Count; i++)
                if (mods[i].Active) Call(mods[i], action);
        }

        public static void MenuLoad() { Each(m => m.OnMenuLoad()); }
        public static void GameLoad() { Each(m => m.OnGameLoad()); }
        public static void Update() { if (mods.Count > 0) Each(m => m.Update()); }
        public static void FixedUpdate() { if (mods.Count > 0) Each(m => m.FixedUpdate()); }
        public static void OnGUI() { if (mods.Count > 0) Each(m => m.OnGUI()); }
        public static void SessionStart() { Each(m => m.OnSessionStart()); }
        public static void PlayerJoined(int id, string name) { Each(m => m.OnPlayerJoined(id, name)); }
        public static void PlayerLeft(int id, string name) { Each(m => m.OnPlayerLeft(id, name)); }

        /// <summary>Sitzung vorbei: Mods informieren, Server-Mods ausschalten.</summary>
        public static void SessionEnd()
        {
            Each(m => m.OnSessionEnd());
            ActivateServerMods(null);
        }

        public static void Message(string modId, int from, byte[] data)
        {
            for (int i = 0; i < mods.Count; i++)
            {
                LoadedMod m = mods[i];
                if (!m.Active || Safe(() => m.Mod.ID, null) != modId) continue;
                Call(m, mod => mod.OnMessage(from, data));
            }
        }
    }
}