using System;
using System.IO;
using UnityEngine;

namespace ProjectM.Client
{
    /// <summary>
    /// Client-local settings persistence + application. Loads <c>settings.json</c> from
    /// <c>Application.persistentDataPath</c> at boot (<see cref="RuntimeInitializeOnLoadMethod"/>) and applies
    /// Graphics (Screen / QualitySettings / targetFrameRate) + Audio (<c>AudioListener.volume = Master</c>;
    /// <see cref="GameVolume"/> Music/Sfx bus trims). The single source of truth for the UITK
    /// <c>SettingsScreen</c> shared by the main menu + the in-game pause overlay. Saves are atomic
    /// (temp file + <c>File.Replace</c>). <c>JsonUtility</c> keeps it asmdef-ref-free. Never replicated.
    /// </summary>
    public static class SettingsService
    {
        public static GameSettings Current { get; private set; } = GameSettings.Defaults();

        static string FilePath => Path.Combine(Application.persistentDataPath, "settings.json");

        [RuntimeInitializeOnLoadMethod(RuntimeInitializeLoadType.BeforeSceneLoad)]
        static void Boot()
        {
            Load();
            Apply(Current);
        }

        /// <summary>Read settings from disk (or defaults if absent/corrupt). Returns the loaded value.</summary>
        public static GameSettings Load()
        {
            try
            {
                if (File.Exists(FilePath))
                {
                    var json = File.ReadAllText(FilePath);
                    var s = JsonUtility.FromJson<GameSettings>(json);
                    if (s.Version != GameSettings.CurrentVersion)
                        s = Migrate(s);
                    Current = s.Clamped();
                }
                else
                {
                    Current = GameSettings.Defaults();
                }
            }
            catch (Exception e)
            {
                Debug.LogWarning($"[SettingsService] Load failed ({e.Message}); using defaults.");
                Current = GameSettings.Defaults();
            }
            return Current;
        }

        /// <summary>Clamp + version-stamp + atomically write to disk; updates <see cref="Current"/>.</summary>
        public static void Save(GameSettings settings)
        {
            settings = settings.Clamped();
            settings.Version = GameSettings.CurrentVersion;
            Current = settings;
            try
            {
                var json = JsonUtility.ToJson(settings, true);
                var tmp = FilePath + ".tmp";
                File.WriteAllText(tmp, json);
                if (File.Exists(FilePath)) File.Replace(tmp, FilePath, null);
                else File.Move(tmp, FilePath);
            }
            catch (Exception e)
            {
                Debug.LogWarning($"[SettingsService] Save failed: {e.Message}");
            }
        }

        /// <summary>Apply settings to the live engine. Master rides AudioListener.volume; buses are per-call trims.</summary>
        public static void Apply(GameSettings s)
        {
            s = s.Clamped();

            // Graphics
            QualitySettings.SetQualityLevel(s.QualityLevel, true);
            QualitySettings.vSyncCount = s.VSync;
            var mode = (FullScreenMode)s.FullScreenMode;
            if (s.RefreshHz > 0)
                Screen.SetResolution(s.ResWidth, s.ResHeight, mode, new RefreshRate { numerator = (uint)s.RefreshHz, denominator = 1 });
            else
                Screen.SetResolution(s.ResWidth, s.ResHeight, mode);
            Application.targetFrameRate = s.TargetFps; // -1 = uncapped (ignored while vSync > 0)

            // Audio
            AudioListener.volume = s.Master;
            GameVolume.Music = s.Music;
            GameVolume.Sfx = s.Sfx;
        }

        /// <summary>Convenience for the settings UI: persist then apply.</summary>
        public static void SaveAndApply(GameSettings s)
        {
            Save(s);
            Apply(Current);
        }

        // Forward-compatible migration: fill from current defaults, preserve any recognizable old values.
        // Additive-only as the schema grows (never throws on an unknown version).
        static GameSettings Migrate(GameSettings old)
        {
            var def = GameSettings.Defaults();
            if (old.ResWidth > 0) def.ResWidth = old.ResWidth;
            if (old.ResHeight > 0) def.ResHeight = old.ResHeight;
            if (old.Master > 0f) def.Master = old.Master;
            if (old.Music > 0f) def.Music = old.Music;
            if (old.Sfx > 0f) def.Sfx = old.Sfx;
            def.Version = GameSettings.CurrentVersion;
            return def;
        }
    }
}