using Unity.Entities;
using UnityEngine;

namespace ProjectM.Client
{
    /// <summary>
    /// Client-only ATMOSPHERE cross-fade for the two-region world. A managed presentation system
    /// (SystemBase, main thread, NO Burst) in <see cref="PresentationSystemGroup"/> that OBSERVES the
    /// follow-camera's world-space X and lerps <see cref="RenderSettings"/> fog + Trilight sky-ambient between
    /// the lush cyan meadow base (origin) and the hostile orange arid expedition (+1000 X) — mirroring
    /// HudSystem's region split at camera X &gt; 500. The directional light + skybox + post-FX volume stay
    /// GLOBAL; only fog colour/density + ambient sky colour shift per region. Pure presentation: never mutates
    /// the simulation, no ECS query (camera + RenderSettings only). Knobs live in
    /// <see cref="WorldAtmosphereConfig"/> (falls back to baked defaults when absent). Guarded to the gameplay
    /// "Game" scene so it never restyles the menu. Fog enable/mode + equator/ground ambient are baked into the
    /// scene; this only drives the per-region deltas.
    /// </summary>
    [WorldSystemFilter(WorldSystemFilterFlags.ClientSimulation)]
    [UpdateInGroup(typeof(PresentationSystemGroup))]
    public partial class WorldAtmosphereSystem : SystemBase
    {
        Camera _cam;

        protected override void OnUpdate()
        {
            if (UnityEngine.SceneManagement.SceneManager.GetActiveScene().name != "Game") return;
            if (_cam == null) _cam = Camera.main;
            if (_cam == null) return;

            var cfg = WorldAtmosphereConfig.Instance;
            float boundary = cfg != null ? cfg.BoundaryX : 500f;
            float half = cfg != null ? Mathf.Max(1f, cfg.BlendHalfWidth) : 80f;

            Color baseFog = cfg != null ? cfg.BaseFogColor : new Color(0.784f, 0.878f, 0.824f, 1f);
            float baseDen = cfg != null ? cfg.BaseFogDensity : 0.006f;
            Color baseAmb = cfg != null ? cfg.BaseAmbientSky : new Color(0.725f, 0.831f, 0.949f, 1f);
            Color expFog = cfg != null ? cfg.ExpeditionFogColor : new Color(0.851f, 0.549f, 0.227f, 1f);
            float expDen = cfg != null ? cfg.ExpeditionFogDensity : 0.010f;
            Color expAmb = cfg != null ? cfg.ExpeditionAmbientSky : new Color(0.910f, 0.769f, 0.604f, 1f);

            float x = _cam.transform.position.x;
            float t = Mathf.Clamp01((x - (boundary - half)) / (2f * half));
            t = t * t * (3f - 2f * t); // smoothstep

            RenderSettings.fogColor = Color.Lerp(baseFog, expFog, t);
            RenderSettings.fogDensity = Mathf.Lerp(baseDen, expDen, t);
            RenderSettings.ambientSkyColor = Color.Lerp(baseAmb, expAmb, t);
        }
    }
}