using Unity.Entities;
using UnityEngine;

namespace ProjectM.Client
{
    /// <summary>
    /// Client-only water-column ATMOSPHERE for the LANTERN seabed (deep-sea murk). 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 + flat ambient between the
    /// base-shelf murk (origin) and the deeper out-shelf murk (+1000 X) — mirroring HudSystem's region split
    /// at camera X &gt; 500. The skybox stays empty and the post-FX volume GLOBAL; only fog colour/density +
    /// ambient shift per region. Pure presentation: never mutates the simulation. Knobs live in
    /// <see cref="WorldAtmosphereConfig"/> (falls back to baked LANTERN-murk defaults when absent). Gated by
    /// <see cref="ScenePolicy.IsGameplayScene"/> so it never restyles the menu or ArtStaging. Per-room-biome
    /// murk variants key on the replicated RunInfo.CurrentBiome (re-meant to depth/water flavors — the old
    /// meadow/arid/blight palettes died in the LANTERN realignment).
    /// </summary>
    [WorldSystemFilter(WorldSystemFilterFlags.ClientSimulation)]
    [UpdateInGroup(typeof(PresentationSystemGroup))]
    public partial class WorldAtmosphereSystem : SystemBase
    {
        Camera _cam;

        protected override void OnUpdate()
        {
            if (!ScenePolicy.IsGameplayScene()) 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;

            // LANTERN murk defaults (match the ArtStaging source-of-truth hues; density is the play-readability knob).
            Color baseFog = cfg != null ? cfg.BaseFogColor : new Color(0.02f, 0.10f, 0.12f, 1f);
            float baseDen = cfg != null ? cfg.BaseFogDensity : 0.035f;
            Color baseAmb = cfg != null ? cfg.BaseAmbientSky : new Color(0.03f, 0.055f, 0.08f, 1f);
            Color expFog = cfg != null ? cfg.ExpeditionFogColor : new Color(0.015f, 0.075f, 0.10f, 1f);
            float expDen = cfg != null ? cfg.ExpeditionFogDensity : 0.04f;
            Color expAmb = cfg != null ? cfg.ExpeditionAmbientSky : new Color(0.02f, 0.045f, 0.07f, 1f);

            // 2026-08-07 audit purge: per-room murk flavors (kelp shallows / crush-dark trench / gloam bloom)
            // keyed off RunInfo.CurrentBiome. The run FSM is deleted, so the out-shelf murk config above is the
            // whole look. Re-key this off LANTERN's pocket type when Phase 2 lands — the colour constants are in
            // git if the three flavors are wanted back.


            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);
        }
    }
}