using System.Collections.Generic;
using ProjectM.Simulation;
using Unity.Entities;
using Unity.Mathematics;
using Unity.NetCode;
using Unity.Transforms;
using UnityEngine;

namespace ProjectM.Client
{
    /// <summary>
    /// Slice 1, Feature B — client-only enemy world-space HEALTH BARS (one pooled world-space Canvas per live Husk).
    /// Observe-only presentation <see cref="SystemBase"/> in <see cref="PresentationSystemGroup"/> that reads replicated
    /// state and never mutates the sim or destroys a ghost. SELF-QUERIES enemies (<c>Health</c> + <c>LocalTransform</c>
    /// <see cref="EnemyTag"/>) and self-detects the damage edge from a per-enemy <c>LastHp</c> stored on the bar entry:
    /// a decrease arms/refreshes that enemy's bar (sticky for <see cref="HealthBarShowDuration"/>, then fades). A bar
    /// stays permanently on below <see cref="HealthBarAlwaysOnThreshold"/> HP; when more than <see cref="HealthBarPoolLimit"/>
    /// bars exist, distant ones (beyond <see cref="FeelConfig.HealthBarMaxDistSq"/> of the local player) are hidden.
    /// Billboards to the main camera. Prunes its cache against its own seen-set EVERY frame (a despawn drops the bar).
    /// Extracted from CombatFeedbackSystem; owns its own FX-root + UI materials.
    /// </summary>
    [WorldSystemFilter(WorldSystemFilterFlags.ClientSimulation)]
    [UpdateInGroup(typeof(PresentationSystemGroup))]
    public partial class EnemyHealthBarSystem : SystemBase
    {
        // CanvasGo == null => a tracking-only entry (enemy seen, not yet damaged, so no bar built). LastHp/MaxHp/Pos are
        // refreshed from the live query each frame; LastHp is the self-owned damage-edge source (was the core's _cache).
        struct HealthBarEntry
        {
            public GameObject CanvasGo; public UnityEngine.UI.Image Fill; public UnityEngine.UI.Image Bg;
            public float ShowTimer; public bool Visible;
            public float LastHp; public float MaxHp; public float3 Pos;
            // Track B: last values actually pushed to uGUI, so a bar that is merely showing pushes nothing.
            // CreateHealthBar seeds these to -1 (a struct would otherwise default them to 0, which is a
            // legitimate frac and would skip the first render of a fully-drained bar).
            public float LastFrac; public float LastAlpha;
        }

        const int HealthBarPoolLimit = 24;
        const float HealthBarShowDuration = 3f;
        const float HealthBarFadeDuration = 0.5f;
        const float HealthBarAlwaysOnThreshold = 0.25f;
        const float HealthBarWorldYOffset = 2.3f;

        readonly Dictionary<Entity, HealthBarEntry> _healthBars = new();
        readonly List<Entity> _barStale = new();
        readonly List<Entity> _barKeys = new();
        readonly HashSet<Entity> _seen = new();   // own enemy seen-set (per-frame prune)
        Material _barBgMat, _barFillMat;
        Transform _fxRoot;
        Entity _localPlayer = Entity.Null;

        protected override void OnStartRunning()
        {
            if (_fxRoot != null) return;
            _fxRoot = new GameObject("~EnemyHealthBarFX").transform;
            // Health-bar materials (UI/Default = always-included URP-compatible UI shader; per-instance Image.color carries alpha).
            Shader uiShader = Shader.Find("UI/Default") ?? Shader.Find("Sprites/Default");
            _barBgMat = new Material(uiShader) { name = "HealthBarBg" };
            _barFillMat = new Material(uiShader) { name = "HealthBarFill" };
        }

        protected override void OnDestroy()
        {
            if (_fxRoot != null) Object.Destroy(_fxRoot.gameObject);
            if (_barBgMat != null) Object.Destroy(_barBgMat);
            if (_barFillMat != null) Object.Destroy(_barFillMat);
            foreach (var kv in _healthBars)
                if (kv.Value.CanvasGo != null) Object.Destroy(kv.Value.CanvasGo);
        }

        protected override void OnUpdate()
        {
            float dt = SystemAPI.Time.DeltaTime;
            var cam = Camera.main;

            // Predicted/physics jobs writing these must finish before this main-thread read.
            EntityManager.CompleteDependencyBeforeRO<Health>();
            EntityManager.CompleteDependencyBeforeRO<LocalTransform>();

            // Local player (drives the pool-cap distance gate).
            _localPlayer = Entity.Null;
            float3 localPos = default;
            foreach (var (xf, entity) in SystemAPI.Query<RefRO<LocalTransform>>()
                         .WithAll<GhostOwnerIsLocal, PlayerTag>().WithEntityAccess())
            {
                _localPlayer = entity;
                localPos = xf.ValueRO.Position;
            }

            // Self-query enemies: track HP per enemy to self-detect the damage edge; a decrease arms/refreshes the bar.
            _seen.Clear();
            foreach (var (health, xf, entity) in
                     SystemAPI.Query<RefRO<Health>, RefRO<LocalTransform>>().WithAll<EnemyTag>().WithEntityAccess())
            {
                _seen.Add(entity);
                float cur = health.ValueRO.Current;
                float max = health.ValueRO.Max;
                float3 pos = xf.ValueRO.Position;

                bool existed = _healthBars.TryGetValue(entity, out var entry);
                bool damaged = existed && cur < entry.LastHp - 0.001f; // own damage edge (was core _cache prev.Hp)
                entry.LastHp = cur; entry.MaxHp = max; entry.Pos = pos;
                _healthBars[entity] = entry;
                if (damaged) ShowHealthBar(entity); // arm/refresh this enemy's bar on a damage edge
            }

            UpdateHealthBars(dt, cam, localPos);
        }

        // ---- Enemy Health Bars (Slice 1, Feature B) — pooled world-space Canvas, on-damage sticky + fade ----

        void ShowHealthBar(Entity entity)
        {
            if (!_healthBars.TryGetValue(entity, out var entry) || entry.CanvasGo == null)
                entry = CreateHealthBar(entity);
            entry.ShowTimer = HealthBarShowDuration;
            if (!entry.Visible) { entry.CanvasGo.SetActive(true); entry.Visible = true; }
            _healthBars[entity] = entry; // struct — must re-assign
        }

        HealthBarEntry CreateHealthBar(Entity entity)
        {
            var go = new GameObject("EnemyHPBar");
            if (_fxRoot != null) go.transform.SetParent(_fxRoot, false);
            var canvas = go.AddComponent<Canvas>();
            canvas.renderMode = RenderMode.WorldSpace;
            canvas.sortingOrder = 5; // below the UITK HUD (50); above world geometry
            var rt = go.GetComponent<RectTransform>();
            rt.sizeDelta = new Vector2(1.2f, 0.14f);

            var bgGo = new GameObject("Bg");
            bgGo.transform.SetParent(go.transform, false);
            var bgRt = bgGo.AddComponent<RectTransform>();
            bgRt.anchorMin = Vector2.zero; bgRt.anchorMax = Vector2.one;
            bgRt.offsetMin = bgRt.offsetMax = Vector2.zero;
            var bgImg = bgGo.AddComponent<UnityEngine.UI.Image>();
            bgImg.material = _barBgMat;
            bgImg.color = new Color(0.05f, 0.05f, 0.06f, 0.82f);

            var fillGo = new GameObject("Fill");
            fillGo.transform.SetParent(go.transform, false);
            var fillRt = fillGo.AddComponent<RectTransform>();
            fillRt.anchorMin = Vector2.zero; fillRt.anchorMax = Vector2.one;
            fillRt.offsetMin = new Vector2(0.02f, 0.02f);
            fillRt.offsetMax = new Vector2(-0.02f, -0.02f);
            var fillImg = fillGo.AddComponent<UnityEngine.UI.Image>();
            fillImg.material = _barFillMat;
            fillImg.color = new Color(0.88f, 0.22f, 0.14f, 1f);
            fillImg.type = UnityEngine.UI.Image.Type.Simple; // a sprite-less UI Image ignores fillAmount (it draws a full quad) ->
            fillImg.raycastTarget = false;                   // the bar empties by sizing the fill RectTransform (anchorMax.x = frac) in UpdateHealthBars

            go.SetActive(false);
            _healthBars.TryGetValue(entity, out var prev); // preserve tracking (LastHp/MaxHp/Pos) recorded by the scan loop
            var entry = new HealthBarEntry
            {
                CanvasGo = go, Fill = fillImg, Bg = bgImg, ShowTimer = 0f, Visible = false,
                LastHp = prev.LastHp, MaxHp = prev.MaxHp, Pos = prev.Pos,
                LastFrac = -1f, LastAlpha = -1f // force the first visual push (a real frac/alpha is never negative)
            };
            _healthBars[entity] = entry;
            return entry;
        }

        // Per-frame: prune dead bars (own seen-set), pool-cap by distance, billboard + fade.
        void UpdateHealthBars(float dt, Camera cam, float3 localPlayerPos)
        {
            if (_healthBars.Count > 0)
            {
                _barStale.Clear();
                foreach (var kv in _healthBars)
                    if (!_seen.Contains(kv.Key)) _barStale.Add(kv.Key);
                for (int i = 0; i < _barStale.Count; i++)
                {
                    var e2 = _barStale[i];
                    if (_healthBars[e2].CanvasGo != null) Object.Destroy(_healthBars[e2].CanvasGo);
                    _healthBars.Remove(e2);
                }
            }
            if (_healthBars.Count == 0) return;

            // Cap keys on the number of BUILT bars (not the tracking-only entries), matching the original threshold.
            int createdBars = 0;
            foreach (var kv in _healthBars) if (kv.Value.CanvasGo != null) createdBars++;
            bool capBars = _localPlayer != Entity.Null && createdBars > HealthBarPoolLimit;

            _barKeys.Clear();
            foreach (var k in _healthBars.Keys) _barKeys.Add(k);
            for (int i = 0; i < _barKeys.Count; i++)
            {
                var key = _barKeys[i];
                var entry = _healthBars[key];
                if (entry.CanvasGo == null) continue; // tracking-only (undamaged) — no bar built yet

                float frac = entry.MaxHp > 0f ? math.saturate(entry.LastHp / entry.MaxHp) : 1f;
                bool alwaysOn = frac < HealthBarAlwaysOnThreshold;

                if (capBars && math.lengthsq(entry.Pos - localPlayerPos) > FeelConfig.HealthBarMaxDistSq)
                {
                    if (entry.Visible) { entry.CanvasGo.SetActive(false); entry.Visible = false; }
                    _healthBars[key] = entry;
                    continue;
                }

                if (!alwaysOn) entry.ShowTimer -= dt;
                bool shouldShow = alwaysOn || entry.ShowTimer > -HealthBarFadeDuration;
                if (shouldShow)
                {
                    if (!entry.Visible) { entry.CanvasGo.SetActive(true); entry.Visible = true; }
                    if (cam != null)
                    {
                        entry.CanvasGo.transform.position = (Vector3)entry.Pos + Vector3.up * HealthBarWorldYOffset;
                        entry.CanvasGo.transform.rotation = cam.transform.rotation; // billboard
                    }
                    float alpha = (!alwaysOn && entry.ShowTimer < 0f)
                        ? 1f - math.saturate(-entry.ShowTimer / HealthBarFadeDuration) : 1f;
                    // Track B: these ran unconditionally for every visible bar every frame. Writing
                    // anchorMax triggers OnRectTransformDimensionsChange and an Image.color write dirties the
                    // canvas — so a bar that is merely SHOWING (not changing) used to keep re-laying-out uGUI.
                    // Epsilon-gated: a bar only pushes when its fill or fade actually moved.
                    if (entry.Fill != null && (math.abs(frac - entry.LastFrac) > 0.002f || math.abs(alpha - entry.LastAlpha) > 0.002f))
                    {
                        var c = entry.Fill.color; c.a = alpha; entry.Fill.color = c;
                        entry.Fill.rectTransform.anchorMax = new Vector2(frac, 1f);
                        if (entry.Bg != null) { var bgc = entry.Bg.color; bgc.a = 0.82f * alpha; entry.Bg.color = bgc; }
                        entry.LastFrac = frac; entry.LastAlpha = alpha;
                    }
                }
                else if (entry.Visible) { entry.CanvasGo.SetActive(false); entry.Visible = false; }

                _healthBars[key] = entry;
            }
        }
    }
}