// Assets/_Project/Scripts/Gameplay/SelectionRingVisual.cs
using UnityEngine;

namespace TD.Gameplay
{
    /// <summary>
    /// Local-only visual indicator for builder selection. Sits as a child of the
    /// builder prefab. Subscribes to <see cref="SelectionState.OnSelectionChanged"/>
    /// and toggles the visibility of its own renderers (and any descendant
    /// renderers) when the parent builder becomes selected/unselected.
    /// </summary>
    /// <remarks>
    /// <para><b>Pure local visualization.</b> No NetworkBehaviour. Selection is a
    /// UI concept — every client renders selection state for its own player only.
    /// This component has no networked state.</para>
    ///
    /// <para><b>Why a separate component.</b> Keeps Builder focused on gameplay
    /// state. The visual prefab structure can change independently
    /// (disc → ring → decal projector → animated effect) without touching gameplay
    /// code. The contract is just "renderers visible when selected."</para>
    ///
    /// <para><b>Why renderer-toggle, not GameObject.SetActive.</b> Disabling our
    /// own GameObject would prevent OnEnable/Update from running, which would
    /// break the SelectionState subscription lifecycle (we'd never receive the
    /// "you're selected again" event). Toggling the renderers' enabled state
    /// achieves the same visual effect without breaking the event flow.</para>
    ///
    /// <para><b>Prefab setup.</b> Attach this component to a child GameObject of
    /// the Builder prefab. The child carries (or has descendants carrying) a
    /// flattened cylinder mesh sitting just above the ground plane, with an
    /// unlit transparent green material. The component handles initial visibility
    /// — leave the renderer enabled in the prefab; we'll turn it off in Awake
    /// until selection fires.</para>
    /// </remarks>
    public class SelectionRingVisual : MonoBehaviour
    {
        // Cached parent builder, resolved in Awake.
        private Builder parentBuilder;

        // Cached renderers (this object plus all descendants). Captured once in
        // Awake to avoid per-event GetComponentsInChildren allocations.
        private Renderer[] cachedRenderers;

        // Tracks subscription state so OnDisable / OnDestroy unsubscribe correctly,
        // and so Update can retry subscription if SelectionState wasn't ready at OnEnable.
        private bool subscribed;

        private void Awake()
        {
            parentBuilder = GetComponentInParent<Builder>();
            if (parentBuilder == null)
            {
                Debug.LogError("[SelectionRingVisual] No Builder component found on " +
                               "self or any parent. Disabling.");
                enabled = false;
                return;
            }

            cachedRenderers = GetComponentsInChildren<Renderer>(includeInactive: true);

            // Start hidden. If selection fires later (including the auto-select
            // in Builder.OnNetworkSpawn), HandleSelectionChanged will turn the
            // renderers back on.
            SetRenderersVisible(false);
        }

        private void OnEnable()
        {
            TrySubscribe();
        }

        private void OnDisable()
        {
            Unsubscribe();
        }

        private void OnDestroy()
        {
            Unsubscribe();
        }

        // Per-frame fallback: if SelectionState wasn't available at OnEnable
        // (scene load ordering), keep trying. Cost is one null-check per frame
        // until subscription succeeds, then nothing.
        private void Update()
        {
            if (!subscribed) TrySubscribe();
        }

        private void TrySubscribe()
        {
            if (subscribed) return;
            var sel = SelectionState.Instance;
            if (sel == null) return;

            sel.OnSelectionChanged += HandleSelectionChanged;
            subscribed = true;

            // Sync to current state — selection may have happened before we subscribed
            // (e.g., Builder.OnNetworkSpawn auto-selecting before this Awake runs).
            HandleSelectionChanged(sel.SelectedBuilder);
        }

        private void Unsubscribe()
        {
            if (!subscribed) return;
            var sel = SelectionState.Instance;
            if (sel != null) sel.OnSelectionChanged -= HandleSelectionChanged;
            subscribed = false;
        }

        private void HandleSelectionChanged(Builder newSelection)
        {
            SetRenderersVisible(newSelection == parentBuilder);
        }

        private void SetRenderersVisible(bool visible)
        {
            if (cachedRenderers == null) return;
            foreach (var rend in cachedRenderers)
            {
                if (rend != null) rend.enabled = visible;
            }
        }
    }
}