Emberwild/Assets/GAME/Script/Building/BuildGhost.cs

using UnityEngine;

namespace Ashwild.Building
{
    /// <summary>
    /// Placement validity for a build ghost. Each frame BuildManager calls Evaluate with the
    /// obstruction mask it owns (configured in one place, not per ghost prefab), which box-overlaps
    /// the ghost's footprint against those layers (other structures, props, players — never the
    /// ground it rests on) and shows the result by adding a valid or invalid overlay material on top
    /// of each renderer's base materials (not by tinting them). BuildManager reads <see cref="IsValid"/>
    /// to allow or block the build. The footprint collider is only a bounds source: the overlap test
    /// reads its dimensions directly rather than relying on physics contacts.
    /// </summary>
    [DisallowMultipleComponent]
    public class BuildGhost : MonoBehaviour
    {
        #region Serialized Fields

        [Header("Footprint")]
        [Tooltip("Box whose bounds define the volume tested for obstructions. Sized in the prefab.")]
        [SerializeField] private BoxCollider footprint;

        [Header("Overlay Materials")]
        [Tooltip("Renderers the overlay is added onto. Auto-filled from children if left empty.")]
        [SerializeField] private Renderer[] renderers;

        [Tooltip("Material added on top of the base ones when the spot is buildable (green).")]
        [SerializeField] private Material validOverlay;

        [Tooltip("Material added on top of the base ones when the spot is blocked (red).")]
        [SerializeField] private Material invalidOverlay;

        #endregion

        #region State

        /// <summary>
        /// Whether the ghost is currently on a buildable spot (no obstruction overlap).
        /// </summary>
        public bool IsValid { get; private set; }

        /// <summary>
        /// Each renderer's original materials, so the overlay can be appended without losing them.
        /// </summary>
        private Material[][] baseMaterials;

        /// <summary>
        /// The validity reflected by the currently applied overlay, so we only swap on a real change.
        /// </summary>
        private bool lastValid;
        private bool overlayApplied;

        private readonly Collider[] overlapResults = new Collider[8];

        #endregion

        #region Unity Lifecycle

        /// <summary>
        /// Auto-collects renderers when none were assigned and caches their base materials.
        /// </summary>
        private void Awake()
        {
            if (renderers == null || renderers.Length == 0)
                renderers = GetComponentsInChildren<Renderer>(true);

            baseMaterials = new Material[renderers.Length][];
            for (int i = 0; i < renderers.Length; i++)
                baseMaterials[i] = renderers[i] != null ? renderers[i].sharedMaterials : new Material[0];
        }

        #endregion

        #region Public API

        /// <summary>
        /// Re-tests the footprint against the obstruction layers (passed in by BuildManager, which
        /// owns the mask so it is configured in one place), swaps the overlay material when validity
        /// changed, and returns the result. A ghost with no footprint is always considered valid.
        /// </summary>
        public bool Evaluate(LayerMask obstructionMask)
        {
            IsValid = !IsObstructed(obstructionMask);

            if (!overlayApplied || IsValid != lastValid)
            {
                ApplyOverlay(IsValid ? validOverlay : invalidOverlay);
                lastValid = IsValid;
                overlayApplied = true;
            }

            return IsValid;
        }

        #endregion

        #region Internal

        /// <summary>
        /// Box-overlaps the footprint against the obstruction layers, ignoring triggers.
        /// </summary>
        private bool IsObstructed(LayerMask obstructionMask)
        {
            if (footprint == null) return false;

            Transform t = footprint.transform;
            Vector3 center = t.TransformPoint(footprint.center);
            Vector3 halfExtents = Vector3.Scale(footprint.size, t.lossyScale) * 0.5f;

            int count = Physics.OverlapBoxNonAlloc(center, halfExtents, overlapResults, t.rotation, obstructionMask, QueryTriggerInteraction.Ignore);
            return count > 0;
        }

        /// <summary>
        /// Rebuilds each renderer's material list as "base materials + overlay", so the overlay
        /// draws on top of the model instead of replacing it. Skips when no overlay is assigned.
        /// </summary>
        private void ApplyOverlay(Material overlay)
        {
            if (overlay == null) return;

            for (int i = 0; i < renderers.Length; i++)
            {
                Renderer r = renderers[i];
                if (r == null) continue;

                Material[] baseMats = baseMaterials[i];
                Material[] combined = new Material[baseMats.Length + 1];
                for (int j = 0; j < baseMats.Length; j++)
                    combined[j] = baseMats[j];
                combined[baseMats.Length] = overlay;

                r.materials = combined;
            }
        }

        #endregion
    }
}