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

using System.Collections.Generic;
using FishNet.Object;
using UnityEngine;
using Ashwild.Inventory;
using Ashwild.Player;

namespace Ashwild.Building
{
    /// <summary>
    /// The whole local build experience in one place: it owns the buildable catalog, populates the
    /// menu view when it opens, and drives placement once a card is picked — aim, grid quantise,
    /// socket snapping, validity and confirm/cancel. This is the deliberate cohesive boundary: all of
    /// "what the local player does to build" lives here, while the shared, server-authoritative side
    /// (committed structures + the networked ghost object) is the separate BuildRegistry. One clean
    /// seam between local UX and networked world state — not a split per micro-responsibility.
    ///
    /// The ghost is a real NetworkObject: on a card pick this asks BuildRegistry to spawn one owned by
    /// us, which hands it back through <see cref="AttachGhost"/>; we then drive its transform locally
    /// (client-authoritative NetworkTransform replicates it to teammates). On confirm we commit the
    /// pose to BuildRegistry and despawn the ghost. A single scene instance, driven by the local-only
    /// bus — no per-player copies, no owner gating. Menu view stays a dumb, data-agnostic view.
    /// </summary>
    [DisallowMultipleComponent]
    public class BuildManager : MonoBehaviour
    {
        #region Serialized Fields

        [Header("References")]
        [SerializeField] private BuildMenuUI menuUI;

        [Header("Catalog")]
        [Tooltip("Every structure the player can build, shown as cards in this order.")]
        [SerializeField] private BuildableData[] catalog;

        [Header("Aim")]
        [Tooltip("Optional camera whose forward is the aim ray. Leave empty to use Camera.main — the local player's FPS camera at runtime.")]
        [SerializeField] private Camera aimCamera;

        [Tooltip("Maximum distance, in metres, at which the ghost can be placed.")]
        [SerializeField] private float placeRange = 8f;

        [Tooltip("Surfaces the ghost is allowed to snap onto (ground, existing structures).")]
        [SerializeField] private LayerMask groundMask = ~0;

        [Header("Grid Fallback")]
        [Tooltip("Quantise the ghost to a world grid when no socket is in range. Off = free placement.")]
        [SerializeField] private bool useGrid = true;

        [Tooltip("World cell size the ghost quantises to when the grid is on and no socket is in range.")]
        [SerializeField] private float gridSize = 1f;

        [Tooltip("Degrees the ghost yaws per scroll notch while placing.")]
        [SerializeField] private float rotationStep = 90f;

        [Header("Placement Mode")]
        [Tooltip("Continuous build: after confirming a placement, immediately re-arm another ghost of the same structure (to chain walls/floors) instead of returning to idle. Off = place one at a time.")]
        [SerializeField] private bool continuousBuild = false;

        [Header("Snapping")]
        [Tooltip("Radius around the aim in which a matching existing socket pulls the ghost in.")]
        [SerializeField] private float snapRadius = 1.25f;

        [Tooltip("Layer of the snap-point trigger colliders on built structures.")]
        [SerializeField] private LayerMask snapPointMask;

        [Header("Validity")]
        [Tooltip("Layers that block a build (structures, props, players). Must NOT include the ground.")]
        [SerializeField] private LayerMask obstructionMask;

        [Tooltip("Metres shaved off each side of the footprint before testing obstructions. Connected pieces meet exactly flush, so without a small inset every snapped build would report its own neighbour as blocking. Keep it well under the thinnest structure.")]
        [SerializeField] private float obstructionPadding = 0.03f;

        [Header("Demolition")]
        [Tooltip("Layers the demolition aim can hit to target a committed structure. Narrow this to the structures' layer so walls, roofs, etc. are the only demolishable hits.")]
        [SerializeField] private LayerMask buildMask = ~0;

        [Tooltip("Overlay material added on top of the aimed build while it is the demolition target (e.g. a translucent red 'about to break' pass). Should be a transparent/additive material since it draws over the model.")]
        [SerializeField] private Material demolitionMaterial;

        [Header("Hammer Wear")]
        [Tooltip("Durability (uses) spent on the equipped hammer for each successful placement or demolition. Requires the hammer's ItemData to be uses-tracked (Has Uses + Max Uses). A depleted hammer blocks building/demolishing until repaired. Set to 0 for a hammer that never wears.")]
        [SerializeField] private int hammerUsesPerAction = 1;

        #endregion

        #region State

        /// <summary>
        /// The single scene instance, so BuildRegistry can hand a freshly spawned ghost back here.
        /// </summary>
        public static BuildManager Instance { get; private set; }

        /// <summary>
        /// The buildables currently shown, in card order, so a picked index maps back to its data.
        /// </summary>
        private readonly List<BuildableData> visible = new List<BuildableData>();

        /// <summary>
        /// The buildable being positioned (and its network id), or null/0 when idle.
        /// </summary>
        private BuildableData active;
        private ushort activeId;

        /// <summary>
        /// The live networked ghost we own and drive, or null while idle or awaiting its spawn.
        /// </summary>
        private GameObject ghost;
        private BuildGhost ghostView;
        private BuildSnapPoint[] ghostSnaps;

        /// <summary>
        /// Whether the ghost's current pose came from a socket connection rather than the free/grid aim.
        /// Kept as state rather than recomputed because the pose and the validity check happen in two
        /// steps, and because a frame whose aim ray hits nothing leaves the ghost — and so its
        /// connection — exactly as it was.
        /// </summary>
        private bool ghostIsConnected;

        /// <summary>
        /// The ghost's current yaw for grid placement, stepped by the scroll wheel.
        /// </summary>
        private float yaw;

        /// <summary>
        /// The local player's aim transform (camera), resolved lazily and shared by placement and
        /// demolition.
        /// </summary>
        private Transform aim;

        /// <summary>
        /// The committed build currently under the demolition aim, or null when none is targeted.
        /// </summary>
        private BuiltStructure demoTarget;

        /// <summary>
        /// Frame the ghost was attached, so a click landing that frame never confirms instantly.
        /// </summary>
        private int placementBeganFrame;

        /// <summary>
        /// Bumped on every spawn request so a ghost from a superseded request (picked again during
        /// the spawn round-trip) is rejected and despawned instead of leaking into the scene.
        /// </summary>
        private int spawnToken;

        /// <summary>
        /// Last spot validity pushed to teammates (-1 = none sent yet, 0 = invalid, 1 = valid), so the
        /// networked ghost overlay is only replicated when it actually flips — never every frame.
        /// </summary>
        private int lastSentValidity = -1;

        private readonly Collider[] snapResults = new Collider[16];
        private readonly Collider[] obstructionResults = new Collider[8];

        /// <summary>
        /// Floor for the padded half-extents, so a very thin piece (a floor slab a few centimetres deep)
        /// cannot have the inset collapse its footprint to zero — or invert it — and stop testing at all.
        /// </summary>
        private const float MinHalfExtent = 0.01f;

        /// <summary>
        /// Reused buffer for the active build's cost lines, rebuilt and pushed to the crosshair each
        /// time the price or its affordability changes — so no per-refresh allocation.
        /// </summary>
        private readonly List<BuildCostView> costView = new List<BuildCostView>();

        #endregion

        #region Unity Lifecycle

        /// <summary>
        /// Registers the scene singleton BuildRegistry calls back into.
        /// </summary>
        private void Awake()
        {
            Instance = this;
        }

        /// <summary>
        /// Clears the singleton — mirrors Awake.
        /// </summary>
        private void OnDestroy()
        {
            if (Instance == this) Instance = null;
        }

        /// <summary>
        /// Subscribes to the menu open state and the placement inputs while enabled.
        /// </summary>
        private void OnEnable()
        {
            PlayerEvents.BuildMenuOpenChanged += HandleMenuOpenChanged;
            PlayerEvents.AttackPressed += HandleConfirm;
            PlayerEvents.BuildCancelRequested += HandleCancel;
            PlayerEvents.HotbarScroll += HandleRotate;
            PlayerEvents.BuildRotatePressed += HandleRotateKey;
            PlayerEvents.DemolishModeChanged += HandleDemolishModeChanged;
            PlayerEvents.InventorySlotChanged += HandleInventoryChanged;
        }

        /// <summary>
        /// Unsubscribes and tears down any live placement — mirrors OnEnable exactly.
        /// </summary>
        private void OnDisable()
        {
            PlayerEvents.BuildMenuOpenChanged -= HandleMenuOpenChanged;
            PlayerEvents.AttackPressed -= HandleConfirm;
            PlayerEvents.BuildCancelRequested -= HandleCancel;
            PlayerEvents.HotbarScroll -= HandleRotate;
            PlayerEvents.BuildRotatePressed -= HandleRotateKey;
            PlayerEvents.DemolishModeChanged -= HandleDemolishModeChanged;
            PlayerEvents.InventorySlotChanged -= HandleInventoryChanged;

            EndPlacement();
            ClearDemoTarget();
        }

        /// <summary>
        /// Each frame, in exactly one mode: in demolition mode it tracks which build the player aims
        /// at; otherwise it drives the owned ghost along the aim. Both are frozen while input is locked
        /// (e.g. the menu reopened over a placement), and leaving demolition mode clears the target.
        /// </summary>
        private void Update()
        {
            if (PlayerEvents.IsDemolishing && !PlayerEvents.InputLocked)
            {
                UpdateDemolitionTarget();
                return;
            }
            ClearDemoTarget();

            if (ghost == null) return;
            if (PlayerEvents.InputLocked) return;

            UpdateGhostPose();
            EvaluateGhost();
        }

        #endregion

        #region Menu

        /// <summary>
        /// Populates the menu view from the catalog when it opens; nothing to do on close.
        /// </summary>
        private void HandleMenuOpenChanged(bool open)
        {
            if (!open) return;
            PopulateMenu();
        }

        /// <summary>
        /// Builds one card payload per non-null catalog entry and pushes it into the menu view,
        /// keeping a parallel list so a picked index maps back to its buildable.
        /// </summary>
        private void PopulateMenu()
        {
            if (menuUI == null)
            {
                Debug.LogError("[BuildManager] No BuildMenuUI assigned — cannot populate the menu.", this);
                return;
            }

            visible.Clear();
            List<BuildCardView> cards = new List<BuildCardView>();
            foreach (BuildableData data in catalog)
            {
                if (data == null) continue;
                visible.Add(data);
                cards.Add(new BuildCardView(data.Icon, data.DisplayName));
            }

            menuUI.Populate(cards, HandleCardSelected);
        }

        /// <summary>
        /// A card was picked: close the menu (which unlocks input) and start positioning the chosen
        /// structure — its ghost is spawned networked and handed back via AttachGhost.
        /// </summary>
        private void HandleCardSelected(int index)
        {
            if (index < 0 || index >= visible.Count) return;
            BuildableData data = visible[index];
            if (data == null || data.GhostPrefab == null)
            {
                Debug.LogError("[BuildManager] Picked buildable is null or has no Ghost Prefab.", this);
                return;
            }

            ushort id = BuildableDatabase.Instance != null ? BuildableDatabase.Instance.GetId(data) : (ushort)0;
            if (id == 0)
            {
                Debug.LogError($"[BuildManager] '{data.DisplayName}' absent de la BuildableDatabase — lance Tools ▸ Ashwild ▸ Rebuild Buildable Database.", this);
                return;
            }
            if (BuildRegistry.Instance == null)
            {
                Debug.LogError("[BuildManager] No BuildRegistry in the scene / session — cannot spawn the ghost.", this);
                return;
            }

            EndPlacement();

            active = data;
            activeId = id;
            yaw = 0f;
            int token = ++spawnToken;

            PlayerEvents.RaiseBuildMenuToggleRequested();
            PlayerEvents.RaiseBuildPlacingChanged(true);
            PublishCostView();
            BuildRegistry.Instance.RequestSpawnGhost(id, token);
        }

        #endregion

        #region Placement

        /// <summary>
        /// Receives the networked ghost BuildRegistry spawned for us: caches its validity/snap
        /// components, resolves the aim and starts driving it. A ghost from a superseded or already
        /// cancelled request (its token no longer matches) is despawned immediately, so no orphan
        /// lingers even when the player re-picks during the spawn round-trip.
        /// </summary>
        public void AttachGhost(GameObject go, int token)
        {
            if (go == null) return;

            if (token != spawnToken || active == null)
            {
                if (BuildRegistry.Instance != null)
                    BuildRegistry.Instance.RequestDespawnGhost(go.GetComponent<NetworkObject>());
                return;
            }

            ghost = go;
            ghostView = go.GetComponentInChildren<BuildGhost>(true);
            ghostSnaps = go.GetComponentsInChildren<BuildSnapPoint>(true);
            ResolveAim();

            lastSentValidity = -1;
            ghostIsConnected = false;
            placementBeganFrame = Time.frameCount;
            UpdateGhostPose();
            EvaluateGhost();
        }

        /// <summary>
        /// Pushes the current verdict into the ghost's look each frame. No-op when no ghost is live.
        /// </summary>
        private void EvaluateGhost()
        {
            if (ghostView == null) return;

            PlacementVerdict verdict = EvaluatePlacement();
            ghostView.SetState(verdict);
            ReplicateValidity(verdict == PlacementVerdict.Valid);
        }

        /// <summary>
        /// The single answer to "can the active structure be committed at the ghost's current pose?",
        /// used both to tint the preview and to gate the confirm — so what the player sees and what the
        /// button does can never disagree. It is recomputed on demand rather than cached, since a cached
        /// verdict would be one frame stale depending on the input/Update order.
        ///
        /// The reasons are tested most-spatial first: a structure that needs a connection and has none is
        /// reported before an obstruction, and both before affordability, so the player is always told
        /// about the problem that moving the mouse can actually fix.
        ///
        /// A CONNECTED ghost skips the obstruction test entirely: the socket already decided where the
        /// piece belongs, and real modular geometry interpenetrates far more than any tolerance can absorb
        /// (a wall's head runs up into the ceiling it supports, a frame overlaps the slab it sits in).
        /// Shrinking the footprint was tried and is not enough — the only rule that holds is that an
        /// authored connection IS the validity check. Free placement still tests obstructions normally,
        /// so the padding below continues to matter there.
        /// </summary>
        private PlacementVerdict EvaluatePlacement()
        {
            if (active == null) return PlacementVerdict.Blocked;

            if (active.Support == PlacementSupport.SnapOnly && !ghostIsConnected)
                return PlacementVerdict.Unsupported;

            if (!ghostIsConnected && IsFootprintObstructed()) return PlacementVerdict.Blocked;

            if (!active.CanAfford(PlayerInventory.Instance)) return PlacementVerdict.Unaffordable;

            return PlacementVerdict.Valid;
        }

        /// <summary>
        /// Box-overlaps the ghost's footprint against the obstruction layers, ignoring triggers. The box
        /// is shrunk by <see cref="obstructionPadding"/> on every side: snapped pieces meet exactly flush
        /// by construction, so an un-inset test would report the very neighbour the player is building
        /// against. The inset is small enough that a real intruder inside the volume — a chest, a player,
        /// another structure — is still caught. A ghost without a footprint is never obstructed.
        /// </summary>
        private bool IsFootprintObstructed()
        {
            BoxCollider footprint = ghostView != null ? ghostView.Footprint : null;
            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;
            halfExtents = Vector3.Max(halfExtents - Vector3.one * obstructionPadding, Vector3.one * MinHalfExtent);

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

        /// <summary>
        /// Pushes the ghost's spot validity to teammates through BuildRegistry, but only when it flips —
        /// so a remote ghost shows the same green/red as here without a per-frame RPC stream. Affordability
        /// stays local (the placer's private inventory), so only IsValid crosses the wire.
        /// </summary>
        private void ReplicateValidity(bool valid)
        {
            int state = valid ? 1 : 0;
            if (state == lastSentValidity) return;
            lastSentValidity = state;

            if (BuildRegistry.Instance != null && ghost != null)
                BuildRegistry.Instance.SetGhostValidity(ghost.GetComponent<NetworkObject>(), valid);
        }

        /// <summary>
        /// Left-click: demolishes the aimed build while in demolition mode, otherwise commits the
        /// ghost's pose to the registry (spawned for everyone), spends a use of the equipped hammer and
        /// consumes the resource cost from the local inventory (client-authoritative, exactly like
        /// crafting). In continuous build mode it then re-arms a fresh ghost of the same structure
        /// (keeping the current yaw, so pieces chain edge-to-edge); otherwise it ends the placement.
        ///
        /// Placement itself is gated by the one verdict the preview is already showing, so the button can
        /// never accept what the ghost paints as refused. The remaining guards are input/session
        /// conditions rather than placement rules — input locked, the very frame the ghost was attached,
        /// no registry in the session, and a hammer out of durability.
        /// </summary>
        private void HandleConfirm()
        {
            if (PlayerEvents.IsDemolishing)
            {
                TryDemolish();
                return;
            }

            if (ghost == null) return;
            if (PlayerEvents.InputLocked) return;
            if (Time.frameCount == placementBeganFrame) return;
            if (EvaluatePlacement() != PlacementVerdict.Valid) return;
            if (BuildRegistry.Instance == null) return;
            if (!TryConsumeHammerUse()) return;

            BuildRegistry.Instance.RequestBuild(activeId, ghost.transform.position, ghost.transform.rotation);

            ConsumeCost();

            if (continuousBuild && active != null)
            {
                RearmGhost();
                return;
            }

            EndPlacement();
        }

        /// <summary>
        /// The hammer's cancel request (a right-click tap while placing): cancels the current placement
        /// (even while the ghost is still spawning). Routed through the bus so this stays the single
        /// place that ends a placement — the hammer is the sole arbiter of the click.
        /// </summary>
        private void HandleCancel()
        {
            if (active == null) return;
            EndPlacement();
        }

        /// <summary>
        /// Scroll wheel: yaws the ghost by one rotation step (repurposed from the hotbar, which
        /// ignores the scroll while a build is being placed).
        /// </summary>
        private void HandleRotate(float scroll)
        {
            if (ghost == null) return;
            if (PlayerEvents.InputLocked) return;

            if (scroll > 0f) yaw += rotationStep;
            else if (scroll < 0f) yaw -= rotationStep;
        }

        /// <summary>
        /// R key: yaws the ghost by one rotation step in the same direction as a scroll-up, so the
        /// build can be turned without the mouse wheel. Ignored when no ghost is being placed.
        /// </summary>
        private void HandleRotateKey()
        {
            if (ghost == null) return;
            if (PlayerEvents.InputLocked) return;

            yaw += rotationStep;
        }

        /// <summary>
        /// Poses the ghost each frame: quantise the aim hit to the grid with the current yaw, then
        /// let a nearby matching socket pull it into an exact connection (sockets win over the grid).
        /// Leaves the ghost where it was — connection included — when the ray hits nothing in range.
        /// </summary>
        private void UpdateGhostPose()
        {
            if (aim == null) return;
            if (!Physics.Raycast(aim.position, aim.forward, out RaycastHit hit, placeRange, groundMask))
                return;

            ghost.transform.SetPositionAndRotation(SnapToGrid(hit.point), Quaternion.Euler(0f, yaw, 0f));
            ghostIsConnected = TrySnapToSockets();
        }

        /// <summary>
        /// Rounds the X/Z of a point to the grid, keeping its height. No-op when the grid is
        /// toggled off or its cell size is non-positive (free placement).
        /// </summary>
        private Vector3 SnapToGrid(Vector3 point)
        {
            if (!useGrid || gridSize <= 0f) return point;

            float x = Mathf.Round(point.x / gridSize) * gridSize;
            float z = Mathf.Round(point.z / gridSize) * gridSize;
            return new Vector3(x, point.y, z);
        }

        /// <summary>
        /// Snaps the ghost to a single existing socket: across all of the ghost's own sockets, finds
        /// the closest free compatible world socket within snap range and translates so that one pair
        /// coincides. Because it commits to the single nearest ghost-socket↔world-socket pair (not the
        /// socket nearest the aim), the ghost picks one connection instead of hovering between two.
        /// Rotation stays the player's grid yaw, so pieces meet edge-to-edge once oriented.
        ///
        /// Returns whether a connection was actually made, which is what lets the caller trust the pose
        /// and skip the obstruction test for it.
        /// </summary>
        private bool TrySnapToSockets()
        {
            if (ghostSnaps == null || ghostSnaps.Length == 0) return false;
            if (snapPointMask == 0) return false;

            BuildSnapPoint bestGhost = null;
            BuildSnapPoint bestWorld = null;
            float bestSqr = snapRadius * snapRadius;

            foreach (BuildSnapPoint gs in ghostSnaps)
            {
                if (gs == null) continue;

                int count = Physics.OverlapSphereNonAlloc(gs.transform.position, snapRadius, snapResults, snapPointMask, QueryTriggerInteraction.Collide);
                for (int i = 0; i < count; i++)
                {
                    BuildSnapPoint world = snapResults[i].GetComponentInParent<BuildSnapPoint>();
                    if (world == null) continue;
                    if (world.IsOccupied) continue;
                    if (world.Category != gs.Category) continue;
                    if (world.transform.IsChildOf(ghost.transform)) continue;

                    // Only connect sockets that face each other (opposite forwards), so a piece lands
                    // adjacent instead of overlapping the one it snaps to.
                    if (Vector3.Dot(gs.transform.forward, world.transform.forward) > -0.5f) continue;

                    float sqr = (gs.transform.position - world.transform.position).sqrMagnitude;
                    if (sqr < bestSqr) { bestSqr = sqr; bestGhost = gs; bestWorld = world; }
                }
            }

            if (bestGhost == null || bestWorld == null) return false;

            ghost.transform.position += bestWorld.transform.position - bestGhost.transform.position;
            return true;
        }

        /// <summary>
        /// Ends the current placement: despawns the networked ghost, clears state and flags the bus
        /// idle. Safe to call when nothing is in flight.
        /// </summary>
        private void EndPlacement()
        {
            DespawnGhost();

            if (active != null)
            {
                active = null;
                activeId = 0;
                PlayerEvents.RaiseBuildPlacingChanged(false);
                PlayerEvents.RaiseBuildCostChanged(null);
            }
        }

        /// <summary>
        /// Continuous build: after committing a piece, drops the spent ghost and asks the registry for a
        /// fresh one of the same structure so the player keeps placing without reopening the menu. Keeps
        /// <see cref="active"/>/<see cref="activeId"/> and the current yaw, and stays "placing" on the
        /// bus. The token bump makes any in-flight ghost from the old request reject itself in AttachGhost.
        /// </summary>
        private void RearmGhost()
        {
            DespawnGhost();

            if (BuildRegistry.Instance == null)
            {
                EndPlacement();
                return;
            }

            int token = ++spawnToken;
            BuildRegistry.Instance.RequestSpawnGhost(activeId, token);
        }

        /// <summary>
        /// Despawns the networked ghost we own and clears its cached components, without touching the
        /// active buildable or the bus. Safe to call when no ghost is live.
        /// </summary>
        private void DespawnGhost()
        {
            if (ghost != null)
            {
                if (BuildRegistry.Instance != null)
                    BuildRegistry.Instance.RequestDespawnGhost(ghost.GetComponent<NetworkObject>());
                ghost = null;
            }
            ghostView = null;
            ghostSnaps = null;
            lastSentValidity = -1;
            ghostIsConnected = false;
        }

        /// <summary>
        /// Resolves and caches the local player's aim transform — the assigned camera, else the
        /// runtime Camera.main (the FPS camera). Logs once when neither is found.
        /// </summary>
        private Transform ResolveAim()
        {
            if (aim != null) return aim;

            aim = aimCamera != null ? aimCamera.transform : (Camera.main != null ? Camera.main.transform : null);
            if (aim == null)
                Debug.LogError("[BuildManager] Pas de caméra d'aim (Camera.main introuvable — la caméra du joueur est-elle taguée MainCamera ?).", this);
            return aim;
        }

        #endregion

        #region Build Cost

        /// <summary>
        /// Refreshes the crosshair cost display when the inventory changes mid-placement (a resource was
        /// spent or picked up), so its affordability colouring stays live. No-op while idle.
        /// </summary>
        private void HandleInventoryChanged(int slotIndex)
        {
            if (active == null) return;
            PublishCostView();
        }

        /// <summary>
        /// Rebuilds the active build's cost lines into the reused buffer — each with the local player's
        /// current affordability — and pushes them to the crosshair via the bus. Clears the display when
        /// idle or when the build is free (no cost lines).
        /// </summary>
        private void PublishCostView()
        {
            BuildCost[] cost = active != null ? active.Cost : null;
            if (cost == null || cost.Length == 0)
            {
                PlayerEvents.RaiseBuildCostChanged(null);
                return;
            }

            PlayerInventory inv = PlayerInventory.Instance;
            costView.Clear();
            foreach (BuildCost line in cost)
            {
                if (line.item == null) continue;
                int owned = inv != null ? inv.CountItem(line.item) : 0;
                bool affordable = owned >= line.quantity;
                costView.Add(new BuildCostView(line.item.Icon, owned, line.quantity, affordable));
            }
            PlayerEvents.RaiseBuildCostChanged(costView);
        }

        /// <summary>
        /// Spends the active build's cost from the local inventory after a committed placement. Client-
        /// authoritative like crafting — the inventory change refreshes the cost view through
        /// <see cref="HandleInventoryChanged"/>. No-op for a free build or when offline.
        /// </summary>
        private void ConsumeCost()
        {
            BuildCost[] cost = active != null ? active.Cost : null;
            if (cost == null || cost.Length == 0) return;

            PlayerInventory inv = PlayerInventory.Instance;
            if (inv == null) return;

            foreach (BuildCost line in cost)
            {
                if (line.item == null) continue;
                inv.RemoveItemByData(line.item, line.quantity);
            }
        }

        #endregion

        #region Public API

        /// <summary>
        /// Whether confirming a placement immediately re-arms another ghost of the same structure
        /// (continuous build) instead of returning to idle. Settable so a key or menu toggle can flip it.
        /// </summary>
        public bool ContinuousBuild
        {
            get => continuousBuild;
            set => continuousBuild = value;
        }

        /// <summary>
        /// Flips continuous build on/off — wire this to a key or a menu toggle so the player can switch
        /// between chaining placements and placing one at a time.
        /// </summary>
        public void ToggleContinuousBuild() => continuousBuild = !continuousBuild;

        #endregion

        #region Demolition

        /// <summary>
        /// Leaving demolition mode drops any current target so the crosshair returns to normal; entering
        /// it needs nothing here — Update starts tracking on the next frame.
        /// </summary>
        private void HandleDemolishModeChanged(bool on)
        {
            if (!on) ClearDemoTarget();
        }

        /// <summary>
        /// Casts the aim ray for a committed build and moves the demolition highlight when the target
        /// changes: the previous build removes its overlay and the new one gets the demolition material
        /// added on top, so exactly the aimed build reads as "about to break".
        /// </summary>
        private void UpdateDemolitionTarget()
        {
            Transform a = ResolveAim();
            if (a == null) { ClearDemoTarget(); return; }

            BuiltStructure hit = null;
            if (Physics.Raycast(a.position, a.forward, out RaycastHit info, placeRange, buildMask, QueryTriggerInteraction.Ignore))
                hit = info.collider.GetComponentInParent<BuiltStructure>();

            if (hit == demoTarget) return;

            if (demoTarget != null) demoTarget.ClearHighlight();
            demoTarget = hit;
            if (demoTarget != null) demoTarget.Highlight(demolitionMaterial);
        }

        /// <summary>
        /// Left-click while demolishing: spends a hammer use and asks the registry to remove the aimed
        /// build for everyone (which refunds resources by remaining health). Blocked when the hammer is
        /// out of durability. The target stays until the next frame re-evaluates, so a miss simply
        /// retargets.
        /// </summary>
        private void TryDemolish()
        {
            if (demoTarget == null) return;
            if (!TryConsumeHammerUse()) return;

            demoTarget.RequestDemolish();
        }

        /// <summary>
        /// Spends the configured durability on the equipped hammer for one build action, returning
        /// whether the action may proceed. A depleted hammer returns false so the placement/demolition
        /// is blocked (like any worn-out tool); a hammer with no durability authored, a zero cost, or no
        /// inventory simply passes without wear. The hammer is the selected hotbar item while building,
        /// so spending the selected tool's use targets it.
        /// </summary>
        private bool TryConsumeHammerUse()
        {
            PlayerInventory inv = PlayerInventory.Instance;
            if (inv == null) return true;
            return inv.ConsumeSelectedToolUse(hammerUsesPerAction);
        }

        /// <summary>
        /// Drops the current demolition target, restoring its authored materials. Safe to call when
        /// nothing is targeted.
        /// </summary>
        private void ClearDemoTarget()
        {
            if (demoTarget == null) return;
            demoTarget.ClearHighlight();
            demoTarget = null;
        }

        #endregion
    }
}