using UnityEngine;

namespace Ashwild.Building
{
    /// <summary>
    /// Why a placement is or is not allowed. Produced in one place (BuildManager.EvaluatePlacement) and
    /// consumed by both the ghost's look and the confirm gate, so the preview can never disagree with
    /// what pressing the button actually does — the two used to be decided separately and could drift.
    ///
    /// Splitting the failure into distinct reasons is the point: a single "invalid" state left the
    /// player staring at a red ghost with no way to tell a blocked spot from an unpayable one.
    /// </summary>
    public enum PlacementVerdict
    {
        /// <summary>Buildable here, right now.</summary>
        Valid,

        /// <summary>The footprint overlaps something on the obstruction layers.</summary>
        Blocked,

        /// <summary>The structure requires a socket connection (PlacementSupport.SnapOnly) and has none.</summary>
        Unsupported,

        /// <summary>The spot itself is fine, but the player cannot pay the cost.</summary>
        Unaffordable
    }

    /// <summary>
    /// The visual state of a build ghost — a pure view over a <see cref="PlacementVerdict"/>.
    ///
    /// It decides nothing: BuildManager owns the layer masks, runs the obstruction query and produces
    /// the verdict, then hands it here to be rendered. (It used to run the overlap itself using a mask
    /// passed in from outside, which mixed deciding with displaying and put the physics query away from
    /// the data that configures it.)
    ///
    /// The look is applied by ADDING an overlay material on top of each renderer's authored materials
    /// rather than replacing them, so the model keeps its own look underneath the tint. The footprint
    /// BoxCollider is exposed purely as a bounds source — it stays disabled on the prefab, because the
    /// obstruction mask includes the layer the ghost itself sits on and an enabled collider would make
    /// the preview report itself as blocked.
    /// </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, and kept disabled — it is read as dimensions, never used for physics contacts.")]
        [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("Added on top of the base materials when the spot is buildable (green).")]
        [SerializeField] private Material validOverlay;

        [Tooltip("Added for every reason the build is refused — blocked, unsupported or unaffordable.")]
        [SerializeField] private Material invalidOverlay;

        #endregion

        #region State

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

        /// <summary>
        /// The overlay currently applied, so we only rebuild the material lists when it actually changes.
        /// </summary>
        private Material lastOverlay;
        private bool overlayApplied;

        #endregion

        #region Public API

        /// <summary>
        /// The footprint volume, for BuildManager to read its centre and size when testing obstructions.
        /// Null on a ghost authored without one, which BuildManager treats as "never obstructed".
        /// </summary>
        public BoxCollider Footprint => footprint;

        #endregion

        #region Unity Lifecycle

        /// <summary>
        /// Auto-collects renderers when none were assigned, caches their base materials, then shows the
        /// valid overlay immediately so the ghost reads as a semi-transparent preview from the very first
        /// frame — on every client, not just the owner. On a remote copy nobody runs the evaluation, so
        /// without this the ghost would sit in its opaque base materials until (and unless) a validity
        /// update lands; the owner's own evaluation overrides this on its next frame anyway.
        /// </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];

            SetOverlay(validOverlay);
        }

        #endregion

        #region Display

        /// <summary>
        /// Shows the look matching a verdict. The single entry point the owner drives every frame.
        /// Every refusal shares the one invalid material — the verdict still distinguishes the reasons for
        /// the confirm gate (and for anything that wants to surface them later), the preview just does not
        /// colour-code them.
        /// </summary>
        public void SetState(PlacementVerdict verdict)
            => SetOverlay(verdict == PlacementVerdict.Valid ? validOverlay : invalidOverlay);

        /// <summary>
        /// Applies the shared valid/blocked look on a remote copy from the placer's replicated spot
        /// validity (routed through BuildRegistry). Remotes only ever see these two states — the placer's
        /// private "unaffordable" and "unsupported" reasons are never sent — so a teammate sees green on
        /// a buildable spot and red otherwise, matching where the placer can actually build.
        /// </summary>
        public void SetRemoteValidity(bool valid) => SetOverlay(valid ? validOverlay : invalidOverlay);

        /// <summary>
        /// Sets the current overlay, rebuilding the renderers' material lists only when it actually
        /// changes — the single funnel every state path goes through, so the change-guard stays in one place.
        /// </summary>
        private void SetOverlay(Material overlay)
        {
            if (overlayApplied && overlay == lastOverlay) return;
            ApplyOverlay(overlay);
            lastOverlay = overlay;
            overlayApplied = true;
        }

        /// <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
    }
}