using UnityEngine;

/// <summary>
/// 部署格位高亮：拖动卡牌时在目标格位显示一块发光地板。
/// 绿色 = 可以放置；红色 = 该格已被占用 / 不可放置。
/// 全场只需要一个，由 DefenseGameFlowController 在布阵阶段创建。
/// </summary>
public class DeployHighlight : MonoBehaviour
{
    public static DeployHighlight Instance { get; private set; }

    private static readonly Color FreeColor = new Color(0.25f, 1f, 0.45f, 0.55f);
    private static readonly Color BlockedColor = new Color(1f, 0.28f, 0.28f, 0.55f);

    private GameObject plate;
    private Material plateMaterial;
    private int shownCell = -1;

    /// <summary>高亮当前是否可见。</summary>
    public bool IsVisible => plate != null && plate.activeSelf;

    /// <summary>当前显示的是否是"不可放置"（红色）。</summary>
    public bool IsBlocked { get; private set; }

    /// <summary>当前高亮所在的格位，-1 表示没有。</summary>
    public int ShownCell => shownCell;

    public static DeployHighlight Ensure()
    {
        if (Instance != null) return Instance;

        var go = new GameObject("DeployHighlight");
        Instance = go.AddComponent<DeployHighlight>();
        Instance.Build();
        return Instance;
    }

    private void Awake()
    {
        if (Instance == null)
        {
            Instance = this;
            Build();
        }
    }

    private void Build()
    {
        if (plate != null) return;

        plate = GameObject.CreatePrimitive(PrimitiveType.Cube);
        plate.name = "CellPlate";
        plate.transform.SetParent(transform, false);
        plate.transform.localRotation = Quaternion.identity;
        plate.transform.localScale = new Vector3(DeployGrid.CellWidth * 0.96f, 0.02f, DeployGrid.CellDepth * 0.96f);

        // 高亮只是视觉提示，不需要碰撞
        var collider = plate.GetComponent<Collider>();
        if (collider != null)
        {
            Destroy(collider);
        }

        var shader = Shader.Find("Sprites/Default") ?? Shader.Find("Unlit/Color");
        plateMaterial = new Material(shader);
        plateMaterial.name = "DeployHighlightMat";
        plateMaterial.color = FreeColor;

        var renderer = plate.GetComponent<Renderer>();
        renderer.sharedMaterial = plateMaterial;
        renderer.shadowCastingMode = UnityEngine.Rendering.ShadowCastingMode.Off;
        renderer.receiveShadows = false;

        plate.SetActive(false);
    }

    /// <summary>在指定格位显示高亮。blocked = true 显示红色。</summary>
    public void Show(int cellIndex, bool blocked)
    {
        if (plate == null) Build();
        if (!DeployGrid.IsValidIndex(cellIndex))
        {
            Hide();
            return;
        }

        var pos = DeployGrid.CellPosition(cellIndex);
        plate.transform.position = new Vector3(pos.x, DeployGrid.GridY + 0.05f, pos.z);
        plateMaterial.color = blocked ? BlockedColor : FreeColor;
        IsBlocked = blocked;

        if (shownCell != cellIndex || !plate.activeSelf)
        {
            plate.SetActive(true);
            shownCell = cellIndex;
        }
    }

    public void Hide()
    {
        if (plate != null && plate.activeSelf)
        {
            plate.SetActive(false);
        }
        shownCell = -1;
        IsBlocked = false;
    }

    private void OnDestroy()
    {
        if (Instance == this) Instance = null;
    }
}