OpponentDragSpawner.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.UI;
using UnityEngine.EventSystems;

public class OpponentDragSpawner : MonoBehaviour, IRoundCallback, IManaChangeCallback, IDragDropListener
{

    [SerializeField] Opponent opponent;
    [SerializeField] Color disabledPreviewSpriteColor = new Color(0.5f, 0.5f, 0.5f, 1f);
    [SerializeField] Color disabledCostTextColor = Color.red;
    [SerializeField] List<AudioClip> spawnOpponentSfx;

    Image previewSprite;
    Text costText;
    Color defaultCostTextColor;
    BaseCameraController cameraController;

    void Start()
    {
        previewSprite = transform.Find("OpponentImage").GetComponent<Image>();
        costText = transform.Find("Cost").GetComponent<Text>();
        defaultCostTextColor = costText.color;
        previewSprite.sprite = opponent.enemySprite;
        costText.text = opponent.enemyCost.ToString();
        cameraController = Camera.main.GetComponent<BaseCameraController>();

        var eventTrigger = GetComponent<EventTrigger>();

        var beginDragEvent = new EventTrigger.Entry();
        beginDragEvent.eventID = EventTriggerType.BeginDrag;
        beginDragEvent.callback.AddListener((data) => OnBeginDrag((PointerEventData)data));
        eventTrigger.triggers.Add(beginDragEvent);

        StatsManager.instance.manaChangeCallbacks.Add(this);
        RoundController.instance.roundCallbacks.Add(this);

        UpdateDisplayStates();
    }

    void OnBeginDrag(PointerEventData eventData)
    {
        if (!CanSpawnEnemy() || !StatsManager.instance.ModifyMana(-opponent.enemyCost))
        {
            return;
        }
        var newEnemy = Instantiate(opponent.enemyPrefab);
        DragDestroyController.instance.HandoffEnemy(newEnemy, this);
        cameraController.PlayRandomGlobalAudioClip(spawnOpponentSfx);
    }

    void UpdateDisplayStates()
    {
        previewSprite.color = CanSpawnEnemy() ? Color.white : disabledPreviewSpriteColor;
        costText.color = StatsManager.instance.CanModifyMana(-opponent.enemyCost) ? defaultCostTextColor : disabledCostTextColor;
    }

    bool CanSpawnEnemy()
    {
        return !RoundController.instance.roundRunning && StatsManager.instance.CanModifyMana(-opponent.enemyCost);
    }

    public void OnDragDropped(GameObject enemy, bool validPosition)
    {
        if (!validPosition)
        {
            Destroy(enemy);
            StatsManager.instance.ModifyMana(enemy.GetComponent<Enemy>().opponentType.enemyCost);
        }
    }

    public void OnRoundStart()
    {
        UpdateDisplayStates();
    }

    public void OnRoundEnd(bool won)
    {
        UpdateDisplayStates();
    }

    public void OnManaChanged(int oldValue, int newValue)
    {
        UpdateDisplayStates();
    }

}