proto_rts/Assets/Scripts/Building.cs

using System;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.InputSystem;

// TODO: The actual building logic and the construction logic should be separated!
[RequireComponent(typeof(BoxCollider2D), typeof(SpriteRenderer))]
public class Building : MonoBehaviour
{
	private struct WorkOrder
	{
		public float startTime;
		public float duration;
		public Action completed;
	}

	[Serializable]
	public struct UnitCommand
	{
		public Unit unit;
		public Key keyControl;
		public int cost;
		public float buildDuration;
	}
	
	[NonSerialized] public BoxCollider2D buildingCollider;

	public int maxQueueCount;
	public float constructionTime;
	public bool startBuilt;
	public int buildingCost;
	public List<UnitCommand> buildableUnits;

	[NonSerialized] public bool isUnderConstruction = true;

	private readonly Queue<WorkOrder> _workQueue = new Queue<WorkOrder>();
	private WorkOrder _currentWorkOrder;

	private bool _hasCurrentWorkOrder;

	// In seconds.
	private float _currentConstructionProgress;
	private readonly Color _constructionColor = Color.black;
	private SpriteRenderer _sprite;

	private Transform _transform;

	private void Start()
	{
		buildingCollider = GetComponent<BoxCollider2D>();
		_sprite = GetComponent<SpriteRenderer>();
		isUnderConstruction = !startBuilt;
		_transform = transform;
	}

	public void UpdateBuildProgress(float amount)
	{
		if (isUnderConstruction)
		{
			_currentConstructionProgress += amount;
			if (_currentConstructionProgress >= constructionTime)
			{
				isUnderConstruction = false;
			}

			_sprite.color = Color.Lerp(_constructionColor, Color.white,
				_currentConstructionProgress / constructionTime);
		}
	}

	private void Update()
	{
		if (_hasCurrentWorkOrder)
		{
			if (Time.time > _currentWorkOrder.startTime + _currentWorkOrder.duration)
			{
				_currentWorkOrder.completed();
				_hasCurrentWorkOrder = false;
			}
		}
		else
		{
			// Could probably do all this once we complete the order.
			// Would also need to do it when we receive an order.
			if (_workQueue.Count > 0)
			{
				_currentWorkOrder = _workQueue.Dequeue();
				_currentWorkOrder.startTime = Time.time;
				_hasCurrentWorkOrder = true;
			}
		}
	}

	public void ProcessKeyInput(Key key)
	{
		if (isUnderConstruction)
		{
			return;
		}
		
		foreach (var command in buildableUnits)
		{
			if (command.keyControl == key)
			{
				if (command.cost > Team.Minerals)
				{
					// TODO: announcer.
					Debug.LogWarning("You've not enough minerals");
					break;
				}

				if (maxQueueCount > _workQueue.Count)
				{
					Team.Minerals -= command.cost;
					_workQueue.Enqueue(new WorkOrder
					{
						startTime = Time.time,
						duration = command.buildDuration,
						completed = () =>
						{
							var unitGo = Instantiate(command.unit,
								_transform.position, _transform.rotation);
							Team.AllUnits.Add(unitGo);
						}
					});
				}
			}
		}
	}
}