proto_racer/Assets/Scripts/CarLogic.cs

using UnityEngine;
using UnityEngine.InputSystem;

[RequireComponent(typeof(Rigidbody2D))]
public class CarLogic : MonoBehaviour
{
	public InputAction steeringAction;
	public InputAction accelerationAction;
	public InputAction brakeAction;

	public float accelerationAmount = 10;
	[Tooltip("In degrees")] 
	public float steeringAnglePerSecond = 10;

	public float maxAcceleration = 100;
	public float brakingAmount;
	public float wheelAccelerationFactor = 6.0f;

	private Rigidbody2D _rigidbody;
	private Transform _transform;
	private float _currentAcceleration;
	private int _wheelOnRoadCount = 0;
	private float _maxAcceleration;
	private float _wheelAccelerationOffset;

	public float CurrentAccelerationRatio()
	{
		return _currentAcceleration / maxAcceleration;
	}
	
	private void Awake()
	{
		_rigidbody = GetComponent<Rigidbody2D>();
		_transform = transform;
		_maxAcceleration = maxAcceleration;
		_wheelAccelerationOffset = wheelAccelerationFactor - 4;
	}

	private void OnEnable()
	{
		steeringAction.Enable();
		accelerationAction.Enable();
		brakeAction.Enable();

		var wheels = GetComponentsInChildren<Wheel>();
		foreach (var wheel in wheels)
		{
			wheel.wheelOffRoad = WheelOffRoad;
			wheel.wheelOnRoad = WheelOnRoad;
		}

		_wheelOnRoadCount = 0;
	}

	private void OnDisable()
	{
		steeringAction.Disable();
		accelerationAction.Disable();
		brakeAction.Disable();
	}

	private void WheelOffRoad()
	{
		_wheelOnRoadCount--;
		_maxAcceleration = ((_wheelOnRoadCount + _wheelAccelerationOffset) / wheelAccelerationFactor) * maxAcceleration;
	}

	private void WheelOnRoad()
	{
		_wheelOnRoadCount++;
		_maxAcceleration = ((_wheelOnRoadCount + _wheelAccelerationOffset) / wheelAccelerationFactor) * maxAcceleration;
	}

	private void Update()
	{
		var steeringValue = steeringAction.ReadValue<float>();
		var accelerationValue = accelerationAction.ReadValue<float>();
		var brakeValue = brakeAction.ReadValue<float>();

		if (accelerationValue <= 0)
		{
			_currentAcceleration -= _rigidbody.drag * Time.deltaTime;
		}

		_currentAcceleration += accelerationValue * accelerationAmount * Time.deltaTime;
		
		_currentAcceleration -= brakeValue * brakingAmount * Time.deltaTime;

		// TODO: reverse logic.
		_currentAcceleration = Mathf.Clamp(_currentAcceleration, 0, _maxAcceleration);
		
		if (_currentAcceleration > 0.01)
		{
			var newAngle = steeringValue * steeringAnglePerSecond * Time.deltaTime;
			_transform.Rotate(Vector3.forward, newAngle, Space.World);
		}

		_rigidbody.velocity = _transform.up * _currentAcceleration;
	}
}