How do I change Raycast's direction based on movement input?

Hey everyone!

I'm making a game where when the player presses one of the WASD keys, the character moves in the direction associated with the key until it collides with an object in front. (A bit like Tomb of The Mask)

I got the movement part down, but my problem is, I want to limit the player, to only be able to move while stationary (when he hit an object in front of it). I was thinking a Ray-cast is probably the best way to go here, but I don't know how to set it up so it's direction changes depending on which key was pressed.

I know the "isMoving" thing is kinda doing that, but it's working a bit choppy and it creates a little wait time between 2 inputs bc the velocity of the object doesn't go down to 0 instantly

Here's my code so far:

 using UnityEngine;
 
 public class PlayerController : MonoBehaviour
 {
     // PRIVATE GET COMPONENTS
     Collider2D _boxCollider2d;
     Rigidbody2D _rigidBody;
 
 
     // PUBLIC COMPONENTS
 
     // PUBLIC VARIABLES
     public float moveSpeed = 200;
 
     // PRIVATE VARIABLES
     Vector2 movement;
 
     bool isMoving;
 
     // BUILT IN FUNCTIONS
     //###################################################################//
     private void Start()
     {
         _boxCollider2d = GetComponent<Collider2D>();
         _rigidBody = GetComponent<Rigidbody2D>();
     }
 
     private void Update()
     {
         CheckMovement();
     }
 
     private void FixedUpdate()
     {
         PlayerMovement();
     }
 
     private void OnCollisionEnter2D(Collision2D other)
     {
         _rigidBody.velocity = new Vector2(0, 0);
     }
 
     // CUSTOM FUNCTIONS //
     //###################################################################//
     void PlayerMovement()
     {
         bool leftDir = Input.GetKeyDown(KeyCode.A);
         bool rightDir = Input.GetKeyDown(KeyCode.D);
         bool upDir = Input.GetKeyDown(KeyCode.W);
         bool downDir = Input.GetKeyDown(KeyCode.S);
 
 
         if (leftDir && !isMoving)
         {
             _rigidBody.velocity = Vector2.left * moveSpeed * Time.deltaTime;
         }
         if (rightDir && !isMoving)
         {
             _rigidBody.velocity = Vector2.right * moveSpeed * Time.deltaTime;
         }
         if (upDir && !isMoving)
         {
             _rigidBody.velocity = Vector2.up * moveSpeed * Time.deltaTime;
         }
         if (downDir && !isMoving)
         {
             _rigidBody.velocity = Vector2.down * moveSpeed * Time.deltaTime;
         }
     }
 
     void CheckMovement()
     {
         movement = new Vector2(Input.GetAxis("Horizontal"),     
                                Input.GetAxis("Vertical"));
 
         if (_rigidBody.velocity.x != 0 || _rigidBody.velocity.y != 0)
         {
             isMoving = true;
         }
         else
         {
             isMoving = false;
         }
     }
 }