import torch
from torch.utils.data import DataLoader


def validation(actor, validation_dataset, batch_size):
    """
    Evaluate the actor model on the validation dataset.
    
    Args:
        actor: Trained model to evaluate
        validation_dataset: Dataset for validation
        batch_size: Size of mini-batches used in evaluation

    Returns:
        Tensor of total costs for each sample in the validation set
    """
    actor.eval()  # Set model to evaluation mode
    val_dataloader = DataLoader(dataset=validation_dataset,
                                batch_size=batch_size,
                                collate_fn=validation_dataset.collate)

    scores = []

    with torch.no_grad():
        for batch in val_dataloader:
            actor_output = actor(batch)
            cost = actor_output['total_time'].view(-1)
            scores.append(cost)

    return torch.cat(scores, dim=0)