Sure, here is a test case generator for the given competitive programming problem "A: Cabbage":

```python
import random

def tcgen():
    N = random.randint(1, 1000)
    M = random.randint(0, N)
    A = random.randint(1, 1000)
    B = random.randint(A, 1000)  # Ensure B is at least A
    D = [random.randint(1, 1000) for _ in range(N)]
    
    return N, M, A, B, D

# Example usage:
for _ in range(5):  # Generate 5 test cases
    N, M, A, B, D = tcgen()
    print(f"{N} {M} {A} {B}")
    print(" ".join(map(str, D)))
```

### Explanation:

1. **N**: Number of leaves, randomly generated between 1 and 1000.
2. **M**: Minimum number of leaves required for cooking, randomly generated between 0 and N.
3. **A**: Minimum dirtiness threshold to consider a leaf for discarding, randomly generated between 1 and 1000.
4. **B**: Maximum dirtiness threshold to reconsider a leaf for discarding, randomly generated between A and 1000 to ensure \(A \leq B\).
5. **D**: List of dirtiness values for each leaf, randomly generated between 1 and 1000 for N leaves.

This generator ensures that the generated values conform to the given constraints and provide a variety of test cases for thorough testing.