"""
Extract von Mises stress from CHEXA elements
Auto-generated by Atomizer Phase 3 - pyNastran Research Agent

Pattern: solid_stress
Element Type: CTETRA
Result Type: stress
API: model.ctetra_stress[subcase] or model.chexa_stress[subcase]
"""

from pathlib import Path
from typing import Dict, Any
import numpy as np
from pyNastran.op2.op2 import OP2


def extract_solid_stress(op2_file: Path, subcase: int = 1, element_type: str = 'ctetra'):
    """Extract stress from solid elements."""
    from pyNastran.op2.op2 import OP2
    import numpy as np

    model = OP2()
    model.read_op2(str(op2_file))

    # Get stress object for element type
    # In pyNastran, stress is stored in model.op2_results.stress
    stress_attr = f"{element_type}_stress"

    if not hasattr(model, 'op2_results') or not hasattr(model.op2_results, 'stress'):
        raise ValueError(f"No stress results in OP2")

    stress_obj = model.op2_results.stress
    if not hasattr(stress_obj, stress_attr):
        raise ValueError(f"No {element_type} stress results in OP2")

    stress = getattr(stress_obj, stress_attr)[subcase]
    itime = 0

    # Extract von Mises if available
    if stress.is_von_mises:  # Property, not method
        von_mises = stress.data[itime, :, 9]  # Column 9 is von Mises
        max_stress = float(np.max(von_mises))

        # Get element info
        element_ids = [eid for (eid, node) in stress.element_node]
        max_stress_elem = element_ids[np.argmax(von_mises)]

        return {
            'max_von_mises': max_stress,
            'max_stress_element': int(max_stress_elem)
        }
    else:
        raise ValueError("von Mises stress not available")


if __name__ == '__main__':
    # Example usage
    import sys
    if len(sys.argv) > 1:
        op2_file = Path(sys.argv[1])
        result = extract_solid_stress(op2_file)
        print(f"Extraction result: {result}")
    else:
        print("Usage: python {sys.argv[0]} <op2_file>")