"""Create constraint lambdas from expressions."""

import re


def make_constraint_lambda(expr_str):
    """Create a lambda function from a constraint expression.

    Transforms resource identifiers to res dict access and creates a lambda
    with restricted builtins.

    Args:
        expr_str: Constraint expression like "E[3] >= 50" or "B[2] + S[2] >= 100"

    Returns:
        A lambda function: lambda res: <evaluated_expression>

    Raises:
        Exception: If expression fails to eval
    """
    # Transform identifiers to res subscript access: E -> res["E"], B -> res["B"], etc.
    expr = re.sub(r'\b([A-Z])\b', r'res["\1"]', expr_str)

    # Create lambda with restricted builtins (no imports, no dangerous functions)
    return eval(f"lambda res: {expr}", {"__builtins__": {}})