"""Identifier sanitization for Terraform resource names.

Converts arbitrary resource names into valid Terraform identifiers
matching the pattern: ^[a-zA-Z_][a-zA-Z0-9_]*$
"""

import re


def sanitize_identifier(name: str) -> str:
    """Convert a resource name to a valid Terraform identifier.

    Terraform identifiers must match: ^[a-zA-Z_][a-zA-Z0-9_]*$

    Rules applied:
    - Replace any character not in [a-zA-Z0-9_] with underscore
    - Collapse multiple consecutive underscores into one
    - If result starts with a digit, prepend an underscore
    - If result is empty or only underscores, return "_resource"

    Args:
        name: Any string resource name.

    Returns:
        A valid Terraform identifier derived from the input.
    """
    # Replace any non-alphanumeric/underscore character with underscore
    result = re.sub(r"[^a-zA-Z0-9_]", "_", name)

    # Collapse multiple consecutive underscores into one
    result = re.sub(r"_+", "_", result)

    # If result is only underscores or empty, return fallback
    if not result or result.strip("_") == "":
        return "_resource"

    # If starts with a digit, prepend underscore
    if result[0].isdigit():
        result = "_" + result

    return result