import re

from jinja2 import Environment, StrictUndefined, UndefinedError, meta


class Constants:
    MissingVariablePattern = var_pattern = r"\{\{\s*([a-zA-Z_][a-zA-Z0-9_.\[\]'\"]*)\s*\}\}"


def get_missing_variables(template_source: str, template_data: dict) -> set[str]:
    # quick check - catch top-level undefineds
    env = Environment(undefined=StrictUndefined)
    ast = env.parse(template_source)
    undeclared_vars = meta.find_undeclared_variables(ast)
    missing_vars = undeclared_vars - set(template_data.keys())

    # nested undefined won't be caught; let's check for those
    if not missing_vars:
        # try rendering to catch nested undefineds (dotted attributes, list/dict access)
        try:
            template = env.from_string(template_source)
            template.render(template_data)
        except UndefinedError:
            # matches: {{ var }}, {{ var.attr }}, {{ var[0] }}, {{ var['key'] }}, {{ var.attr[0] }}
            matches = re.findall(Constants.MissingVariablePattern, template_source)

            for match in matches:
                root = match.split("[")[0].split(".")[0]

                # just check if the 'root' of the variable exists in the provided data
                # if it does, add the whole match as missing
                if root in template_data:
                    missing_vars.add(match)

            if not missing_vars:
                raise  # re-raise if we couldn't determine missing vars

    return missing_vars