"""
Module implementing message related functions and classes.
"""
from typing import Type, TypeVar

QuestionInst = TypeVar('QuestionInst', bound='Question')


class MessageError(Exception):
    pass


def source_code(text: str, include_delims: bool = False) -> list[str]:
    """
    Extracts all source code sections from the given text, i. e. all lines
    surrounded by lines tarting with '```'. If 'include_delims' is True,
    the surrounding lines are included, otherwise they are omitted. The
    result list contains every source code section as a single string.
    The order in the list represents the order of the sections in the text.
    """
    code_sections: list[str] = []
    code_lines: list[str] = []
    in_code_block = False

    for line in text.split('\n'):
        if line.strip().startswith('```'):
            if include_delims:
                code_lines.append(line)
            if in_code_block:
                code_sections.append('\n'.join(code_lines) + '\n')
                code_lines.clear()
            in_code_block = not in_code_block
        elif in_code_block:
            code_lines.append(line)

    return code_sections


class Question(str):
    """
    A single question with a defined prefix.
    """
    prefix = '=== QUESTION ==='

    def __new__(cls: Type[QuestionInst], string: str) -> QuestionInst:
        """
        Make sure the question string does not contain the prefix.
        """
        if cls.prefix in string:
            raise MessageError(f"Question '{string}' contains the prefix '{cls.prefix}'")
        instance = super().__new__(cls, string)
        return instance