import configparser
import textwrap
from functools import partial
from pathlib import Path
from typing import Any, Callable, Dict, NoReturn, Optional

import tomli

INI_USAGE = """
(config)
...
[mypy.plugins.django_stubs]
    django_settings_module: str (required)
...
"""
TOML_USAGE = """
(config)
...
[tool.django-stubs]
django_settings_module = str (required)
...
"""
INVALID_FILE = "mypy config file is not specified or found"
COULD_NOT_LOAD_FILE = "could not load configuration file"
MISSING_SECTION = "no section [{section}] found".format
MISSING_DJANGO_SETTINGS = "missing required 'django_settings_module' config"
INVALID_SETTING = "invalid {key!r}: the setting must be a boolean".format


def exit_with_error(msg: str, is_toml: bool = False) -> NoReturn:
    """Using mypy's argument parser, raise `SystemExit` to fail hard if validation fails.

    Considering that the plugin's startup duration is around double as long as mypy's, this aims to
    import and construct objects only when that's required - which happens once and terminates the
    run. Considering that most of the runs are successful, there's no need for this to linger in the
    global scope.
    """
    from mypy.main import CapturableArgumentParser

    handler = CapturableArgumentParser(
        prog="(django-stubs) mypy", usage=textwrap.dedent(TOML_USAGE if is_toml else INI_USAGE)
    )
    handler.error(msg)


class DjangoPluginConfig:
    __slots__ = ("django_settings_module",)
    django_settings_module: str

    def __init__(self, config_file: Optional[str]) -> None:
        if not config_file:
            exit_with_error(INVALID_FILE)

        filepath = Path(config_file)
        if not filepath.is_file():
            exit_with_error(INVALID_FILE)

        if filepath.suffix.lower() == ".toml":
            self.parse_toml_file(filepath)
        else:
            self.parse_ini_file(filepath)

    def parse_toml_file(self, filepath: Path) -> None:
        toml_exit: Callable[[str], NoReturn] = partial(exit_with_error, is_toml=True)
        try:
            with filepath.open(mode="rb") as f:
                data = tomli.load(f)
        except (tomli.TOMLDecodeError, OSError):
            toml_exit(COULD_NOT_LOAD_FILE)

        try:
            config: Dict[str, Any] = data["tool"]["django-stubs"]
        except KeyError:
            toml_exit(MISSING_SECTION(section="tool.django-stubs"))

        if "django_settings_module" not in config:
            toml_exit(MISSING_DJANGO_SETTINGS)

        self.django_settings_module = config["django_settings_module"]
        if not isinstance(self.django_settings_module, str):
            toml_exit("invalid 'django_settings_module': the setting must be a string")

    def parse_ini_file(self, filepath: Path) -> None:
        parser = configparser.ConfigParser()
        try:
            with filepath.open(encoding="utf-8") as f:
                parser.read_file(f, source=str(filepath))
        except OSError:
            exit_with_error(COULD_NOT_LOAD_FILE)

        section = "mypy.plugins.django-stubs"
        if not parser.has_section(section):
            exit_with_error(MISSING_SECTION(section=section))

        if not parser.has_option(section, "django_settings_module"):
            exit_with_error(MISSING_DJANGO_SETTINGS)

        self.django_settings_module = parser.get(section, "django_settings_module").strip("'\"")