"""Validated, secret-free runtime configuration."""

from __future__ import annotations

import os
from collections.abc import Mapping
from dataclasses import dataclass

try:
    from enum import StrEnum
except ImportError:
    from enum import Enum

    class StrEnum(str, Enum):  # noqa: UP042
        def __str__(self) -> str:
            return str(self.value)


class ConfigurationError(ValueError):
    """Raised when non-secret runtime configuration is unsafe or invalid."""


class Environment(StrEnum):
    DEVELOPMENT = "development"
    RESEARCH = "research"
    PAPER = "paper"
    PRODUCTION = "production"


class LogLevel(StrEnum):
    DEBUG = "DEBUG"
    INFO = "INFO"
    WARNING = "WARNING"
    ERROR = "ERROR"


@dataclass(frozen=True, slots=True)
class Settings:
    """Non-secret process configuration.

    Credentials are intentionally absent. Provider adapters receive secrets from a
    dedicated future secret-provider boundary, not from this general settings object.
    """

    environment: Environment
    log_level: LogLevel

    @property
    def is_production(self) -> bool:
        return self.environment is Environment.PRODUCTION


def load_settings(environ: Mapping[str, str] | None = None) -> Settings:
    """Load and validate supported non-secret environment variables."""

    source = os.environ if environ is None else environ
    environment_value = source.get("DRIFT_ENVIRONMENT", Environment.DEVELOPMENT.value).lower()
    log_level_value = source.get("DRIFT_LOG_LEVEL", LogLevel.INFO.value).upper()

    try:
        environment = Environment(environment_value)
    except ValueError as exc:
        valid_values = ", ".join(member.value for member in Environment)
        raise ConfigurationError(f"DRIFT_ENVIRONMENT must be one of: {valid_values}.") from exc

    try:
        log_level = LogLevel(log_level_value)
    except ValueError as exc:
        valid_values = ", ".join(member.value for member in LogLevel)
        raise ConfigurationError(f"DRIFT_LOG_LEVEL must be one of: {valid_values}.") from exc

    return Settings(environment=environment, log_level=log_level)