"""
Implements loading and providing the configuration of the radar instance. Usage should be straight-forward:

	>>> from . import _config
	>>> config = _config.load()
	>>> config.locations
	['New York City', 'Jersey City']

An example configuration file looks like this:

	[Waterspout Radar]
	db = .waterspout/db.json
	key = <secret key>

	[Locations]
	New York City
	Jersey City
"""

import configparser
import dataclasses
import os
import typing


@dataclasses.dataclass
class Config:
	db: str
	key: str
	locations: typing.List[str]


class ConfigError(Exception):
	"Raised when configuration could not be loaded or was malformed."


def effective_pathname(pathname: str = None) -> str:
	"Pathname of the configuration file based on optional *pathname*, environment, and default."
	return pathname or os.getenv("WATERSPOUT_RADAR_CONFIG") or "waterspout-radar.ini"


def load(pathname: str) -> Config:
	"Loads configuration from a file at *pathname*. May raise ConfigError when content does not meet expectations."
	config = configparser.ConfigParser(allow_no_value=True)
	config.read(pathname)
	raw = {}
	errors = []

	def _load_key(section, name, target=None, type=None, default=None, required=False):
		target = target or name
		try:
			value = config[section][name]
			if type:
				value = type(value)
			raw[target] = value
		except (KeyError, ValueError):
			if default:
				raw[target] = default
			if required:
				errors.append(f"Config is missing required field: {pathname}: {section}: {name}")

	_load_key("Waterspout Radar", "db", default="radar.json")
	_load_key("Waterspout Radar", "key", required=True)
	try:
		raw["locations"] = list(config["Locations"])
	except KeyError:
		errors.append(f"Config is missing Locations: {pathname}")
	if errors:
		raise ConfigError(*errors)
	return Config(**raw)