#!/usr/bin/with-contenv python3

import json
import os
import sys

from json.decoder import JSONDecodeError

SETTINGS_FILE_PATH = "/config/settings.json"


def setting_name_env_var_name(setting_name):
    return "TRANSMISSION_{}".format(setting_name.replace("-", "_").upper())


def main():
    # check file exists and is writable, just in case..
    if not os.path.exists(SETTINGS_FILE_PATH):
        raise Exception(f"Settings file '{SETTINGS_FILE_PATH}' does not exist.")
    if not os.path.isfile(SETTINGS_FILE_PATH):
        raise Exception(f"Settings file '{SETTINGS_FILE_PATH}' is a directory.")
    if not os.access(SETTINGS_FILE_PATH, os.W_OK):
        raise Exception(f"Settings file '{SETTINGS_FILE_PATH}' is not writable.")

    # read settings file
    settings_json = None
    with open(SETTINGS_FILE_PATH, "r") as f:
        settings_json = json.loads(f.read())

    # update settings with ENV vars
    for setting_name in settings_json:
        env_var_name = setting_name_env_var_name(setting_name)
        env_var_value = os.getenv(env_var_name)

        if env_var_value is not None:
            setting_type = type(settings_json[setting_name])
            if setting_type == bool:
                setting_value = env_var_value.lower() == "true"
            else:
                setting_value = setting_type(env_var_value)

            print(f"From ENV setting '{setting_name}'='{setting_value}'.")
            settings_json[setting_name] = setting_value

    with open(SETTINGS_FILE_PATH, "w", encoding="utf-8") as f:
        json.dump(settings_json, f, ensure_ascii=False, indent=4)
        print("Transmission settings file saved.")


if __name__ == "__main__":
    try:
        print("Applying transmission env-var-settings mod...")
        main()
    except Exception as e:
        print(f"Failed to apply transmission env-var-settings mod with error: '{e}'.", file=sys.stderr)
    else:
        print("Applied transmission env-var-settings mod successfully.")
    finally:
        sys.exit(0)