You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: settings.rs
    path of file: ./repos/mCaptcha/src
    
    the code of the file until where you have to start completion: // Copyright (C) 2022  Aravinth Manivannan <realaravinth@batsense.net>
// SPDX-FileCopyrightText: 2023 Aravinth Manivannan <realaravinth@batsense.net>
//
// SPDX-License-Identifier: AGPL-3.0-or-later

use std::path::Path;
use std::{env, fs};

use config::builder::DefaultState;
use config::{Config, ConfigBuilder, ConfigError, File};
use derive_more::Display;

use serde::{Deserialize, Serialize};
use url::Url;

#[derive(Debug, Clone, Deserialize, Eq, PartialEq)]
pub struct Server {
    pub port: u32,
    pub domain: String,
    pub cookie_secret: String,
    pub ip: String,
    // TODO: remove
    pub url_prefix: Option<String>,
    pub proxy_has_tls: bool,
}

#[derive(Debug, Clone, Deserialize, Eq, PartialEq)]
pub struct Captcha {
    pub salt: String,
    pub gc: u64,
    pub runners: Option<usize>,
    pub queue_length: usize,
    pub enable_stats: bool,
    pub default_difficulty_strategy: DefaultDifficultyStrategy,
}

#[derive(Debug, Clone, Deserialize, Eq, PartialEq)]
pub struct DefaultDifficultyStrategy {
    pub avg_traffic_difficulty: u32,
    pub avg_traffic_time: Option<u32>,
    pub peak_sustainable_traffic_difficulty: u32,
    pub peak_sustainable_traffic_time: Option<u32>,
    pub broke_my_site_traffic_time: Option<u32>,
    pub broke_my_site_traffic_difficulty: u32,
    pub duration: u32,
}

#[derive(Debug, Clone, Deserialize, Eq, PartialEq)]
pub struct Smtp {
    pub from: String,
    pub reply: String,
    pub url: String,
    pub username: String,
    pub password: String,
    pub port: u16,
}

impl Server {
    #[cfg(not(tarpaulin_include))]
    pub fn get_ip(&self) -> String {
        format!("{}:{}", self.
    
    fn env_override_works() {
        use crate::tests::get_settings;
        let init_settings = get_settings();
        // so that it can be tested outside the macro (helper) too
        let mut new_settings;

        macro_rules! helper {


            ($env:expr, $val:expr, $val_typed:expr, $($param:ident).+) => {
                println!("Setting env var {} to {} for test", $env, $val);
                env::set_var($env, $val);
                new_settings = get_settings();
                assert_eq!(new_settings.$($param).+, $val_typed);
                assert_ne!(new_settings.$($param).+, init_settings.$($param).+);
                env::remove_var($env);
            };


            ($env:expr, $val:expr, $($param:ident).+) => {
                helper!($env, $val.to_string(), $val, $($param).+);
            };
        }

        /* top level */
        helper!("MCAPTCHA_debug", false, debug);
        helper!("MCAPTCHA_commercial", true, commercial);
        helper!("MCAPTCHA_allow_registration", false, allow_registration);
        helper!("MCAPTCHA_allow_demo", false, allow_demo);

        /* database_type */

        helper!(
            "DATABASE_URL",
            "postgres://postgres:password@localhost:5432/postgres",
            database.url
        );
        assert_eq!(new_settings.database.database_type, DBType::Postgres);
        helper!(
            "DATABASE_URL",
            "mysql://maria:password@localhost/maria",
            database.url
        );
        assert_eq!(new_settings.database.database_type, DBType::Maria);
        helper!("MCAPTCHA_database_POOL", 1000, database.pool);

        /* redis */

        /* redis.url */
        let env = "MCAPTCHA_redis_URL";
        let val = "redis://redis.example.org";
        println!("Setting env var {} to {} for test", env, val);
        env::set_var(env, val);
        new_settings = get_settings();
        assert_eq!(new_settings.redis.as_ref().unwrap().url, val);
        assert_ne!(
            new_settings.redis.as_ref().unwrap().url,
            init_settings.redis.as_ref().unwrap().url
        );
        env::remove_var(env);

        /* redis.pool */
        let env = "MCAPTCHA_redis_POOL";
        let val = 999;
        println!("Setting env var {} to {} for test", env, val);
        env::set_var(env, val.to_string());
        new_settings = get_settings();
        assert_eq!(new_settings.redis.as_ref().unwrap().pool, val);
        assert_ne!(
            new_settings.redis.as_ref().unwrap().pool,
            init_settings.redis.as_ref().unwrap().pool
        );
        env::remove_var(env);

        helper!("PORT", 0, server.port);
        helper!("MCAPTCHA_server_DOMAIN", "example.org", server.domain);
        helper!(
            "MCAPTCHA__server_COOKIE_SECRET",
            "dafasdfsdf",
            server.cookie_secret
        );
        helper!("MCAPTCHA__server_IP", "9.9.9.9", server.ip);
        helper!("MCAPTCHA__server_PROXY_HAS_TLS", true, server.proxy_has_tls);

        /* captcha */

        helper!("MCAPTCHA_captcha_SALT", "foobarasdfasdf", captcha.salt);
        helper!("MCAPTCHA_captcha_GC", 500, captcha.gc);
        helper!(
            "MCAPTCHA_captcha_RUNNERS",
            "500",
            Some(500),
            captcha.runners
        );

        helper!("MCAPTCHA_captcha_QUEUE_LENGTH", 500, captcha.queue_length);
        helper!("MCAPTCHA_captcha_ENABLE_STATS", false, captcha.enable_stats);
        helper!(
            "MCAPTCHA_captcha_DEFAULT_DIFFICULTY_STRATEGY_avg_traffic_difficulty",
            999,
            captcha.default_difficulty_strategy.avg_traffic_difficulty
        );
        helper!("MCAPTCHA_captcha_DEFAULT_DIFFICULTY_STRATEGY_peak_sustainable_traffic_difficulty", 999 , captcha.default_difficulty_strategy.peak_sustainable_traffic_difficulty);
        helper!("MCAPTCHA_captcha_DEFAULT_DIFFICULTY_STRATEGY_broke_my_site_traffic_difficulty", 999 , captcha.default_difficulty_strategy.broke_my_site_traffic_difficulty);
        helper!(
            "MCAPTCHA_captcha_DEFAULT_DIFFICULTY_STRATEGY_duration",
            999,
            captcha.default_difficulty_strategy.duration
        );
        helper!(
            "MCAPTCHA_captcha_DEFAULT_DIFFICULTY_STRATEGY_avg_traffic_time",
            "10",
            Some(10),
            captcha.default_difficulty_strategy.avg_traffic_time
        );

        helper!(
            "MCAPTCHA_captcha_DEFAULT_DIFFICULTY_STRATEGY_peak_sustainable_traffic_time",
            "20",
            Some(20),
            captcha
                .default_difficulty_strategy
                .peak_sustainable_traffic_time
        );

        helper!(
            "MCAPTCHA_captcha_DEFAULT_DIFFICULTY_STRATEGY_broke_my_site_traffic_time",
            "30",
            Some(30),
            captcha
                .default_difficulty_strategy
                .broke_my_site_traffic_time
        );

        /* SMTP */

        let vals = [
            "MCAPTCHA_smtp_FROM",
            "MCAPTCHA_smtp_REPLY",
            "MCAPTCHA_smtp_URL",
            "MCAPTCHA_smtp_USERNAME",
            "MCAPTCHA_smtp_PASSWORD",
            "MCAPTCHA_smtp_PORT",
        ];
        for env in vals.iter() {
            println!("Setting env var {} to {} for test", env, env);
            env::set_var(env, env);
        }

        let port = 9999;
        env::set_var("MCAPTCHA_smtp_PORT", port.to_string());

        new_settings = get_settings();
        let smtp_new = new_settings.smtp.as_ref().unwrap();
        let smtp_old = init_settings.smtp.as_ref().unwrap();
        assert_eq!(smtp_new.from, "MCAPTCHA_smtp_FROM");
        assert_eq!(smtp_new.reply, "MCAPTCHA_smtp_REPLY");
        assert_eq!(smtp_new.username, "MCAPTCHA_smtp_USERNAME");
        assert_eq!(smtp_new.password, "MCAPTCHA_smtp_PASSWORD");
        assert_eq!(smtp_new.port, port);
        assert_ne!(smtp_new, smtp_old);

        for env in vals.iter() {
            env::remove_var(env);
        }
    }