//! Configuration data that origins from environment variables.
//! Unlike the configuration data in `LIB_CFG` which is sourced only once when
//! Tp-Note is launched, the `SETTINGS` object may be sourced more often in
//! order to follow changes in the related environment variables.

use crate::config::LIB_CFG;
#[cfg(feature = "lang-detection")]
use crate::config::TMPL_FILTER_GET_LANG_ALL;
use crate::error::LibCfgError;
#[cfg(feature = "lang-detection")]
use lingua;
#[cfg(feature = "lang-detection")]
use lingua::IsoCode639_1;
use parking_lot::RwLock;
use std::borrow::Cow;
use std::collections::BTreeMap;
use std::env;
#[cfg(feature = "lang-detection")]
use std::str::FromStr;
#[cfg(target_family = "windows")]
use windows_sys::Win32::Globalization::GetUserDefaultLocaleName;
#[cfg(target_family = "windows")]
use windows_sys::Win32::System::SystemServices::LOCALE_NAME_MAX_LENGTH;

/// The name of the environment variable which can be optionally set to
/// overwrite the `scheme_default` configuration file setting.
pub const ENV_VAR_TPNOTE_SCHEME: &str = "TPNOTE_SCHEME";

/// The name of the environment variable which can be optionally set to
/// overwrite the `filename.extension_default` configuration file setting.
pub const ENV_VAR_TPNOTE_EXTENSION_DEFAULT: &str = "TPNOTE_EXTENSION_DEFAULT";

/// Name of the environment variable, that can be optionally
/// used to overwrite the user's default language setting, which is
/// accessible as `{{ lang }}` template variable and used in various
/// templates.
pub const ENV_VAR_TPNOTE_LANG: &str = "TPNOTE_LANG";

/// Name of the environment variable, that can be optionally
/// used to overwrite the user's `tmpl.filter.get_lang` and `tmpl.filter.map_lang`
/// configuration file setting.
pub const ENV_VAR_TPNOTE_LANG_DETECTION: &str = "TPNOTE_LANG_DETECTION";

/// Name of the environment variable, that can be optionally
/// used to overwrite the user's login name. The result is accessible as
/// `{{ username }}` template variable and used in various templates.
pub const ENV_VAR_TPNOTE_USER: &str = "TPNOTE_USER";

/// Name of the `LOGNAME` environment variable.
const ENV_VAR_LOGNAME: &str = "LOGNAME";

/// Name of the `USERNAME` environment variable.
const ENV_VAR_USERNAME: &str = "USERNAME";

/// Name of the `USER` environment variable.
const ENV_VAR_USER: &str = "USER";

/// Name of the `LANG` environment variable.
#[cfg(not(target_family = "windows"))]
const ENV_VAR_LANG: &str = "LANG";

#[derive(Debug)]
#[allow(dead_code)]
/// Indicates how the `get_lang` filter operates.
pub(crate) enum FilterGetLang {
    /// The filter is disabled and returns the empty string.
    Disabled,
    /// All available (about 76) languages are selected as search candidates.
    /// This causes the filter execution to take some time (up to 5 seconds).
    AllLanguages,
    /// A list of language tags the algorithm considers as potential candidates
    /// to determinate the natural language.
    #[cfg(feature = "lang-detection")]
    SomeLanguages(Vec<IsoCode639_1>),
    /// A list of language tags the algorithm considers as potential candidates
    /// to determinate the natural language.
    #[cfg(not(feature = "lang-detection"))]
    SomeLanguages(Vec<String>),
    /// The filter configuration could not be read and converted properly.
    Error(LibCfgError),
}

/// Struct containing additional user configuration read from or depending
/// on environment variables.
#[derive(Debug)]
#[allow(dead_code)]
pub(crate) struct Settings {
    /// This is the index as the schemes are listed in the config file.
    pub current_scheme: usize,
    /// This has the format of a login name.
    pub author: String,
    /// [RFC 5646, Tags for the Identification of Languages](http://www.rfc-editor.org/rfc/rfc5646.txt)
    pub lang: String,
    /// Extension without dot, e.g. `md`
    pub extension_default: String,
    /// See defintion of type.
    pub filter_get_lang: FilterGetLang,
    /// The keys and values from
    /// `LIB_CFG.schemes[settings.current_scheme].tmpl.filter_btmap_lang` in the `BTreeMap`
    /// with the user's default language and region added.
    pub filter_map_lang_btmap: Option<BTreeMap<String, String>>,
}

const DEFAULT_SETTINGS: Settings = Settings {
    current_scheme: 0,
    author: String::new(),
    lang: String::new(),
    extension_default: String::new(),
    filter_get_lang: FilterGetLang::Disabled,
    filter_map_lang_btmap: None,
};

impl Default for Settings {
    #[cfg(not(any(test, doc)))]
    /// Defaults to empty lists and values.
    fn default() -> Self {
        DEFAULT_SETTINGS
    }

    #[cfg(any(test, doc))]
    /// Defaults to test values.
    /// Do not use outside of tests.
    fn default() -> Self {
        let mut settings = DEFAULT_SETTINGS;
        settings.author = String::from("testuser");
        settings.lang = String::from("ab-AB");
        settings.extension_default = String::from("md");
        settings
    }
}

/// Global mutable varible of type `Settings`.
#[cfg(not(test))]
pub(crate) static SETTINGS: RwLock<Settings> = RwLock::new(DEFAULT_SETTINGS);

#[cfg(test)]
lazy_static::lazy_static! {
/// Global default for `SETTINGS` in test environments.
pub(crate) static ref SETTINGS: RwLock<Settings> = RwLock::new(DEFAULT_SETTINGS);
}

/// Like `Settings::update`, with `scheme_source = SchemeSource::Force("default")`
/// and `force_lang = None`.
/// This is used in doctests only.
pub fn set_test_default_settings() -> Result<(), LibCfgError> {
    let mut settings = SETTINGS.write();
    settings.update(SchemeSource::Force("default"), None)
}

/// How should `update_settings` collect the right scheme?
pub(crate) enum SchemeSource<'a> {
    /// Ingore `TPNOTE_SCHEME_NEW_DEFAULT`, take this.
    Force(&'a str),
    /// Take the value `lib_cfg.scheme_sync_default`.
    SchemeSyncDefault,
    /// Take `TPNOTE_SCHEME_NEW_DEFAULT`, or, if not defined take this.
    SchemeNewDefault(&'a str),
}

impl Settings {
    /// (Re)read environment variables and store them in the global `SETTINGS`
    /// object. Some data originates from `LIB_CFG`.
    /// First sets `SETTINGS.current_scheme`:
    /// 1. If `force_theme` is `Some(scheme)`, gets the index and stores result, or,
    /// 2. if `force_theme` is `Some("")`, stores `lib_cfg.scheme_sync_default`, or,
    /// 3. reads the environment variable `TPNOTE_SCHEME_NEW_DEFAULT` or, -if empty-
    /// 4. copies `scheme_new_default` into `SETTINGS.curent_scheme`.
    /// Then, sets all other fields.
    /// `force_lang=Some(_)` disables the `get_lang` filter by setting
    /// `filter_get_lang` to `FilterGetLang::Disabled`.
    /// When `force_lang` is `Some(l)`, sets `SETTINGS.current_lang` with `l`.
    pub(crate) fn update(
        &mut self,
        scheme_source: SchemeSource,
        force_lang: Option<&str>,
    ) -> Result<(), LibCfgError> {
        self.update_current_scheme(scheme_source)?;
        self.update_author();
        self.update_extension_default();
        self.update_lang(force_lang);
        self.update_filter_get_lang(force_lang);
        self.update_filter_map_lang_btmap();
        self.update_env_lang_detection();

        log::trace!(
            "`SETTINGS` updated (reading config + env. vars.):\n{:#?}",
            self
        );

        if let FilterGetLang::Error(e) = &self.filter_get_lang {
            Err(e.clone())
        } else {
            Ok(())
        }
    }

    /// Sets `SETTINGS.current_scheme`:
    fn update_current_scheme(&mut self, scheme_source: SchemeSource) -> Result<(), LibCfgError> {
        let lib_cfg = LIB_CFG.read_recursive();

        let scheme = match scheme_source {
            SchemeSource::Force(s) => Cow::Borrowed(s),
            SchemeSource::SchemeSyncDefault => Cow::Borrowed(&*lib_cfg.scheme_sync_default),
            SchemeSource::SchemeNewDefault(s) => match env::var(ENV_VAR_TPNOTE_SCHEME) {
                Ok(ed_env) if !ed_env.is_empty() => Cow::Owned(ed_env),
                Err(_) | Ok(_) => Cow::Borrowed(s),
            },
        };
        self.current_scheme = lib_cfg.scheme_idx(scheme.as_ref())?;
        Ok(())
    }

    /// Set `SETTINGS.author` to content of the first not empty environment
    /// variable: `TPNOTE_USER`, `LOGNAME` or `USER`.
    fn update_author(&mut self) {
        let author = env::var(ENV_VAR_TPNOTE_USER).unwrap_or_else(|_| {
            env::var(ENV_VAR_LOGNAME).unwrap_or_else(|_| {
                env::var(ENV_VAR_USERNAME)
                    .unwrap_or_else(|_| env::var(ENV_VAR_USER).unwrap_or_default())
            })
        });

        // Store result.
        self.author = author;
    }

    /// Read the environment variable `TPNOTE_EXTENSION_DEFAULT` or -if empty-
    /// the configuration file variable `filename.extension_default` into
    /// `SETTINGS.extension_default`.
    fn update_extension_default(&mut self) {
        // Get the environment variable if it exists.
        let ext = match env::var(ENV_VAR_TPNOTE_EXTENSION_DEFAULT) {
            Ok(ed_env) if !ed_env.is_empty() => ed_env,
            Err(_) | Ok(_) => {
                let lib_cfg = LIB_CFG.read_recursive();
                lib_cfg.scheme[self.current_scheme]
                    .filename
                    .extension_default
                    .to_string()
            }
        };
        self.extension_default = ext;
    }

    /// If `lang=None` read the environment variable `TPNOTE_LANG` or
    /// -if not defined- `LANG` into `SETTINGS.lang`.
    /// If `force_lang=Some(l)`, copy `l` in `settings.lang`.
    fn update_lang(&mut self, force_lang: Option<&str>) {
        // Overwrite environment setting.
        if let Some(l) = force_lang {
            if !l.is_empty() {
                self.lang = l.to_string();
                return;
            }
        }

        // Get the user's language tag.
        // [RFC 5646, Tags for the Identification of Languages](http://www.rfc-editor.org/rfc/rfc5646.txt)
        let mut lang = String::new();
        // Get the environment variable if it exists.
        let tpnotelang = env::var(ENV_VAR_TPNOTE_LANG).ok();
        // Unix/MacOS version.
        #[cfg(not(target_family = "windows"))]
        if let Some(tpnotelang) = tpnotelang {
            lang = tpnotelang;
        } else {
            // [Linux: Define Locale and Language Settings -
            // ShellHacks](https://www.shellhacks.com/linux-define-locale-language-settings/)
            if let Ok(lang_env) = env::var(ENV_VAR_LANG) {
                if !lang_env.is_empty() {
                    // [ISO 639](https://en.wikipedia.org/wiki/List_of_ISO_639-1_codes) language code.
                    let mut language = "";
                    // [ISO 3166](https://en.wikipedia.org/wiki/ISO_3166-1#Current_codes) country code.
                    let mut territory = "";
                    if let Some((l, lang_env)) = lang_env.split_once('_') {
                        language = l;
                        if let Some((t, _codeset)) = lang_env.split_once('.') {
                            territory = t;
                        }
                    }
                    lang = language.to_string();
                    lang.push('-');
                    lang.push_str(territory);
                }
            }
        }

        // Get the user's language tag.
        // Windows version.
        #[cfg(target_family = "windows")]
        if let Some(tpnotelang) = tpnotelang {
            lang = tpnotelang;
        } else {
            let mut buf = [0u16; LOCALE_NAME_MAX_LENGTH as usize];
            let len = unsafe { GetUserDefaultLocaleName(buf.as_mut_ptr(), buf.len() as i32) };
            if len > 0 {
                lang = String::from_utf16_lossy(&buf[..((len - 1) as usize)]);
            }
        };

        // Store result.
        self.lang = lang;
    }

    /// Read language list from
    /// `LIB_CFG.schemes[settings.scheme].tmpl.filter.get_lang`, add the user's
    /// default language subtag and store them in `SETTINGS.filter_get_lang`
    /// as `FilterGetLang::SomeLanguages(l)` `enum` variant.
    /// If `SETTINGS.filter_get_lang` contains a tag `TMPL_FILTER_GET_LANG_ALL`,
    /// all languages are selected by setting `FilterGetLang::AllLanguages`.
    /// Errors are stored in the `FilterGetLang::Error(e)` variant.
    /// If `force_lang` is `Some(_)`, set `FilterGetLang::Disabled`
    #[cfg(feature = "lang-detection")]
    fn update_filter_get_lang(&mut self, force_lang: Option<&str>) {
        if force_lang.is_some() {
            self.filter_get_lang = FilterGetLang::Disabled;
            return;
        }

        let lib_cfg = LIB_CFG.read_recursive();

        let mut all_languages_selected = false;
        // Read and convert ISO codes from config object.
        match lib_cfg.scheme[self.current_scheme]
            .tmpl
            .filter
            .get_lang
            .iter()
            // Skip if this is the pseudo tag for all languages.
            .filter(|&l| {
                if l == TMPL_FILTER_GET_LANG_ALL {
                    all_languages_selected = true;
                    // Skip this string.
                    false
                } else {
                    // Continue.
                    true
                }
            })
            .map(|l| {
                IsoCode639_1::from_str(l).map_err(|_| {
                    // The error path.
                    // Produce list of all available langugages.
                    let mut all_langs = lingua::Language::all()
                        .iter()
                        .map(|l| {
                            let mut s = l.iso_code_639_1().to_string();
                            s.push_str(", ");
                            s
                        })
                        .collect::<Vec<String>>();
                    all_langs.sort();
                    let mut all_langs = all_langs.into_iter().collect::<String>();
                    all_langs.truncate(all_langs.len() - ", ".len());
                    // Insert data into error object.
                    LibCfgError::ParseLanguageCode {
                        language_code: l.into(),
                        all_langs,
                    }
                })
            })
            .collect::<Result<Vec<IsoCode639_1>, LibCfgError>>()
        {
            // The happy path.
            Ok(mut iso_codes) => {
                if all_languages_selected {
                    // Store result.
                    self.filter_get_lang = FilterGetLang::AllLanguages;
                } else {
                    // Add the user's language subtag as reported from the OS.
                    // Silently ignore if anything goes wrong here.
                    if !self.lang.is_empty() {
                        if let Some((lang_subtag, _)) = self.lang.split_once('-') {
                            if let Ok(iso_code) = IsoCode639_1::from_str(lang_subtag) {
                                if !iso_codes.contains(&iso_code) {
                                    iso_codes.push(iso_code);
                                }
                            }
                        }
                    }

                    // Check if there are at least 2 languages in the list.
                    self.filter_get_lang = match iso_codes.len() {
                        0 => FilterGetLang::Disabled,
                        1 => FilterGetLang::Error(LibCfgError::NotEnoughLanguageCodes {
                            language_code: iso_codes[0].to_string(),
                        }),
                        _ => FilterGetLang::SomeLanguages(iso_codes),
                    }
                }
            }
            // The error path.
            Err(e) =>
            // Store error.
            {
                self.filter_get_lang = FilterGetLang::Error(e);
            }
        }
    }

    #[cfg(not(feature = "lang-detection"))]
    /// Disable filter.
    fn update_filter_get_lang(&mut self, _force_lang: Option<&str>) {
        self.filter_get_lang = FilterGetLang::Disabled;
    }

    /// Read keys and values from
    /// `LIB_CFG.schemes[self.current_scheme].tmpl.filter_btmap_lang` in the `BTreeMap`.
    /// Add the user's default language and region.
    fn update_filter_map_lang_btmap(&mut self) {
        let mut btm = BTreeMap::new();
        let lib_cfg = LIB_CFG.read_recursive();
        for l in &lib_cfg.scheme[self.current_scheme].tmpl.filter.map_lang {
            if l.len() >= 2 {
                btm.insert(l[0].to_string(), l[1].to_string());
            };
        }
        // Insert the user's default language and region in the Map.
        if !self.lang.is_empty() {
            if let Some((lang_subtag, _)) = self.lang.split_once('-') {
                // Do not overwrite existing languages.
                if !lang_subtag.is_empty() && !btm.contains_key(lang_subtag) {
                    btm.insert(lang_subtag.to_string(), self.lang.to_string());
                }
            };
        }

        // Store result.
        self.filter_map_lang_btmap = Some(btm);
    }

    /// Reads the environment variable `LANG_DETECTION`. If not empty,
    /// parse the content and overwrite the `self.filter_get_lang` and
    /// the `self.filter_map_lang` variables.
    #[cfg(feature = "lang-detection")]
    fn update_env_lang_detection(&mut self) {
        if let Ok(env_var) = env::var(ENV_VAR_TPNOTE_LANG_DETECTION) {
            if env_var.is_empty() {
                // Early return.
                self.filter_get_lang = FilterGetLang::Disabled;
                self.filter_map_lang_btmap = None;
                log::debug!(
                    "Empty env. var. `{}` disables the `lang-detection` feature.",
                    ENV_VAR_TPNOTE_LANG_DETECTION
                );
                return;
            }

            // Read and convert ISO codes from config object.
            let mut hm: BTreeMap<String, String> = BTreeMap::new();
            let mut all_languages_selected = false;
            match env_var
                .split(',')
                .map(|t| {
                    let t = t.trim();
                    if let Some((lang_subtag, _)) = t.split_once('-') {
                        // Do not overwrite existing languages.
                        if !lang_subtag.is_empty() && !hm.contains_key(lang_subtag) {
                            hm.insert(lang_subtag.to_string(), t.to_string());
                        };
                        lang_subtag
                    } else {
                        t
                    }
                })
                // Check if this is the pseudo tag `TMPL_FILTER_GET_LANG_ALL `.
                .filter(|&l| {
                    if l == TMPL_FILTER_GET_LANG_ALL {
                        all_languages_selected = true;
                        // Skip this string.
                        false
                    } else {
                        // Continue.
                        true
                    }
                })
                .map(|l| {
                    IsoCode639_1::from_str(l.trim()).map_err(|_| {
                        // The error path.
                        // Produce list of all available langugages.
                        let mut all_langs = lingua::Language::all()
                            .iter()
                            .map(|l| {
                                let mut s = l.iso_code_639_1().to_string();
                                s.push_str(", ");
                                s
                            })
                            .collect::<Vec<String>>();
                        all_langs.sort();
                        let mut all_langs = all_langs.into_iter().collect::<String>();
                        all_langs.truncate(all_langs.len() - ", ".len());
                        // Insert data into error object.
                        LibCfgError::ParseLanguageCode {
                            language_code: l.into(),
                            all_langs,
                        }
                    })
                })
                .collect::<Result<Vec<IsoCode639_1>, LibCfgError>>()
            {
                // The happy path.
                Ok(mut iso_codes) => {
                    // Add the user's language subtag as reported from the OS.
                    // Continue the happy path.
                    if !self.lang.is_empty() {
                        if let Some(lang_subtag) = self.lang.split('-').next() {
                            if let Ok(iso_code) = IsoCode639_1::from_str(lang_subtag) {
                                if !iso_codes.contains(&iso_code) {
                                    iso_codes.push(iso_code);
                                }
                                // Check if there is a remainder (region code).
                                if lang_subtag != self.lang && !hm.contains_key(lang_subtag) {
                                    hm.insert(lang_subtag.to_string(), self.lang.to_string());
                                }
                            }
                        }
                    }
                    // Store result.
                    if all_languages_selected {
                        self.filter_get_lang = FilterGetLang::AllLanguages;
                    } else {
                        self.filter_get_lang = match iso_codes.len() {
                            0 => FilterGetLang::Disabled,
                            1 => FilterGetLang::Error(LibCfgError::NotEnoughLanguageCodes {
                                language_code: iso_codes[0].to_string(),
                            }),
                            _ => FilterGetLang::SomeLanguages(iso_codes),
                        }
                    }
                    self.filter_map_lang_btmap = Some(hm);
                }
                // The error path.
                Err(e) =>
                // Store error.
                {
                    self.filter_get_lang = FilterGetLang::Error(e);
                }
            }
        }
    }

    /// Ignore the environment variable `LANG_DETECTION`.
    #[cfg(not(feature = "lang-detection"))]
    fn update_env_lang_detection(&mut self) {
        if let Ok(env_var) = env::var(ENV_VAR_TPNOTE_LANG_DETECTION) {
            if !env_var.is_empty() {
                self.filter_get_lang = FilterGetLang::Disabled;
                self.filter_map_lang_btmap = None;
                log::debug!(
                    "Ignoring the env. var. `{}`. The `lang-detection` feature \
                 is not included in this build.",
                    ENV_VAR_TPNOTE_LANG_DETECTION
                );
            }
        }
    }
}
#[cfg(test)]
mod tests {
    use super::*;
    /// Attention: as these test-functions run in parallel, make sure that
    /// each environment variable appears in one function only!

    #[test]
    fn test_update_author_setting() {
        let mut settings = Settings::default();
        env::set_var(ENV_VAR_LOGNAME, "testauthor");
        settings.update_author();
        assert_eq!(settings.author, "testauthor");
    }

    #[test]
    fn test_update_extension_default_setting() {
        let mut settings = Settings::default();
        env::set_var(ENV_VAR_TPNOTE_EXTENSION_DEFAULT, "markdown");
        settings.update_extension_default();
        assert_eq!(settings.extension_default, "markdown");

        let mut settings = Settings::default();
        std::env::remove_var(ENV_VAR_TPNOTE_EXTENSION_DEFAULT);
        settings.update_extension_default();
        assert_eq!(settings.extension_default, "md");
    }

    #[test]
    #[cfg(not(target_family = "windows"))]
    fn test_update_lang_setting() {
        // Test 1
        let mut settings = Settings::default();
        env::remove_var(ENV_VAR_TPNOTE_LANG);
        env::set_var(ENV_VAR_LANG, "en_GB.UTF-8");
        settings.update_lang(None);
        assert_eq!(settings.lang, "en-GB");

        // Test empty input.
        let mut settings = Settings::default();
        env::remove_var(ENV_VAR_TPNOTE_LANG);
        env::set_var(ENV_VAR_LANG, "");
        settings.update_lang(None);
        assert_eq!(settings.lang, "");

        // Test precedence of `TPNOTE_LANG`.
        let mut settings = Settings::default();
        env::set_var(ENV_VAR_TPNOTE_LANG, "it-IT");
        env::set_var(ENV_VAR_LANG, "en_GB.UTF-8");
        settings.update_lang(None);
        assert_eq!(settings.lang, "it-IT");
    }

    #[test]
    fn test_update_filter_get_lang_setting() {
        // Test 1.
        let mut settings = Settings {
            lang: "en-GB".to_string(),
            ..Default::default()
        };
        settings.update_filter_get_lang(None);

        if let FilterGetLang::SomeLanguages(ofgl) = settings.filter_get_lang {
            let output_filter_get_lang = ofgl
                .iter()
                .map(|l| {
                    let mut l = l.to_string();
                    l.push(' ');
                    l
                })
                .collect::<String>();
            assert_eq!(output_filter_get_lang, "en fr de ");
        } else {
            panic!("Wrong variant: {:?}", settings.filter_get_lang);
        }

        //
        // Test 2.
        let mut settings = Settings {
            lang: "it-IT".to_string(),
            ..Default::default()
        };
        settings.update_filter_get_lang(None);

        if let FilterGetLang::SomeLanguages(ofgl) = settings.filter_get_lang {
            let output_filter_get_lang = ofgl
                .iter()
                .map(|l| {
                    let mut l = l.to_string();
                    l.push(' ');
                    l
                })
                .collect::<String>();
            assert_eq!(output_filter_get_lang, "en fr de it ");
        } else {
            panic!("Wrong variant: {:?}", settings.filter_get_lang);
        }
    }

    #[test]
    fn test_update_filter_map_lang_hmap_setting() {
        // Test 1.
        let mut settings = Settings {
            lang: "it-IT".to_string(),
            ..Default::default()
        };
        settings.update_filter_map_lang_btmap();

        let output_filter_map_lang = settings.filter_map_lang_btmap.unwrap();

        assert_eq!(output_filter_map_lang.get("de").unwrap(), "de-DE");
        assert_eq!(output_filter_map_lang.get("et").unwrap(), "et-ET");
        assert_eq!(output_filter_map_lang.get("it").unwrap(), "it-IT");

        //
        // Test short `settings.lang`.
        let mut settings = Settings {
            lang: "it".to_string(),
            ..Default::default()
        };
        settings.update_filter_map_lang_btmap();

        let output_filter_map_lang = settings.filter_map_lang_btmap.unwrap();

        assert_eq!(output_filter_map_lang.get("de").unwrap(), "de-DE");
        assert_eq!(output_filter_map_lang.get("et").unwrap(), "et-ET");
        assert_eq!(output_filter_map_lang.get("it"), None);
    }

    #[test]
    fn test_update_env_lang_detection() {
        // Test 1.
        // Test short `settings.lang`.
        let mut settings = Settings {
            lang: "en-GB".to_string(),
            ..Default::default()
        };
        env::set_var(ENV_VAR_TPNOTE_LANG_DETECTION, "fr-FR, de-DE, hu");
        settings.update_env_lang_detection();

        if let FilterGetLang::SomeLanguages(ofgl) = settings.filter_get_lang {
            let output_filter_get_lang = ofgl
                .iter()
                .map(|l| {
                    let mut l = l.to_string();
                    l.push(' ');
                    l
                })
                .collect::<String>();
            assert_eq!(output_filter_get_lang, "fr de hu en ");
        } else {
            panic!("Wrong variant: {:?}", settings.filter_get_lang);
        }

        let output_filter_map_lang = settings.filter_map_lang_btmap.unwrap();
        assert_eq!(output_filter_map_lang.get("de").unwrap(), "de-DE");
        assert_eq!(output_filter_map_lang.get("fr").unwrap(), "fr-FR");
        assert_eq!(output_filter_map_lang.get("en").unwrap(), "en-GB");

        //
        // Test 2.
        let mut settings = Settings {
            lang: "en-GB".to_string(),
            ..Default::default()
        };
        env::set_var(ENV_VAR_TPNOTE_LANG_DETECTION, "de-DE, de-AT, en-US");
        settings.update_env_lang_detection();

        if let FilterGetLang::SomeLanguages(ofgl) = settings.filter_get_lang {
            let output_filter_get_lang = ofgl
                .iter()
                .map(|l| {
                    let mut l = l.to_string();
                    l.push(' ');
                    l
                })
                .collect::<String>();
            assert_eq!(output_filter_get_lang, "de de en ");
        } else {
            panic!("Wrong variant: {:?}", settings.filter_get_lang);
        }
        let output_filter_map_lang = settings.filter_map_lang_btmap.unwrap();
        assert_eq!(output_filter_map_lang.get("de").unwrap(), "de-DE");
        assert_eq!(output_filter_map_lang.get("en").unwrap(), "en-US");

        //
        // Test 3.
        let mut settings = Settings {
            lang: "en-GB".to_string(),
            ..Default::default()
        };
        env::set_var(ENV_VAR_TPNOTE_LANG_DETECTION, "de-DE, +all, en-US");
        settings.update_env_lang_detection();

        assert!(matches!(
            settings.filter_get_lang,
            FilterGetLang::AllLanguages
        ));
        let output_filter_map_lang = settings.filter_map_lang_btmap.unwrap();
        assert_eq!(output_filter_map_lang.get("de").unwrap(), "de-DE");
        assert_eq!(output_filter_map_lang.get("en").unwrap(), "en-US");

        //
        // Test 4.
        let mut settings = Settings {
            lang: "en-GB".to_string(),
            ..Default::default()
        };
        env::set_var(ENV_VAR_TPNOTE_LANG_DETECTION, "de-DE, de-AT, en");
        settings.update_env_lang_detection();

        if let FilterGetLang::SomeLanguages(ofgl) = settings.filter_get_lang {
            let output_filter_get_lang = ofgl
                .iter()
                .map(|l| {
                    let mut l = l.to_string();
                    l.push(' ');
                    l
                })
                .collect::<String>();
            assert_eq!(output_filter_get_lang, "de de en ");
        } else {
            panic!("Wrong variant: {:?}", settings.filter_get_lang);
        }
        let output_filter_map_lang = settings.filter_map_lang_btmap.unwrap();
        assert_eq!(output_filter_map_lang.get("de").unwrap(), "de-DE");
        assert_eq!(output_filter_map_lang.get("en").unwrap(), "en-GB");

        //
        // Test 5.
        let mut settings = Settings {
            lang: "en-GB".to_string(),
            ..Default::default()
        };
        env::set_var(ENV_VAR_TPNOTE_LANG_DETECTION, "de-DE, +all, de-AT, en");
        settings.update_env_lang_detection();

        assert!(matches!(
            settings.filter_get_lang,
            FilterGetLang::AllLanguages
        ));
        let output_filter_map_lang = settings.filter_map_lang_btmap.unwrap();
        assert_eq!(output_filter_map_lang.get("de").unwrap(), "de-DE");
        assert_eq!(output_filter_map_lang.get("en").unwrap(), "en-GB");

        //
        // Test empty env. var.
        let mut settings = Settings {
            lang: "".to_string(),
            ..Default::default()
        };
        env::set_var(ENV_VAR_TPNOTE_LANG_DETECTION, "");
        settings.update_env_lang_detection();

        assert!(matches!(settings.filter_get_lang, FilterGetLang::Disabled));
        assert!(settings.filter_map_lang_btmap.is_none());

        //
        // Test faulty `settings.lang`.
        let mut settings = Settings {
            lang: "xy-XY".to_string(),
            ..Default::default()
        };
        env::set_var(ENV_VAR_TPNOTE_LANG_DETECTION, "en-GB, fr");
        settings.update_env_lang_detection();

        if let FilterGetLang::SomeLanguages(ofgl) = settings.filter_get_lang {
            let output_filter_get_lang = ofgl
                .iter()
                .map(|l| {
                    let mut l = l.to_string();
                    l.push(' ');
                    l
                })
                .collect::<String>();
            assert_eq!(output_filter_get_lang, "en fr ");
        } else {
            panic!("Wrong variant: {:?}", settings.filter_get_lang);
        }
        let output_filter_map_lang = settings.filter_map_lang_btmap.unwrap();
        assert_eq!(output_filter_map_lang.get("en").unwrap(), "en-GB");

        //
        // Test faulty entry in list.
        let mut settings = Settings {
            lang: "en-GB".to_string(),
            ..Default::default()
        };
        env::set_var(ENV_VAR_TPNOTE_LANG_DETECTION, "de-DE, xy-XY");
        settings.update_env_lang_detection();

        assert!(matches!(settings.filter_get_lang, FilterGetLang::Error(..)));
        assert!(settings.filter_map_lang_btmap.is_none());
        //
        // Test empty list.
        let mut settings = Settings {
            lang: "en-GB".to_string(),
            ..Default::default()
        };
        env::set_var(ENV_VAR_TPNOTE_LANG_DETECTION, "");
        settings.update_env_lang_detection();

        assert!(matches!(settings.filter_get_lang, FilterGetLang::Disabled));
        assert!(settings.filter_map_lang_btmap.is_none());
    }
}