control units from LC_ALL with config fallback

README.md

@@ -39,6 +39,43 @@ killall cosmic-panel
 
 The panel will relaunch automatically and load the updated applet.
 
+## Configuration
+
+### Temperature and wind units
+
+By default, the applet lets [wttr.in](https://wttr.in) pick units based on
+your IP-based location (so users in the US get Fahrenheit, everyone else
+gets Celsius).
+
+At startup the applet additionally inspects your measurement locale
+(`LC_MEASUREMENT`, then `LC_ALL`, then `LANG`). Locales in the US,
+Liberia, the Bahamas, Belize, the Cayman Islands, and Palau are requested
+as Fahrenheit / USCS; all other locales fall through to the wttr.in
+default.
+
+To override the choice explicitly, set `COSMIC_WEATHER_UNITS`:
+
+| Value  | Meaning                                   |
+| ------ | ----------------------------------------- |
+| `u`    | Fahrenheit, mph (USCS)                    |
+| `m`    | Celsius, km/h (metric)                    |
+| `M`    | Celsius, m/s                              |
+| `auto` | (or unset) Use locale / geolocation       |
+
+Because the applet is launched by `cosmic-panel`, a persistent override
+is easiest to set on that service, e.g.:
+
+```sh
+systemctl --user edit cosmic-panel
+# In the override file:
+# [Service]
+# Environment=COSMIC_WEATHER_UNITS=u
+
+systemctl --user restart cosmic-panel
+```
+
+Changes take effect after the applet is restarted.
+
 ## Localization
 
 [Fluent](https://projectfluent.org/) is used for localization. Translation files are in the [i18n directory](./i18n). To add a new language, copy the [English (en) localization](./i18n/en), rename the directory to the target [ISO 639-1 language code](https://en.wikipedia.org/wiki/List_of_ISO_639-1_codes), and translate the message values.

src/app.rs

@@ -12,6 +12,8 @@ use cosmic::iced_core::Shadow;
 use futures_util::{SinkExt, StreamExt};
 use std::time::Duration;
 
+use crate::config::Units;
+
 const WTTR_URL: &str = "https://wttr.lerch.org";
 const WEATHER_UPDATE_INTERVAL_MINUTES: u64 = 15;
 const REQUEST_TIMEOUT_SECS: u64 = 15;
@@ -59,6 +61,8 @@ pub struct AppModel {
     rectangle_tracker: Option<RectangleTracker<u32>>,
     /// Number of consecutive fetch retries (for captive portal / network issues)
     retry_count: u32,
+    /// Unit system to request from wttr.in (None = let the service geolocate).
+    units: Option<Units>,
 }
 
 /// Messages emitted by the applet.
@@ -76,7 +80,7 @@ pub enum Message {
 
 impl cosmic::Application for AppModel {
     type Executor = cosmic::executor::Default;
-    type Flags = ();
+    type Flags = Option<Units>;
     type Message = Message;
     const APP_ID: &'static str = "org.lerch.weather";
 
@@ -90,7 +94,7 @@ impl cosmic::Application for AppModel {
 
     fn init(
         core: cosmic::Core,
-        _flags: Self::Flags,
+        flags: Self::Flags,
     ) -> (Self, Task<cosmic::Action<Self::Message>>) {
         let app = AppModel {
             core,
@@ -103,9 +107,11 @@ impl cosmic::Application for AppModel {
             rectangle: Rectangle::default(),
             rectangle_tracker: None,
             retry_count: 0,
+            units: flags,
         };
 
-        let command = Task::perform(fetch_weather(), |result| {
+        let units = app.units;
+        let command = Task::perform(fetch_weather(units), |result| {
             cosmic::Action::App(Message::WeatherUpdate(result))
         });
 
@@ -328,8 +334,9 @@ impl cosmic::Application for AppModel {
                                 "Scheduling retry {}/{MAX_RETRIES} in {delay}s",
                                 self.retry_count
                             );
+                            let units = self.units;
                             return Task::perform(
-                                fetch_weather_delayed(delay),
+                                fetch_weather_delayed(delay, units),
                                 |result| cosmic::Action::App(Message::WeatherUpdate(result)),
                             );
                         }
@@ -354,7 +361,8 @@ impl cosmic::Application for AppModel {
             }
             Message::RefreshWeather => {
                 self.retry_count = 0;
-                Task::perform(fetch_weather(), |result| {
+                let units = self.units;
+                Task::perform(fetch_weather(units), |result| {
                     cosmic::Action::App(Message::WeatherUpdate(result))
                 })
             }
@@ -363,7 +371,8 @@ impl cosmic::Application for AppModel {
                 self.retry_count = 0;
                 // Clear cached full weather so the popup re-fetches on next open
                 self.full_weather.clear();
-                Task::perform(fetch_weather(), |result| {
+                let units = self.units;
+                Task::perform(fetch_weather(units), |result| {
                     cosmic::Action::App(Message::WeatherUpdate(result))
                 })
             }
@@ -445,7 +454,8 @@ impl AppModel {
             .max_height(1080.0);
 
         if self.full_weather.is_empty() {
-            let fetch_task = Task::perform(fetch_full_weather(), |result| {
+            let units = self.units;
+            let fetch_task = Task::perform(fetch_full_weather(units), |result| {
                 cosmic::Action::App(Message::FullWeatherUpdate(result))
             });
             Task::batch([get_popup(popup_settings), fetch_task])
@@ -455,14 +465,17 @@ impl AppModel {
     }
 }
 
-async fn fetch_weather() -> Result<(String, String), String> {
+async fn fetch_weather(units: Option<Units>) -> Result<(String, String), String> {
     let client = reqwest::Client::builder()
         .timeout(Duration::from_secs(REQUEST_TIMEOUT_SECS))
         .build()
         .map_err(|e| e.to_string())?;
 
     let response = client
-        .get(format!("{WTTR_URL}/?format=%l|%c|%t"))
+        .get(format!(
+            "{WTTR_URL}/?format=%l|%c|%t{suffix}",
+            suffix = units_suffix(units)
+        ))
         .send()
         .await
         .map_err(|e| e.to_string())?;
@@ -501,14 +514,14 @@ fn format_current_time() -> String {
         .unwrap_or_default()
 }
 
-async fn fetch_full_weather() -> Result<String, String> {
+async fn fetch_full_weather(units: Option<Units>) -> Result<String, String> {
     let client = reqwest::Client::builder()
         .timeout(Duration::from_secs(REQUEST_TIMEOUT_SECS))
         .build()
         .map_err(|e| e.to_string())?;
 
     let response = client
-        .get(format!("{WTTR_URL}?A&T"))
+        .get(format!("{WTTR_URL}?A&T{suffix}", suffix = units_suffix(units)))
         .send()
         .await
         .map_err(|e| e.to_string())?;
@@ -538,7 +551,19 @@ fn retry_delay(retry_count: u32) -> u64 {
 }
 
 /// Fetch weather after waiting `delay_secs`, used for retry backoff.
-async fn fetch_weather_delayed(delay_secs: u64) -> Result<(String, String), String> {
+async fn fetch_weather_delayed(
+    delay_secs: u64,
+    units: Option<Units>,
+) -> Result<(String, String), String> {
     tokio::time::sleep(Duration::from_secs(delay_secs)).await;
-    fetch_weather().await
+    fetch_weather(units).await
+}
+
+/// Build the URL suffix that selects a unit system on wttr.in.
+/// Returns an empty string when no explicit choice has been made.
+fn units_suffix(units: Option<Units>) -> String {
+    match units {
+        Some(u) => format!("&{}", u.query_param()),
+        None => String::new(),
+    }
 }

src/config.rs

@@ -1,3 +1,147 @@
 // SPDX-License-Identifier: MIT
 
-// Config module placeholder - currently unused
+//! Runtime configuration for the applet.
+//!
+//! Currently only handles temperature/wind unit selection for wttr.in.
+//! Units are resolved once at startup from (in order):
+//!   1. The `COSMIC_WEATHER_UNITS` environment variable
+//!      (values: `u`, `m`, `M`, or `auto`/empty to fall through).
+//!   2. The user's measurement locale (`LC_MEASUREMENT`, then `LC_ALL`,
+//!      then `LANG`). Fahrenheit-using locales map to `Uscs`; everything
+//!      else falls through.
+//!   3. `None`, which leaves the choice to wttr.in's IP-based geolocation
+//!      (the previous behavior).
+
+/// Unit system to request from wttr.in.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum Units {
+    /// Celsius, km/h. Corresponds to wttr.in's `m` flag.
+    Metric,
+    /// Celsius, m/s. Corresponds to wttr.in's `M` flag.
+    MetricMs,
+    /// Fahrenheit, mph. Corresponds to wttr.in's `u` flag.
+    Uscs,
+}
+
+impl Units {
+    /// Single-letter flag understood by wttr.in (e.g. appended as `&u`).
+    pub const fn query_param(self) -> &'static str {
+        match self {
+            Self::Metric => "m",
+            Self::MetricMs => "M",
+            Self::Uscs => "u",
+        }
+    }
+}
+
+/// Locales whose measurement convention is Fahrenheit / USCS.
+/// Source: CLDR measurement-system data (US, Liberia, Bahamas, Belize,
+/// Cayman Islands, Palau).
+const USCS_LOCALES: &[&str] = &["en_US", "en_LR", "en_BS", "en_BZ", "en_KY", "en_PW"];
+
+/// Resolve the units to request at applet startup.
+///
+/// Returns `None` when neither the env var nor the locale gives a
+/// definitive answer, in which case wttr.in decides based on the
+/// client's geolocation.
+#[must_use]
+pub fn resolve_units() -> Option<Units> {
+    if let Some(u) = units_from_env() {
+        return u;
+    }
+    units_from_locale()
+}
+
+/// Parse `COSMIC_WEATHER_UNITS`.
+///
+/// Returns:
+/// - `Some(Some(units))` — explicit override.
+/// - `Some(None)` — explicit `auto` or empty; caller should still return
+///   `None` overall (skip locale detection? No — we want `auto` to mean
+///   "fall through to locale", so this returns `None` to signal fall-through).
+/// - `None` — env var unset; fall through.
+///
+/// To keep the control flow simple we collapse all fall-through cases to
+/// a single `None` return and only return `Some(Some(_))` for an explicit
+/// unit choice.
+fn units_from_env() -> Option<Option<Units>> {
+    let raw = std::env::var("COSMIC_WEATHER_UNITS").ok()?;
+    let trimmed = raw.trim();
+    if trimmed.is_empty() || trimmed.eq_ignore_ascii_case("auto") {
+        return None;
+    }
+    let parsed = match trimmed {
+        "u" | "U" => Some(Units::Uscs),
+        "m" => Some(Units::Metric),
+        "M" => Some(Units::MetricMs),
+        other => {
+            eprintln!(
+                "COSMIC_WEATHER_UNITS={other:?} is not recognized; \
+                 expected one of: u, m, M, auto"
+            );
+            return None;
+        }
+    };
+    Some(parsed)
+}
+
+/// Inspect measurement-related locale env vars and map to `Units`.
+fn units_from_locale() -> Option<Units> {
+    for var in ["LC_MEASUREMENT", "LC_ALL", "LANG"] {
+        if let Ok(val) = std::env::var(var) {
+            if let Some(units) = classify_locale(&val) {
+                return Some(units);
+            }
+        }
+    }
+    None
+}
+
+/// Strip codeset (`.UTF-8`) and modifier (`@euro`) and check the
+/// language_TERRITORY prefix against the USCS list.
+fn classify_locale(value: &str) -> Option<Units> {
+    let trimmed = value.trim();
+    if trimmed.is_empty() || trimmed == "C" || trimmed == "POSIX" {
+        return None;
+    }
+    let without_codeset = trimmed.split('.').next().unwrap_or(trimmed);
+    let without_modifier = without_codeset.split('@').next().unwrap_or(without_codeset);
+    if USCS_LOCALES
+        .iter()
+        .any(|l| l.eq_ignore_ascii_case(without_modifier))
+    {
+        Some(Units::Uscs)
+    } else {
+        None
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn query_params() {
+        assert_eq!(Units::Metric.query_param(), "m");
+        assert_eq!(Units::MetricMs.query_param(), "M");
+        assert_eq!(Units::Uscs.query_param(), "u");
+    }
+
+    #[test]
+    fn classify_known_uscs_locales() {
+        assert_eq!(classify_locale("en_US.UTF-8"), Some(Units::Uscs));
+        assert_eq!(classify_locale("en_US"), Some(Units::Uscs));
+        assert_eq!(classify_locale("en_LR.UTF-8"), Some(Units::Uscs));
+        assert_eq!(classify_locale("en_BZ@something"), Some(Units::Uscs));
+    }
+
+    #[test]
+    fn classify_non_uscs_locales() {
+        assert_eq!(classify_locale("fi_FI.UTF-8"), None);
+        assert_eq!(classify_locale("en_GB.UTF-8"), None);
+        assert_eq!(classify_locale("de_DE"), None);
+        assert_eq!(classify_locale("C"), None);
+        assert_eq!(classify_locale("POSIX"), None);
+        assert_eq!(classify_locale(""), None);
+    }
+}

src/main.rs

@@ -11,6 +11,15 @@ fn main() -> cosmic::iced::Result {
     // Enable localizations to be applied.
     i18n::init(&requested_languages);
 
-    // Starts the applet's event loop with `()` as the application's flags.
-    cosmic::applet::run::<app::AppModel>(())
+    // Resolve unit preference once at startup. This checks the
+    // COSMIC_WEATHER_UNITS env var first, then measurement locale vars,
+    // falling back to `None` (let wttr.in decide by IP).
+    let units = config::resolve_units();
+    match units {
+        Some(u) => eprintln!("Weather units resolved to {u:?} (wttr.in flag: {})", u.query_param()),
+        None => eprintln!("Weather units not explicitly set; deferring to wttr.in geolocation"),
+    }
+
+    // Starts the applet's event loop, passing the resolved units as flags.
+    cosmic::applet::run::<app::AppModel>(units)
 }