Use hex values in languages.yaml

build.rs

@@ -11,6 +11,7 @@ fn main() -> Result<(), Box<dyn Error>> {
     let out_dir = env::var("OUT_DIR").unwrap();
     let mut tera = Tera::new("src/**/*.tera.rs")?;
     tera.register_filter("strip_color_indices", strip_color_indices);
+    tera.register_filter("hextorgb", hex_to_rgb);
 
     let lang_data: serde_json::Value = serde_yaml::from_reader(File::open("languages.yaml")?)?;
     let context = Context::from_value(serde_json::json!({
@@ -41,3 +42,34 @@ fn strip_color_indices(
         COLOR_INDEX_REGEX.replace_all(s, "").to_string(),
     ));
 }
+
+/// Converts a hex string to an object with keys `r`, `g`, `b`.
+fn hex_to_rgb(
+    value: &tera::Value,
+    _args: &HashMap<String, tera::Value>,
+) -> tera::Result<tera::Value> {
+    let hex_string = match value {
+        tera::Value::String(s) => s,
+        _ => return Err(tera::Error::msg("expected string")),
+    };
+    let hex_string = match hex_string.strip_prefix("#") {
+        Some(s) => s,
+        None => return Err(tera::Error::msg("expected hex string starting with `#`")),
+    };
+    if hex_string.len() != 6 {
+        return Err(tera::Error::msg("expected a 6 digit hex string"));
+    }
+    let channel_bytes = match u32::from_str_radix(&hex_string, 16) {
+        Ok(n) => n,
+        Err(_) => return Err(tera::Error::msg("expected a valid hex string")),
+    };
+    let r = (channel_bytes >> 16) & 0xFF;
+    let g = (channel_bytes >> 8) & 0xFF;
+    let b = channel_bytes & 0xFF;
+
+    Ok(serde_json::json!({
+        "r": r,
+        "g": g,
+        "b": b,
+    }))
+}