fix: correct flag emoji for ISO alpha-3 region code (#5557)

* fix: correct flag emoji for ISO alpha-3 region code

* fix: use rust_iso3166 to convert ISO3 region code

* fix: validate ISO country code when generating flag emoji

* fix: correct icon encoding for unlock test in specific regions

---------

Co-authored-by: Tunglies <77394545+Tunglies@users.noreply.github.com>

src-tauri/src/cmd/media_unlock_checker/utils.rs

@@ -1,4 +1,5 @@
 use chrono::Local;
+use rust_iso3166;
 
 pub fn get_local_date_string() -> String {
     let now = Local::now();
@@ -6,16 +7,70 @@ pub fn get_local_date_string() -> String {
 }
 
 pub fn country_code_to_emoji(country_code: &str) -> String {
-    let country_code = country_code.to_uppercase();
-    if country_code.len() < 2 {
-        return String::new();
-    }
+    let uc = country_code.to_ascii_uppercase();
 
-    let bytes = country_code.as_bytes();
+    // 长度校验：仅允许 2 或 3
+    match uc.len() {
+        2 => {
+            // 校验是否是合法 alpha2
+            if rust_iso3166::from_alpha2(&uc).is_none() {
+                return String::new();
+            }
+            alpha2_to_emoji(&uc)
+        }
+        3 => {
+            // 转换并校验 alpha3
+            match rust_iso3166::from_alpha3(&uc) {
+                Some(c) => {
+                    let alpha2 = c.alpha2.to_ascii_uppercase();
+                    alpha2_to_emoji(&alpha2)
+                }
+                None => String::new(),
+            }
+        }
+        _ => String::new(),
+    }
+}
+
+fn alpha2_to_emoji(alpha2: &str) -> String {
+    let bytes = alpha2.as_bytes();
     let c1 = 0x1F1E6 + (bytes[0] as u32) - ('A' as u32);
     let c2 = 0x1F1E6 + (bytes[1] as u32) - ('A' as u32);
-
     char::from_u32(c1)
-        .and_then(|c1| char::from_u32(c2).map(|c2| format!("{c1}{c2}")))
+        .and_then(|x| char::from_u32(c2).map(|y| format!("{x}{y}")))
         .unwrap_or_default()
 }
+
+#[cfg(test)]
+mod tests {
+    use super::country_code_to_emoji;
+
+    #[test]
+    fn country_code_to_emoji_iso2() {
+        assert_eq!(country_code_to_emoji("CN"), "🇨🇳");
+        assert_eq!(country_code_to_emoji("us"), "🇺🇸");
+    }
+
+    #[test]
+    fn country_code_to_emoji_iso3() {
+        assert_eq!(country_code_to_emoji("CHN"), "🇨🇳");
+        assert_eq!(country_code_to_emoji("USA"), "🇺🇸");
+    }
+
+    #[test]
+    fn country_code_to_emoji_invalid() {
+        assert_eq!(country_code_to_emoji("XXX"), "");
+        assert_eq!(country_code_to_emoji("ZZ"), "");
+    }
+
+    #[test]
+    fn country_code_to_emoji_short() {
+        assert_eq!(country_code_to_emoji("C"), "");
+        assert_eq!(country_code_to_emoji(""), "");
+    }
+
+    #[test]
+    fn country_code_to_emoji_long() {
+        assert_eq!(country_code_to_emoji("CNAAA"), "");
+    }
+}