Add support for Android plurals in strings.xml format

Implements parsing, serialization, and conversion of <plurals> elements in Android strings.xml files. Updates the Format struct to include plurals, adds conversion logic between internal Resource and Android format for plurals, and provides comprehensive tests for plural handling and round-trip conversions.

Author: WendellXY

langcodec/src/converter.rs

@@ -606,3 +606,100 @@ pub fn merge_resources(
 
     Ok(merged)
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::types::{Entry, EntryStatus, Metadata, Plural, PluralCategory, Translation};
+    use std::collections::{BTreeMap, HashMap};
+
+    #[test]
+    fn test_convert_csv_to_android_strings_en() {
+        let tmp = tempfile::tempdir().unwrap();
+        let input = tmp.path().join("in.csv");
+        let output = tmp.path().join("strings.xml");
+
+        // CSV with header and two rows
+        std::fs::write(
+            &input,
+            "key,en,fr\nhello,Hello,Bonjour\nbye,Goodbye,Au revoir\n",
+        )
+        .unwrap();
+
+        convert(&input, FormatType::CSV, &output, FormatType::AndroidStrings(Some("en".into())))
+            .unwrap();
+
+        // Read back as Android to verify
+        let android = crate::formats::AndroidStringsFormat::read_from(&output).unwrap();
+        // ensure we have only strings for the selected language
+        assert_eq!(android.strings.len(), 2);
+        let mut names: Vec<&str> = android.strings.iter().map(|s| s.name.as_str()).collect();
+        names.sort();
+        assert_eq!(names, vec!["bye", "hello"]);
+        let hello = android.strings.iter().find(|s| s.name == "hello").unwrap();
+        assert_eq!(hello.value, "Hello");
+        let bye = android.strings.iter().find(|s| s.name == "bye").unwrap();
+        assert_eq!(bye.value, "Goodbye");
+    }
+
+    #[test]
+    fn test_convert_xcstrings_plurals_to_android() {
+        let tmp = tempfile::tempdir().unwrap();
+        let input = tmp.path().join("in.xcstrings");
+        let output = tmp.path().join("strings.xml");
+
+        // Build a Resource with a plural entry for English
+        let mut custom = HashMap::new();
+        custom.insert("source_language".into(), "en".into());
+        custom.insert("version".into(), "1.0".into());
+
+        let mut forms = BTreeMap::new();
+        forms.insert(PluralCategory::One, "One apple".to_string());
+        forms.insert(PluralCategory::Other, "%d apples".to_string());
+
+        let res = Resource {
+            metadata: Metadata {
+                language: "en".into(),
+                domain: "domain".into(),
+                custom,
+            },
+            entries: vec![Entry {
+                id: "apples".into(),
+                value: Translation::Plural(Plural { id: "apples".into(), forms }),
+                comment: Some("Count apples".into()),
+                status: EntryStatus::Translated,
+                custom: HashMap::new(),
+            }],
+        };
+
+        // Write XCStrings input
+        let xc = crate::formats::XcstringsFormat::try_from(vec![res]).unwrap();
+        xc.write_to(&input).unwrap();
+
+        // Convert to Android (English)
+        convert(&input, FormatType::Xcstrings, &output, FormatType::AndroidStrings(Some("en".into())))
+            .unwrap();
+
+        // Read back as Android
+        let android = crate::formats::AndroidStringsFormat::read_from(&output).unwrap();
+        assert_eq!(android.plurals.len(), 1);
+        let p = &android.plurals[0];
+        assert_eq!(p.name, "apples");
+        // Should include at least 'one' and 'other'
+        let mut qs: Vec<_> = p
+            .items
+            .iter()
+            .map(|i| match i.quantity {
+                PluralCategory::One => ("one", i.value.clone()),
+                PluralCategory::Other => ("other", i.value.clone()),
+                PluralCategory::Zero => ("zero", i.value.clone()),
+                PluralCategory::Two => ("two", i.value.clone()),
+                PluralCategory::Few => ("few", i.value.clone()),
+                PluralCategory::Many => ("many", i.value.clone()),
+            })
+            .collect();
+        qs.sort_by(|a, b| a.0.cmp(&b.0));
+        assert!(qs.iter().any(|(q, v)| *q == "one" && v == "One apple"));
+        assert!(qs.iter().any(|(q, v)| *q == "other" && v == "%d apples"));
+    }
+}