feat: multiple-CSV import

src/import/csv_parser.rs

@@ -56,6 +56,28 @@ pub fn parse_csv(path: &Path) -> Result<Vec<Value>> {
     Ok(records)
 }
 
+/// Parse multiple CSV files and merge into a single JSON array.
+/// Each record gets a "File" field set to the filename stem (e.g., "sales" from "sales.csv").
+pub fn merge_csvs(paths: &[impl AsRef<Path>]) -> Result<Vec<Value>> {
+    let mut all_records = Vec::new();
+    for path in paths {
+        let path = path.as_ref();
+        let stem = path
+            .file_stem()
+            .and_then(|s| s.to_str())
+            .unwrap_or("unknown")
+            .to_string();
+        let records = parse_csv(path)?;
+        for mut record in records {
+            if let Value::Object(ref mut map) = record {
+                map.insert("File".to_string(), Value::String(stem.clone()));
+            }
+            all_records.push(record);
+        }
+    }
+    Ok(all_records)
+}
+
 fn parse_csv_field(field: &str) -> Value {
     if field.is_empty() {
         return Value::Null;
@@ -158,6 +180,40 @@ mod tests {
         assert_eq!(records[0]["Active"], Value::String("true".to_string()));
     }
 
+    #[test]
+    fn merge_csvs_adds_file_field_from_stem() {
+        let dir = tempdir().unwrap();
+        let sales = dir.path().join("sales.csv");
+        let expenses = dir.path().join("expenses.csv");
+        fs::write(&sales, "Region,Revenue\nEast,100\nWest,200").unwrap();
+        fs::write(&expenses, "Region,Revenue\nEast,50\nWest,75").unwrap();
+
+        let records = merge_csvs(&[sales, expenses]).unwrap();
+        assert_eq!(records.len(), 4);
+        assert_eq!(records[0]["File"], Value::String("sales".to_string()));
+        assert_eq!(records[1]["File"], Value::String("sales".to_string()));
+        assert_eq!(records[2]["File"], Value::String("expenses".to_string()));
+        assert_eq!(records[3]["File"], Value::String("expenses".to_string()));
+        // Original fields preserved
+        assert_eq!(records[0]["Region"], Value::String("East".to_string()));
+        assert_eq!(
+            records[2]["Revenue"],
+            Value::Number(serde_json::Number::from(50))
+        );
+    }
+
+    #[test]
+    fn merge_csvs_single_file_works() {
+        let dir = tempdir().unwrap();
+        let path = dir.path().join("data.csv");
+        fs::write(&path, "Name,Value\nA,1").unwrap();
+
+        let records = merge_csvs(&[path]).unwrap();
+        assert_eq!(records.len(), 1);
+        assert_eq!(records[0]["File"], Value::String("data".to_string()));
+        assert_eq!(records[0]["Name"], Value::String("A".to_string()));
+    }
+
     #[test]
     fn parse_checking_csv_format() {
         // Simulates the format of /Users/edwlan/Downloads/Checking1.csv