feat(korea): add KoreanStockID helpers for kr_<code>.ks/kq ↔ Yahoo symbol

StockMonitor/Utils/KoreanStockID.swift

@@ -0,0 +1,32 @@
+import Foundation
+
+/// Helpers for converting between Stockbar's internal Korean stock ID
+/// (`kr_<6digit>.ks` for KOSPI, `kr_<6digit>.kq` for KOSDAQ) and Yahoo
+/// Finance symbol (`005930.KS`, `293490.KQ`).
+enum KoreanStockID {
+
+    /// Stockbar-internal ID prefix for Korean stocks.
+    static let prefix = "kr_"
+
+    /// Returns true if `id` looks like a Korean stock ID. Case-insensitive on the prefix.
+    static func isKorean(_ id: String) -> Bool {
+        let lower = id.lowercased()
+        guard lower.hasPrefix(prefix) else { return false }
+        return lower.count > prefix.count
+    }
+
+    /// Convert internal ID → Yahoo symbol. Returns nil for non-Korean IDs.
+    /// e.g. `kr_005930.ks` → `005930.KS`
+    static func toYahooSymbol(_ id: String) -> String? {
+        guard isKorean(id) else { return nil }
+        let lower = id.lowercased()
+        let suffix = String(lower.dropFirst(prefix.count))
+        return suffix.uppercased()
+    }
+
+    /// Convert Yahoo symbol → internal ID. Always succeeds.
+    /// e.g. `005930.KS` → `kr_005930.ks`
+    static func fromYahooSymbol(_ symbol: String) -> String {
+        return prefix + symbol.lowercased()
+    }
+}