Refactor auto-translations and add caching

Changelog-Added: Add auto-translation caching to ruduce api usage
Closes: #843

damus/Util/Translator.swift

@@ -20,18 +20,18 @@ public struct Translator {
         self.userSettingsStore = userSettingsStore
     }
 
-    public func translate(_ text: String, from sourceLanguage: String, to targetLanguage: String) async throws -> String? {
+    public func translate(_ text: String, from sourceLanguage: String, to targetLanguage: String) async throws -> TranslationWithLanguage? {
         switch userSettingsStore.translation_service {
         case .libretranslate:
             return try await translateWithLibreTranslate(text, from: sourceLanguage, to: targetLanguage)
         case .deepl:
             return try await translateWithDeepL(text, from: sourceLanguage, to: targetLanguage)
         case .none:
-            return text
+            return nil
         }
     }
 
-    private func translateWithLibreTranslate(_ text: String, from sourceLanguage: String, to targetLanguage: String) async throws -> String? {
+    private func translateWithLibreTranslate(_ text: String, from sourceLanguage: String, to targetLanguage: String) async throws -> TranslationWithLanguage? {
         let url = try makeURL(userSettingsStore.libretranslate_url, path: "/translate")
 
         var request = URLRequest(url: url)
@@ -51,10 +51,12 @@ public struct Translator {
             let translatedText: String
         }
         let response: Response = try await decodedData(for: request)
-        return response.translatedText
+        let translation = response.translatedText
+
+        return TranslationWithLanguage(translation: translation, language: targetLanguage)
     }
 
-    private func translateWithDeepL(_ text: String, from sourceLanguage: String, to targetLanguage: String) async throws -> String? {
+    private func translateWithDeepL(_ text: String, from sourceLanguage: String, to targetLanguage: String) async throws -> TranslationWithLanguage? {
         if userSettingsStore.deepl_api_key == "" {
             return nil
         }
@@ -68,10 +70,9 @@ public struct Translator {
 
         struct RequestBody: Encodable {
             let text: [String]
-            let source_lang: String
             let target_lang: String
         }
-        let body = RequestBody(text: [text], source_lang: sourceLanguage.uppercased(), target_lang: targetLanguage.uppercased())
+        let body = RequestBody(text: [text], target_lang: targetLanguage.uppercased())
         request.httpBody = try encoder.encode(body)
 
         struct Response: Decodable {
@@ -83,7 +84,13 @@ public struct Translator {
         }
 
         let response: Response = try await decodedData(for: request)
-        return response.translations.map { $0.text }.joined(separator: " ")
+
+        if response.translations.isEmpty {
+            return nil
+        }
+
+        let translation = response.translations.map { $0.text }.joined(separator: " ")
+        return TranslationWithLanguage(translation: translation, language: response.translations.first!.detected_source_language)
     }
 
     private func makeURL(_ baseUrl: String, path: String) throws -> URL {
@@ -104,6 +111,11 @@ public struct Translator {
     }
 }
 
+public struct TranslationWithLanguage {
+    let translation: String
+    let language: String
+}
+
 private extension URLSession {
     func data(for request: URLRequest) async throws -> Data {
         var task: URLSessionDataTask?