Add LibreTranslate integration for machine translating notes from other languages

damus/Models/LibreTranslateServer.swift

@@ -0,0 +1,44 @@
+//
+//  LibreTranslateServer.swift
+//  damus
+//
+//  Created by Terry Yiu on 1/21/23.
+//
+
+import Foundation
+
+enum LibreTranslateServer: String, CaseIterable, Identifiable {
+    var id: String { self.rawValue }
+
+    struct Model: Identifiable, Hashable {
+        var id: String { self.tag }
+        var tag: String
+        var displayName: String
+        var url: String?
+    }
+
+    case none
+    case argosopentech
+    case terraprint
+    case vern
+    case custom
+
+    var model: Model {
+        switch self {
+        case .none:
+            return .init(tag: self.rawValue, displayName: NSLocalizedString("None", comment: "Dropdown option for selecting no translation server."), url: nil)
+        case .argosopentech:
+            return .init(tag: self.rawValue, displayName: "translate.argosopentech.com", url: "https://translate.argosopentech.com")
+        case .terraprint:
+            return .init(tag: self.rawValue, displayName: "translate.terraprint.co", url: "https://translate.terraprint.co")
+        case .vern:
+            return .init(tag: self.rawValue, displayName: "lt.vern.cc", url: "https://lt.vern.cc")
+        case .custom:
+            return .init(tag: self.rawValue, displayName: NSLocalizedString("Custom", comment: "Dropdown option for selecting a custom translation server."), url: nil)
+        }
+    }
+
+    static var allModels: [Model] {
+        return Self.allCases.map { $0.model }
+    }
+}

damus/Models/UserSettingsStore.swift

@@ -6,6 +6,7 @@
 //
 
 import Foundation
+import Vault
 
 class UserSettingsStore: ObservableObject {
     @Published var default_wallet: Wallet {
@@ -26,6 +27,44 @@ class UserSettingsStore: ObservableObject {
         }
     }
 
+    @Published var libretranslate_server: LibreTranslateServer {
+        didSet {
+            if oldValue == libretranslate_server {
+                return
+            }
+
+            UserDefaults.standard.set(libretranslate_server.rawValue, forKey: "libretranslate_server")
+
+            libretranslate_api_key = ""
+
+            if libretranslate_server == .custom || libretranslate_server == .none {
+                libretranslate_url = ""
+            } else {
+                libretranslate_url = libretranslate_server.model.url!
+            }
+        }
+    }
+
+    @Published var libretranslate_url: String {
+        didSet {
+            UserDefaults.standard.set(libretranslate_url, forKey: "libretranslate_url")
+        }
+    }
+
+    @Published var libretranslate_api_key: String {
+        didSet {
+            do {
+                if libretranslate_api_key == "" {
+                    try clearLibreTranslateApiKey()
+                } else {
+                    try saveLibreTranslateApiKey(libretranslate_api_key)
+                }
+            } catch {
+                // No-op.
+            }
+        }
+    }
+
     init() {
         if let defaultWalletName = UserDefaults.standard.string(forKey: "default_wallet"),
            let default_wallet = Wallet(rawValue: defaultWalletName)
@@ -37,5 +76,40 @@ class UserSettingsStore: ObservableObject {
         show_wallet_selector = UserDefaults.standard.object(forKey: "show_wallet_selector") as? Bool ?? true
 
         left_handed = UserDefaults.standard.object(forKey: "left_handed") as? Bool ?? false
+
+        if let translationServerName = UserDefaults.standard.string(forKey: "libretranslate_server"),
+           let translationServer = LibreTranslateServer(rawValue: translationServerName) {
+            self.libretranslate_server = translationServer
+            libretranslate_url = translationServer.model.url ?? UserDefaults.standard.object(forKey: "libretranslate_url") as? String ?? ""
+        } else {
+            // Note from @tyiu:
+            // Default server is disabled by default for now until we gain some confidence that it is working well in production.
+            // Instead of throwing all Damus users onto feature immediately, allow for discovery of feature organically.
+            // Also, we are connecting to servers listed as mirrors on the official LibreTranslate GitHub README that do not require API keys.
+            // However, we have not asked them for permission to use, so we're trying to be good neighbors for now.
+            // Opportunity: spin up dedicated trusted LibreTranslate server that requires an API key for any access (or higher rate limit access).
+            libretranslate_server = .none
+            libretranslate_url = ""
+        }
+
+        do {
+            libretranslate_api_key = try Vault.getPrivateKey(keychainConfiguration: DamusLibreTranslateKeychainConfiguration())
+        } catch {
+            libretranslate_api_key = ""
+        }
+    }
+
+    func saveLibreTranslateApiKey(_ apiKey: String) throws {
+        try Vault.savePrivateKey(apiKey, keychainConfiguration: DamusLibreTranslateKeychainConfiguration())
+    }
+
+    func clearLibreTranslateApiKey() throws {
+        try Vault.deletePrivateKey(keychainConfiguration: DamusLibreTranslateKeychainConfiguration())
     }
 }
+
+struct DamusLibreTranslateKeychainConfiguration: KeychainConfiguration {
+    var serviceName = "damus"
+    var accessGroup: String? = nil
+    var accountName = "libretranslate_apikey"
+}