Add ping-type message logic

Author: backslash-f

Sources/ObservableWebSocketClient/Interface/ObservableWebSocketClient.swift

@@ -25,6 +25,11 @@ public final class ObservableWebSocketClient: Identifiable, Equatable, Codable,
 
     public let websocketURL: URL
 
+    private var pingTimer: Timer?
+    private let pingTimerInterval: TimeInterval?
+    private let pingMessage: String?
+    private let pingMessageWithGeneratedId: ((String) -> String)?
+
     private(set) var service: ObservableWebSocketService
 
     var cancellables = Set<AnyCancellable>()
@@ -34,23 +39,77 @@ public final class ObservableWebSocketClient: Identifiable, Equatable, Codable,
     /// Creates an `ObservableWebSocketClient` instance.
     ///
     /// - Parameters:
+    ///   - id: Optional unique ID of the instance. If absent, an instance of `UUID` will be used instead.
     ///   - websocketURL: The WebSocket `URL` to connect to, starting with `wss`.
-    ///   E.g., `wss://endpoint.com`
-    public convenience init(websocketURL: URL) {
-        self.init(websocketURL: websocketURL,
-                  message: nil,
-                  error: nil)
-    }
-
+    ///   For example:
+    ///      ```
+    ///      wss://endpoint.com
+    ///      ```
+    ///   - message: Optional `CodableWebSocketMessage`. Useful for mocking the instance's state.
+    ///   - error: Optional `ObservableWebSocketClientError`. Useful for mocking the instance's state.
+    ///   - pingTimerInterval: The value passed in (`TimeInterval`) will cause a timer to
+    ///   continuously send ping-type messages to the WS server, keeping the connection alive.
+    ///   - pingMessage: The ping-type `String` message.
+    ///   For example:
+    ///       ```
+    ///       "{\"id\": \"\(myId)\", \"type\": \"ping\"}"
+    ///       ```
+    ///   - pingMessageWithGeneratedId: The ping-type `String` message, including
+    ///   a dynamically generated ID. The closure (`(String) -> String`) takes a `String`
+    ///   (the generated ID) and returns a modified message string incorporating that ID.
+    ///   Notice that if `pingMessage` is also passed in, `pingMessage` will be used instead
+    ///   (causing `pingMessageWithGeneratedId` to be ignored). Usage Example:
+    ///       ```
+    ///       webSocketClient = .init(
+    ///         websocketURL: someWebSocketURL,
+    ///         pingTimerInterval: 18,
+    ///         pingMessageWithGeneratedId: { generatedId in
+    ///           "{\"id\": \"\(generatedId)\", \"type\": \"ping\"}"
+    ///         }
+    ///       )
+    ///       // The above will send the WS server (every 18 seconds)
+    ///       // a message like this:
+    ///       // {"id": "some-random-uuid", "type": "ping"}
+    ///       ```
     public init(id: UUID = .init(),
                 websocketURL: URL,
                 message: CodableWebSocketMessage? = nil,
-                error: ObservableWebSocketClientError? = nil) {
+                error: ObservableWebSocketClientError? = nil,
+                pingTimerInterval: TimeInterval? = nil,
+                pingMessage: String? = nil,
+                pingMessageWithGeneratedId: ((String) -> String)? = nil) {
         self.id = id
         self.websocketURL = websocketURL
         self.codableMessage = message
         self.error = error
+        self.pingTimerInterval = pingTimerInterval
+        self.pingMessage = pingMessage
+        self.pingMessageWithGeneratedId = pingMessageWithGeneratedId
         self.service = ObservableWebSocketService(url: websocketURL)
+
         observeWebSocketConnection()
+        startPingTimer()
+    }
+
+    deinit {
+        pingTimer?.invalidate()
+    }
+}
+
+// MARK: - Private
+
+private extension ObservableWebSocketClient {
+    func startPingTimer() {
+        if let pingTimerInterval,
+           pingMessage?.isEmpty == false || pingMessageWithGeneratedId != nil {
+            pingTimer = Timer.scheduledTimer(
+                withTimeInterval: pingTimerInterval, repeats: true) { [weak self] _ in
+                    if let message = self?.pingMessage {
+                        self?.sendMessage(message)
+                    } else if let messageWithGeneratedId = self?.pingMessageWithGeneratedId {
+                        self?.sendMessageWithGeneratedId(messageWithGeneratedId)
+                    }
+                }
+        }
     }
 }