refactored code and added retry mechanism

program/Sources/amiunlocked/config.swift

@@ -0,0 +1,23 @@
+import Configuration
+
+// Start a configuration manager, load configuration from an adjacent
+// `config.json` file, cast config values to appropriate types, and
+// fail if required config values are not present
+struct Config {
+  var url: String
+  var writeKey: String
+  init() {
+    let manager = ConfigurationManager()
+    manager.load(file: "config.json")
+    url = manager["url"] as? String ?? ""
+    writeKey = manager["writeKey"] as? String ?? ""
+
+    if url == "" {
+      fatalError("The config parameter 'url' is required. Set it in 'config.json' and please try again.")
+    }
+
+    if writeKey == "" {
+      fatalError("The config parameter 'writeKey' is required. Set it in 'config.json' and please try again.")
+    }
+  }
+}

program/Sources/amiunlocked/main.swift

@@ -1,74 +1,27 @@
 import Cocoa
-import Configuration
 import Foundation
-import Just
 
 // Enumerate valid states for our computer: "locked" and "unlocked"
 enum State: String {
   case locked
   case unlocked
 }
 
-// Section: Configuration
-// Start a configuration manager, load configuration from an adjacent
-// `config.json` file, cast config values to appropriate types, and
-// fail if required config values are not present
-let manager = ConfigurationManager()
-manager.load(file: "config.json")
-let url = manager["url"] as? String ?? ""
-let writeKey = manager["writeKey"] as? String ?? ""
+var sync = Sync()
 
-if url == "" {
-  fatalError("The config parameter 'url' is required. Set it in 'config.json' and please try again.")
-}
-
-if writeKey == "" {
-  fatalError("The config parameter 'writeKey' is required. Set it in 'config.json' and please try again.")
-}
-
-// Section: Network Requests
-// Functions to create UTC timestamps and make network requests
-// to the kvdb bucket with a given `State`
-func getISOTimestamp() -> String {
-  if #available(macOS 10.12, *) {
-    let date = Date()
-    let dateFormatter = ISO8601DateFormatter()
-    return dateFormatter.string(from: date)
-  } else {
-    fatalError("This process only runs on macOS 10.12+.")
-  }
-}
-
-func sendRequest(state: State) {
-  let r = Just.post(
-    url,
-    json: ["state": state.rawValue, "updatedAt": getISOTimestamp()],
-    auth: (writeKey, "")
-  )
-  if r.ok {
-    NSLog("Network: request succeeded")
-  } else {
-    NSLog("Network: request failed")
-  }
-}
-
-// Section: Event Listeners
-// The event listeners listening for `screenIsLocked` and `screenIsUnlocked`
-// events, and the callback function to log and make a network request in
-// response to a triggered event
-func logAndSendRequest(notification: Notification, state: State) {
+func logAndSync(notification: Notification, state: State) {
   NSLog("Event: \(notification.name.rawValue)")
-  sendRequest(state: state)
+  sync.initializeSync(state: state)
 }
 
 let dnc = DistributedNotificationCenter.default()
 
 dnc.addObserver(forName: .init("com.apple.screenIsLocked"), object: nil, queue: .main) { notification in
-  logAndSendRequest(notification: notification, state: State.locked)
+  logAndSync(notification: notification, state: State.locked)
 }
 
 dnc.addObserver(forName: .init("com.apple.screenIsUnlocked"), object: nil, queue: .main) { notification in
-  logAndSendRequest(notification: notification, state: State.unlocked)
+  logAndSync(notification: notification, state: State.unlocked)
 }
 
 // Let's do this thing!

program/Sources/amiunlocked/sync.swift

@@ -0,0 +1,61 @@
+import Cocoa
+import Just
+
+private func getISOTimestamp() -> String {
+  if #available(macOS 10.12, *) {
+    let date = Date()
+    let dateFormatter = ISO8601DateFormatter()
+    return dateFormatter.string(from: date)
+  } else {
+    fatalError("This process only runs on macOS 10.12+.")
+  }
+}
+
+class Sync {
+  private static let config = Config()
+
+  enum SyncStatus {
+    case pending(nextState: State)
+    case success
+    case failure(retryState: State)
+  }
+
+  var syncStatus: SyncStatus = .success
+  private var task: DispatchWorkItem?
+
+  func initializeSync(state: State) {
+    syncStatus = .pending(nextState: state)
+    handleSync()
+  }
+
+  private func handleSync() {
+    if task != nil { task!.cancel() }
+
+    switch syncStatus {
+    case let .pending(nextState):
+      sendRequest(state: nextState)
+    case .success:
+      break
+    case let .failure(retryState):
+      syncStatus = .pending(nextState: retryState)
+      sendRequest(state: retryState)
+    }
+  }
+
+  private func sendRequest(state: State) {
+    let r = Just.post(
+      Sync.config.url,
+      json: ["state": state.rawValue, "updatedAt": getISOTimestamp()],
+      auth: (Sync.config.writeKey, "")
+    )
+    if r.ok {
+      NSLog("Network: request succeeded")
+      syncStatus = .success
+    } else {
+      NSLog("Network: request failed")
+      syncStatus = .failure(retryState: state)
+      task = DispatchWorkItem { self.handleSync() }
+      DispatchQueue.main.asyncAfter(deadline: DispatchTime.now() + 2, execute: task!)
+    }
+  }
+}