use os_log for iOS/tvOS 10+ (#229)

* add os_log for iOS/tvOS 10+

* add os_log for iOS/tvOS 10+

* changes per review comments

* Revert "changes per review comments"

This reverts commit b39511e.

* changes per review comments

* fix per review comments

Author: jaeopt

OptimizelySDK/Customization/DefaultLogger.swift

@@ -15,6 +15,7 @@
 ***************************************************************************/
 
 import Foundation
+import os.log
 
 open class DefaultLogger: OPTLogger {
     private static var _logLevel: OptimizelyLogLevel?
@@ -30,15 +31,36 @@ open class DefaultLogger: OPTLogger {
         }
     }
 
+    var osLogUsed = false
+    
     required public init() {
     }
 
     open func log(level: OptimizelyLogLevel, message: String) {
         if level > DefaultLogger.logLevel {
             return
         }
-        let message = "[OPTIMIZELY][" + level.name + "] " + message
-
-        NSLog(message)
+        
+        if #available(iOS 10.0, tvOS 10.0, *) {
+            var osLogType: OSLogType
+            
+            switch level {
+            case .error: osLogType = .error
+            case .info: osLogType = .info
+            case .debug: osLogType = .debug
+            default: osLogType = .default
+            }
+            
+            os_log("[%{public}@] %{public}@", log: .optimizely, type: osLogType, level.name, message)
+            osLogUsed = true
+        } else {
+            let message = "[OPTIMIZELY][" + level.name + "] " + message
+            NSLog(message)
+        }
     }
 }
+
+@available(iOS 10.0, tvOS 10.0, *)
+extension OSLog {
+    static let optimizely = OSLog(subsystem: "com.optimizely.swift-sdk", category: "OPTIMIZELY")
+}

OptimizelySDK/OptimizelyTests/OptimizelyTests-Common/LoggerTests.swift

@@ -36,6 +36,20 @@ class LoggerTests: XCTestCase {
         }
         XCTAssertTrue(CustomLogger.logCount == 0)
     }
+
+    // MARK: - DefaultLogger Tests
+
+    func testLog_UseOSLog() {
+        let logger = DefaultLogger()
+        logger.i("Log Message")
+        
+        if #available(iOS 10.0, tvOS 10.0, *) {
+            XCTAssertTrue(logger.osLogUsed)
+        } else {
+            XCTAssertFalse(logger.osLogUsed)
+        }
+    }
+    
 }
 
 private class CustomLogger: OPTLogger {
@@ -57,3 +71,4 @@ private class CustomLogger: OPTLogger {
         CustomLogger.logCount += 1
     }
 }
+