#166: Re-write MXLogger in Swift

* Add logging tests that cover file rotation.

* Re-write MXLogger in Swift.

UnitTests/Sources/LoggingTests.swift

@@ -23,7 +23,7 @@ class LoggingTests: XCTestCase {
     }
 
     override func setUpWithError() throws {
-        // Put setup code here. This method is called before the invocation of each test method in the class.
+        MXLogger.deleteLogFiles()
     }
 
     override func tearDownWithError() throws {
@@ -31,12 +31,7 @@ class LoggingTests: XCTestCase {
     }
 
     func testFileLogging() throws {
-        MXLogger.deleteLogFiles()
-        guard let logFiles = MXLogger.logFiles() else {
-            XCTFail(Constants.genericFailure)
-            return
-        }
-        XCTAssertTrue(logFiles.isEmpty)
+        XCTAssertTrue(MXLogger.logFiles.isEmpty)
 
         let log = UUID().uuidString
 
@@ -44,22 +39,105 @@ class LoggingTests: XCTestCase {
         configuration.redirectLogsToFiles = true
         MXLog.configure(configuration)
         MXLog.debug(log)
-        guard let logFile = MXLogger.logFiles().first else {
+        guard let logFile = MXLogger.logFiles.first else {
             XCTFail(Constants.genericFailure)
             return
         }
 
-        let content = try String(contentsOfFile: logFile)
+        let content = try String(contentsOf: logFile)
         XCTAssert(content.contains(log))
     }
+    
+    func testFileRotationOnLaunch() throws {
+        // Given a fresh launch with no logs.
+        XCTAssertTrue(MXLogger.logFiles.isEmpty)
+        
+        // When launching the app 5 times.
+        let launchCount = 5
+        for index in 0..<launchCount {
+            let configuration = MXLogConfiguration()
+            configuration.redirectLogsToFiles = true
+            MXLog.configure(configuration) // This call is only made at app launch.
+            MXLog.debug("Launch \(index + 1)")
+        }
+        
+        // Then 5 log files should be created each with the correct contents.
+        let logFiles = MXLogger.logFiles
+        
+        XCTAssertEqual(logFiles.count, launchCount, "The number of log files should match the number of launches.")
+        try verifyContents(of: logFiles, after: launchCount)
+    }
+    
+    func testMaxLogFileCount() throws {
+        // Given a fresh launch with no logs.
+        XCTAssertTrue(MXLogger.logFiles.isEmpty)
+        
+        // When launching the app 10 times, with a maxLogCount of 5.
+        let launchCount = 10
+        let logFileCount = 5
+        for index in 0..<launchCount {
+            let configuration = MXLogConfiguration()
+            configuration.maxLogFilesCount = UInt(logFileCount)
+            configuration.redirectLogsToFiles = true
+            MXLog.configure(configuration) // This call is only made at app launch.
+            MXLog.debug("Launch \(index + 1)")
+        }
+        
+        // Then only 5 log files should be stored on disk, with the contents of launches 6 to 10.
+        let logFiles = MXLogger.logFiles
+        
+        XCTAssertEqual(logFiles.count, logFileCount, "The number of log files should match the number of launches.")
+        try verifyContents(of: logFiles, after: launchCount)
+    }
+    
+    func testLogFileSizeLimit() throws {
+        // Given a fresh launch with no logs.
+        XCTAssertTrue(MXLogger.logFiles.isEmpty)
+        
+        // When launching the app 10 times, with a max total log size of 25KB and logging ~5KB data each time.
+        let launchCount = 10
+        let logFileSizeLimit = 25 * 1024
+        for index in 0..<launchCount {
+            let configuration = MXLogConfiguration()
+            configuration.logFilesSizeLimit = UInt(logFileSizeLimit)
+            configuration.redirectLogsToFiles = true
+            MXLog.configure(configuration) // This call is only made at app launch.
+            MXLog.debug("Launch \(index + 1)")
+            
+            // Add ~5KB of logs
+            for _ in 0..<5 {
+                let string = [String](repeating: "a", count: 1024).joined()
+                MXLog.debug(string)
+            }
+        }
+        
+        // Then only the most recent log files should be stored on disk.
+        let logFiles = MXLogger.logFiles
+        
+        XCTAssertGreaterThan(logFiles.count, 0, "There should be at least one log file created.")
+        XCTAssertLessThan(logFiles.count, launchCount, "Some of the log files should have been removed trimmed.")
+        try verifyContents(of: logFiles, after: launchCount)
+    }
+    
+    /// Verifies that the log files all contain the correct `Launch #` based on the index
+    /// in the file name and the number of launches of the app.
+    func verifyContents(of logFiles: [URL], after launchCount: Int) throws {
+        for logFile in logFiles {
+            let regex = /\d+/
+            let fileIndex = logFile.lastPathComponent.firstMatch(of: regex)?.0 ?? "0"
+            
+            guard let index = Int(fileIndex) else {
+                XCTFail(Constants.genericFailure)
+                return
+            }
+            
+            let content = try String(contentsOf: logFile)
+            XCTAssertTrue(content.contains("Launch \(launchCount - index)"), "The log files should be for the most recent launches in reverse chronological order.")
+        }
+    }
 
     func testLogLevels() throws {
-        MXLogger.deleteLogFiles()
-        guard let logFiles = MXLogger.logFiles() else {
-            XCTFail(Constants.genericFailure)
-            return
-        }
-        XCTAssert(logFiles.isEmpty)
+        XCTAssert(MXLogger.logFiles.isEmpty)
 
         let log = UUID().uuidString
 
@@ -68,22 +146,17 @@ class LoggingTests: XCTestCase {
         configuration.redirectLogsToFiles = true
         MXLog.configure(configuration)
         MXLog.debug(log)
-        guard let logFile = MXLogger.logFiles().first else {
+        guard let logFile = MXLogger.logFiles.first else {
             XCTFail(Constants.genericFailure)
             return
         }
 
-        let content = try String(contentsOfFile: logFile)
+        let content = try String(contentsOf: logFile)
         XCTAssertFalse(content.contains(log))
     }
 
     func testSubLogName() {
-        MXLogger.deleteLogFiles()
-        guard let logFiles = MXLogger.logFiles() else {
-            XCTFail(Constants.genericFailure)
-            return
-        }
-        XCTAssert(logFiles.isEmpty)
+        XCTAssert(MXLogger.logFiles.isEmpty)
 
         let subLogName = "nse"
 
@@ -92,11 +165,11 @@ class LoggingTests: XCTestCase {
         configuration.redirectLogsToFiles = true
         MXLog.configure(configuration)
         MXLog.debug(UUID().uuidString)
-        guard let logFile = MXLogger.logFiles().first else {
+        guard let logFile = MXLogger.logFiles.first else {
             XCTFail(Constants.genericFailure)
             return
         }
 
-        XCTAssertTrue(logFile.contains(subLogName))
+        XCTAssertTrue(logFile.lastPathComponent.contains(subLogName))
     }
 }