COVIDSafe code from version 2.0 (#37)

CovidSafe/Herald/Sensor/Data/TextFile.swift

@@ -0,0 +1,71 @@
+//
+//  TextFile.swift
+//
+//  Copyright 2020 VMware, Inc.
+//  SPDX-License-Identifier: MIT
+//
+
+import Foundation
+
+class TextFile {
+    private let logger = ConcreteSensorLogger(subsystem: "Sensor", category: "Data.TextFile")
+    private var file: URL?
+    private let queue: DispatchQueue
+    
+    init(filename: String) {
+        file = try? FileManager.default
+        .url(for: .documentDirectory, in: .userDomainMask, appropriateFor: nil, create: true)
+        .appendingPathComponent(filename)
+        queue = DispatchQueue(label: "Sensor.Data.TextFile(\(filename))")
+    }
+    
+    func empty() -> Bool {
+        guard let file = file else {
+            return true
+        }
+        return !FileManager.default.fileExists(atPath: file.path)
+    }
+    
+    /// Append line to new or existing file
+    func write(_ line: String) {
+        queue.sync {
+            guard let file = file else {
+                return
+            }
+            guard let data = (line+"\n").data(using: .utf8) else {
+                return
+            }
+            if FileManager.default.fileExists(atPath: file.path) {
+                if let fileHandle = try? FileHandle(forWritingTo: file) {
+                    fileHandle.seekToEndOfFile()
+                    fileHandle.write(data)
+                    fileHandle.closeFile()
+                }
+            } else {
+                try? data.write(to: file, options: .atomicWrite)
+            }
+        }
+    }
+    
+    /// Overwrite file content
+    func overwrite(_ content: String) {
+        queue.sync {
+            guard let file = file else {
+                return
+            }
+            guard let data = content.data(using: .utf8) else {
+                return
+            }
+            try? data.write(to: file, options: .atomicWrite)
+        }
+    }
+    
+    /// Quote value for CSV output if required.
+    static func csv(_ value: String) -> String {
+        guard value.contains(",") || value.contains("\"") || value.contains("'") || value.contains("’") else {
+            return value
+        }
+        return "\"" + value + "\""
+
+    }
+}