Add CSV export for days

TempTrack/Storage/CsvConverter.swift

@@ -0,0 +1,40 @@
+import Foundation
+
+struct CsvConverter {
+
+    private let dateFormatter: DateFormatter
+
+    init() {
+        dateFormatter = .init()
+        dateFormatter.dateStyle = .short
+        dateFormatter.timeStyle = .medium
+    }
+
+    private var header: String {
+        "Index;Date;Sensor 0;Sensor 1\n"
+    }
+
+    func convert(measurements: [TemperatureMeasurement]) -> String {
+        header + measurements.enumerated().map { (index, measurement) -> String in
+            let parts: [String] = [
+                "\(index)",
+                dateFormatter.string(from: measurement.date),
+                convert(measurement.sensor0),
+                convert(measurement.sensor1)
+            ]
+
+            return parts.joined(separator: ";")
+        }.joined(separator: "\n")
+    }
+
+    private func convert(_ value: TemperatureValue) -> String {
+        switch value {
+        case .notFound:
+            return ""
+        case .invalidMeasurement:
+            return "?"
+        case .value(let value):
+            return String(format:"%.1f", value)
+        }
+    }
+}