Refactoring I.

- Revamp whole DB to Display flow
- Filter Pipeline, arbitrary filtering and sorting
- Binary tree arrays for faster lookup & manipulation
- DB: introducing custom functions
- DB scheme: split req into heap & cache
- cache written by GlassVPN only
- heap written by Main App only
- Introducing DB separation: DBCore, DBCommon, DBAppOnly
- Introducing DB data sources: TestDataSource, GroupedDomainDataSource, RecordingsDB, DomainFilter
- Background sync: Move entries from cache to heap and notify all observers
- GlassVPN: Binary tree filter lookup
- GlassVPN: Reusing prepared statement

main/Extensions/Time.swift

@@ -0,0 +1,74 @@
+import Foundation
+
+private let dateTimeFormat = DateFormatter(withFormat: "yyyy-MM-dd  HH:mm:ss")
+
+extension DateFormatter {
+	convenience init(withFormat: String) {
+		self.init()
+		dateFormat = withFormat
+	}
+}
+
+extension Timestamp {
+	/// Time string with format `yyyy-MM-dd  HH:mm:ss`
+	func asDateTime() -> String {
+		dateTimeFormat.string(from: Date.init(timeIntervalSince1970: Double(self)))
+	}
+	
+	/// Convert `Timestamp` to `Date`
+	func toDate() -> Date {
+		Date(timeIntervalSince1970: Double(self))
+	}
+	
+	/// Current time as `Timestamp` (second accuracy)
+	static func now() -> Timestamp {
+		Timestamp(Date().timeIntervalSince1970)
+	}
+	
+	/// Create `Timestamp` with `now() - minutes * 60`
+	static func past(minutes: Int) -> Timestamp {
+		now() - Timestamp(minutes * 60)
+	}
+}
+
+extension Timer {
+	/// Recurring timer maintains a strong reference to `target`.
+	@discardableResult static func repeating(_ interval: TimeInterval, call selector: Selector, on target: Any, userInfo: Any? = nil) -> Timer {
+		Timer.scheduledTimer(timeInterval: interval, target: target, selector: selector,
+							 userInfo: userInfo, repeats: true)
+	}
+}
+
+struct TimeFormat {
+	/// Time string with format `HH:mm`
+	static func from(_ duration: Timestamp) -> String {
+		String(format: "%02d:%02d", duration / 60, duration % 60)
+	}
+	
+	/// Duration string with format `HH:mm` or `HH:mm.sss`
+	static func from(_ duration: TimeInterval, millis: Bool = false) -> String {
+		let t = Int(duration)
+		if millis {
+			let mil = Int(duration * 1000) % 1000
+			return String(format: "%02d:%02d.%03d", t / 60, t % 60, mil)
+		}
+		return String(format: "%02d:%02d", t / 60, t % 60)
+	}
+	
+	/// Duration string with format `HH:mm` or `HH:mm.sss` since reference date
+	static func since(_ date: Date, millis: Bool = false) -> String {
+		from(Date().timeIntervalSince(date), millis: millis)
+	}
+	
+	/// Formatted duration string, e.g., `20 min` or `7 days`
+	/// - Parameters:
+	///   - minutes: Duration in minutes
+	///   - style: Default: `.short`
+	static func short(minutes: Int, style: DateComponentsFormatter.UnitsStyle = .short) -> String? {
+		let dcf = DateComponentsFormatter()
+		dcf.maximumUnitCount = 1
+		dcf.allowedUnits = [.day, .hour, .minute]
+		dcf.unitsStyle = style
+		return dcf.string(from: DateComponents(minute: minutes))
+	}
+}