support iOS 13 dark mode

CHANGELOG.md

@@ -4,6 +4,11 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/)
 and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.html).
 
+## [Unreleased]
+
+### Added
+- support iOS 13 dark mode.
+
 ## [1.3.9] - 2019-09-12
 
 ### Fixed

Sources/BatteryView.swift

@@ -49,7 +49,7 @@ extension Int {
     /// label shown over battery when the level is undefined or out of range
     @IBInspectable open dynamic var noLevelText: String? = "?"
 
-    @IBInspectable open dynamic var borderColor: UIColor = .black {
+    @IBInspectable open dynamic var borderColor: UIColor = .foreground {
         didSet {
             bodyOutline.borderColor = borderColor.cgColor
             terminalOutline.borderColor = borderColor.cgColor
@@ -181,7 +181,7 @@ extension Int {
         case .fullBattery:
             terminalOpening.backgroundColor = currentFillColor.cgColor
         case 0 ..< .fullBattery:
-            terminalOpening.backgroundColor = (backgroundColor ?? .white).cgColor
+            terminalOpening.backgroundColor = (backgroundColor ?? .background).cgColor
         default:
             terminalOpening.backgroundColor = noLevelColor.cgColor
         }
@@ -214,3 +214,21 @@ extension CALayer {
         return CGPoint(x: frame.midX, y: frame.midY)
     }
 }
+
+extension UIColor {
+    static var background: UIColor {
+        if #available(iOS 13, *) {
+            return .systemBackground
+        } else {
+            return .white
+        }
+    }
+
+    static var foreground: UIColor {
+        if #available(iOS 13, *) {
+            return .label
+        } else {
+            return .black
+        }
+    }
+}