feat(transforms): Add UIColor transform for swift (#250)

Added UIColor transform for swift based on apple's spec:
https://developer.apple.com/documentation/uikit/uicolor/1621925-init

re #161

.eslintrc.json

@@ -4,7 +4,8 @@
   },
   "env": {
     "node": true,
-    "mocha": true
+    "mocha": true,
+    "jest": true
   },
   "globals": {
     "Buffer": true,

__tests__/common/transforms.test.js

@@ -277,6 +277,22 @@ describe('common', () => {
       });
     });
 
+    describe('color/UIColorSwift', () => {
+      it('should handle normal colors', () => {
+        var value = transforms["color/UIColorSwift"].transformer({
+          value: "#aaaaaa"
+        });
+        expect(value).toBe("UIColor(red: 0.67, green: 0.67, blue: 0.67, alpha:1)");
+      });
+
+      it('should handle colors with transparency', () => {
+        var value = transforms["color/UIColorSwift"].transformer({
+          value: "#aaaaaa99"
+        });
+        expect(value).toBe("UIColor(red: 0.67, green: 0.67, blue: 0.67, alpha:0.6)");
+      });
+    });
+
 
     describe('color/css', () => {
       it('should handle normal colors', () => {

lib/common/transforms.js

@@ -336,6 +336,29 @@ module.exports = {
     }
   },
 
+    /**
+   * Transforms the value into an UIColor swift class for iOS
+   *
+   * ```swift
+   * // Matches: prop.attributes.category === 'color'
+   * // Returns:
+   * UIColor(red: 0.67, green: 0.67, blue: 0.67, alpha:0.6)
+   * ```
+   *
+   * @memberof Transforms
+   */
+  'color/UIColorSwift': {
+    type: 'value',
+    matcher: isColor,
+    transformer: function (prop) {
+      const { r, g, b, a } = Color(prop.value).toRgb();
+      const rFixed = (r / 255.0).toFixed(2);
+      const gFixed = (g / 255.0).toFixed(2);
+      const bFixed = (b / 255.0).toFixed(2);
+      return `UIColor(red: ${rFixed}, green: ${gFixed}, blue: ${bFixed}, alpha:${a})`;
+    }
+  },
+
   /**
    * Transforms the value into a hex or rgb string depending on if it has transparency
    *