add helpers

lib/Helpers/Units.h

@@ -0,0 +1,40 @@
+#include <Arduino.h>
+#include <inttypes.h>
+
+#ifndef _UNITS_H
+#define _UNITS_H
+
+#define COLOR_TEMP_MAX_MIREDS 370
+#define COLOR_TEMP_MIN_MIREDS 153
+
+class Units {
+public:
+  template <typename T, typename V>
+  static T rescale(T value, V newMax, float oldMax = 255.0) {
+    return round(value * (newMax / oldMax));
+  }
+
+  static uint8_t miredsToBrightness(uint8_t mireds, uint8_t maxValue = 255) {
+      // MiLight CCT bulbs range from 2700K-6500K, or ~370.3-153.8 mireds. Note
+      // that mireds are inversely correlated with color temperature.
+      uint32_t tempMireds = constrain(mireds, COLOR_TEMP_MIN_MIREDS, COLOR_TEMP_MAX_MIREDS);
+
+      uint8_t scaledTemp = round(
+        maxValue*
+        (tempMireds - COLOR_TEMP_MIN_MIREDS)
+          /
+        static_cast<double>(COLOR_TEMP_MAX_MIREDS - COLOR_TEMP_MIN_MIREDS)
+      );
+
+      return (maxValue - scaledTemp);
+  }
+
+  static uint8_t brightnessToMireds(uint8_t value, uint8_t maxValue = 255) {
+    uint8_t reverseValue = maxValue - value;
+    uint8_t scaled = rescale(reverseValue, (COLOR_TEMP_MAX_MIREDS - COLOR_TEMP_MIN_MIREDS), maxValue);
+
+    return COLOR_TEMP_MIN_MIREDS + scaled;
+  }
+};
+
+#endif