1 files changed, 32 insertions, 0 deletions
diff --git a/src/use-sunlight.js b/src/use-sunlight.js
new file mode 100644
index 0000000..2ca279b
--- /dev/null
+++ b/src/use-sunlight.js
@@ -0,0 +1,32 @@
+import { useState } from 'react'
+import { useGeolocation as globalUseGeolocation } from './use-geolocation'
+import { useInterval } from './use-interval'
+import suncalc from 'suncalc'
+
+export const computeLightLevel = (
+  { loading, latitude, longitude },
+  date = new Date()
+) => {
+  if (loading || !latitude || !longitude) return 0
+  let { altitude } = suncalc.getPosition(date, latitude, longitude)
+  if (altitude < 0) {
+    altitude += 2 * Math.PI
+  }
+  // on or below the horizon is considered "no light"
+  if (altitude >= Math.PI) return 0
+  // otherwise, return a relative altitude
+  // where n is an int in [0,10]
+  // and 10 represents the zenith (straight over your head)
+  return Math.round(10 * Math.sin(altitude))
+}
+
+// make a location hook injectable such that we can test this
+export const useSunlight = (useGeolocation = globalUseGeolocation) => {
+  const geoLocation = useGeolocation()
+
+  const [lightLevel, setLightLevel] = useState(computeLightLevel(geoLocation))
+  useInterval(() => {
+    setLightLevel(computeLightLevel(geoLocation))
+  }, 1000)
+  return [lightLevel]
+}