1 files changed, 24 insertions, 0 deletions
diff --git a/lib/weather.lua b/lib/weather.lua
index ac1f4cf..f8c7517 100644
--- a/lib/weather.lua
+++ b/lib/weather.lua
@@ -113,4 +113,28 @@ function M.arrow(deg)
   return ARROWS[i + 1]
 end
 
+-- Fraction of daylight elapsed, clamped to 0..1.
+--
+-- OWM returns TODAY's sunrise and sunset, so before dawn this is negative and
+-- after dusk it is over 1. Clamping parks the dot at the corresponding end of
+-- the arc, which is the cheap correct-enough behaviour; multi-day astronomy
+-- buys nothing for a dot on a curve.
+function M.sun_t(now, sunrise, sunset)
+  if type(now) ~= 'number' or type(sunrise) ~= 'number'
+     or type(sunset) ~= 'number' then return nil end
+  local span = sunset - sunrise
+  if span <= 0 then return 0 end   -- polar day/night or bad data: no division
+  local t = (now - sunrise) / span
+  if t < 0 then return 0 elseif t > 1 then return 1 end
+  return t
+end
+
+-- Whether the sun is up. Inclusive at both ends, matching the polybar script's
+-- comparison, so the instant of sunrise draws the day face.
+function M.is_day(now, sunrise, sunset)
+  if type(now) ~= 'number' or type(sunrise) ~= 'number'
+     or type(sunset) ~= 'number' then return true end
+  return now >= sunrise and now <= sunset
+end
+
 return M