feat: add sun position along the daylight arc

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

2 files changed, 50 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
diff --git a/test/test_weather.lua b/test/test_weather.lua
index e18aa15..1d35748 100644
--- a/test/test_weather.lua
+++ b/test/test_weather.lua
@@ -127,4 +127,30 @@ assert(weather.arrow(0) == '\u{2193}', 'a north wind blows southward')
 assert(weather.arrow(180) == '\u{2191}', 'a south wind blows northward')
 assert(weather.arrow(nil) == '', 'no direction draws nothing')
 
+-- === Sun position =========================================================
+-- t is the fraction of daylight elapsed, and the widget uses it to place the
+-- dot along the arc. Sunrise 1000, sunset 2000, so midday is 1500.
+assert(weather.sun_t(1000, 1000, 2000) == 0, 'at sunrise t is 0')
+assert(weather.sun_t(1500, 1000, 2000) == 0.5, 'at midday t is half')
+assert(weather.sun_t(2000, 1000, 2000) == 1, 'at sunset t is 1')
+
+-- OWM reports today's sunrise and sunset, so between midnight and sunrise the
+-- numerator is negative. The clamp is the whole handling; without it the dot
+-- would be drawn off the left end of the arc.
+assert(weather.sun_t(500, 1000, 2000) == 0, 'before dawn clamps to 0')
+assert(weather.sun_t(9999, 1000, 2000) == 1, 'after dusk clamps to 1')
+
+-- Degenerate input must not divide by zero.
+assert(weather.sun_t(1500, 2000, 2000) == 0, 'zero-length day gives 0, not nan')
+assert(weather.sun_t(nil, 1000, 2000) == nil, 'missing now gives nil')
+assert(weather.sun_t(1500, nil, 2000) == nil, 'missing sunrise gives nil')
+
+-- is_day drives both the icon face and the dot's colour: a dot parked at the
+-- end of the arc must not read as a sun that is still up.
+assert(weather.is_day(1500, 1000, 2000) == true, 'midday is day')
+assert(weather.is_day(1000, 1000, 2000) == true, 'sunrise counts as day')
+assert(weather.is_day(2000, 1000, 2000) == true, 'sunset counts as day')
+assert(weather.is_day(500, 1000, 2000) == false, 'before dawn is night')
+assert(weather.is_day(2500, 1000, 2000) == false, 'after dusk is night')
+
 print('test_weather: all assertions passed')