Fix ObservationEvents infinite loop (#110)

In some cases new iterations of rise-transit-set calculations are not
more precise than the previous ones. Quite the opposite, it is
apparently possible to loop indefinitely over some values without ever
crossing the targeted precision.

This introduces a limit of 5 iterations. Passed this limit, it is
admitted that the program in its current form will not achieve a better
precision.

Fixes #109

lib/astronoby/events/observation_events.rb

@@ -7,6 +7,7 @@ class ObservationEvents
       RISING_SETTING_HOUR_ANGLE_RATIO_RANGE = (-1..1)
       EARTH_SIDEREAL_ROTATION_RATE = 360.98564736629
       ITERATION_PRECISION = 0.0001
+      ITERATION_LIMIT = 5
 
       attr_reader :rising_time,
         :rising_azimuth,
@@ -89,10 +90,11 @@ def compute
 
       def iterate(initial_rising, initial_transit, initial_setting)
         delta = 1
+        iteration = 1
         corrected_rising = initial_rising
         corrected_transit = initial_transit
         corrected_setting = initial_setting
-        until delta < ITERATION_PRECISION
+        until delta < ITERATION_PRECISION || iteration > ITERATION_LIMIT
           iterate = RiseTransitSetIteration.new(
             observer: @observer,
             date: @date,
@@ -108,6 +110,7 @@ def iterate(initial_rising, initial_transit, initial_setting)
           corrected_rising = rationalize_decimal_time corrected_rising + iterate[0]
           corrected_transit = rationalize_decimal_time corrected_transit + iterate[1]
           corrected_setting = rationalize_decimal_time corrected_setting + iterate[2]
+          iteration += 1
         end
         [corrected_rising, corrected_transit, corrected_setting]
       end

spec/astronoby/bodies/moon_spec.rb

@@ -416,7 +416,7 @@
       end
     end
 
-    it "returns the sunrise time on 1991-03-14" do
+    it "returns the moonrise time on 1991-03-14" do
       time = Time.utc(1991, 3, 14)
       observer = Astronoby::Observer.new(
         latitude: Astronoby::Angle.from_degrees(48.8566),
@@ -431,6 +431,20 @@
       # Time from IMCCE: 1991-03-14T05:08:08
     end
 
+    it "returns moonrise time on 2024-11-10" do
+      time = Time.utc(2024, 11, 10)
+      observer = Astronoby::Observer.new(
+        latitude: Astronoby::Angle.from_degrees(41.02054),
+        longitude: Astronoby::Angle.from_degrees(-72.15608)
+      )
+      moon = described_class.new(time: time)
+      observation_events = moon.observation_events(observer: observer)
+
+      rising_time = observation_events.rising_time
+
+      expect(rising_time).to eq Time.utc(2024, 11, 10, 18, 49, 45)
+    end
+
     describe "#rising_azimuth" do
       it "returns the moonrise azimuth on 2024-05-31" do
         time = Time.utc(2024, 5, 31)