Fix error

Made by accident, IDEA warned before committing, but as I always see some warnings there I just clicked without thinking

.idea/misc.xml

@@ -8,5 +8,5 @@
       </list>
     </option>
   </component>
-  <component name="ProjectRootManager" version="2" languageLevel="JDK_21" default="true" project-jdk-name="temurin-21" project-jdk-type="JavaSDK" />
+  <component name="ProjectRootManager" version="2" languageLevel="JDK_17" default="true" project-jdk-name="graalvm-ce-17" project-jdk-type="JavaSDK" />
 </project>

src/main/java/eu/m724/wtapi/provider/Providers.java

@@ -3,7 +3,7 @@ package eu.m724.wtapi.provider;
 import eu.m724.wtapi.provider.exception.NoSuchProviderException;
 import eu.m724.wtapi.provider.thunder.ThunderProvider;
 import eu.m724.wtapi.provider.thunder.impl.blitzortung.BlitzortungProvider;
-import eu.m724.wtapi.provider.twilight.ApproximateTwilightTimeProvider;
+import eu.m724.wtapi.provider.twilight.impl.approximate.ApproximateTwilightTimeProvider;
 import eu.m724.wtapi.provider.twilight.TwilightTimeProvider;
 import eu.m724.wtapi.provider.weather.WeatherProvider;
 import eu.m724.wtapi.provider.weather.impl.openweathermap.OpenWeatherMapProvider;

src/main/java/eu/m724/wtapi/provider/twilight/CacheableTwilightTimeProvider.java

@@ -0,0 +1,40 @@
+package eu.m724.wtapi.provider.twilight;
+
+import eu.m724.wtapi.object.Coordinates;
+import eu.m724.wtapi.object.Twilight;
+
+import java.time.LocalDate;
+
+// TODO reconsider if this is necessary and doesn't actually harm performance
+/**
+ * A {@link TwilightTimeProvider} that can cache some calculations to be faster
+ *
+ * @param <T> An implementation of {@link TwilightTimeCache} where you store whatever you need
+ */
+public abstract class CacheableTwilightTimeProvider<T extends TwilightTimeCache> extends TwilightTimeProvider {
+    /**
+     * Calculates sunrise and sunset for provided coordinates
+     *
+     * @param cache {@link T}, implementation of {@link TwilightTimeCache}
+     * @param coordinates Coordinates of the observer
+     * @return {@link Twilight}
+     * @see #initializeCache(LocalDate)
+     */
+    public abstract Twilight calculateTwilightTime(T cache, Coordinates coordinates);
+
+    /**
+     * Initializes cache for provided date
+     *
+     * @param date The UTC date
+     * @return ready to use cache
+     */
+    public abstract T initializeCache(LocalDate date);
+
+    @Override
+    public Twilight calculateTwilightTime(LocalDate date, Coordinates coordinates) {
+        return calculateTwilightTime(
+                initializeCache(date),
+                coordinates
+        );
+    }
+}

src/main/java/eu/m724/wtapi/provider/twilight/TwilightTimeCache.java

@@ -0,0 +1,4 @@
+package eu.m724.wtapi.provider.twilight;
+
+public interface TwilightTimeCache {
+}

src/main/java/eu/m724/wtapi/provider/twilight/impl/approximate/ApproximateTwilightTimeCache.java

@@ -0,0 +1,9 @@
+package eu.m724.wtapi.provider.twilight.impl.approximate;
+
+import eu.m724.wtapi.provider.twilight.TwilightTimeCache;
+
+import java.time.LocalDate;
+
+public record ApproximateTwilightTimeCache(LocalDate date, double equationOfTime,
+                                           double declination) implements TwilightTimeCache {
+}

src/main/java/eu/m724/wtapi/provider/twilight/impl/approximate/ApproximateTwilightTimeProvider.java

@@ -1,7 +1,8 @@
-package eu.m724.wtapi.provider.twilight;
+package eu.m724.wtapi.provider.twilight.impl.approximate;
 
 import eu.m724.wtapi.object.Coordinates;
 import eu.m724.wtapi.object.Twilight;
+import eu.m724.wtapi.provider.twilight.CacheableTwilightTimeProvider;
 
 import java.time.Duration;
 import java.time.LocalDate;
@@ -9,13 +10,40 @@ import java.time.LocalDate;
 import static java.lang.Math.*;
 
 /**
- * Calculates approximate sunrise and sunset times
- * Usually off by a few minutes, except the Poles which, during polar days, are up to few hours inaccurate
- * Adapted from: <a href="https://gml.noaa.gov/grad/solcalc/solareqns.PDF">https://gml.noaa.gov/grad/solcalc/solareqns.PDF</a>
+ * Calculates approximate sunrise and sunset times<br>
+ * Usually off by a few minutes, except the Poles which, during polar days, are up to few hours inaccurate<br>
+ * I don't know why, I just copied stuff and maybe transformed a bit, I don't actually understand the topic<br>
+ * Source: <a href="https://gml.noaa.gov/grad/solcalc/solareqns.PDF">https://gml.noaa.gov/grad/solcalc/solareqns.PDF</a>
  */
-public class ApproximateTwilightTimeProvider extends TwilightTimeProvider {
+public class ApproximateTwilightTimeProvider extends CacheableTwilightTimeProvider<ApproximateTwilightTimeCache> {
     @Override
-    public Twilight calculateTwilightTime(LocalDate date, Coordinates coordinates) {
+    public Twilight calculateTwilightTime(ApproximateTwilightTimeCache cache, Coordinates coordinates) {
+        double declination = cache.declination();
+        double equationOfTime = cache.equationOfTime();
+
+        double latRad = toRadians(coordinates.latitude);
+        // 90.833 deg = 1.5853349194640094 rad
+        double n1 = cos(1.5853349194640094) / (cos(latRad) * cos(declination));
+        double n2 = tan(latRad) * tan(declination);
+        double hourAngle = acos(n1 - n2);
+
+        double hourAngleDeg = 4 * toDegrees(hourAngle);
+
+        // sunrise = 720 - 4 * (coordinates.longitude + hourAngleDeg) - equationOfTime
+        // sunset = 720 - 4 * (coordinates.longitude - hourAngleDeg) - equationOfTime
+        double solarNoon = 720 - 4 * coordinates.longitude - equationOfTime;
+        double sunrise = solarNoon - hourAngleDeg;
+        double sunset = solarNoon + hourAngleDeg;
+
+        return new Twilight(
+                cache.date(),
+                Duration.ofMillis((long) (sunrise * 60000)),
+                Duration.ofMillis((long) (sunset * 60000))
+        );
+    }
+
+    @Override
+    public ApproximateTwilightTimeCache initializeCache(LocalDate date) {
         int dayOfYear = date.getDayOfYear() - 1; // -1 because we have to start from zero
         // 2 * PI / 365 = 0.01721420632103996
         double fractionalYear = 0.01721420632103996 * dayOfYear;
@@ -33,24 +61,10 @@ public class ApproximateTwilightTimeProvider extends TwilightTimeProvider {
                 - 0.002697 * cos(3 * fractionalYear)
                 + 0.00148 * sin(3 * fractionalYear);
 
-        double latRad = toRadians(coordinates.latitude);
-        // 90.833 deg = 1.5853349194640094 rad
-        double n1 = cos(1.5853349194640094) / (cos(latRad) * cos(declination));
-        double n2 = tan(latRad) * tan(declination);
-        double hourAngle = acos(n1 - n2);
-
-        double hourAngleDeg = 4 * toDegrees(hourAngle);
-
-        // sunrise = 720 - 4 * (coordinates.longitude + hourAngleDeg) - equationOfTime
-        // sunset = 720 - 4 * (coordinates.longitude - hourAngleDeg) - equationOfTime
-        double solarNoon = 720 - 4 * coordinates.longitude - equationOfTime;
-        double sunrise = solarNoon - hourAngleDeg;
-        double sunset = solarNoon + hourAngleDeg;
-
-        return new Twilight(
+        return new ApproximateTwilightTimeCache(
                 date,
-                Duration.ofMillis((long) (sunrise * 60000)),
-                Duration.ofMillis((long) (sunset * 60000))
+                equationOfTime,
+                declination
         );
     }
 }

src/test/java/eu/m724/wtapi/twilight/ApproximateTwilightTimeTest.java

@@ -2,12 +2,13 @@ package eu.m724.wtapi.twilight;
 
 import eu.m724.wtapi.object.Coordinates;
 import eu.m724.wtapi.object.Twilight;
-import eu.m724.wtapi.provider.twilight.ApproximateTwilightTimeProvider;
+import eu.m724.wtapi.provider.twilight.impl.approximate.ApproximateTwilightTimeProvider;
 import eu.m724.wtapi.provider.twilight.TwilightTimeProvider;
 import org.junit.Test;
 
 import java.time.LocalDate;
 
+// TODO also test cached
 public class ApproximateTwilightTimeTest {
     /**
      * Acceptable discrepancy in minutes