New feature: sunrise and sunset calculation

src/main/java/eu/m724/wtapi/object/Twilight.java

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+package eu.m724.wtapi.object;
+
+import java.time.Duration;
+import java.time.LocalDate;
+
+public class Twilight {
+    /**
+     * The date this object contains times for
+     */
+    public final LocalDate date;
+
+    /**
+     * Time of sunrise relative to UTC midnight of the date
+     */
+    public final Duration sunrise;
+
+    /**
+     * Time of sunset relative to UTC midnight of the date
+     */
+    public final Duration sunset;
+
+    public Twilight(LocalDate date, Duration sunrise, Duration sunset) {
+        this.date = date;
+        this.sunrise = sunrise;
+        this.sunset = sunset;
+    }
+}

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

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+package eu.m724.wtapi.provider.twilight;
+
+import eu.m724.wtapi.object.Coordinates;
+import eu.m724.wtapi.object.Twilight;
+
+import java.time.Duration;
+import java.time.LocalDate;
+
+import static java.lang.Math.*;
+
+public class SimpleTwilightTimeProvider extends TwilightTimeProvider {
+    @Override
+    public Twilight calculateTwilightTime(LocalDate date, Coordinates coordinates) {
+        int dayOfYear = date.getDayOfYear() - 1; // -1 because we have to start from zero
+        // 2 * PI / 365 = 0.01721420632103996
+        double fractionalYear = 0.01721420632103996 * dayOfYear;
+
+        double equationOfTime = 229.18 * (0.000075
+                + 0.001868 * cos(fractionalYear)
+                - 0.032077 * sin(fractionalYear)
+                - 0.014615 * cos(2 * fractionalYear)
+                - 0.040849 * sin(2 * fractionalYear));
+        double declination = 0.006918
+                - 0.399912 * cos(fractionalYear)
+                + 0.070257 * sin(fractionalYear)
+                - 0.006758 * cos(2 * fractionalYear)
+                + 0.000907 * sin(2 * fractionalYear)
+                - 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(
+                date,
+                Duration.ofMillis((long) (sunrise * 60000)),
+                Duration.ofMillis((long) (sunset * 60000))
+        );
+    }
+}

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

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+package eu.m724.wtapi.provider.twilight;
+
+import eu.m724.wtapi.object.Coordinates;
+import eu.m724.wtapi.object.Twilight;
+
+import java.time.LocalDate;
+
+// TODO make this an interface? also consider new name
+/**
+ * Twilight refers to sunset and sunrise time<br>
+ * Is it the correct term? I don't know
+ */
+public abstract class TwilightTimeProvider {
+    /**
+     * Calculates sunrise and sunset for provided coordinates
+     *
+     * @param date UTC date
+     * @param coordinates Coordinates of the observer
+     * @return {@link Twilight}
+     */
+    public abstract Twilight calculateTwilightTime(LocalDate date, Coordinates coordinates);
+}

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

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+package eu.m724.wtapi.twilight;
+
+import eu.m724.wtapi.object.Coordinates;
+import eu.m724.wtapi.object.Twilight;
+import eu.m724.wtapi.provider.twilight.SimpleTwilightTimeProvider;
+import eu.m724.wtapi.provider.twilight.TwilightTimeProvider;
+import org.junit.Test;
+
+import java.time.LocalDate;
+
+public class ApproximateTwilightTimeTest {
+    /**
+     * Acceptable discrepancy in minutes
+     */
+    public static final int ACCEPTABLE_DIFFERENCE = 10;
+
+    @Test
+    public void approximateTest() {
+        TwilightTimeProvider provider = new SimpleTwilightTimeProvider();
+
+        testLocation(provider, 26, 6, 2023, 53.123394, 23.0864867, 122, 1139);
+        testLocation(provider, 13, 11, 2040, 45.432427, -122.3899276, 907, 1481);
+        testLocation(provider, 23, 3, 2021, 55.5024161, 9.6801853, 315, 1061);
+        testLocation(provider, 6, 8,1990, -72.012117, 2.5240873, 600, 832);
+        // TODO this is broken so fix
+        //testLocation(provider, 6, 9,2021, 82.498665, -62.3458366, 74, 1351); // date not on purpose as this was the first sunset in that location. first sunset since 5th april
+    }
+
+    private void testLocation(TwilightTimeProvider provider, int day, int month, int year, double latitude, double longitude, int actualSunrise, int actualSunset) {
+        LocalDate date = LocalDate.of(year, month, day);
+        Coordinates coordinates = new Coordinates(latitude, longitude);
+
+        Twilight twilight = provider.calculateTwilightTime(date, coordinates);
+        System.out.println();
+        System.out.println(date);
+        System.out.println(coordinates.latitude + " " + coordinates.longitude);
+
+        System.out.println("Calculated sunrise: " + date.atStartOfDay().plus(twilight.sunrise));
+        System.out.println("Actual sunrise: " + date.atStartOfDay().plusMinutes(actualSunrise));
+        assert Math.abs(twilight.sunrise.toMinutes() - actualSunrise) < ACCEPTABLE_DIFFERENCE;
+
+        System.out.println("Calculated sunset: " + date.atStartOfDay().plus(twilight.sunset));
+        System.out.println("Actual sunset: " + date.atStartOfDay().plusMinutes(actualSunset));
+        assert Math.abs(twilight.sunset.toMinutes() - actualSunset) < ACCEPTABLE_DIFFERENCE;
+    }
+}

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

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+package eu.m724.wtapi.twilight;
+
+import eu.m724.wtapi.object.Coordinates;
+import eu.m724.wtapi.object.Twilight;
+import eu.m724.wtapi.provider.twilight.TwilightTimeProvider;
+
+import java.time.Duration;
+import java.time.LocalDate;
+
+public class MockTwilightTimeProvider extends TwilightTimeProvider {
+    @Override
+    public Twilight calculateTwilightTime(LocalDate date, Coordinates coordinates) {
+        int time = (int) (coordinates.latitude + coordinates.longitude);
+        return new Twilight(
+                date,
+                Duration.ofMinutes(-time),
+                Duration.ofMinutes(time)
+        );
+    }
+}

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

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+package eu.m724.wtapi.twilight;
+
+import eu.m724.wtapi.object.Coordinates;
+import eu.m724.wtapi.object.Twilight;
+import eu.m724.wtapi.provider.twilight.TwilightTimeProvider;
+import org.junit.Test;
+
+import java.time.LocalDate;
+
+public class MockTwilightTimeTest {
+    @Test
+    public void testTwilight() {
+        TwilightTimeProvider provider = new MockTwilightTimeProvider();
+
+        LocalDate date = LocalDate.of(2077, 4, 20);
+        Coordinates coordinates = new Coordinates(52.4796012, 62.1847245);
+        Twilight twilight = provider.calculateTwilightTime(date, coordinates);
+
+        assert twilight.date.equals(date);
+        assert twilight.sunrise.getSeconds() == -6840;
+        assert twilight.sunset.getSeconds() == 6840;
+    }
+}