feat: refactor base day algorithms

src/main/kotlin/org/javafreedom/khol/BaseCalculationAlgorithm.kt

@@ -0,0 +1,9 @@
+package org.javafreedom.khol
+
+import kotlinx.datetime.LocalDate
+
+fun interface BaseCalculationAlgorithm {
+
+    fun calculateBaseDate(year: Int): LocalDate
+
+}

src/main/kotlin/org/javafreedom/khol/Declaration.kt

@@ -3,6 +3,8 @@ package org.javafreedom.khol
 import kotlinx.datetime.DateTimeUnit
 import kotlinx.datetime.LocalDate
 import kotlinx.datetime.plus
+import org.javafreedom.khol.algorithm.FirstAdvent
+import org.javafreedom.khol.algorithm.GregorianEasterSundayGauss
 
 sealed class Declaration(open val name: String,
                          open val validFromYear: Int,
@@ -28,8 +30,10 @@ sealed class Declaration(open val name: String,
         override val validIn: Set<String> = emptySet()
     ) : Declaration(name, validFromYear, validIn) {
 
+        private val gregorianEasterSundayAlgorithm = GregorianEasterSundayGauss()
+
         override fun concreteForYear(year: Int): LocalDate {
-            val value = HolidayCalculusUtil.gregorianEasterSunday(year).plus(this.offset, DateTimeUnit.DAY)
+            val value = gregorianEasterSundayAlgorithm.calculateBaseDate(year).plus(this.offset, DateTimeUnit.DAY)
             return LocalDate(year, value.month, value.dayOfMonth)
         }
     }
@@ -41,8 +45,10 @@ sealed class Declaration(open val name: String,
         override val validIn: Set<String> = emptySet()
     ) : Declaration(name, validFromYear, validIn) {
 
+        private val firstAdventAlgorithm = FirstAdvent()
+
         override fun concreteForYear(year: Int): LocalDate {
-            val value = HolidayCalculusUtil.firstAdvent(year).plus(this.offset, DateTimeUnit.DAY)
+            val value = firstAdventAlgorithm.calculateBaseDate(year).plus(this.offset, DateTimeUnit.DAY)
             return LocalDate(year, value.month, value.dayOfMonth)
         }
     }

src/main/kotlin/org/javafreedom/khol/algorithm/FirstAdvent.kt

@@ -0,0 +1,23 @@
+@file:Suppress("detekt:style:MagicNumber")
+package org.javafreedom.khol.algorithm
+
+import kotlinx.datetime.DayOfWeek
+import kotlinx.datetime.DateTimeUnit
+import kotlinx.datetime.LocalDate
+import kotlinx.datetime.plus
+import org.javafreedom.khol.BaseCalculationAlgorithm
+
+class FirstAdvent : BaseCalculationAlgorithm {
+
+    override fun calculateBaseDate(year: Int): LocalDate {
+        // Find November 30th of the given year
+        val november30 = LocalDate(year, 11, 30)
+        // Get the day of the week for November 30th
+        val dayOfWeek = november30.dayOfWeek
+        // Calculate how many days to add to get to the nearest Sunday (Advent starts)
+        val daysToSunday = (DayOfWeek.SUNDAY.value - dayOfWeek.value + 7) % 7
+        // The first Advent Sunday is the Sunday closest to or on November 30th
+        return november30.plus(daysToSunday, DateTimeUnit.DAY)
+    }
+
+}

src/main/kotlin/org/javafreedom/khol/HolidayCalculusUtil.kt → src/main/kotlin/org/javafreedom/khol/algorithm/GregorianEasterSundayGauss.kt

@@ -1,17 +1,12 @@
 @file:Suppress("detekt:style:MagicNumber")
+package org.javafreedom.khol.algorithm
 
-package org.javafreedom.khol
-
-import kotlinx.datetime.DateTimeUnit
-import kotlinx.datetime.DayOfWeek
 import kotlinx.datetime.LocalDate
-import kotlinx.datetime.plus
+import org.javafreedom.khol.BaseCalculationAlgorithm
+
+class GregorianEasterSundayGauss : BaseCalculationAlgorithm {
 
-object HolidayCalculusUtil {
-    /**
-     * Computus algoritym
-     */
-    fun gregorianEasterSunday(year: Int) : LocalDate {
+    override fun calculateBaseDate(year: Int): LocalDate {
         // Golden number (position of the year in the 19-year Metonic cycle)
         val goldenNumber = year % 19
 
@@ -61,14 +56,4 @@ object HolidayCalculusUtil {
         return LocalDate(year, month, day)
     }
 
-    fun firstAdvent(year: Int): LocalDate {
-        // Find November 30th of the given year
-        val november30 = LocalDate(year, 11, 30)
-        // Get the day of the week for November 30th
-        val dayOfWeek = november30.dayOfWeek
-        // Calculate how many days to add to get to the nearest Sunday (Advent starts)
-        val daysToSunday = (DayOfWeek.SUNDAY.value - dayOfWeek.value + 7) % 7
-        // The first Advent Sunday is the Sunday closest to or on November 30th
-        return november30.plus(daysToSunday, DateTimeUnit.DAY)
-    }
 }

src/test/kotlin/org/javafreedom/khol/algorithm/FirstAdventTest.kt

@@ -0,0 +1,24 @@
+package org.javafreedom.khol.algorithm
+
+import kotlinx.datetime.number
+import kotlin.test.Test
+import kotlin.test.assertEquals
+
+class FirstAdventTest {
+
+    private val firstAdvent = FirstAdvent()
+
+    @Test
+    fun testFirstAdvent() {
+        val result0 = firstAdvent.calculateBaseDate(2024)
+        assertEquals(2024, result0.year)
+        assertEquals(12, result0.month.number)
+        assertEquals(1, result0.dayOfMonth)
+
+        val result1 = firstAdvent.calculateBaseDate(2023)
+        assertEquals(2023, result1.year)
+        assertEquals(12, result1.month.number)
+        assertEquals(3, result1.dayOfMonth)
+    }
+
+}

src/test/kotlin/org/javafreedom/khol/HolidayCalculusUtilTest.kt → src/test/kotlin/org/javafreedom/khol/algorithm/GregorianEasterSundayGaussTest.kt

@@ -1,44 +1,32 @@
-package org.javafreedom.khol
+package org.javafreedom.khol.algorithm
 
 import kotlinx.datetime.number
-import org.javafreedom.khol.HolidayCalculusUtil.firstAdvent
-import org.javafreedom.khol.HolidayCalculusUtil.gregorianEasterSunday
 import kotlin.test.Test
 import kotlin.test.assertEquals
 
 private data class EasterCalculusArguments(val year: Int, val month: Int, val day: Int)
 
-class HolidayCalculusUtilTest {
+class GregorianEasterSundayGaussTest {
 
     private val argumentsList = mutableListOf(
         EasterCalculusArguments(2008, 3, 23),
         EasterCalculusArguments(2015, 4, 5),
         EasterCalculusArguments(2017, 4, 16),
         EasterCalculusArguments(2018, 4, 1),
         EasterCalculusArguments(2019, 4, 21),
-        EasterCalculusArguments(2027, 3, 28))
+        EasterCalculusArguments(2027, 3, 28)
+    )
+
+    private val sut = GregorianEasterSundayGauss()
 
     @Test
     fun testEasterSunday() {
         argumentsList.forEach {
-            val result = gregorianEasterSunday(it.year)
+            val result = sut.calculateBaseDate(it.year)
             assertEquals(it.year, result.year)
             assertEquals(it.month, result.month.number)
             assertEquals(it.day, result.dayOfMonth)
         }
     }
 
-    @Test
-    fun testFirstAdvent() {
-        val result0 = firstAdvent(2024)
-        assertEquals(2024, result0.year)
-        assertEquals(12, result0.month.number)
-        assertEquals(1, result0.dayOfMonth)
-
-        val result1 = firstAdvent(2023)
-        assertEquals(2023, result1.year)
-        assertEquals(12, result1.month.number)
-        assertEquals(3, result1.dayOfMonth)
-    }
-
 }