Add rangeTo support for java.util.Date

src/main/kotlin/me/moallemi/tools/daterange/date/DateExt.kt

@@ -0,0 +1,5 @@
+package me.moallemi.tools.daterange.date
+
+import java.util.Date
+
+operator fun Date.rangeTo(other: Date) = DateRange(this, other)

src/main/kotlin/me/moallemi/tools/daterange/date/DateIterator.kt

@@ -0,0 +1,27 @@
+package me.moallemi.tools.daterange.date
+
+import java.util.Calendar
+import java.util.Date
+import java.util.Locale
+
+class DateIterator(
+    startDate: Date,
+    private val endDate: Date,
+    private val stepDays: Int
+) : Iterator<Date> {
+
+    private val calendar = Calendar.getInstance(Locale.getDefault())
+    private var currentDate = startDate
+
+    override fun hasNext() = currentDate <= endDate
+
+    override fun next(): Date {
+        val next = currentDate
+
+        calendar.time = currentDate
+        calendar.add(Calendar.DATE, stepDays)
+        currentDate = calendar.time
+
+        return next
+    }
+}

src/main/kotlin/me/moallemi/tools/daterange/date/DateRange.kt

@@ -0,0 +1,15 @@
+package me.moallemi.tools.daterange.date
+
+import java.util.Date
+
+class DateRange(
+    override val start: Date,
+    override val endInclusive: Date,
+    private val stepDays: Int = 1
+) : Iterable<Date>, ClosedRange<Date> {
+
+    override fun iterator(): Iterator<Date> =
+        DateIterator(start, endInclusive, stepDays)
+
+    infix fun step(days: Int) = DateRange(start, endInclusive, days)
+}

src/test/kotlin/me/moallemi/tools/daterange/date/DateRangeTest.kt

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+package me.moallemi.tools.daterange.date
+
+import java.text.SimpleDateFormat
+import java.util.Calendar
+import java.util.Locale
+import junit.framework.TestCase.assertEquals
+import org.junit.Test
+
+class DateRangeTest {
+
+    private val calendar = Calendar.getInstance(Locale.getDefault())
+    private val simpleDateFormat = SimpleDateFormat("yyyy-MM-dd", Locale.getDefault())
+
+    @Test
+    fun testRange() {
+        val expected = listOf(
+            "2020-01-01",
+            "2020-01-02",
+            "2020-01-03",
+            "2020-01-04",
+            "2020-01-05"
+        )
+        calendar.set(2020, 0, 1)
+        val startDate = calendar.time
+        calendar.set(2020, 0, 5)
+        val endDate = calendar.time
+
+        val actual = (startDate..endDate).map {
+            simpleDateFormat.format(it)
+        }
+
+        assertEquals(expected, actual)
+    }
+
+    @Test
+    fun testStep() {
+        val expected = listOf(
+            "2020-01-01",
+            "2020-01-03",
+            "2020-01-05"
+        )
+        calendar.set(2020, 0, 1)
+        val startDate = calendar.time
+        calendar.set(2020, 0, 5)
+        val endDate = calendar.time
+
+        val actual = (startDate..endDate step 2).map {
+            simpleDateFormat.format(it)
+        }
+
+        assertEquals(expected, actual)
+    }
+}