data: add TimeBridge helpers for epoch-millis ↔ kotlin.time.Instant

app/src/main/java/de/jeanlucmakiola/calendula/data/calendar/TimeBridge.kt

@@ -0,0 +1,7 @@
+package de.jeanlucmakiola.calendula.data.calendar
+
+import kotlin.time.Instant
+
+fun Long.toKotlinInstantFromEpochMillis(): Instant = Instant.fromEpochMilliseconds(this)
+
+fun Instant.toEpochMillis(): Long = toEpochMilliseconds()

app/src/test/java/de/jeanlucmakiola/calendula/data/calendar/TimeBridgeTest.kt

@@ -0,0 +1,26 @@
+package de.jeanlucmakiola.calendula.data.calendar
+
+import com.google.common.truth.Truth.assertThat
+import kotlin.time.Instant
+import org.junit.jupiter.api.Test
+
+class TimeBridgeTest {
+
+    @Test
+    fun `epoch millis round-trips through Instant`() {
+        val original = 1_717_840_800_000L // 2024-06-08T10:00:00Z
+        val instant = original.toKotlinInstantFromEpochMillis()
+        assertThat(instant.toEpochMillis()).isEqualTo(original)
+    }
+
+    @Test
+    fun `zero millis maps to Instant epoch`() {
+        assertThat(0L.toKotlinInstantFromEpochMillis()).isEqualTo(Instant.fromEpochMilliseconds(0L))
+    }
+
+    @Test
+    fun `negative epoch millis is supported`() {
+        val original = -1_000_000L
+        assertThat(original.toKotlinInstantFromEpochMillis().toEpochMillis()).isEqualTo(original)
+    }
+}