feat(intent): create events from external ACTION_INSERT launches (#30)

Register an intent-filter for ACTION_INSERT on the events dir mime type
(vnd.android.cursor.dir/event), the way the AOSP calendar accepts one, so
other apps and widgets (e.g. the Todo Agenda widget) can launch Calendula
to create a new event.

MainActivity.insertFormOrNull parses the standard CalendarContract extras
(EXTRA_EVENT_BEGIN_TIME/END_TIME/ALL_DAY, Events.TITLE/DESCRIPTION/
EVENT_LOCATION/RRULE) into a prefilled EventForm via the pure, unit-tested
buildInsertEventForm — omitted fields fall back to the same defaults the
in-app "new event" uses (next full hour, +1h). The form is routed through
the existing single-event prefill channel (RootScreen → CalendarHost →
the create form for review), with calendarId left null so it resolves to
the last-used / first-writable calendar. No new permission is needed
(WRITE_CALENDAR is already held), and the user still explicitly saves.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

app/src/test/java/de/jeanlucmakiola/calendula/domain/InsertEventFormTest.kt

@@ -0,0 +1,115 @@
+package de.jeanlucmakiola.calendula.domain
+
+import com.google.common.truth.Truth.assertThat
+import kotlinx.datetime.LocalDate
+import kotlinx.datetime.LocalDateTime
+import kotlinx.datetime.LocalTime
+import kotlinx.datetime.TimeZone
+import kotlinx.datetime.atStartOfDayIn
+import kotlinx.datetime.toInstant
+import org.junit.jupiter.api.Test
+import kotlin.time.Instant
+
+class InsertEventFormTest {
+
+    private val zone = TimeZone.UTC
+
+    // A fixed "now" at 2026-01-15T10:20:00Z; the next full hour is 11:00.
+    private val now = LocalDateTime(2026, 1, 15, 10, 20).toInstant(zone)
+
+    private fun build(
+        beginMillis: Long? = null,
+        endMillis: Long? = null,
+        isAllDay: Boolean = false,
+        title: String? = null,
+        description: String? = null,
+        location: String? = null,
+        rrule: String? = null,
+    ): EventForm = buildInsertEventForm(
+        beginMillis = beginMillis,
+        endMillis = endMillis,
+        isAllDay = isAllDay,
+        title = title,
+        description = description,
+        location = location,
+        rrule = rrule,
+        zone = zone,
+        now = now,
+    )
+
+    private fun millis(dateTime: LocalDateTime): Long = dateTime.toInstant(zone).toEpochMilliseconds()
+
+    @Test
+    fun `timed event maps all provided fields`() {
+        val start = LocalDateTime(2026, 3, 1, 14, 30)
+        val end = LocalDateTime(2026, 3, 1, 15, 45)
+        val form = build(
+            beginMillis = millis(start),
+            endMillis = millis(end),
+            title = "Standup",
+            description = "Daily",
+            location = "Room 1",
+            rrule = "FREQ=DAILY",
+        )
+        assertThat(form.calendarId).isNull() // resolves to last-used / first-writable
+        assertThat(form.isAllDay).isFalse()
+        assertThat(form.start).isEqualTo(start)
+        assertThat(form.end).isEqualTo(end)
+        assertThat(form.title).isEqualTo("Standup")
+        assertThat(form.description).isEqualTo("Daily")
+        assertThat(form.location).isEqualTo("Room 1")
+        assertThat(form.rrule).isEqualTo("FREQ=DAILY")
+    }
+
+    @Test
+    fun `missing times default to the next full hour and a one-hour duration`() {
+        val form = build(title = "Quick note")
+        assertThat(form.start).isEqualTo(LocalDateTime(2026, 1, 15, 11, 0))
+        assertThat(form.end).isEqualTo(LocalDateTime(2026, 1, 15, 12, 0))
+        assertThat(form.title).isEqualTo("Quick note")
+    }
+
+    @Test
+    fun `timed event with only a start gets a one-hour end`() {
+        val start = LocalDateTime(2026, 5, 2, 9, 0)
+        val form = build(beginMillis = millis(start))
+        assertThat(form.start).isEqualTo(start)
+        assertThat(form.end).isEqualTo(LocalDateTime(2026, 5, 2, 10, 0))
+    }
+
+    @Test
+    fun `an end before the start is ignored and falls back to plus one hour`() {
+        val start = LocalDateTime(2026, 5, 2, 9, 0)
+        val badEnd = LocalDateTime(2026, 5, 2, 8, 0)
+        val form = build(beginMillis = millis(start), endMillis = millis(badEnd))
+        assertThat(form.end).isEqualTo(LocalDateTime(2026, 5, 2, 10, 0))
+    }
+
+    @Test
+    fun `all-day event uses UTC dates and decrements the exclusive end`() {
+        val startMillis = LocalDate(2026, 1, 1).atStartOfDayIn(TimeZone.UTC).toEpochMilliseconds()
+        val endExclusive = LocalDate(2026, 1, 3).atStartOfDayIn(TimeZone.UTC).toEpochMilliseconds()
+        val form = build(beginMillis = startMillis, endMillis = endExclusive, isAllDay = true, title = "Trip")
+        assertThat(form.isAllDay).isTrue()
+        assertThat(form.start.date).isEqualTo(LocalDate(2026, 1, 1))
+        assertThat(form.end.date).isEqualTo(LocalDate(2026, 1, 2))
+        // Placeholder wall-clock times survive a switch back to a timed event.
+        assertThat(form.start.time).isEqualTo(LocalTime(9, 0))
+        assertThat(form.end.time).isEqualTo(LocalTime(10, 0))
+    }
+
+    @Test
+    fun `all-day event without an end is a single day`() {
+        val startMillis = LocalDate(2026, 6, 10).atStartOfDayIn(TimeZone.UTC).toEpochMilliseconds()
+        val form = build(beginMillis = startMillis, isAllDay = true)
+        assertThat(form.start.date).isEqualTo(LocalDate(2026, 6, 10))
+        assertThat(form.end.date).isEqualTo(LocalDate(2026, 6, 10))
+    }
+
+    @Test
+    fun `a leading RRULE prefix is stripped and a blank rule becomes null`() {
+        assertThat(build(rrule = "RRULE:FREQ=WEEKLY").rrule).isEqualTo("FREQ=WEEKLY")
+        assertThat(build(rrule = "   ").rrule).isNull()
+        assertThat(build(rrule = null).rrule).isNull()
+    }
+}