data: add CalendarDataSource seam returning domain lists (not Cursors)

Deviation from Plan 02: changing from Cursor-returning interface to
domain-returning interface so the repository unit tests can use a simple
fake without constructing ContentObserver/Handler/Looper on the JVM
(which would either crash or no-op via the mockable.jar stubs).

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

@@ -0,0 +1,112 @@
+package de.jeanlucmakiola.calendula.data.calendar
+
+import android.content.ContentResolver
+import android.content.ContentUris
+import android.content.Context
+import android.database.ContentObserver
+import android.database.Cursor
+import android.os.Handler
+import android.os.Looper
+import android.provider.CalendarContract
+import dagger.hilt.android.qualifiers.ApplicationContext
+import de.jeanlucmakiola.calendula.domain.Attendee
+import de.jeanlucmakiola.calendula.domain.CalendarSource
+import de.jeanlucmakiola.calendula.domain.EventDetail
+import de.jeanlucmakiola.calendula.domain.EventInstance
+import javax.inject.Inject
+import javax.inject.Singleton
+
+/**
+ * Domain-shaped seam over Android's ContentResolver. Returns parsed lists so
+ * the repository can be unit-tested without constructing Cursors or
+ * ContentObservers on the JVM.
+ *
+ * Cursor handling and the ContentObserver-to-listener bridge live entirely
+ * in AndroidCalendarDataSource.
+ */
+interface CalendarDataSource {
+    fun calendars(): List<CalendarSource>
+    fun instances(beginMillis: Long, endMillis: Long): List<EventInstance>
+    fun eventDetail(eventId: Long): EventDetail?
+    fun registerChangeListener(listener: () -> Unit)
+    fun unregisterChangeListener(listener: () -> Unit)
+}
+
+@Singleton
+class AndroidCalendarDataSource @Inject constructor(
+    @ApplicationContext private val context: Context,
+) : CalendarDataSource {
+
+    private val resolver: ContentResolver get() = context.contentResolver
+    private val observers = mutableMapOf<() -> Unit, ContentObserver>()
+
+    override fun calendars(): List<CalendarSource> = resolver.query(
+        CalendarContract.Calendars.CONTENT_URI,
+        CalendarProjection.COLUMNS,
+        null, null,
+        CalendarContract.Calendars.CALENDAR_DISPLAY_NAME + " ASC",
+    )?.use { it.mapAll(::toCalendarSource) } ?: emptyList()
+
+    override fun instances(beginMillis: Long, endMillis: Long): List<EventInstance> {
+        val uri = CalendarContract.Instances.CONTENT_URI.buildUpon().apply {
+            ContentUris.appendId(this, beginMillis)
+            ContentUris.appendId(this, endMillis)
+        }.build()
+        return resolver.query(
+            uri,
+            InstanceProjection.COLUMNS,
+            null, null,
+            CalendarContract.Instances.BEGIN + " ASC",
+        )?.use { c -> c.mapAllNotNull { CursorColumnReader(c).toEventInstance() } } ?: emptyList()
+    }
+
+    override fun eventDetail(eventId: Long): EventDetail? {
+        val attendees = queryAttendees(eventId)
+        return resolver.query(
+            ContentUris.withAppendedId(CalendarContract.Events.CONTENT_URI, eventId),
+            EventDetailProjection.COLUMNS,
+            null, null, null,
+        )?.use { c ->
+            if (!c.moveToFirst()) null
+            else CursorColumnReader(c).toEventDetailCore(attendees)
+        }
+    }
+
+    override fun registerChangeListener(listener: () -> Unit) {
+        val obs = object : ContentObserver(Handler(Looper.getMainLooper())) {
+            override fun onChange(selfChange: Boolean) {
+                listener()
+            }
+        }
+        observers[listener] = obs
+        resolver.registerContentObserver(
+            CalendarContract.CONTENT_URI,
+            /* notifyForDescendants = */ true,
+            obs,
+        )
+    }
+
+    override fun unregisterChangeListener(listener: () -> Unit) {
+        observers.remove(listener)?.let { resolver.unregisterContentObserver(it) }
+    }
+
+    private fun queryAttendees(eventId: Long): List<Attendee> = resolver.query(
+        CalendarContract.Attendees.CONTENT_URI,
+        AttendeeProjection.COLUMNS,
+        CalendarContract.Attendees.EVENT_ID + " = ?",
+        arrayOf(eventId.toString()),
+        null,
+    )?.use { c -> c.mapAll { CursorColumnReader(c).toAttendee() } } ?: emptyList()
+
+    private fun toCalendarSource(c: Cursor): CalendarSource = CursorColumnReader(c).toCalendarSource()
+
+    /** Iterate every row and map; skips nothing. */
+    private inline fun <T> Cursor.mapAll(mapper: (Cursor) -> T): List<T> = buildList {
+        while (moveToNext()) add(mapper(this@mapAll))
+    }
+
+    /** Iterate every row and map; drops nulls. */
+    private inline fun <T : Any> Cursor.mapAllNotNull(mapper: (Cursor) -> T?): List<T> = buildList {
+        while (moveToNext()) mapper(this@mapAllNotNull)?.let(::add)
+    }
+}