data: add CalendarPrefs (hidden calendar ids in DataStore)

app/src/main/java/de/jeanlucmakiola/calendula/data/prefs/CalendarPrefs.kt

@@ -0,0 +1,44 @@
+package de.jeanlucmakiola.calendula.data.prefs
+
+import androidx.datastore.core.DataStore
+import androidx.datastore.preferences.core.Preferences
+import androidx.datastore.preferences.core.edit
+import androidx.datastore.preferences.core.stringPreferencesKey
+import kotlinx.coroutines.flow.Flow
+import kotlinx.coroutines.flow.map
+import javax.inject.Inject
+import javax.inject.Singleton
+
+/**
+ * App-side preference for "calendars the user has hidden in this app",
+ * separate from the system's per-calendar VISIBLE flag.
+ *
+ * Persisted as a comma-separated string of Long ids; non-numeric tokens are
+ * silently dropped (defensive — see CalendarPrefsTest).
+ */
+@Singleton
+class CalendarPrefs @Inject constructor(
+    private val store: DataStore<Preferences>,
+) {
+
+    val hiddenCalendarIds: Flow<Set<Long>> = store.data.map { prefs ->
+        prefs[HIDDEN_IDS_KEY].orEmpty()
+            .split(',')
+            .mapNotNull { it.trim().toLongOrNull() }
+            .toSet()
+    }
+
+    suspend fun setHiddenCalendarIds(ids: Set<Long>) {
+        store.edit { prefs ->
+            if (ids.isEmpty()) {
+                prefs.remove(HIDDEN_IDS_KEY)
+            } else {
+                prefs[HIDDEN_IDS_KEY] = ids.sorted().joinToString(",")
+            }
+        }
+    }
+
+    companion object {
+        internal val HIDDEN_IDS_KEY = stringPreferencesKey("hidden_calendar_ids")
+    }
+}