Ensure the user can join the call even if they has joined a call in another session.

features/call/api/src/main/kotlin/io/element/android/features/call/api/CurrentCall.kt

@@ -0,0 +1,25 @@
+/*
+ * Copyright 2024 New Vector Ltd.
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only
+ * Please see LICENSE in the repository root for full details.
+ */
+
+package io.element.android.features.call.api
+
+import io.element.android.libraries.matrix.api.core.RoomId
+
+/**
+ * Value for the local current call.
+ */
+sealed interface CurrentCall {
+    data object None : CurrentCall
+
+    data class RoomCall(
+        val roomId: RoomId,
+    ) : CurrentCall
+
+    data class ExternalUrl(
+        val url: String,
+    ) : CurrentCall
+}

features/call/api/src/main/kotlin/io/element/android/features/call/api/CurrentCallObserver.kt

@@ -0,0 +1,19 @@
+/*
+ * Copyright 2024 New Vector Ltd.
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only
+ * Please see LICENSE in the repository root for full details.
+ */
+
+package io.element.android.features.call.api
+
+import kotlinx.coroutines.flow.StateFlow
+
+interface CurrentCallObserver {
+    /**
+     * The current call state flow, which will be updated when the active call changes.
+     * This value reflect the local state of the call. It is not updated if the user answers
+     * a call from another session.
+     */
+    val currentCall: StateFlow<CurrentCall>
+}