Bug 1845905 - Add a utility to create store lazily

app/src/main/java/org/mozilla/fenix/components/StoreProvider.kt

@@ -4,6 +4,8 @@
 
 package org.mozilla.fenix.components
 
+import androidx.annotation.MainThread
+import androidx.annotation.VisibleForTesting
 import androidx.lifecycle.ViewModel
 import androidx.lifecycle.ViewModelProvider
 import androidx.lifecycle.ViewModelStoreOwner
@@ -33,6 +35,7 @@ class StoreProvider<T : Store<*, *>>(
  *
  * @param createStore Callback to create a new [Store], used when the [ViewModel] is first created.
  */
+@VisibleForTesting
 class StoreProviderFactory<T : Store<*, *>>(
     private val createStore: () -> T,
 ) : ViewModelProvider.Factory {
@@ -42,3 +45,17 @@ class StoreProviderFactory<T : Store<*, *>>(
         return StoreProvider(createStore()) as VM
     }
 }
+
+/**
+ * Helper function for lazy creation of a [Store] instance scoped to a [ViewModelStoreOwner].
+ *
+ * @param createStore Function that creates a [Store] instance.
+ */
+@MainThread
+fun <T : Store<*, *>> ViewModelStoreOwner.lazyStore(
+    createStore: () -> T,
+): Lazy<T> {
+    return lazy(mode = LazyThreadSafetyMode.NONE) {
+        StoreProvider.get(this, createStore)
+    }
+}

app/src/test/java/org/mozilla/fenix/components/StoreProviderTest.kt

@@ -63,4 +63,28 @@ class StoreProviderTest {
         StoreProvider.get(fragment, createStore)
         assertFalse(createCalled)
     }
+
+    @Test
+    fun `WHEN store is created lazily THEN createStore is only invoked on access`() {
+        val fragment = createAddedTestFragment { Fragment() }
+
+        var createCalled = false
+        val createStore = {
+            createCalled = true
+            basicStore
+        }
+
+        val store by fragment.lazyStore(createStore)
+        // The store is not created yet.
+        assertFalse(createCalled)
+
+        assertEquals(basicStore, store)
+        // The store is only created when it's used.
+        assertTrue(createCalled)
+
+        // The store is not created again.
+        createCalled = false
+        fragment.lazyStore(createStore).value
+        assertFalse(createCalled)
+    }
 }