extensions: Strip out logic for shared pref callback into extension

Signed-off-by: Aayush Gupta <aayushgupta219@gmail.com>

app/src/main/java/com/aurora/extensions/SharedPreferences.kt

@@ -0,0 +1,41 @@
+/*
+ * SPDX-FileCopyrightText: 2025 The Calyx Institute
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ */
+
+package com.aurora.extensions
+
+import android.content.SharedPreferences
+import kotlinx.coroutines.CoroutineScope
+import kotlinx.coroutines.channels.awaitClose
+import kotlinx.coroutines.flow.SharingStarted
+import kotlinx.coroutines.flow.StateFlow
+import kotlinx.coroutines.flow.callbackFlow
+import kotlinx.coroutines.flow.stateIn
+
+/**
+ * Extension method to observe changes in shared preferences as a flow
+ */
+fun <T> SharedPreferences.observeAsStateFlow(
+    key: String,
+    scope: CoroutineScope,
+    started: SharingStarted = SharingStarted.Eagerly,
+    initial: T,
+    valueProvider: () -> T
+): StateFlow<T> =
+    callbackFlow {
+        val listener =
+            SharedPreferences.OnSharedPreferenceChangeListener { _, changedKey ->
+                if (changedKey == key) {
+                    trySend(valueProvider())
+                }
+            }
+
+        // Emit the initial value
+        trySend(valueProvider())
+
+        registerOnSharedPreferenceChangeListener(listener)
+        awaitClose {
+            unregisterOnSharedPreferenceChangeListener(listener)
+        }
+    }.stateIn(scope, started, initial)

app/src/main/java/com/aurora/store/viewmodel/dispenser/DispenserViewModel.kt

@@ -6,21 +6,15 @@
 package com.aurora.store.viewmodel.dispenser
 
 import android.content.Context
-import android.content.SharedPreferences
 import androidx.core.content.edit
 import androidx.lifecycle.ViewModel
 import androidx.lifecycle.viewModelScope
+import com.aurora.extensions.observeAsStateFlow
 import com.aurora.store.util.Preferences
 import com.aurora.store.util.Preferences.PREFERENCE_DISPENSER_URLS
 import dagger.hilt.android.lifecycle.HiltViewModel
 import dagger.hilt.android.qualifiers.ApplicationContext
-import kotlinx.coroutines.channels.awaitClose
-import kotlinx.coroutines.flow.SharingStarted
-import kotlinx.coroutines.flow.StateFlow
-import kotlinx.coroutines.flow.callbackFlow
-import kotlinx.coroutines.flow.stateIn
 import javax.inject.Inject
-import kotlin.collections.toMutableSet
 
 @HiltViewModel
 class DispenserViewModel @Inject constructor(
@@ -33,21 +27,12 @@ class DispenserViewModel @Inject constructor(
         set(value) = sharedPreferences.edit { putStringSet(PREFERENCE_DISPENSER_URLS, value) }
         get() = sharedPreferences.getStringSet(PREFERENCE_DISPENSER_URLS, emptySet()) ?: emptySet()
 
-    val dispensers: StateFlow<Set<String>>
+    val dispensers = sharedPreferences.observeAsStateFlow(
-        get() {
+        key = PREFERENCE_DISPENSER_URLS,
-            return callbackFlow {
+        scope = viewModelScope,
-                val listener = SharedPreferences.OnSharedPreferenceChangeListener { _, changedKey ->
+        initial = emptySet(),
-                    if (changedKey == PREFERENCE_DISPENSER_URLS) trySend(_dispensers)
+        valueProvider = { _dispensers }
-                }
+    )
-
-                trySend(_dispensers)
-
-                sharedPreferences.registerOnSharedPreferenceChangeListener(listener)
-                awaitClose {
-                    sharedPreferences.unregisterOnSharedPreferenceChangeListener(listener)
-                }
-            }.stateIn(viewModelScope, SharingStarted.Eagerly, emptySet())
-        }
 
     fun addDispenser(url: String) {
         _dispensers = _dispensers.toMutableSet().apply {