[Jetsnack] Snackbar support (android#645)

Jetsnack/app/src/main/java/com/example/jetsnack/model/SnackbarManager.kt

@@ -0,0 +1,50 @@
+/*
+ * Copyright 2021 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.example.jetsnack.model
+
+import androidx.annotation.StringRes
+import java.util.UUID
+import kotlinx.coroutines.flow.MutableStateFlow
+import kotlinx.coroutines.flow.StateFlow
+import kotlinx.coroutines.flow.asStateFlow
+import kotlinx.coroutines.flow.update
+
+data class Message(val id: Long, @StringRes val messageId: Int)
+
+/**
+ * Class responsible for managing Snackbar messages to show on the screen
+ */
+object SnackbarManager {
+
+    private val _messages: MutableStateFlow<List<Message>> = MutableStateFlow(emptyList())
+    val messages: StateFlow<List<Message>> get() = _messages.asStateFlow()
+
+    fun showMessage(@StringRes messageTextId: Int) {
+        _messages.update { currentMessages ->
+            currentMessages + Message(
+                id = UUID.randomUUID().mostSignificantBits,
+                messageId = messageTextId
+            )
+        }
+    }
+
+    fun setMessageShown(messageId: Long) {
+        _messages.update { currentMessages ->
+            currentMessages.filterNot { it.id == messageId }
+        }
+    }
+}

Jetsnack/app/src/main/java/com/example/jetsnack/ui/JetsnackApp.kt

@@ -17,30 +17,67 @@
 package com.example.jetsnack.ui
 
 import androidx.compose.foundation.layout.padding
+import androidx.compose.material.SnackbarHost
+import androidx.compose.material.rememberScaffoldState
 import androidx.compose.runtime.Composable
+import androidx.compose.runtime.LaunchedEffect
+import androidx.compose.runtime.collectAsState
+import androidx.compose.runtime.getValue
 import androidx.compose.runtime.remember
 import androidx.compose.ui.Modifier
+import androidx.compose.ui.res.stringResource
 import androidx.navigation.compose.rememberNavController
+import com.example.jetsnack.model.SnackbarManager
 import com.example.jetsnack.ui.components.JetsnackScaffold
+import com.example.jetsnack.ui.components.JetsnackSnackbar
 import com.example.jetsnack.ui.home.HomeSections
 import com.example.jetsnack.ui.home.JetsnackBottomBar
 import com.example.jetsnack.ui.theme.JetsnackTheme
 import com.google.accompanist.insets.ProvideWindowInsets
+import com.google.accompanist.insets.systemBarsPadding
 
 @Composable
 fun JetsnackApp() {
     ProvideWindowInsets {
         JetsnackTheme {
             val tabs = remember { HomeSections.values() }
             val navController = rememberNavController()
+            val scaffoldState = rememberScaffoldState()
+
             JetsnackScaffold(
-                bottomBar = { JetsnackBottomBar(navController = navController, tabs = tabs) }
+                bottomBar = { JetsnackBottomBar(navController = navController, tabs = tabs) },
+                snackbarHost = {
+                    SnackbarHost(
+                        hostState = it,
+                        modifier = Modifier.systemBarsPadding(),
+                        snackbar = { snackbarData -> JetsnackSnackbar(snackbarData) }
+                    )
+                },
+                scaffoldState = scaffoldState
             ) { innerPaddingModifier ->
                 JetsnackNavGraph(
                     navController = navController,
                     modifier = Modifier.padding(innerPaddingModifier)
                 )
             }
+
+            // Handle Snackbar messages
+            val currentMessages by SnackbarManager.messages.collectAsState()
+            if (currentMessages.isNotEmpty()) {
+                val message = currentMessages[0]
+                val messageText: String = stringResource(message.messageId)
+
+                // Effect running in a coroutine that displays the Snackbar on the screen
+                // If there's a change to messageText, SnackbarManager, or scaffoldState, the
+                // previous effect will be cancelled and a new one will start with the new values
+                LaunchedEffect(messageText, SnackbarManager, scaffoldState) {
+                    // Display the snackbar on the screen. `showSnackbar` is a function
+                    // that suspends until the snackbar disappears from the screen
+                    scaffoldState.snackbarHostState.showSnackbar(messageText)
+                    // Once the snackbar is gone or dismissed, notify the SnackbarManager
+                    SnackbarManager.setMessageShown(message.id)
+                }
+            }
         }
     }
 }

Jetsnack/app/src/main/java/com/example/jetsnack/ui/components/Snackbar.kt

@@ -0,0 +1,55 @@
+/*
+ * Copyright 2021 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.example.jetsnack.ui.components
+
+import androidx.compose.material.MaterialTheme
+import androidx.compose.material.Snackbar
+import androidx.compose.material.SnackbarData
+import androidx.compose.runtime.Composable
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.graphics.Color
+import androidx.compose.ui.graphics.Shape
+import androidx.compose.ui.unit.Dp
+import androidx.compose.ui.unit.dp
+import com.example.jetsnack.ui.theme.JetsnackTheme
+
+/**
+ * An alternative to [androidx.compose.material.Snackbar] utilizing
+ * [com.example.jetsnack.ui.theme.JetsnackColors]
+ */
+@Composable
+fun JetsnackSnackbar(
+    snackbarData: SnackbarData,
+    modifier: Modifier = Modifier,
+    actionOnNewLine: Boolean = false,
+    shape: Shape = MaterialTheme.shapes.small,
+    backgroundColor: Color = JetsnackTheme.colors.uiBackground,
+    contentColor: Color = JetsnackTheme.colors.textSecondary,
+    actionColor: Color = JetsnackTheme.colors.brand,
+    elevation: Dp = 6.dp
+) {
+    Snackbar(
+        snackbarData = snackbarData,
+        modifier = modifier,
+        actionOnNewLine = actionOnNewLine,
+        shape = shape,
+        backgroundColor = backgroundColor,
+        contentColor = contentColor,
+        actionColor = actionColor,
+        elevation = elevation
+    )
+}

Jetsnack/app/src/main/java/com/example/jetsnack/ui/home/cart/Cart.kt

@@ -87,9 +87,9 @@ import com.google.accompanist.insets.statusBarsHeight
 @Composable
 fun Cart(
     onSnackClick: (Long) -> Unit,
-    modifier: Modifier = Modifier
+    modifier: Modifier = Modifier,
+    viewModel: CartViewModel = viewModel(factory = CartViewModel.provideFactory())
 ) {
-    val viewModel: CartViewModel = viewModel()
     val orderLines by viewModel.orderLines.collectAsState()
     val inspiredByCart = remember { SnackRepo.getInspiredByCart() }
     Cart(

Jetsnack/app/src/main/java/com/example/jetsnack/ui/home/cart/CartViewModel.kt

@@ -17,8 +17,11 @@
 package com.example.jetsnack.ui.home.cart
 
 import androidx.lifecycle.ViewModel
+import androidx.lifecycle.ViewModelProvider
+import com.example.jetsnack.R
 import com.example.jetsnack.model.OrderLine
 import com.example.jetsnack.model.SnackRepo
+import com.example.jetsnack.model.SnackbarManager
 import kotlinx.coroutines.flow.MutableStateFlow
 import kotlinx.coroutines.flow.StateFlow
 
@@ -27,31 +30,47 @@ import kotlinx.coroutines.flow.StateFlow
  *
  * TODO: Move data to Repository so it can be displayed and changed consistently throughout the app.
  */
-class CartViewModel : ViewModel() {
+class CartViewModel(
+    private val snackbarManager: SnackbarManager,
+    snackRepository: SnackRepo
+) : ViewModel() {
+
     private val _orderLines: MutableStateFlow<List<OrderLine>> =
-        MutableStateFlow(SnackRepo.getCart())
+        MutableStateFlow(snackRepository.getCart())
     val orderLines: StateFlow<List<OrderLine>> get() = _orderLines
 
-    fun removeSnack(snackId: Long) {
-        _orderLines.value = _orderLines.value.filter { it.snack.id != snackId }
-    }
+    // Logic to show errors every few requests
+    private var requestCount = 0
+    private fun shouldRandomlyFail(): Boolean = ++requestCount % 5 == 0
 
     fun increaseSnackCount(snackId: Long) {
-        val currentCount = _orderLines.value.first { it.snack.id == snackId }.count
-        updateSnackCount(snackId, currentCount + 1)
+        if (!shouldRandomlyFail()) {
+            val currentCount = _orderLines.value.first { it.snack.id == snackId }.count
+            updateSnackCount(snackId, currentCount + 1)
+        } else {
+            snackbarManager.showMessage(R.string.cart_increase_error)
+        }
     }
 
     fun decreaseSnackCount(snackId: Long) {
-        val currentCount = _orderLines.value.first { it.snack.id == snackId }.count
-        if (currentCount == 1) {
-            // remove snack from cart
-            removeSnack(snackId)
+        if (!shouldRandomlyFail()) {
+            val currentCount = _orderLines.value.first { it.snack.id == snackId }.count
+            if (currentCount == 1) {
+                // remove snack from cart
+                removeSnack(snackId)
+            } else {
+                // update quantity in cart
+                updateSnackCount(snackId, currentCount - 1)
+            }
         } else {
-            // update quantity in cart
-            updateSnackCount(snackId, currentCount - 1)
+            snackbarManager.showMessage(R.string.cart_decrease_error)
         }
     }
 
+    fun removeSnack(snackId: Long) {
+        _orderLines.value = _orderLines.value.filter { it.snack.id != snackId }
+    }
+
     private fun updateSnackCount(snackId: Long, count: Int) {
         _orderLines.value = _orderLines.value.map {
             if (it.snack.id == snackId) {
@@ -61,4 +80,19 @@ class CartViewModel : ViewModel() {
             }
         }
     }
+
+    /**
+     * Factory for CartViewModel that takes SnackbarManager as a dependency
+     */
+    companion object {
+        fun provideFactory(
+            snackbarManager: SnackbarManager = SnackbarManager,
+            snackRepository: SnackRepo = SnackRepo
+        ): ViewModelProvider.Factory = object : ViewModelProvider.Factory {
+            @Suppress("UNCHECKED_CAST")
+            override fun <T : ViewModel?> create(modelClass: Class<T>): T {
+                return CartViewModel(snackbarManager, snackRepository) as T
+            }
+        }
+    }
 }

Jetsnack/app/src/main/res/values/strings.xml

@@ -53,6 +53,8 @@
     <string name="cart_shipping_label">Shipping &amp; Handling</string>
     <string name="cart_total_label">Total</string>
     <string name="cart_checkout">Checkout</string>
+    <string name="cart_increase_error">There was an error and the quantity couldn\'t be increased. Please try again.</string>
+    <string name="cart_decrease_error">There was an error and the quantity couldn\'t be decreased. Please try again.</string>
     <string name="label_remove">Remove item</string>
 
     <!-- Quantity Selector -->

Jetsnack/buildSrc/src/main/java/com/example/jetsnack/buildsrc/Dependencies.kt

@@ -38,7 +38,7 @@ object Libs {
     }
 
     object Coroutines {
-        private const val version = "1.5.1"
+        private const val version = "1.5.2"
         const val core = "org.jetbrains.kotlinx:kotlinx-coroutines-core:$version"
         const val android = "org.jetbrains.kotlinx:kotlinx-coroutines-android:$version"
         const val test = "org.jetbrains.kotlinx:kotlinx-coroutines-test:$version"