Add basic budget details tab

Twigs/Budget/BudgetDetailsView.swift

@@ -9,25 +9,35 @@
 import SwiftUI
 
 struct BudgetDetailsView: View {
+    @EnvironmentObject var transactionDataStore: TransactionDataStore
+    @State var sumId: String = ""
+    let budget: Budget
+
+    @ViewBuilder
     var body: some View {
         ScrollView {
             VStack {
-//                ProgressView(value: .constant(50.0, maxValue: 100))
-//                CategoryListView(budget)
+                switch transactionDataStore.sums[sumId] {
+                case .failure(.loading):
+                    ActivityIndicator(isAnimating: .constant(true), style: .large).onAppear {
+                        if self.sumId == "" {
+                            self.sumId = transactionDataStore.sum(budgetId: self.budget.id)
+                        }
+                    }
+                case .success(let sum):
+                    Text("Current Balance:")
+                    Text(verbatim: sum.balance.toCurrencyString())
+                        .foregroundColor(sum.balance < 0 ? .red : .green)
+                default:
+                    Text("An error has ocurred")
+                }
             }
         }
     }
-    
-    let dataStoreProvider: DataStoreProvider
-    let budget: Budget
-    init(_ dataStoreProvider: DataStoreProvider, budget: Budget) {
-        self.dataStoreProvider = dataStoreProvider
-        self.budget = budget
-    }
 }
 
 struct BudgetDetailsView_Previews: PreviewProvider {
     static var previews: some View {
-        BudgetDetailsView(MockDataStoreProvider(), budget: MockBudgetRepository.budget)
+        BudgetDetailsView(budget: MockBudgetRepository.budget)
     }
 }

Twigs/TabbedBudgetView.swift

@@ -12,11 +12,21 @@ struct TabbedBudgetView: View {
     @EnvironmentObject var categoryDataStore: CategoryDataStore
     let budget: Budget
     @State var isAddingTransaction = false
-    @State var selectedTab: Int = 0
     @State var categoryRequestId: String = ""
     
     var body: some View {
         TabView {
+            BudgetDetailsView(budget: self.budget)
+                .tabItem {
+                    Image(systemName: "briefcase.circle.fill")
+                    Text("Overview")
+                }
+                .tag(0)
+                .onAppear {
+                    if categoryRequestId == "" {
+                        categoryRequestId = categoryDataStore.getCategories(budgetId: budget.id, archived: false)
+                    }
+                }
             TransactionListView(self.budget)
                 .sheet(isPresented: $isAddingTransaction,
                        onDismiss: {
@@ -30,32 +40,17 @@ struct TabbedBudgetView: View {
                     Image(systemName: "dollarsign.circle.fill")
                     Text("transactions")
                 }
-                .tag(0)
-                .onAppear {
-                    selectedTab = 0
-                    if categoryRequestId == "" {
-                        categoryRequestId = categoryDataStore.getCategories(budgetId: budget.id, archived: false)
-                    }
-                }
             
             // TODO: Figure out why this is breaking when requestId is set from inside CategoryListView
             CategoryListView(self.budget, requestId: categoryRequestId).tabItem {
                 Image(systemName: "chart.pie.fill")
                 Text("categories")
             }
-            .tag(1)
-            .onAppear {
-                selectedTab = 1
-            }
             
             ProfileView().tabItem {
                 Image(systemName: "person.circle.fill")
                 Text("profile")
             }
-            .tag(2)
-            .onAppear {
-                selectedTab = 2
-            }
         }.navigationBarItems(
             trailing: HStack {
                 NavigationLink(destination: EmptyView()) {
@@ -69,10 +64,6 @@ struct TabbedBudgetView: View {
                 }
             }
         )
-            .onAppear {
-                // Prefetch categories to avoid tab switching bug
-                _ = categoryDataStore.getCategories(budgetId: budget.id)
-            }
     }
     
     init (_ budget: Budget) {

Twigs/Transaction/TransactionDataStore.swift

@@ -16,7 +16,7 @@ class TransactionDataStore: ObservableObject {
     
     @Published var transaction: Result<Transaction, NetworkError> = .failure(.unknown)
     
-    @Published var sums: [String:Result<BalanceResponse, NetworkError>] = [:]
+    @Published var sums: [String:Result<BalanceResponse, NetworkError>] = ["": .failure(.loading)]
 
     func getTransactions(_ budgetId: String, categoryId: String? = nil, from: Date? = nil, count: Int? = nil, page: Int? = nil) -> String {
         let requestId = "\(budgetId)-\(categoryId ?? "all")"